Stuart <bigdak...@aol.com> wrote: > (Florian) wrote: > > Not without full eclogitization. Eclogitization occurs only at depth >45 > > km and is only partial.
> The lithosphere gets to be about 100km think.
Hu? Only basalt and gabbro Eclogitized, so it concerns only 5-8 km not the whole lithosphere!
> Also, it is on average roughly 600-700K > cooler than the upper mantle. That buys you another 1.5%- 2%. > > See Doglioni et al "What moves slabs":
> Some things in here may make sense, but then... > Statements like the below give me pause with respect to this paper.
> "The high velocity of slab detected by tomography could be related not > to its higher density but to its higher rigidity and viscosity"
Indeed, that statement looks incorrect.
> For starters tomography of slabs is done using P-waves.
Nowadays, tomography is done using S-waves and P-waves.
> The celerity of a P-wave is given by [ (K+4/3U)/R) ]^1/2 where U is the > shear rigidity, K is the incompressibility and R is the density.
Just a reminder, the celerity of S-waves is given by [U/R]^1/2.
> So one wonders how in the world high velocity of the slab could *ever* be > do to a simple change in density? Greater density by itself means slower.
So actually, the higher velocity in the slab could mean that the slab is simply less dense than surrounding material. Interesting. Doglioni argues that oceanic basalt is depleted and serpentinized which support this interpretation but is at odd with the quote above.
> Indeed, the speed of seismic waves increases in slabs because they are > stiffer; temperature has a greater effect on rigidity than it does on > density. You'll also notice that there is no term for viscosity in the > wave speed formula. The slab has higher viscosity because it is cooler. > The viscosity increases with decreasing temperature. It is the higher > stiffness that allows one to > ( That should read "larger rigidity", for that matter the > incompressibility also increases with decreasing temp.) > put bounds on the density through an appropriate equation of state. There > is simply no question that the slab is cooler than the surrounding mantle > and hence more dense. How much more may be arguable, but there is no > question that it is more.
Not so sure. Don L. Anderson has a discussion about tomography problems, and notably the tendancy to wrongly use it as a kind of thermometer:
See paragraph: "Seismic velocity is not a thermometer"
By the way, I note the same confusion, i.e., denser material <=>higher velocity:
"Nevertheless, tomographic images are often interpreted assuming that a simple velocity-density-temperature correlation exists. High velocity (blue) is generally attributed to cold, dense, sinking material, and low velocity (red) as hot, low-density, rising material (Figures 4 & 5)."
Weird, isn't it?
Especially, that a few lines further:
"The African and south Pacific "superplumes" are vast, low-velocity bodies in the lower mantle whose low velocities have been shown to result from anomalously high density and not to high temperature (Trampert et al., 2004)"
thus suggesting again that low velocities region are associated to high density.
> Maybe they meant to say "lower temperature" and "not higher density" but > it still wouldn't make sense. What would imbue these roughly tabular > regions with special stiffness and viscosity?
> I also take issue with his statement that mantle densities are "quite > speculative". I disagree, they are well constrained by modeling the > earth's free oscillations. In fact people are using free oscillations to > work out some of the three dimensional structure of density variations in > the mantle. As far as I know, the mean radial density profile for the > Earth is known to a couple of percent if not better.
Actually, the density profile raises another issue according to Stavros:
"Then seismology tells us that the velocity of both P and S waves increases with depth in the mantle. Density also increases with depth. So, if it was only for density the velocity of seismic waves should decrease with depth. There is no other physically possible way for seismic wave velocity to increase with depth but for the elastic moduli to increase with depth at a faster rate than density. This is impossible though if temperature increases with depth. Experiment has shown that the elastic moduli are very sensitive to temperature; rigidity decreases as temperature increases, and vice versa, and at temperatures above 800 oC rigidity diminishes rapidly. This decrease cannot in any way be compensated by pressure-depth, because the pressure at any depth is below the rigidity and incompressibility thresholds. For example according to the Preliminary Reference Earth Model - PREM the density of crustal rocks at ~10 km depth, is ~2900 kg/m3, the pressure ~0.3 GPa, whereas rigidity mu, and incompressibility K, are ~26.6 and ~52 GPa, respectively. At 77 km the density is ~3375 kg/m3, the static stress ~2.45 GPa, the rigidity ~67.4 GPa, and the incompressibility modulus ~130 GPa. At the depth of 667 km the corresponding values for density rho, pressure, rigidity mu, and incompressibility K are ~4381 kg/m3, ~23.8, ~155 and ~300 GPa, and at 2888 km they are ~5566 kg/m3, ~136, ~294, ~656 GPa."
"The implication is quite clear: Depth and therefore static stress-pressure has no effect on elastic moduli. For seismic wave velocity to increase with depth in the mantle rigidity has to increase with depth; as a result temperature cannot increase with depth. Therefore the seismic wave velocity profile is an approximation of the actual, whereas the conventional temperature profile is not based on observation, experiment and logic, i.e., it is not an approximation of the actual."
So, where is the flaw?
[...]
-- Florian "Toute vérité passe par trois phases. D'abord, elle est ridiculisée; ensuite, elle rencontre une vive opposition avant d'être acceptée comme une totale évidence" - Arthur Schopenhauer
> >>>>>> It looks like the frequency of major events has increased. That is at > >>>>>> odd with the statement that the activity on Mars is gone forever. > >>>>> Umm, increased? Only if you read the graph upside down. According to > >>>>> the > >>>>> graph, between 3.7-4.2 bya there were some 3,500 volcanic episodes. > >>>> <eyes rolling>
> >>>> George, confused as usual. Guess what? impact craters are NOT volcanic > >>>> episodes...
> >>> I read it the same as George. > >>> According to the legend, the little volcano pics with numbers represent > >>> "Major Episodes of Volcanic Activity."
> >> LOL, the numbers represent the age of each Episode. Next time, read the > >> full paper which was cited a few articles above ;-)
> > You are right. Wow! That should have been obvious to me. > > Definite brain glitch.
> Yeah, I made the same mistake. For future reference, Florian. It would help > if you posted a link to the entire article so we can know the context of the > graphs you are referrring to.
Yeah, Florian, ..It's all your fault.
> But you are right in the sense that the graph > doesn't show a decrease in volcanic activity. But it doesn't show an > increase either. It only shows that the volcanic activity has been widely > distributed and sporatic in time as indicated by continued loss of craters > due to lava flows.
See? George is right all along.
> The article makes the point that all the internal heat > within Mars may not have yet dissipated, but it doesn't say that it is > currently active. Only suggests that there could be further activity on the > planet. I think it is possible that some very minor activity could occur in > the furture. But there certainly is no evidence that large scale vulcanism > has occurred in recent times. It certainly appears to make the case that > although Mars may still be tectonically active, it is subtle, probably order > of magnitude less active than Earth, which would indicate that Mars interior > certainly isn't the dynamo that Earth's interior is.
On Mar 30, 2:28 am, auxotectonics_deletethis@nachon_andthis.net
(Florian) wrote: > Stuart <bigdak...@aol.com> wrote: > > (Florian) wrote: > > > Not without full eclogitization. Eclogitization occurs only at depth >45 > > > km and is only partial.
> > The lithosphere gets to be about 100km think.
> Hu? Only basalt and gabbro Eclogitized, so it concerns only 5-8 km not > the whole lithosphere!
No kidding. But 5-8km of oceanic crust isn't going to stop 100km of lithosphere.
> > Also, it is on average roughly 600-700K > > cooler than the upper mantle. That buys you another 1.5%- 2%.
> > Some things in here may make sense, but then... > > Statements like the below give me pause with respect to this paper.
> > "The high velocity of slab detected by tomography could be related not > > to its higher density but to its higher rigidity and viscosity"
> Indeed, that statement looks incorrect.
> > For starters tomography of slabs is done using P-waves.
> Nowadays, tomography is done using S-waves and P-waves.
Its done with surface waves too. Among the first studies to fully document the velocity highs associated with slabs were those back in the early 80's using what was then called residual sphere analysis, even before the use of tomography was wide spread.
> > The celerity of a P-wave is given by [ (K+4/3U)/R) ]^1/2 where U is the > > shear rigidity, K is the incompressibility and R is the density.
> Just a reminder, the celerity of S-waves is given by [U/R]^1/2.
I hadn't forgotten, but thanks.
> > So one wonders how in the world high velocity of the slab could *ever* be > > do to a simple change in density? Greater density by itself means slower.
> So actually, the higher velocity in the slab could mean that the slab is > simply less dense than surrounding material. Interesting. > Doglioni argues that oceanic basalt is depleted and serpentinized which > support this interpretation but is at odd with the quote above.
Yes, according to him, the oceanic moho should not exist. If lighter density components are extracted from the upper mantle, that leaves the lithosphere denser and lower speed according to a naive interpretation of that formula. But density and the elastic moduli have a complex relationship.
> > Indeed, the speed of seismic waves increases in slabs because they are > > stiffer; temperature has a greater effect on rigidity than it does on > > density. You'll also notice that there is no term for viscosity in the > > wave speed formula. The slab has higher viscosity because it is cooler. > > The viscosity increases with decreasing temperature. It is the higher > > stiffness that allows one to > > ( That should read "larger rigidity", for that matter the > > incompressibility also increases with decreasing temp.) > > put bounds on the density through an appropriate equation of state. There > > is simply no question that the slab is cooler than the surrounding mantle > > and hence more dense. How much more may be arguable, but there is no > > question that it is more.
> Not so sure. Don L. Anderson has a discussion about tomography problems, > and notably the tendancy to wrongly use it as a kind of thermometer:
> See paragraph: "Seismic velocity is not a thermometer"
I agree it can be overdone. This is because velocity variations can be due to chemical effects, i.e., changes in composition or the presence of melt. Partial melt is not an issue here nor is it an issue for the vast bulk of the mantle. However, I strongly disagree that this is a problem with respect to slabs. Slabs which we can trace all the way the to the surface, seismically, mechanically, and just about any other way you can think off. As Doglioni is forced to admit, they are stiffer. Moreover we knew this before anyone did seismic tomography. We knew this because of deep-focus seismicity. And since there are not profound major element chemical changes in a slab, the fundamental cause for this stiffness is that on average they are hundreds of degrees cooler than the ambient mantle.
Elsewhere on that page Don talks about the effects of slabs in the transition zone. It is thicker in regions where there is slab, and thinner where there's not. This is a fundamental prediction satisfied. The olivine-Spinel transition at around 400km depth is an exothermic reaction meaning the transition is displaced upwards to lower pressure by cooler termperatures. The spinel olivine to perovskite-olivine transition at around 650km is endothermic, meaning cooler temperature displace the transition lower. Furthermore, seismologists have measured the upward deflection of olivine -> spinel olivine transition.
Sorry. If you think slabs don't have a significant negative thermal anomaly you are in serious denial.
I don't see Don arguing against this point. But welcome to the one- layer vs. two-layer wars.
> By the way, I note the same confusion, i.e., denser material <=>higher > velocity:
> "Nevertheless, tomographic images are often interpreted assuming that a > simple velocity-density-temperature correlation exists. High velocity > (blue) is generally attributed to cold, dense, sinking material, and low > velocity (red) as hot, low-density, rising material (Figures 4 & 5)."
> Weird, isn't it?
> Especially, that a few lines further:
> "The African and south Pacific "superplumes" are vast, low-velocity > bodies in the lower mantle whose low velocities have been shown to > result from anomalously high density and not to high temperature > (Trampert et al., 2004)"
> thus suggesting again that low velocities region are associated to high > density.
Or both density and the low velocities have something to with a change in chemistry with respect to nominal mantle. And this has what to do with slabs?
> > Maybe they meant to say "lower temperature" and "not higher density" but > > it still wouldn't make sense. What would imbue these roughly tabular > > regions with special stiffness and viscosity?
> > I also take issue with his statement that mantle densities are "quite > > speculative". I disagree, they are well constrained by modeling the > > earth's free oscillations. In fact people are using free oscillations to > > work out some of the three dimensional structure of density variations in > > the mantle. As far as I know, the mean radial density profile for the > > Earth is known to a couple of percent if not better.
> Actually, the density profile raises another issue according to Stavros:
Oh great another EEer....
What a surprise.
> "Then seismology tells us that the velocity of both P and S waves > increases with depth in the mantle. Density also increases > with depth. So, if it was only for density the velocity of > seismic waves should decrease with depth.
So far so good.
There is no other physically
> possible way for seismic wave velocity to increase with depth but for > the elastic moduli to increase with depth at a faster rate than density. > This is impossible though if temperature increases with depth. > Experiment has shown that the elastic moduli are very sensitive to > temperature; rigidity decreases as temperature increases, and vice > versa, and at temperatures above 800 oC rigidity diminishes rapidly. > This decrease cannot in any way be compensated by pressure-depth, > because the pressure at any depth is below the rigidity and > incompressibility thresholds.
Define incompressibility and rigidity thresholds
For example according to the Preliminary
> Reference Earth Model - PREM the density of crustal rocks at ~10 km > depth, is ~2900 kg/m3, the pressure ~0.3 GPa, whereas rigidity mu, and > incompressibility K, are ~26.6 and ~52 GPa, respectively. At 77 km the > density is ~3375 kg/m3, the static stress ~2.45 GPa, the rigidity ~67.4 > GPa, and the incompressibility modulus ~130 GPa. At the depth of 667 km > the corresponding values for density rho, pressure, rigidity mu, and > incompressibility K are ~4381 kg/m3, ~23.8, ~155 and ~300 GPa, and at > 2888 km they are ~5566 kg/m3, ~136, ~294, ~656 GPa."
> "The implication is quite clear: Depth and therefore static > stress-pressure has no effect on elastic moduli.
Not to me. Maybe you should ask Don Anderson if the above is clear to him?
There should be no problem finding references to experiments in the peer-reviewed literature which show the elastic moduli are invariant under pressure. Does he have any?
For seismic wave
> velocity to increase with depth in the mantle rigidity has to increase > with depth; as a result temperature cannot increase with depth. > Therefore the seismic wave velocity profile is an approximation of the > actual, whereas the conventional temperature profile is not based on > observation, experiment and logic, i.e., it is not an approximation of > the actual."
Stuart <bigdak...@aol.com> wrote: > On Mar 30, 2:28 am, auxotectonics_deletethis@nachon_andthis.net > (Florian) wrote: > > Hu? Only basalt and gabbro Eclogitized, so it concerns only 5-8 km not > > the whole lithosphere!
> No kidding. But 5-8km of oceanic crust isn't going to stop 100km of > lithosphere.
Stuart, it is the opposite, these 5-8 km of crust are supposed to entrain the whole lithosphere down when they get eclogitized.
Absurd isn't it?
> > > Also, it is on average roughly 600-700K > > > cooler than the upper mantle. That buys you another 1.5%- 2%.
> No response?
> I mean how does Doglioni miss that?
He did not miss it, he argues that the crust has a different composition than the asthenosphere, so that temperature is a marginal parameter considering density. Composition has a larger impact.
"The oceanic lithosphere is a frozen shallow (30-100 km deep) asthenosphere, previously depleted below ridges. Therefore, the oceanic lithosphere is the differentiated lighter upper part of the mantle: then why should it be heavier a priori than the undepleted deeper (100- 300 km) asthenosphere lying beneath the old oceanic lithosphere where a pyrolite density of 3400 kg/m3(Jordan, 1988; Kelly et al., 2003) is inferred? Moreover, hydrothermal activity generates serpentinization of the mantle along the ridge that decreases the density even more."
> > So actually, the higher velocity in the slab could mean that the slab is > > simply less dense than surrounding material. Interesting. > > Doglioni argues that oceanic basalt is depleted and serpentinized which > > support this interpretation but is at odd with the quote above.
> Yes, according to him, the oceanic moho should not exist. If lighter > density components are extracted from the upper mantle, that leaves the > lithosphere denser
Hmmm, when something is depleted, its density is always decreased compared to the original material. You should revise the notion of solvent, solute and solution.
> and lower speed according to a naive interpretation of > that formula.
The impact of a change in density alone is not much significant. A 10% increase in density would account for only a 5% decrease in Vp at constant modulus.
[...]
> > Not so sure. Don L. Anderson has a discussion about tomography problems, > > and notably the tendancy to wrongly use it as a kind of thermometer:
> > See paragraph: "Seismic velocity is not a thermometer"
> I agree it can be overdone. This is because velocity variations can be > due to chemical effects, i.e., changes in composition or the presence of > melt.
Or the presence of water.
> Partial melt is not an issue here nor is it an issue for the vast > bulk of the mantle. However, I strongly disagree that this is a problem > with respect to slabs. Slabs which we can trace all the way the to the > surface, seismically, mechanically, and just about any other way you can > think off. As Doglioni is forced to admit, they are stiffer. Moreover we > knew this before anyone did seismic tomography. We knew this because of > deep-focus seismicity. > And since there are not profound major element > chemical changes in a slab, the fundamental cause for this stiffness is > that on average they are hundreds of degrees cooler than the ambient > mantle.
Deep-focus seismicity is related to phase changes and those changes have certainly an impact that can't be neglected.
> Elsewhere on that page Don talks about the effects of slabs in the > transition zone. It is thicker in regions where there is slab, and thinner > where there's not. This is a fundamental prediction satisfied. The > olivine-Spinel transition at around 400km depth is an exothermic reaction > meaning the transition is displaced upwards to lower pressure by cooler > termperatures. The spinel olivine to perovskite-olivine transition at > around 650km is endothermic, meaning cooler temperature displace the > transition lower. Furthermore, seismologists have measured the upward > deflection of olivine -> spinel olivine transition.
> Sorry. If you think slabs don't have a significant negative thermal > anomaly you are in serious denial.
That's not the lower temperature of a slab that is questionable, but its higher density compared to surrounding material. The point is that cold does not mean denser than surrounding material. 600 K cooler means what? 2% denser?
> I don't see Don arguing against this point. But welcome to the one- > layer vs. two-layer wars.
That's a dead war to me. The one-layer/two-layer war does make sense in the context of convection with ascending and descending flows, not when there is only ascending flows.
> > thus suggesting again that low velocities region are associated to high > > density.
> Or both density and the low velocities have something to > with a change in chemistry with respect to nominal mantle. > And this has what to do with slabs?
Nothing. It was just to point that tomographies are misleading because they can't help to make the difference between composition,density or temperature.
A blue area in a tomography can mean a stiff/cold region and at the same time, a red area in the same tomography can mean a dense area.
> > Actually, the density profile raises another issue according to Stavros:
> Oh great another EEer.... > What a surprise.
> > "Then seismology tells us that the velocity of both P and S waves > > increases with depth in the mantle. Density also increases > > with depth. So, if it was only for density the velocity of > > seismic waves should decrease with depth.
> So far so good.
> > There is no other physically > > possible way for seismic wave velocity to increase with depth but for > > the elastic moduli to increase with depth at a faster rate than density. > > This is impossible though if temperature increases with depth. > > Experiment has shown that the elastic moduli are very sensitive to > > temperature; rigidity decreases as temperature increases, and vice > > versa, and at temperatures above 800 oC rigidity diminishes rapidly. > > This decrease cannot in any way be compensated by pressure-depth, > > because the pressure at any depth is below the rigidity and > > incompressibility thresholds.
> Define incompressibility and rigidity thresholds
I think he means that the incompressibility and rigidity are always much larger than the static pressure, so that the static pressure has no significant influence compared to the modulus. Hu???
> > For example according to the Preliminary > > Reference Earth Model - PREM the density of crustal rocks at ~10 km > > depth, is ~2900 kg/m3, the pressure ~0.3 GPa, whereas rigidity mu, and > > incompressibility K, are ~26.6 and ~52 GPa, respectively. At 77 km the > > density is ~3375 kg/m3, the static stress ~2.45 GPa, the rigidity ~67.4 > > GPa, and the incompressibility modulus ~130 GPa. At the depth of 667 km > > the corresponding values for density rho, pressure, rigidity mu, and > > incompressibility K are ~4381 kg/m3, ~23.8, ~155 and ~300 GPa, and at > > 2888 km they are ~5566 kg/m3, ~136, ~294, ~656 GPa."
> > "The implication is quite clear: Depth and therefore static > > stress-pressure has no effect on elastic moduli.
> Not to me. Maybe you should ask Don Anderson if the above > is clear to him?
Actually, it does not make sense to me either :-)
-- Florian "Toute vérité passe par trois phases. D'abord, elle est ridiculisée; ensuite, elle rencontre une vive opposition avant d'être acceptée comme une totale évidence" - Arthur Schopenhauer
On Apr 1, 11:46 am, auxotectonics_deletethis@nachon_andthis.net
(Florian) wrote: > Stuart <bigdak...@aol.com> wrote: > > On Mar 30, 2:28 am, auxotectonics_deletethis@nachon_andthis.net > > (Florian) wrote: > > > Hu? Only basalt and gabbro Eclogitized, so it concerns only 5-8 km not > > > the whole lithosphere!
> > No kidding. But 5-8km of oceanic crust isn't going to stop 100km of > > lithosphere.
> Stuart, it is the opposite, these 5-8 km of crust are supposed to > entrain the whole lithosphere down when they get eclogitized.
They certainly would help. But who suggests that as the only source of buoyancy?
> Absurd isn't it?
> > > > Also, it is on average roughly 600-700K > > > > cooler than the upper mantle. That buys you another 1.5%- 2%.
> > No response?
> > I mean how does Doglioni miss that?
> He did not miss it, he argues that the crust has a different composition > than the asthenosphere, so that temperature is a marginal parameter > considering density. Composition has a larger impact.
Maybe. Maybe not. I agree that how subduction gets going is an interesting problem. What keeps it going is a less interesting one.
> "The oceanic lithosphere is a frozen shallow (30-100 km deep) > asthenosphere, previously depleted below ridges. Therefore, the oceanic > lithosphere is the differentiated lighter upper part of the mantle: then > why should it be heavier a priori than the undepleted deeper (100- 300 > km) asthenosphere lying beneath the old oceanic lithosphere where a > pyrolite density of 3400 kg/m3(Jordan, 1988; Kelly et al., 2003) is > inferred? Moreover, hydrothermal activity generates serpentinization of > the mantle along the ridge that decreases the density even more."
Th question is, does it compensate for the cooler temperatures. If it does, than this raises more issues for subduction initiation.
> > > So actually, the higher velocity in the slab could mean that the slab is > > > simply less dense than surrounding material. Interesting. > > > Doglioni argues that oceanic basalt is depleted and serpentinized which > > > support this interpretation but is at odd with the quote above.
> > Yes, according to him, the oceanic moho should not exist. If lighter > > density components are extracted from the upper mantle, that leaves the > > lithosphere denser
> Hmmm, when something is depleted, its density is always decreased > compared to the original material.
Reference?
>You should revise the notion of > solvent, solute and solution
Basalt is extracted from mantle at low pressure. Basalt is less dense than (mantle - basalt) at low pressure. Basalt has a density of 2.7. Peridotite is at least > 3.0
> > and lower speed according to a naive interpretation of > > that formula.
> The impact of a change in density alone is not much significant. A 10% > increase in density would account for only a 5% decrease in Vp at > constant modulus.
This is very simple. The Moho represents a sharp increase in body wave speed.
No increase, no Moho.The reason for the increase is because of a change in moduli.
And of course the key-phrase here "at constant modulus".
As I've said before density and the moduli have a complex relationship.
> > > Not so sure. Don L. Anderson has a discussion about tomography problems, > > > and notably the tendancy to wrongly use it as a kind of thermometer:
> > > See paragraph: "Seismic velocity is not a thermometer"
> > I agree it can be overdone. This is because velocity variations can be > > due to chemical effects, i.e., changes in composition or the presence of > > melt.
> Or the presence of water.
> > Partial melt is not an issue here nor is it an issue for the vast > > bulk of the mantle. However, I strongly disagree that this is a problem > > with respect to slabs. Slabs which we can trace all the way the to the > > surface, seismically, mechanically, and just about any other way you can > > think off. As Doglioni is forced to admit, they are stiffer. Moreover we > > knew this before anyone did seismic tomography. We knew this because of > > deep-focus seismicity. > > And since there are not profound major element > > chemical changes in a slab, the fundamental cause for this stiffness is > > that on average they are hundreds of degrees cooler than the ambient > > mantle.
> Deep-focus seismicity is related to phase changes and those changes have > certainly an impact that can't be neglected.
Its affected by the phase changes, but not because of them. There are plenty of earthquakes within the slab far from the phase changes.
> > Elsewhere on that page Don talks about the effects of slabs in the > > transition zone. It is thicker in regions where there is slab, and thinner > > where there's not. This is a fundamental prediction satisfied. The > > olivine-Spinel transition at around 400km depth is an exothermic reaction > > meaning the transition is displaced upwards to lower pressure by cooler > > termperatures. The spinel olivine to perovskite-olivine transition at > > around 650km is endothermic, meaning cooler temperature displace the > > transition lower. Furthermore, seismologists have measured the upward > > deflection of olivine -> spinel olivine transition.
> > Sorry. If you think slabs don't have a significant negative thermal > > anomaly you are in serious denial.
> That's not the lower temperature of a slab that is questionable, but its > higher density compared to surrounding material. The point is that cold > does not mean denser than surrounding material. 600 K cooler means what? > 2% denser?
That would be all the mantle needs to convect vigorously.
> > I don't see Don arguing against this point. But welcome to the one- > > layer vs. two-layer wars.
> That's a dead war to me. The one-layer/two-layer war does make sense in > the context of convection with ascending and descending flows, not when > there is only ascending flows.
Its dead to you because of an overcommitment to a non-scientific hypothesis.
> > > thus suggesting again that low velocities region are associated to high > > > density.
> > Or both density and the low velocities have something to > > with a change in chemistry with respect to nominal mantle. > > And this has what to do with slabs?
> Nothing. It was just to point that tomographies are misleading because > they can't help to make the difference between composition,density or > temperature.
> A blue area in a tomography can mean a stiff/cold region and at the same > time, a red area in the same tomography can mean a dense area.
Depends on the circumstances. Anderson doesn't agree with you about slabs.
> > > Actually, the density profile raises another issue according to Stavros:
> > Oh great another EEer.... > > What a surprise.
> > > "Then seismology tells us that the velocity of both P and S waves > > > increases with depth in the mantle. Density also increases > > > with depth. So, if it was only for density the velocity of > > > seismic waves should decrease with depth.
> > So far so good.
> > > There is no other physically > > > possible way for seismic wave velocity to increase with depth but for > > > the elastic moduli to increase with depth at a faster rate than density. > > > This is impossible though if temperature increases with depth. > > > Experiment has shown that the elastic moduli are very sensitive to > > > temperature; rigidity decreases as temperature increases, and vice > > > versa, and at temperatures above 800 oC rigidity diminishes rapidly. > > > This decrease cannot in any way be compensated by pressure-depth, > > > because the pressure at any depth is below the rigidity and > > > incompressibility thresholds.
> > Define incompressibility and rigidity thresholds
> I think he means that the incompressibility and rigidity are always much > larger than the static pressure, so that the static pressure has no > significant influence compared to the modulus. Hu???
> > > For example according to the Preliminary > > > Reference Earth Model - PREM the density of crustal rocks at ~10 km > > > depth, is ~2900 kg/m3, the pressure ~0.3 GPa, whereas rigidity mu, and > > > incompressibility K, are ~26.6 and ~52 GPa, respectively. At 77 km the > > > density is ~3375 kg/m3, the static stress ~2.45 GPa, the rigidity ~67.4 > > > GPa, and the incompressibility modulus ~130 GPa. At the depth of 667 km > > > the corresponding values for density rho, pressure, rigidity mu, and > > > incompressibility K are ~4381 kg/m3, ~23.8, ~155 and ~300 GPa, and at > > > 2888 km they are ~5566 kg/m3, ~136, ~294, ~656 GPa."
> > > "The implication is quite clear: Depth and therefore static > > > stress-pressure has no effect on elastic moduli.
> > Not to me. Maybe you should ask Don Anderson if the above > > is clear to him?
> Actually, it does not make sense to me either :-)
Stuart <bigdak...@aol.com> wrote: > On Apr 1, 11:46 am, auxotectonics_deletethis@nachon_andthis.net > (Florian) wrote: > > Stuart, it is the opposite, these 5-8 km of crust are supposed to > > entrain the whole lithosphere down when they get eclogitized.
> They certainly would help. But who suggests that as the only source of > buoyancy?
This is the mainstream explanation for the slab pull. Look for "eclogitization slab pull" in Google Scholar.
> > He did not miss it, he argues that the crust has a different composition > > than the asthenosphere, so that temperature is a marginal parameter > > considering density. Composition has a larger impact.
> Maybe. Maybe not. I agree that how subduction gets going is an > interesting problem. What keeps it going is a less interesting one.
> > "The oceanic lithosphere is a frozen shallow (30-100 km deep) > > asthenosphere, previously depleted below ridges. Therefore, the oceanic > > lithosphere is the differentiated lighter upper part of the mantle: then > > why should it be heavier a priori than the undepleted deeper (100- 300 > > km) asthenosphere lying beneath the old oceanic lithosphere where a > > pyrolite density of 3400 kg/m3(Jordan, 1988; Kelly et al., 2003) is > > inferred? Moreover, hydrothermal activity generates serpentinization of > > the mantle along the ridge that decreases the density even more."
> The question is, does it compensate for the cooler temperatures. If > it does, than this raises more issues for subduction initiation.
You said that the change of density due to temperature is rather marginal (a couple of percent).
> > Hmmm, when something is depleted, its density is always decreased > > compared to the original material.
> Reference?
Do you really need one? When a substance is dissolved in a solvent, and the substance is released by depressurization, then the density of the solution is higher than the solvent alone or the solute.
to quote Anderson: "Residuum left after melt extraction [...] are examples of high-velocity material that has low density and is buoyant."
> >You should revise the notion of > > solvent, solute and solution
> Basalt is extracted from mantle at low pressure. Basalt is less dense > than (mantle - basalt) at low pressure. Basalt has a density of 2.7.
More like 3.0, no?
> Peridotite is at > least 3.0
Exactly. Basalt (extracted at low pressure) and the residuum are less dense than Peridotite.
> > The impact of a change in density alone is not much significant. A 10% > > increase in density would account for only a 5% decrease in Vp at > > constant modulus.
> This is very simple. The Moho represents a sharp increase in body wave > speed.
> No increase, no Moho.The reason for the increase is because of a change in > moduli.
> And of course the key-phrase here "at constant modulus".
> As I've said before density and the moduli have a complex relationship.
This was exactly my point. The change in velocity is related to a change in modulus, not to a change of density.
> > Deep-focus seismicity is related to phase changes and those changes have > > certainly an impact that can't be neglected.
> Its affected by the phase changes, but not because of them. There are > plenty of earthquakes within the slab far from the phase changes.
Hmmm, the mainstream interpretation is that deep-focus earthquake "originate from dehydration and high-pressure structural instabilities occurring in the hydrated part of the lithosphere that sinks into the upper mantle"
> > That's a dead war to me. The one-layer/two-layer war does make sense in > > the context of convection with ascending and descending flows, not when > > there is only ascending flows.
> Its dead to you because of an overcommitment to a non-scientific > hypothesis.
Sorry, but I don't give much credit to a theory that is entirely based on unsupported assumptions. Plate tectonics is actually very naive.
> > Nothing. It was just to point that tomographies are misleading because > > they can't help to make the difference between composition,density or > > temperature.
> > A blue area in a tomography can mean a stiff/cold region and at the same > > time, a red area in the same tomography can mean a dense area.
> Depends on the circumstances.
Too many parameters, not enough constraints. Basically, you can only state: this area is different than this one regarding either composition, phase, density or temperature. Not very helpful.
> Anderson doesn't agree with you about slabs.
Really? I did not notice.
> > Actually, it does not make sense to me either :-)
> Well, when you figure it out explain it to me.
He thinks that the eastic moduli would not increase if the temperature increases too much? I'll let you know.
-- Florian "Toute vérité passe par trois phases. D'abord, elle est ridiculisée; ensuite, elle rencontre une vive opposition avant d'être acceptée comme une totale évidence" - Arthur Schopenhauer
On Apr 1, 10:41 pm, auxotectonics_deletethis@nachon_andthis.net
(Florian) wrote: > Stuart <bigdak...@aol.com> wrote: > > On Apr 1, 11:46 am, auxotectonics_deletethis@nachon_andthis.net > > (Florian) wrote: > > > Stuart, it is the opposite, these 5-8 km of crust are supposed to > > > entrain the whole lithosphere down when they get eclogitized.
> > They certainly would help. But who suggests that as the only source of > > buoyancy?
> This is the mainstream explanation for the slab pull. Look for > "eclogitization slab pull" in Google Scholar.
> > > He did not miss it, he argues that the crust has a different composition > > > than the asthenosphere, so that temperature is a marginal parameter > > > considering density. Composition has a larger impact.
> > Maybe. Maybe not. I agree that how subduction gets going is an > > interesting problem. What keeps it going is a less interesting one.
> > > "The oceanic lithosphere is a frozen shallow (30-100 km deep) > > > asthenosphere, previously depleted below ridges. Therefore, the oceanic > > > lithosphere is the differentiated lighter upper part of the mantle: then > > > why should it be heavier a priori than the undepleted deeper (100- 300 > > > km) asthenosphere lying beneath the old oceanic lithosphere where a > > > pyrolite density of 3400 kg/m3(Jordan, 1988; Kelly et al., 2003) is > > > inferred? Moreover, hydrothermal activity generates serpentinization of > > > the mantle along the ridge that decreases the density even more."
> > The question is, does it compensate for the cooler temperatures. If > > it does, than this raises more issues for subduction initiation.
> You said that the change of density due to temperature is rather > marginal (a couple of percent).
And the compositional density changes are also marginal, its really a question of which come out on top.
Thermal expansion doesn't vary much from rock to rock.
> > > Hmmm, when something is depleted, its density is always decreased > > > compared to the original material.
> > Reference?
> Do you really need one? > When a substance is dissolved in a solvent, and the substance is > released by depressurization, then the density of the solution is higher > than the solvent alone or the solute.
Didn't think that applied to melts.
> to quote Anderson: "Residuum left after melt extraction [...] are > examples of high-velocity material that has low density and is buoyant."
Fill in the ellipses please.
> > >You should revise the notion of > > > solvent, solute and solution
> > Basalt is extracted from mantle at low pressure. Basalt is less dense > > than (mantle - basalt) at low pressure. Basalt has a density of 2.7.
> Exactly. Basalt (extracted at low pressure) and the residuum are less > dense than Peridotite.
> > > The impact of a change in density alone is not much significant. A 10% > > > increase in density would account for only a 5% decrease in Vp at > > > constant modulus.
> > This is very simple. The Moho represents a sharp increase in body wave > > speed.
> > No increase, no Moho.The reason for the increase is because of a change in > > moduli.
> > And of course the key-phrase here "at constant modulus".
> > As I've said before density and the moduli have a complex relationship.
> This was exactly my point. The change in velocity is related to a change > in modulus, not to a change of density.
Which is what I said earlier. So what is your point?
Doglioni and your other reference made a big deal about increased density lowering the wave speed. I merely pointed out that the relationship between moduli and density is complex and a naive interpretation of that formula leads to inconsistencies such as no moho.
> > > Deep-focus seismicity is related to phase changes and those changes have > > > certainly an impact that can't be neglected.
> > Its affected by the phase changes, but not because of them. There are > > plenty of earthquakes within the slab far from the phase changes.
> Hmmm, the mainstream interpretation is that deep-focus earthquake > "originate from dehydration and high-pressure structural instabilities > occurring in the hydrated part of the lithosphere that sinks into the > upper mantle"
I thought you were talking about about the olivine -> olivine-spinel and spinel -> perovskite changes.
> Don't you consider dehydration a "phase change"?
I didn't tend to think of them that way, though clearly they result in a change in structure and are. This reference is pretty old. I think other studies have shown that water may be stable in the transition zone in the form of wadsleyite. So I'm not sure at the moment dehydration reactions are the stressors in the transition zone.
Either way it doesn't change the fact that slabs can accumulate elastic strain and release it in an earthquake.
This is an issue for you and Doglioni to explain if you to insist there is no thermal anomaly associated with slabs.
> [...]
> > > That's a dead war to me. The one-layer/two-layer war does make sense in > > > the context of convection with ascending and descending flows, not when > > > there is only ascending flows.
> > Its dead to you because of an overcommitment to a non-scientific > > hypothesis.
> Sorry, but I don't give much credit to a theory that is entirely based > on unsupported assumptions. Plate tectonics is actually very naive.
Not nearly as naive as an hypothesis that wants to rewrite the laws of physics on the basis of lack of data.
> > > Nothing. It was just to point that tomographies are misleading because > > > they can't help to make the difference between composition,density or > > > temperature.
> > > A blue area in a tomography can mean a stiff/cold region and at the same > > > time, a red area in the same tomography can mean a dense area.
> > Depends on the circumstances.
> Too many parameters, not enough constraints. > Basically, you can only state: this area is different than this one > regarding either composition, phase, density or temperature. Not very > helpful.
> > Anderson doesn't agree with you about slabs.
> Really? I did not notice.
I did.
> > > Actually, it does not make sense to me either :-)
> > Well, when you figure it out explain it to me.
> He thinks that the eastic moduli would not increase if the temperature > increases too much? I'll let you know.
Stuart <bigdak...@aol.com> wrote: > > This is the mainstream explanation for the slab pull. Look for > > "eclogitization slab pull" in Google Scholar.
> Its an important component.
> Did I say otherwise?
No. But I do. So does Doglioni. I wonder how partial eclogitization of less than 10% of the lithosphere could significantly contribute to make it denser than peridotite.
[...]
> > to quote Anderson: "Residuum left after melt extraction [...] are > > examples of high-velocity material that has low density and is buoyant."
> Fill in the ellipses please.
"Residuum left after melt extraction, and cratonic roots are examples of high-velocity material that has low density and is buoyant. "
> > This was exactly my point. The change in velocity is related to a change > > in modulus, not to a change of density.
> Which is what I said earlier. So what is your point?
> Doglioni and your other reference made a big deal about > increased density lowering the wave speed.
Pardon me? Doglioni said:
"The high velocity of slab detected by tomography could be related not to its higher density but to its higher rigidity and viscosity"
a) he clearly emphasizes the rigidity and viscosity b) his statement is incorrect and should rather read: "The high velocity of slab detected by tomography could be related not to its lower density but to its higher rigidity and viscosity"
You have a weird tendancy to twist quotes.
> I merely pointed out > that the relationship between moduli and density is complex > and a naive interpretation of that formula leads to inconsistencies > such as no moho.
That naive interpretation is yours. Should I say strawman?
[...]
> Either way it doesn't change the fact that slabs can accumulate > elastic strain and release it in an earthquake.
> This is an issue for you and Doglioni to explain if you > to insist there is no thermal anomaly associated with slabs.
Yet Another strawman! At first, Anderson is the one who suggests that higher velocities area visible in tomography (full mantle not specifically slabs) might not be systematically related to temperature, but rather to stiffness or lower density.
Secondly, Doglioni suggests that the higher velocity of slabs might not be related to density, but simply to higher rigidity/viscosity. He never states that "there is no thermal anomaly associated with slabs". Me neither.
I said: "It was just to point that tomographies are misleading because they can't help to make the difference between composition, density or temperature."
> > Sorry, but I don't give much credit to a theory that is entirely based > > on unsupported assumptions. Plate tectonics is actually very naive.
> Not nearly as naive as an hypothesis that wants to rewrite the laws > of physics on the basis of lack of data.
Yet another strawman. That's not how Physics works. There are no rewriting of whatever existing laws. There certainly is a lot of new Physics to do.
Besides, planetary growth is not an hypothesis but an observation. Of course, you're also free to believe that the earth is flat despite observations.
[...]
> > Too many parameters, not enough constraints. > > Basically, you can only state: this area is different than this one > > regarding either composition, phase, density or temperature. Not very > > helpful.
> > > Anderson doesn't agree with you about slabs.
> > Really? I did not notice.
> I did.
You're confused by your own strawman.
-- Florian "Toute vérité passe par trois phases. D'abord, elle est ridiculisée; ensuite, elle rencontre une vive opposition avant d'être acceptée comme une totale évidence" - Arthur Schopenhauer
On Apr 3, 12:53 pm, auxotectonics_deletethis@nachon_andthis.net
(Florian) wrote: > Stuart <bigdak...@aol.com> wrote: > > > This is the mainstream explanation for the slab pull. Look for > > > "eclogitization slab pull" in Google Scholar.
> > Its an important component.
> > Did I say otherwise?
> No. But I do. So does Doglioni. I wonder how partial eclogitization of > less than 10% of the lithosphere could significantly contribute to make > it denser than peridotite.
Couple that with it being cooler. Second, thats a pretty big change in density with basalt -> eclogite. You're talking 10% or more. Thats equivalent to a 1% net for the lithosphere on average.
In mantle convection that is huge. Another boost occurs at the 410km discontinuity when olivine -> spinel-olivine. That is an exothermic phase transition, which acts to enhance subductiom.
Doglioni should try and put some numbers together instead of making assertions.
> > > to quote Anderson: "Residuum left after melt extraction [...] are > > > examples of high-velocity material that has low density and is buoyant."
> > Fill in the ellipses please.
> "Residuum left after melt extraction, and cratonic roots are examples of > high-velocity material that has low density and is buoyant. "
> > > This was exactly my point. The change in velocity is related to a change > > > in modulus, not to a change of density.
> > Which is what I said earlier. So what is your point?
> > Doglioni and your other reference made a big deal about > > increased density lowering the wave speed.
> Pardon me? Doglioni said:
> "The high velocity of slab detected by tomography could be related not > to its higher density but to its higher rigidity and viscosity"
> a) he clearly emphasizes the rigidity and viscosity > b) his statement is incorrect and should rather read: > "The high velocity of slab detected by tomography could be related not > to its lower density but to its higher rigidity and viscosity"
> You have a weird tendancy to twist quotes.
You're the one who just rewrote the quote.
Goodness gracious.
I have trouble making sense out of gibberish. And I interpreted his remarks, as written correctly. He rules out higher density cuz in his naive world higher density means lower speed. In the real world density and the elastic moduli have a complex relationship.
yeah its rigid. Its rigid cuz its cooler and its denser cuz its cooler.
Where is viscosity in the P-wave formula? Do you want to rewrite that too?
Hey, I work with what I'm given. Seems like he could have benefited form a more hard-nose review.
> > I merely pointed out > > that the relationship between moduli and density is complex > > and a naive interpretation of that formula leads to inconsistencies > > such as no moho.
> That naive interpretation is yours. Should I say strawman?
I'm sorry. I pegged his remarks correctly. It is you who offer an alternative cuz you find it embarrassing.
> [...]
> > Either way it doesn't change the fact that slabs can accumulate > > elastic strain and release it in an earthquake.
> > This is an issue for you and Doglioni to explain if you > > to insist there is no thermal anomaly associated with slabs.
> Yet Another strawman!
Not at all.
> At first, Anderson is the one who suggests that higher velocities area > visible in tomography (full mantle not specifically slabs)
We are talking about slabs. the only reason you bring this up is to muddy the waters.
>might not be > systematically related to temperature, but rather to stiffness or lower > density.
> Secondly, Doglioni suggests that the higher velocity of slabs might not > be related to density, but simply to higher rigidity/viscosity. He never > states that "there is no thermal anomaly associated with slabs". Me > neither.
Great, and what is responsible for that higher rigidity?
> I said: "It was just to point that tomographies are misleading because > they can't help to make the difference between composition, density or > temperature."
Again, we are talking about very specific structures.
> > > Sorry, but I don't give much credit to a theory that is entirely based > > > on unsupported assumptions. Plate tectonics is actually very naive.
> > Not nearly as naive as an hypothesis that wants to rewrite the laws > > of physics on the basis of lack of data.
> Yet another strawman. That's not how Physics works.
You're right planets accumulating mass and angular moment in just the right amounts is a whole lot better than saying God did it.
> There are no > rewriting of whatever existing laws. There certainly is a lot of new > Physics to do.
Start doing it, then.
> Besides, planetary growth is not an hypothesis but an observation.
No, it is not. There is no unambiguous measurement showing the earth's expansion.
> Of > course, you're also free to believe that the earth is flat despite > observations.
So your saying the evidence for an expanding earth is as strong as the evidence that the Earth is round?
> [...]
> > > Too many parameters, not enough constraints. > > > Basically, you can only state: this area is different than this one > > > regarding either composition, phase, density or temperature. Not very > > > helpful.
> > > > Anderson doesn't agree with you about slabs.
Florian wrote: > Stuart <bigdak...@aol.com> wrote:
> > If you have a massive lava flow it will reduce the crater density by > > burying the craters.
> > On an object like the moon, we knew that the Mare were younger than the > > highlands before any rocks were brought back. Why because they had a lower > > crater density than any place else. Why? because the flood basalts that > > comprise the Mare buried the craters in effect resetting the crater > > density based chronometer.
> Explain that to Georgie who is apparently convinced "that the volcanic > activity has been widely distributed and sporatic in time as indicated > by continued loss of craters due to lava flows." (sic!)
> or again:
> "In other words, volcanic activity has resurfaced the planet, and in > doing so, has erased many prior impacts. That is largely why over time, > the graph shows a DECREASE in impacts - because the surface has been > resculpted by volcanic activity."
> See, you're buddy truly think that the graph shows a decrease in impacts > because of the lava flow resetting the surface, whereas the graph show a > decrease in the DENSITY of craters because there is simply less > asteroids that impacts as time goes by. > Even highschooler know that the frequency of asteroid impacts decrease > with time in the inner solar system. > For sure, If the frequency had been constant with time, that would have > been much easier to date surfaces, but that is not he case (see the work > of Hartmann, Neukum and Ivanov cited below.)
> > George's point flew right over your head.
> Give me a break. See above. I don't even understand why you try to save > the scalp of a moron that can't understand an article nor read a graph > legend.
> > You can assume the bombardment of the moon and other bodies was similar. > > Probably not a great assumption, but better than an order of magnitude.
> "I" don't assume. This assumption was made and jsutified by Neukum > Ivanov and Hartmann to date the surface of Mars from Moon's data. See > in:
> Hartmann, W. K. and Neukum, G. (2001) Space Sci. Rev. 96, 165-194
> I wonder if you worth more than Georgie... I remember you were the one > stating that buoyancy is not related to pressure gradient. What a pity.
> -- > Florian > "Toute v rit passe par trois phases. D'abord, elle est ridiculis e; > ensuite, elle rencontre une vive opposition avant d' tre accept e comme > une totale vidence" - Arthur Schopenhauer
(Just reading this bit...) You have to understand, Florian, you're talking to the Pope and the choirboy, sometimes in role reversal. But broadly we have a BIGPOPE and a scrungy little George - with Aidan generally offering George moral if not physical support from the sidelines of his killfile. It's an in-principle thing. Though in a surprising display of role- reversal a while back George actually abandoned Stuart, ...dumped him in his litter behind a tree in the forest, ...left him to the failing light, the woodland denizens, a bottle of creme de menthe, and headed for the hills, leaving our Stu to his own starlit devices. It's a wonder he's turned up to support George given that noticeably unceremonius behaviour of his. He must have recovered somewhat (Stuart that is) because we heard from him more recently broadcasting from his supermarket trolley behind some warehouses in dockland, something about cardboard. Dry cardboard. He was looking for dry cardboard because the stuff he had was all sozzled from being peeed on (by George and sundry others) because Stu's pockets were full up.
I see further down you have him by the short and curlies on the eclogite transition. But just watch his left hook on rubber numbers. It's something Popes learn early on - about rubber.
Florian wrote: > Stuart <bigdak...@aol.com> wrote:
> > On Mar 24, 11:30 am, auxotectonics_deletethis@nachon_andthis.net > > (Florian) wrote:
> > > More non sense. Of course it is important. It does provide the net > > > force, i.e., the acceleration of the object!
> > So if I don my astronaut suit and enclose myself in a > > vacuum chamber and drop a brick it won't fall cuz there > > is no lithostatic gradient?
> I see, you want to play dumb... Ok.
> NET force= the difference between: > - The buoyancy force, that is dependent on the pressure gradient and > that is pushing the object up > - Gravity pulling the object down.
> Your example is stupid, because by definition, there is no fluid in your > vacuum and therefore no buoyancy force to balance gravity.
> > > It does when the fluid has a way out which is obviosuly the case of the > > > mantle. Considering the mantle is in an enclosed system is unrealistic.
> > Actually, it is a very, very good approximation. Dynamic topography is > > 3 orders of magnitude less than the mantle thickness.
> <eyes rolling>
> Hello, we're discussing the buoyancy of a whole slab which is supposed > to be hundreds km long.
*Tens of thousands* of kilometres long. The same subduction zone (with the same slab going down it) goes all around the Pacific margin. It's where the ocean floor reaches back to the spreading ridges that it frays into transform faults. Ask Stuart how subduction does that - pulls on the ocean floor, ..making it fray all the way back to the ridge. He won't answer me from his trolley. I think he's hoping to snare a passer by... So look out. (The rubber numbers....) He looks really cute in the black one, but don't be fooled. A charlatan of papal purple lurks beneath...
> -- > Florian > "Toute v rit passe par trois phases. D'abord, elle est ridiculis e; > ensuite, elle rencontre une vive opposition avant d' tre accept e comme > une totale vidence" - Arthur Schopenhauer
Stuart wrote: > On Mar 25, 2:14 am, auxotectonics_deletethis@nachon_andthis.net > (Florian) wrote: > > Stuart <bigdak...@aol.com> wrote: > > > On Mar 24, 11:30 am, auxotectonics_deletethis@nachon_andthis.net > > > (Florian) wrote: > > > > More non sense. Of course it is important. It does provide the net > > > > force, i.e., the acceleration of the object!
> > > So if I don my astronaut suit and enclose myself in a > > > vacuum chamber and drop a brick it won't fall cuz there > > > is no lithostatic gradient?
> > I see, you want to play dumb... Ok.
> No just trying to fully make sense of what you write.
> > NET force= the difference between: > > - The buoyancy force, that is dependent on the pressure gradient and > > that is pushing the object up > > - Gravity pulling the object down.
> We seem to be going around in circles and talking past > each other.
> You're concentrating on the forces on the object. I'm > talking about the fluid motions induced by the buoyant > object.
> Again, you seem to think I have a problem with this > basic description you gave above. I don't. I generally don't argue > with 2000 year old principles. However Archimedes couldn't tell > you how fast an object should sink, that required a knowledge > of fluid mechanics he did not possess.
So tell us again, Stuart, ..if the sinking slab drives plate Tectonics, how does subduction cause transform faults? And how does it pull the ocean floor without making any earthquakes all the way to the ridge?
> What I'm telling you is that the fluid > motions (which is what I'm interested in, not the force balance on > the block itself) induced by the sinking object are driven by pressure > variations > not governed by dP/dz = -gR where R is the density of the fluid.
> dP/dz = -gR is a condition for hydrostatic equilibrium in a plane > fluid layer.
> If you don't believe me consult Turcotte and Schubert or any other > book > that works through the equations governing Rayleigh-Benard convection. > In fact, go through Chandraseakhar's stability analysis of the > Rayleigh-Benard > problem.
> I cannot be any more clear than this. You need to show me > that the term -gRo, the lithostatic pressure gradient is present > in the eqs of motion. The pressure that is set up by the motion is > commonly referred to as the *dynamic pressure* and that is what > you wind up in the eqs of motion when you through the derivation.
> Stuart
And you to tell us how a subducting slab makes all that noise when it goes down, but none all the way back to the ridge. What rubber number are you going to turn up in to explain that one, Liberace?
Stuart <bigdak...@aol.com> wrote: > On Apr 3, 12:53 pm, auxotectonics_deletethis@nachon_andthis.net > (Florian) wrote: > > No. But I do. So does Doglioni. I wonder how partial eclogitization of > > less than 10% of the lithosphere could significantly contribute to make > > it denser than peridotite.
> Couple that with it being cooler.
You said cooler was equivalent to 1 may be 2 % denser.
> Second, thats a pretty big change in > density with basalt -> eclogite. You're talking 10% or more. Thats equivalent > to a 1% net for the lithosphere on average.
Not even 1% because eclogitization is only partial. Even 1% is ridiculous considering that the mantle is heterogenous.
By the way Stuart, is there any example of well characterized convection in plastic solids?
> In mantle convection that is huge. Another boost occurs at the 410km > discontinuity when olivine -> spinel-olivine. That is an exothermic phase > transition, which acts to enhance subductiom.
It is the opposite. Models show that the olivine -> spinel transition is apparently not favorable to subduction. It slows it down:
> > "The high velocity of slab detected by tomography could be related not > > to its higher density but to its higher rigidity and viscosity"
> > a) he clearly emphasizes the rigidity and viscosity > > b) his statement is incorrect and should rather read: > > "The high velocity of slab detected by tomography could be related not > > to its lower density but to its higher rigidity and viscosity"
> > You have a weird tendancy to twist quotes.
> You're the one who just rewrote the quote.
We already discussed the quote and I told you it looked incorrect.
> Goodness gracious.
> I have trouble making sense out of gibberish. And I interpreted his > remarks, as written correctly. He rules out higher density cuz in his > naive world > higher density means lower speed. In the real world density and the > elastic moduli have a complex relationship.
> yeah its rigid. Its rigid cuz its cooler and its denser cuz its > cooler.
Jeez, did you already forget the point? The point was that for a material, cooler mean denser. But it does not mean at all that the slab being cooler than surrounding material, would also be denser than surrounding material.
If a slab has a density of 3.0 and his temperature is about 700 K, it won't be denser than peridotite that has a density about 3.3 at 1200 K. Get it?
[...]
> Not at all.
> > At first, Anderson is the one who suggests that higher velocities area > > visible in tomography (full mantle not specifically slabs)
> We are talking about slabs. the only reason you bring this up is > to muddy the waters.
No. I wanted to remind you that tomography are misleading when people try to use them as thermometer, and that colder does not mean necessarly denser when comparing two different materials.
> > Secondly, Doglioni suggests that the higher velocity of slabs might not > > be related to density, but simply to higher rigidity/viscosity. He never > > states that "there is no thermal anomaly associated with slabs". Me > > neither.
> Great, and what is responsible for that higher rigidity?
In slabs? It might be temperature, it might be composition, it might be phase, It might be a mix, how would you know? That's all the issue.
[...]
> > Yet another strawman. That's not how Physics works.
> You're right planets accumulating mass and angular moment in just > the right amounts is a whole lot better than saying God did it.
And YET another strawman. There is no constraints for "just right amounts". The system is dynamic by essence.
> > There are no > > rewriting of whatever existing laws. There certainly is a lot of new > > Physics to do.
> Start doing it, then.
Whatever.
> > Besides, planetary growth is not an hypothesis but an observation.
> No, it is not. There is no unambiguous measurement showing the earth's > expansion.
To restrict the observations of planetary growth to measurment of the earth is ludicrous.
> > Of > > course, you're also free to believe that the earth is flat despite > > observations.
> So your saying the evidence for an expanding earth is as strong > as the evidence that the Earth is round?
Of course it is! For a start, there is no recycling of seafloor whatsoever! No recycling=> growth.
The good news is that you might live long enough to figure out you're completely mistaken.
-- Florian "Toute vérité passe par trois phases. D'abord, elle est ridiculisée; ensuite, elle rencontre une vive opposition avant d'être acceptée comme une totale évidence" - Arthur Schopenhauer
> So your saying the evidence for an expanding earth is as strong > as the evidence that the Earth is round?
'Sright, Stuart. Gravity (however it's supposed to work). In all its manfestations. Why not, as a geophysicist, come out of your bath with your floating leg, and give us some clues about how gravity is supposed to work, instead of keep telling us about convection, pots of soup and cups of tea. Convection is silly. Tell us about gravity, ...and how it's supposed to work at a distance.
Or if you prefer to stick with convection, then maybe you could tell us how convection frictional drag, ridge push, etc etc, manages to combine millimetre-scale symmetry in *its* operation. http://users.indigo.net.au/don/pr/ridgesplit.html
> > > > Too many parameters, not enough constraints. > > > > Basically, you can only state: this area is different than this one > > > > regarding either composition, phase, density or temperature. Not very > > > > helpful.
> > > > > Anderson doesn't agree with you about slabs.
(Florian) wrote: > Stuart <bigdak...@aol.com> wrote: > > On Apr 3, 12:53 pm, auxotectonics_deletethis@nachon_andthis.net > > (Florian) wrote: > > > No. But I do. So does Doglioni. I wonder how partial eclogitization of > > > less than 10% of the lithosphere could significantly contribute to make > > > it denser than peridotite.
> > Couple that with it being cooler.
> You said cooler was equivalent to 1 may be 2 % denser.
> > Second, thats a pretty big change in > > density with basalt -> eclogite. You're talking 10% or more. Thats equivalent > > to a 1% net for the lithosphere on average.
> Not even 1% because eclogitization is only partial. Even 1% is > ridiculous considering that the mantle is heterogenous.
Heterogenous isotopically, not so much in major element chemistry.
There's a difference.
> By the way Stuart, is there any example of well characterized convection > in plastic solids?
Define "plastic". Give me a rheology.
> > In mantle convection that is huge. Another boost occurs at the 410km > > discontinuity when olivine -> spinel-olivine. That is an exothermic phase > > transition, which acts to enhance subductiom.
> It is the opposite. Models show that the olivine -> spinel transition is > apparently not favorable to subduction. It slows it down:
That is in the case of metastability, in which the transition does not occur at the normal P &T and is delayed to higher Pressure. Yes it might mitigate the effect, but there obervations where the 410k discontinuity is displaced upwards.
> > > "The high velocity of slab detected by tomography could be related not > > > to its higher density but to its higher rigidity and viscosity"
> > > a) he clearly emphasizes the rigidity and viscosity > > > b) his statement is incorrect and should rather read: > > > "The high velocity of slab detected by tomography could be related not > > > to its lower density but to its higher rigidity and viscosity"
> > > You have a weird tendancy to twist quotes.
> > You're the one who just rewrote the quote.
> We already discussed the quote and I told you it looked incorrect.
> > I have trouble making sense out of gibberish. And I interpreted his > > remarks, as written correctly. He rules out higher density cuz in his > > naive world > > higher density means lower speed. In the real world density and the > > elastic moduli have a complex relationship.
> > yeah its rigid. Its rigid cuz its cooler and its denser cuz its > > cooler.
> Jeez, did you already forget the point? The point was that for a > material, cooler mean denser. But it does not mean at all that the slab > being cooler than surrounding material, would also be denser than > surrounding material.
Only is its made out of substainially different stuff.
> If a slab has a density of 3.0 and his temperature is about 700 K, it > won't be denser than peridotite that has a density about 3.3 at 1200 K. > Get it?
Where do you get a slab density of 3.0?
> [...]
> > Not at all.
> > > At first, Anderson is the one who suggests that higher velocities area > > > visible in tomography (full mantle not specifically slabs)
> > We are talking about slabs. the only reason you bring this up is > > to muddy the waters.
> No. I wanted to remind you that tomography are misleading when people > try to use them as thermometer, and that colder does not mean necessarly > denser when comparing two different materials.
I don't need a reminder form you. Stick to the subject.
> > > Secondly, Doglioni suggests that the higher velocity of slabs might not > > > be related to density, but simply to higher rigidity/viscosity. He never > > > states that "there is no thermal anomaly associated with slabs". Me > > > neither.
> > Great, and what is responsible for that higher rigidity?
> In slabs? It might be temperature, it might be composition, it might be > phase, It might be a mix, how would you know? That's all the issue.
Its temperature. You're again trying to muddy the waters.
> [...]
> > > Yet another strawman. That's not how Physics works.
> > You're right planets accumulating mass and angular moment in just > > the right amounts is a whole lot better than saying God did it.
> And YET another strawman. There is no constraints for "just right > amounts". The system is dynamic by essence.
Stuart wrote: > Define "plastic". Give me a rheology.
...and stuart will give you another number.
What really is amazing is the legerdemain with which you can pass off such ludicrous crap as legitimate science. Your world of numbers is no more than a world of wonky mirrors, when you can profess to ignore the obviously wrong and self-serving premises you base them on.
> You can have the last word.
> Stuart
You're a fool Stuart. Living proof that education is no prophylactic. You cannot be oblivious to the contradictions of Plate Tectonics, yet you refuse to acknowledge them - and you justify your refusal as 'science'. You abrogate its first responsibility - falsification. You *are* a charlatan. We can just thank God you chose the route of science where your predilections are transparent to any right-thinking person, .. and not the church with its appeal to vulnerable pathos.
It's depressing there are people like you around in science:- ---------------------------------------------------------------------- "Enter peer review. Recycled popular dogma breezes through, but new concepts displease challenged experts. It is difficult to publish, or get a grant for, work contrary to conventional wisdom because many reviewers, editors, and managers obstruct anything that conflicts with their beliefs. My own descriptive work sailed through, but the innovation for which you honor me often did not, and some of my best work was wholly blocked. Keith mentioned my three current major contrarian papers. These are appearing in books with supportive editors because I am now unwilling to probe successive journals for possible chinks in their conventional-wisdom armor. Two of these three multidisciplinary manuscripts were attacked viciously, on personal as well as contextual grounds, by turf-defending specialist reviewers. Other geoscientists whose work I most admire report similar personal and topical obstruction of contrarian papers which ultimately proved to be broadly correct. http://www.geosociety.org/awards/07speeches/sgt.htm --------------------------------------------------------------------------- - ..but thankfully like a virus, you are in 'the vault'
> Florian a écrit dans le message > <1iebzcq.1dhxn5o4dg1n1N%auxotectonics_deletethis@nachon_andthis.net>...
> >Stuart <bigdak...@aol.com> wrote: > >SNIP > >> > Concerning the Navier-Stokes equations you certainly remember that the > >> > acceleration of the fluid is proportional to the *gradient* of > pressure. > >> > Right?
> >> non-hydrostatic pressure gradient in the case of an incompressible > >> fluid.
> >> Again, I'll ask you one more time. > >> What are equation of motions in the case of a > >> fluid with just a hydrostatic gradient?
> >> If you are familiar with NS, this should be easy for you.
> >I'm not particular familiar with NS (after all, I'm far from my field) > >but that should be something like that (inviscid fluid):
> >rho(∂v/∂t+v.del v)=-del p+rho.g
> >-del p is the pressure gradient component.
> >Now your turn, could you please finally answer the question:
> >"Do you agree that the lithostatic pressure gradient is relevant to > >buoyancy, yes or no?"
> >> > Something tell me that I will nail you a second time today...
> >> After the 1-200 times I've nailed you
> >In your wildest dreams, or show me the messages ID.
> >-- > >Florian
> The momentum balance equation for a Newtonian fluid is called the > Navier -Stokes equation. > The equation known as Darcy's law is derived from this equation. This > law forms the basis for ground water motion. It is q = k (h1-h2)/ l > q is called the darcian flux or velocity > h = z + p/rwg " p" contains the hydrostatic pressure > z is the elevation of the base of the manometer relative to some datum where > zo=0
> "A general weak conserval'iveform of Navier-Stokes equations expressed with > respect .... where P is the hydrostatic pressure and its expression iswww.springerlink.com/index/3681N56414R12124.pdf"
Lets be clear. Shallow water models represent the ocean thickness typically in the fashion:
D(x,y,t) = Ho + n(x,y, t)
Where Ho is the undisturbed ocean thickness and n(x,y,t) is the fluctuating component due to a long gravity wave or some other disturbance.
The corresponding pressure is P = rg * ( Ho + n(x,y,t) ) where rgHo is the hyrdostatic pressure, cuz it is the pressure when there is no topographic disturbance and no motion.
The dynamic pressure rgn(x,y,t) is what is driving the flow associated with the long wave. Because long waves as their name implies, have long wavelengths the pressure disturbances they produce are felt at the bottom of the ocean, hence this is what is measured by DART buoys.
The hydrostatic pressure rgHo disappears from the equation of motion. Whats left is the dynamic pressure. Some people refer to using a "local hydrostatic approx.", but globally, an ocean with a tsunami moving across it is not in hydrostatic equilibrium.
don findlay <d...@tower.net.au> wrote: > Stuart wrote:
> > Define "plastic". Give me a rheology.
> ...and stuart will give you another number.
A french geologist told me a joke recently. I really love it. I try a translation:
What's 2 times 2? A mathematician answers right away: 4! A geologist, hesitates a bit, but finally answers: that must be 4. Then a geophysicist: How much do you want?
Feel free to improve the translation :-)
-- Florian "Toute vérité passe par trois phases. D'abord, elle est ridiculisée; ensuite, elle rencontre une vive opposition avant d'être acceptée comme une totale évidence" - Arthur Schopenhauer
(Florian) wrote: > don findlay <d...@tower.net.au> wrote: > > Stuart wrote:
> > > Define "plastic". Give me a rheology.
> > ...and stuart will give you another number.
> A french geologist told me a joke recently. > I really love it. I try a translation:
> What's 2 times 2? > A mathematician answers right away: 4! > A geologist, hesitates a bit, but finally answers: that must be 4. > Then a geophysicist: How much do you want?
> Feel free to improve the translation :-)
A geophysicist walks into a McDonalds and orders a whopper.
The expanding earther says "Want fries with that?"
> On Apr 4, 10:52 pm, auxotectonics_deletethis@nachon_andthis.net
> (Florian) wrote: > > don findlay <d...@tower.net.au> wrote: > > > Stuart wrote:
> > > > Define "plastic". Give me a rheology.
> > > ...and stuart will give you another number.
> > A french geologist told me a joke recently. > > I really love it. I try a translation:
> > What's 2 times 2? > > A mathematician answers right away: 4! > > A geologist, hesitates a bit, but finally answers: that must be 4. > > Then a geophysicist: How much do you want?
> > Feel free to improve the translation :-)
> A geophysicist walks into a McDonalds and orders a whopper.
Indeed !,a geophysicist would only ask for something that is not on the menu - try Burger King.
The people behind the counter of fast food chains are effecient and do their jobs properly,convection cell/ee guys do not.
Stuart wrote: > On Mar 24, 7:03 am, "Jean" <jean.len...@wanadoo.fr> wrote: > > Florian a écrit dans le message > > <1iebzcq.1dhxn5o4dg1n1N%auxotectonics_deletethis@nachon_andthis.net>...
> > >Stuart <bigdak...@aol.com> wrote: > > >SNIP > > >> > Concerning the Navier-Stokes equations you certainly remember that the > > >> > acceleration of the fluid is proportional to the *gradient* of > > pressure. > > >> > Right?
> > >> non-hydrostatic pressure gradient in the case of an incompressible > > >> fluid.
> > >> Again, I'll ask you one more time. > > >> What are equation of motions in the case of a > > >> fluid with just a hydrostatic gradient?
> > >> If you are familiar with NS, this should be easy for you.
> > >I'm not particular familiar with NS (after all, I'm far from my field) > > >but that should be something like that (inviscid fluid):
> > >rho(∂v/∂t+v.del v)=-del p+rho.g
> > >-del p is the pressure gradient component.
> > >Now your turn, could you please finally answer the question:
> > >"Do you agree that the lithostatic pressure gradient is relevant to > > >buoyancy, yes or no?"
> > >> > Something tell me that I will nail you a second time today...
> > >> After the 1-200 times I've nailed you
> > >In your wildest dreams, or show me the messages ID.
> > >-- > > >Florian
> > The momentum balance equation for a Newtonian fluid is called the > > Navier -Stokes equation. > > The equation known as Darcy's law is derived from this equation. This > > law forms the basis for ground water motion. It is q = k (h1-h2)/ l > > q is called the darcian flux or velocity > > h = z + p/rwg " p" contains the hydrostatic pressure > > z is the elevation of the base of the manometer relative to some datum where > > zo=0
> > "A general weak conserval'iveform of Navier-Stokes equations expressed with > > respect .... where P is the hydrostatic pressure and its expression iswww.springerlink.com/index/3681N56414R12124.pdf"
> Lets be clear. Shallow water models represent the ocean thickness > typically in the fashion:
> D(x,y,t) = Ho + n(x,y, t)
> Where Ho is the undisturbed ocean thickness and n(x,y,t) is the > fluctuating component due to > a long gravity wave or some other disturbance.
> The corresponding pressure is P = rg * ( Ho + n(x,y,t) ) where rgHo is > the hyrdostatic pressure, cuz > it is the pressure when there is no topographic disturbance and no > motion.
> The dynamic pressure rgn(x,y,t) is what is driving the flow associated > with the long wave. Because long > waves as their name implies, have long wavelengths the pressure > disturbances they produce are felt > at the bottom of the ocean, hence this is what is measured by DART > buoys.
> The hydrostatic pressure rgHo disappears from the equation of motion. > Whats left is the dynamic pressure. > Some people refer to using a "local hydrostatic approx.", but > globally, an ocean with a tsunami > moving across it is not in hydrostatic equilibrium.
> Stuart
Florian said:- "So could you please answer this question: What makes a slab sink if its density is initially lower than that of the upper mantle?" to which you replied:- " Yawn. It is dynamically unimportant. "
Why don't you tell it like it is? That it's the continental lithosphere pushing the oceanic one down. Or that it's the dyke at the ridges ("Ridge-push") doing it - ten centimetres of it, ...pushing half a world of ocean floor and 200kilometres of oceanic lithospheric thickness down the gurgler. Or maybe that it's the cooling off the ridge flanks that's doing the pushing.
(You and your bloody Navier-stokes equations...) Aidan toadying I can understand but it has me beat why Florian says anything half-ways respectable to you at all.
Stuart <bigdak...@aol.com> wrote: > On Apr 4, 12:08 pm, auxotectonics_deletethis@nachon_andthis.net > (Florian) wrote: > > Not even 1% because eclogitization is only partial. Even 1% is > > ridiculous considering that the mantle is heterogenous.
> Heterogenous isotopically, not so much in major element chemistry.
The mantle is swallowing stuff that likely make it very heterogenous, hence the marble cake model proposed by Allègre.
> > By the way Stuart, is there any example of well characterized convection > > in plastic solids?
> Define "plastic". Give me a rheology.
"Plastic solid: A material that deforms continuously and permanently when submitted to a shearing stress in excess of its yield value."
So give me any example of plastic solids that were oberved to convect.
> > > In mantle convection that is huge. Another boost occurs at the 410km > > > discontinuity when olivine -> spinel-olivine. That is an exothermic phase > > > transition, which acts to enhance subductiom.
> > It is the opposite. Models show that the olivine -> spinel transition is > > apparently not favorable to subduction. It slows it down:
> That is in the case of metastability, in which the transition does not > occur at the normal P &T and is delayed to higher Pressure.
Isn't it always the case in slabs?
> Yes it might mitigate the effect, but there obervations where the 410k > discontinuity is displaced upwards.
Something is missing in this sentence.
> > We already discussed the quote and I told you it looked incorrect.
> So? Did I twist the quote or not?
Yes, you said he emphasizes density over modulus whereas the quote says the opposite.
> > Jeez, did you already forget the point? The point was that for a > > material, cooler mean denser. But it does not mean at all that the slab > > being cooler than surrounding material, would also be denser than > > surrounding material.
> Only is its made out of substainially different stuff.
Which is quite the case: mafic crust+ ultramafic lithospheric mantle.
> > If a slab has a density of 3.0 and his temperature is about 700 K, it > > won't be denser than peridotite that has a density about 3.3 at 1200 K. > > Get it?
> Where do you get a slab density of 3.0?
Well, ok, may be a bit more. The crust (pillow+dikes+Gabbro) has a density of 2.7 to 3.0 according to you: "basalts has a density of 2.7" and "2.7 - 3.0 on the high side". There is the serpentinized peridotite (density about 2.6) and peridotite (3.3).
Do you have any reference describing density-temperature relationship for peridotite?
[...]
> > In slabs? It might be temperature, it might be composition, it might be > > phase, It might be a mix, how would you know? That's all the issue.
> Its temperature. You're again trying to muddy the waters.
It is stiffness. And stiffness depends on more than temperature.
[...]
> Your invincible ignorance is on par with that of flat earthers.
And you hide your head in the sand.
Could you please explain me that pattern in the framework of plate tectonics:
If you don't realize that fresh lithopshere is emplaced and overrides some of the old one, they you must be sick. There is no recycling there, only new layers that partly superpose over old ones in accord to earth growth.
-- Florian "Toute vérité passe par trois phases. D'abord, elle est ridiculisée; ensuite, elle rencontre une vive opposition avant d'être acceptée comme une totale évidence" - Arthur Schopenhauer
(Florian) wrote: > Stuart <bigdak...@aol.com> wrote: > > On Apr 4, 12:08 pm, auxotectonics_deletethis@nachon_andthis.net > > (Florian) wrote: > > > Not even 1% because eclogitization is only partial. Even 1% is > > > ridiculous considering that the mantle is heterogenous.
> > Heterogenous isotopically, not so much in major element chemistry.
> The mantle is swallowing stuff that likely make it very heterogenous, > hence the marble cake model proposed by Allègre.
> > > By the way Stuart, is there any example of well characterized convection > > > in plastic solids?
> > Define "plastic". Give me a rheology.
> "Plastic solid: A material that deforms continuously and permanently > when submitted to a shearing stress in excess of its yield value."
> So give me any example of plastic solids that were oberved to convect.
> > > > In mantle convection that is huge. Another boost occurs at the 410km > > > > discontinuity when olivine -> spinel-olivine. That is an exothermic phase > > > > transition, which acts to enhance subductiom.
> > > It is the opposite. Models show that the olivine -> spinel transition is > > > apparently not favorable to subduction. It slows it down:
> > That is in the case of metastability, in which the transition does not > > occur at the normal P &T and is delayed to higher Pressure.
> Isn't it always the case in slabs?
> > Yes it might mitigate the effect, but there obervations where the 410k > > discontinuity is displaced upwards.
> Something is missing in this sentence.
> > > We already discussed the quote and I told you it looked incorrect.
> > So? Did I twist the quote or not?
> Yes, you said he emphasizes density over modulus whereas the quote says > the opposite.
> > > Jeez, did you already forget the point? The point was that for a > > > material, cooler mean denser. But it does not mean at all that the slab > > > being cooler than surrounding material, would also be denser than > > > surrounding material.
> > Only is its made out of substainially different stuff.
> Which is quite the case: mafic crust+ ultramafic lithospheric mantle.
> > > If a slab has a density of 3.0 and his temperature is about 700 K, it > > > won't be denser than peridotite that has a density about 3.3 at 1200 K. > > > Get it?
> > Where do you get a slab density of 3.0?
> Well, ok, may be a bit more. The crust (pillow+dikes+Gabbro) has a > density of 2.7 to 3.0 according to you: "basalts has a density of 2.7" > and "2.7 - 3.0 on the high side". > There is the serpentinized peridotite (density about 2.6) and peridotite > (3.3).
> Do you have any reference describing density-temperature relationship > for peridotite?
> [...]
> > > In slabs? It might be temperature, it might be composition, it might be > > > phase, It might be a mix, how would you know? That's all the issue.
> > Its temperature. You're again trying to muddy the waters.
> It is stiffness. And stiffness depends on more than temperature.
> [...]
> > Your invincible ignorance is on par with that of flat earthers.
> And you hide your head in the sand.
> Could you please explain me that pattern in the framework of plate > tectonics:
> If you don't realize that fresh lithopshere is emplaced and overrides > some of the old one, they you must be sick. There is no recycling there, > only new layers that partly superpose over old ones in accord to earth > growth.
> -- > Florian > "Toute vérité passe par trois phases. D'abord, elle est ridiculisée; > ensuite, elle rencontre une vive opposition avant d'être acceptée comme > une totale évidence" - Arthur Schopenhauer
You know,this topic was discussed years ago in this forum,basically a tiny growth in the girth of the planet due to the transfer of denser mantle to lighter crust and was accepted as a matter of course given that it is a normal volume increase of crust at the expense of denser mantle -
It is a sort of thing that goes nowhere unless you feel a huge responsibility to promote a minor point.
Over the last 4 years they have added more details to stellar rotational dynamics allowing generalised dynamics to emerge hence the increasing stress on rotational dynamics as the mechanism for crustal motion.As for crustal expansion which is the direction you are going,well,that is not Earth expansion and in some ways I am sorry for giving you more credit than you deserve and I am more irritated at the tectonic guys for dragging that excellent concept down to a standard by sticking with geostationary criteria and throwing 'coriolis' at me like Carsten did 4 years ago.
Looking at thread and how reasoning evolved towards geodynamics and specifically the linking of the Earth's shape with crustal dynamics,sci.geo.geology was a more reasonable place.You fight over surface correlations to draw your conclusions whereas a new geodynamic leaves only clues as to the internal composition and viscosity of the Earth and nothing near the criteria for 'convection cells'.The unfortunate part is that these cells may now ,in the minds of geologists ,have become an established 'fact' and nothing will shake them out of their geostationary mechanism.
> On Apr 5, 12:50 pm, Stuart <bigdak...@aol.com> wrote:
> > On Apr 4, 10:52 pm, auxotectonics_deletethis@nachon_andthis.net
> > (Florian) wrote: > > > don findlay <d...@tower.net.au> wrote: > > > > Stuart wrote:
> > > > > Define "plastic". Give me a rheology.
> > > > ...and stuart will give you another number.
> > > A french geologist told me a joke recently. > > > I really love it. I try a translation:
> > > What's 2 times 2? > > > A mathematician answers right away: 4! > > > A geologist, hesitates a bit, but finally answers: that must be 4. > > > Then a geophysicist: How much do you want?
> > > Feel free to improve the translation :-)
> > A geophysicist walks into a McDonalds and orders a whopper.
> Indeed !,a geophysicist would only ask for something that is not on > the menu - try Burger King.
Stuart wrote: > Maybe. Maybe not. I agree that how subduction gets going is an > interesting problem.
Really? Now this is news. What problem do you see, Stuart? Is it convection drives subduction, ..or subduction drives convection?
There's a nice simple framework for your answer. Which one would you like to begin with? (..since both of them seem to figure in Plate Tectonics as equally correct).
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