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Geological Processes - Science topic

Events and activities of the Earth and its structures.
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I am looking for references about geological process rates to highlight the differences between average rates and episodic rates for teaching purposes. Does anyone know some references? Thank you
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ليس لديه فكره
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Hello Everybody,
My objective is to model the stress-relief mechanism of a clayey meter scale experiment.
Please, share published material and your suggestions for such a small scale experiment.
Thanks  
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This is a good question.
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I understand metasomatism as follows:-
1. It is a geological process which involves the transfer of fluid energy and materials to a new rock system.
2. It always involves contribution of new chemical materials to the intruded and interacted system.
3. It can changes the mineralogy, texture, geochemistry and isotopes of pre-existing rocks during its intrusion and interaction.
4. It is an igneous metasomatic process when the last remaining fluid portion of a crystallizing magma escapes and interacts with the earlier formed rocks.
5. It is a metamorphic metasomatic process when chemically active fluids are expelled out of pre-existing rocks through the rise of pressure-temperature conditions, and then which accumulates to interact with the rocks.
Thank you very much in advance.
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Metamorphism is an isochemical adjustment (be it contactmetamorphic, regional/dynamometamoprhic or burial metamorphic) to changing physical conditions pressure and temperature in the lithosphere. By definition the expulsion of carbon dioxide and water along with an increasing metamorphic grade is not involved in these processes. The lower limit called the very low-grade stage overlaps with the upper part of the diagenesis (around 200°C) and depends on the angle you look at this boundary using siliceous, organic or sulfidic matter. The upper limit is the onset of anatexis between 600 and 800°C which depends on the water content of the system. The metasomatism sensu stricto is a closed system.
Metasomatism is allochemical and an open system where in special zones at a certain P-T level a new mineral partly or wholly different in its chemical composition from the host mineral formed. These mineralizations may be caused by subcritical or supercritical solutions sparked by igneous bodies at different depth (contact -metasomatic / skarn) or in the course of burial or dynamometamorphic processes (see the isochemical analogues above). The replacement of preexisting rock-forming material occurs through chemically active liquids and gases from external sources.
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I am looking for template for the Ti in zircon geothermometer. Can someone help with an excel spreadsheet please?
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[log (ppm Ti-in-zircon) + logSiO2−logTiO2] = (5.711 ± 0.072) − (4800 ± 86/T(K)) (Ferry and Watson, 2007).
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Only Japan and China have been successful so far in extracting methane from gas-hydrate fields, albeit the fact that nearly 40 countries have carried out marine gas-hydrate explorations:
Why is it so?
What are the highly sensitive geological processes that might trigger hazardous situations before, during and after the gas-hydrate production tests?
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The problem with some of the hydrates, is that you will have to use more energy to dig them out of the ground, than you can get back by using them as fuel. Why should you then use them ????
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We have here a small granite stock with an apparently abnormal composition, for which we have not yet a real clue how it originated. The granite is highly evolved, high-K, weakly peraluminous (77 wt% SiO2, 0.06 wt% TiO2, 0.01 MgO, 0.15 CaO, < 0.01 P2O5, Sr < 10 ppm, Co, Ni < 1 ppm etc.). The most interesting feature, however, is the chondritic Nb/Ta ratio of 17.5 (Nb ~ 55 ppm), which is exactly the opposite to what is expected for an evolved granite. Radioactive isotopes imply that the granite is entirely crustal. No field evidence exists that the granite is part of a composite pluton containing less evolved members, i.e., has received its compositional signatures as result of fractional-crystallization differentiation. Thus, the source rock should also be felsic.
Has anybody an idea how such a rock may have generated? What might have been the protolith for this type of granite?
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Dear H-J Förster and Swayoma Bose,
The Nb-Ta composition of your granites is quite interesting. What I can say from my own granite whole-rock compilation is that such Nb-Ta composition (e.g. Nb/Ta ~17.5, Nb~55 ppm, Ta ~3 ppm) is generally only reached by mantle-derived A1-type peralkaline to metaluminous granites.
If you think that this granite is purely crustal in origin. It could suggest that it formed from the melting of either a residual crust or, for example, mantle-derived andesite rocks characterized by high Nb/Ta ratios. If, for example, sediments are submitted to a first event of partial melting at low temperature (until muscovite breakdown), the accumulation of biotite and ilmenite can induce an increase of the Nb/Ta value in the residue. If this residual crust is then submitted to a second partial melting event at high temperature (above biotite breakdown condition), the generated granitic melt can reach a high Nb/Ta value. See Stepanov et al. (2014) for some discussion about such processes.
Regards,
CB
Stepanov, A., Mavrogenes, J.A., Meffre, S., Davidson, P., 2014. The key role of mica during igneous concentration of tantalum. Contrib. to Mineral. Petrol. 167, 1–8. https://doi.org/10.1007/s00410-014-1009-3
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I found some clathrates in fluid inclusions in the fluorite. But what is the significance? Some articles suggest the clathrates present overpressure. really? The temperature of the inclusion in the photograph is 6.0℃.
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The homogenization T of the clathrate, along with other data can tell you what gas-hydrate you have and what chemical system you are looking at.
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Kindly, could any one let me know how to fix the value of concavity index (-0.4) when use TecDEM software. fixing this value is very important to extract the steepness index which could be depend on in the evaluation of tectonics?
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Dear Nisarg,
Although I've never used TecDEM, I've calculated the steepness index manually by extracting area and slope data using ArcGIS. I wrote the entire technique in my recent paper, published in Arabian J Geosciences.
In case, if you want to compare steepness index of many streams, you've to normalize the steepness values using a reference concavity. To easily compute the normalized steepness index you may follow the stream profiler tool and the MATLAB codes developed by Kelin Whipple and his team.
Cheers.
Sumit
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In convergent margins as the arc setting evolve from oceanic to continental arc, metal endowment also may change; for instance, Cu+Au and Cu+Mo porphyry type deposits are predominant in oceanic island arcs and continental arcs, respectively.
However in a single setting, such as a continental arc, special types of deposits may be predominant in some parts. If the age of mineralization be almost similar along the arc (e.g. middle to late Miocene), what other factors control this diversity?
Regards,
Reza
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Dear Mr. Hosseini,
your question points to "mineralization" sensu lato. Therefore it is very difficult to give an all-embracing answer, because in an arc or active continental margin setting you will find magmatic, sedimentary and even metamorphic subsettings which are quite different as to their lithology , P-T and Eh-pH regimes, all of which are of control  on the individual mineral  deposits. In addition to that the geomorphological and paleoclimatic conditions also play a significant role. Remnants of ophiolites near the ocean with magmatic base metal, Cr,, PGE, umber, ochre, and beach sands of olivine are concentrated in such a great variety of settings that you cannot give a simple answer to your question as it is the case for the setting at the opposite end of the magmatic cycle with felsic and intermetiate volcanic, subvolcanic and plutonic rocks which also are enveloped by sedimentary and covered by supergene mineralizations.
I hope it will give you an idea how complex this issue is.
Best regards
H.G.Dill
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I have observed that sometimes a granite,  by its essential mineralogy, doesn't contain any kind of accessory minerals.
No single grain of opaque/ transparent accessory minerals which normally occurs in a granite.
what makes them so cleared off with respect to any kind of accessory minerals?
Is it original composition of magma?
or
is it due to certain physico-chemical conditions/ tectonic setting?
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I also find it hard to believe there are absoluetly no accessory phases present. Granites are by definition coarse grained rocks, so I suppose it would be possible to cut a single thin section and not see any accessory phases. How many sections have been examined? Phases such as apatite can be very difficult to spot using standard light microscopy, so it might be worth putting a few sections under an SEM and looking at them in backscatter mode....you might be surprised what jumps out at you!
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Fuchsite (chromian muscovite) or other chromian silicates are common as the result of metamorphism on ultramafic-mafic protoliths. Hence their occurrence in orogenic gold deposits. However, we have found it as a hydrothermal mineral in IOGC deposits (so far, two of them) in areas in which ultramafic-mafic rock are still unheard of. Please see discussion in the following link:
Has anyone found fuchsite in similar environments? Any idea of its geological implications? Thanks!
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Dear Dr. Camprubi,
there are numerous Cr-bearing phyllosilicates, many of which are supergene in origin and not all of the "green glittering stuff" in the argillaceous alteration zone of mineral deposits qualifies for being named Cr illite or fuchsite. We have studied some argillaceous alteration zones with high Cr contents and micaceous and smectitic material.
I would like to refer to the paper published only recently:
DILL, H.G. (2017)  Residual clay deposits on basement rocks: The impact of climate and the geological setting on supergene argillitization in the Bohemian Massif (Central Europe) and across the globe.- Earth Sciences Reviews 165: 1-58.
There you can find all the common Cr-bearing phyllosilicates and what you can deduce from their presence as to the supergene part of alteration and their parent rocks.
Chromium has favourable sites to be concentrated, the environs of ultramafic rocks and paleosols sensu lato.
Best regards
H.G.Dill
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Some of the zircons bear positive Eu anomaly which i think may be altered magmatic zircons, because the samples is from an altered  zone.
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It is hard to understand a positive Eu anomaly in zircon. As suggested by Mr. León and Moscati, Eu anomaly in zircon depends on fractionation of paragenetic mineral which mostly is feldspar. However,  recent experments demonstrate that Eu and Ce anomalies in zircon are mainly controlled by oxygen fugacity (Trail et al., 2012). Terrestrial zircons crystallized from a normal magma should have a negative or no Eu anomaly which is affected by the Eu2+/Eu3+ratios. The similar geochemistry of  Eu3+ to Sm3+and Gd3+controlled by charge and radius  indicate no Eu anomaly in zircon even under an extermely oxydic condition and/or without feldspar fractionation. Therefore, a positive Eu anomaly in zircon can only be resulted from a nonequilibrium process, such as metamorphism or alteration. However, similar case is rarely reported...
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Yes, the fluid inclusions of halite can express some important information of paleoseawater in some degree. They can only indicate the components of paleoseawater in that time, but can`t reflect why the components of paleoseawater was so, can`t reflect what process the paleoseawater experienced. 
I think the fluid inclusions of halite in some evaporite deposits just can indicate the changes of paleoseawater in that basin in that time, besides, the paleoseawater in that basin in that time may have exchanged with many sources. They can`t indicate the whole and homogeneous components of paleoseawater in that time.
There still need to find new evidences in primary marine stratum in closed basin unmodification. 
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Dear Professor Blessing Adeoti and Sharon Cornelius,
Thanks very much for your great suggestion. It is right to consider the property of halite (primary or secondary).  The salt movement will change the occurrence of primary fluid inclusion in halite. But, before the salt movement, the primary fluid inclusion in halite may contain the chemical components, from marine, terrestrial, or geothermal water.  Because it needs enough time and conditions for precipitation of halite from liquid. When the seawater flow into a basin, some weathering materials around basin will also flow into the basin before the forming of halite. This will change the compositions of liquid in basin. Although it is primary fluid inclusion in halite, it may not be used to indicate the original seawater. Is it right ? The salt movement is equal to a post-reformation or recrystallization, these processes will change the original face of fluid in halite uttermost, I think. Is it right ? Thanks very much.
Best Regards,
Qin
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Hello Researchers,
Well, I have a small question, did anyone knows how to calculate the model  (lattice-strain) for the parenting fluid responsible of a fluorite mineralization besides the derived and calculated fluid from the supposed source, using data from Rare Earth Elements (REE),
thank you so much,
P.S: it will be more easy if someone could provide me with Excel file, thanks
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Dear Professor H.G.Dill,
First of all, I am very thankful to the time and concerns that you showed to my question, also all my gratitude for the documents toward which you oriented me,
Well, I am sorry for the lack of explication, I will try to explain what is going on in my mind in words:
we are conducting a metallogenic study for the fluorite ore deposit in morocco, in this aim we used (REE analyses, C/O isotopes, Sr Isotopes, Pb/ S isotopes, Noble Gazes, and Fluid inclusions), and those days I found that there is a method used  to reconstruct the compositions of  REY   of fluorite if it was precipitate from a granitic magma using a theory called ( Lattice-strain), in fact,  Van Hinsberg (2010) states that the trace element partitioning between minerals and aqueous fluids is systematic and obeys lattice-strain theory. It depends strongly on element complexation in the fluid, but this dependence is predictable and can be accommodated. Unlike fluids, minerals with preserved compositions are readily available in the geological record, and the "lattice-strain" approach
therefore provides a powerful and widely applicable tool to reconstruct a quantitative record of fluid composition for the full range of Earth environments and for its earliest history. (end of quote).
Well, this Idea crossed my mind after that i found that an other PhD student ( that I can't get in thouch with) used it in his final presentation to get his PhD dissertation, I will add a figure to this text, to make it more clear,
I Hope that I was able to explain my thoughts,
best regards,
Oussama ZEMRI
P.S: the references cited:
van Hinsberg, V. J., Migdisov, A. A., & Williams-Jones, A. E. (2010). Reading the mineral record of fluid composition from element partitioning. Geology, 38(9), 847-850.
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The so-called hydrothermally altered zircons, what makes it diffrent from hydrothermal zircons. What is the implication of alteration in zircons in mineral genesis. it is kind of complicated
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I agree with the answers above, but would add that context can tell you a lot. If the zircon is intergrown with hydrothermal ore and gangue minerals that would favor its interpretation as hydrothermal zircon, but if the zircon occurs in relatively unaltered igneous rock, that would favor its interpretation as igneous zircon.
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On a Y+Nb vs. Rb classification diagram (Pearce et al., 1984; Pearce, 1996), all of the Late Mesoproterozoic hornblede gabbros plot in the volcanic arc granitoid fields. Why did not  show Nb-Ta trough. In contrast, the ca. 1222 Ma quartz diorites plot in the within-plate granitoid fields.
Add: The Late Mesoproterozoic mafic intrusive rocks intruded in southwestern part of the Dongman Island in the central-western marginal area of the Korean Peninsula. The mafic intrusive rocks exposed in a NW-SE trending body with ca. 20 m in width and ca. 250 m in length. They consist mainly of the predominant fine- to medium-grained gabbro (ca. 1259 Ma) with minor medium- to coarse-grained quartz monzodiorite (ca. 1222 Ma) and mafic dyke. The ca. 1259 Ma gabbro shows weakly to strongly foliation. It consists of hornblende (40–55%), plagioclase (40–45%), K-feldspar (2–5%), quartz (0–2%) and biotite (3–5%). The ca. 1222 Ma quartz diorite occur intrusively in the gabbro body. Some diorites include gabbro xenoliths. In the boundary between diorite and gabbro, quartz monzodiorite invades along the cracks of gabbro and occur magma melts walls of gabbro reflecting assimilation. The quartz monzodiorite consists of plagioclase (45–55%), hornblende (15–25%), K-feldspar (8–12%), quartz (7–10%) and biotite (5–15%).
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The Pearce´s diagrams fields were buit up using granitc compositions, ie, high silica contents. 
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I'm a PhD student in Geological Sciences and I'm looking at access a HIP to try to sinter natural volcanic materials for tens of hours to days at temperatures up to 900 C and confining pressures up to 25 MPa.
Do any of you know of universities, research groups or facilities with a HIP that would be interested in collaborating on this project? 
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ETH is the best choice for ya I think 
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For example, in some granite samples (low-T I- and S-types), there are lots of zircon cores and grains with U-Pb ages older than emplaced ages of the granites. How to distinguish the inherited zircon from the zircon xenocryst?
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Dear Dr. Zhang,
Zircon xenocryst refers to zircon that was originated from a complete different source of that of the magma, most likely entrained into the magma during assimilation of the wall rock. However, inherited zircon is more ambiguous since you can have inherited zircon incompletely reabsorb from the source that melted and generated your magma. New terminology it is being apply to avoid this confusion, for example zircon autocryst, antecryst and xenocryst. Find attached a paper where this is explained in detail and may help to respond your questin. 
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This is an excellent paper. It contributes both valuable new data and solid interpretations of the origin of Nyakabingo, one of the Rwanda-Uganda “tungsten belt deposits”and its relations to rare-metal pegmatite formation.  
The authors demonstrate by geochemical data the long-assumed connex between parental ca. 1000 Ma so-called G4 granites, tin and tantalum mineralized pegmatites (at Gatumba) and the wolframite-quartz veins at Nyakabingo. Considering the distance of 70 km between the two, a direct flow of liquids and fluids between the Sn and W districts is not insinuated. The assumption is that in both cases, differentiation and fractionation of G4 granite produced mineralizing residual liquids and/or  fluids. The “text-book” model of the relation between  pegmatites and hydrothermal mineralization predicts that the second should follow the first.
The authors used muscovite trace geochemistry to determine and compare the degree of differentiation/fractionation of pegmatites and W-ore veins. Curiously, these data imply that the tungsten mineralizing fluids were expelled at the same fractionation stage as early unmineralized pegmatites.
How is this to be explained? I wonder if the solution would not be the contemporaneous tectonic deformation!
My own mapping of the tungsten belt deposits Bugarama and Nyakabingo (with Günther & Ndutiye), and of the nearby large cassiterite vein fields of Rutongo, and of Wolfgang Frisch at Gifurwe all showed that the veins are tectonically controlled by thin-skinned folding and overthrusting. G4 melt bodies may have been disturbed by tectonic deformation, from a  state of quiet fractionation and differentiation to sudden pressure changes and deformation of the whole melt body as the country rocks heaved.  
“Typically in the Kibara belt, pathways and traps for pegmatite melts, or for metalliferous
hydrothermal fluids, were low-pressure hinge zones of tightening anticlinal folds with axial
planes or cleavage planes on the flanks of folds as feeder and break-through structures. The
compressive stress field was rotated compared to the Mesoproterozoic main deformation and produced fold axes and thrusts cutting earlier folds at sharp to orthogonal angles. Outcrop patterns created by fold interference are visible on geological maps; resulting highs often determined the location of tin granite cupolas or ridges and associated deposits” (citation from Pohl et al. 2014; for research use, I can provide a PDF).
The cause for both the compressive tectonics and the crustal melting that produced the G4 granite suite were the ca. 1 Ga global tectono-magmatic events of the final assembly of Supercontinent Rodinia (the “pan-Rodinian orogenic events” of Li et al. 2008).
 Would you agree?
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This is a fascinating question you have asked. Although I am not familiar with your area of interest I see many similarities with other "tectonic controls" as regards orogenic gold deposits of the Archean that I am familiar with.
I see the emplacement of igneous intrusions (due to their volatiles they force themselves upwards) as a reason for the creation of structures where mineralizing fluids travel. In the end minerals get deposited according to many controlling parameters (salinity, temp., isotope, fluid composition and chemistry of wall-rocks among others) . I have followed Rob Kerrich's work on gold deposits, ever since he visited my gold mine (where I worked, it wasn't mine!) to study the nature of the gold deposits. He has explained those parameters that control deposition of metals in a satisfactory way. 
The tectonic control of Sn-W mineralization in Cornwall, England that I am familiar with has many similarities to your mapping experience in Africa. As far as I know, the mineralization there has not been explained fully yet. Tectonics has been mentioned by several investigators to explain the distribution of metals around the granite intrusions.
To answer your question, I agree many factors play a role including the tectonic control.
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Barren Measures are sandwiched between two thick  coal bearing formations i.e. Barakar and Raniganj, and devoid of coals. What are the reasons for the sudden extinction and reappearance of coal in reference to global tectonic and environment?
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Hi Annapuma,
Possibly the coal measures of NW England gives a clue.
Barren coal measures are of 2 types:
1/. primary barren, as discussed by most respondents;
2/ secondary barren, due to oxidation of coal measures below the unconformity of the Permo-Triassic red beds that formed in a harsh desert environment. In this montane Permo-Triassic landscape, the coal measures were subjected to oxidation by combustion by air at the surface and underground, and by oxidation by groundwater underground.
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I am working on zircons of granitoids where the isolated zircon grains largely show oscillatory zoning revealed in CL images. My immediate attention to experts is that if those zircons originated by the magmatic processes or not?
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As John I Garber pointed out, oscillatory zoning generally  it's considered of magmatic origin. In my short experience I never see metamorphic zircons with oscillatory zoning. Another way to distinguish between magmatic- metamorphic zircons it's with the Th/U ratio (Th/U < 0.1 for metamorphic origin), but not always works as Moller et al 2003 highlights.  
Moller et al 2003 The Use and Abuse of Th-U Ratios in the Interpretation of Zircon
In my knowledge there are two ways to form metamorphic zircon:
1) Precipitation from a melt by anatexis (Roberts & Fingers 1997). Solid crystallization / nucleation occurs due to Zr and Si diffusion processes as a consequence of mineral breakage reactions with sufficient amounts of Zr to favor the crystallization of new zircon (Hoskin & Black, 2000). The most common morphology of this type of zircon is oval, rounded and homogeneous, but with internal zoning. Precipitation from aqueous metamorphic fluids involves the dissolution of part of the zircon and re-precipitation of the dissolved material, nearby in the crystal itself or away from the dissolved zircon, so the habit may change.
2) Dynamic recrystallization of a preexisting zircon crystal (generally igneous) (Pidgeon, 1992; Hoskin & Black, 2000). Recrystallization usually occurs as recrystallization fronts or transgressive lobes cutting the original internal zoning texture. When this process does not occur completely, the crystal acquires domains of oscillatory zoning (of protolite zircon) and domains without zoning (recrystallized homogeneous areas) "phantom zoning ", that is partially recrystallized. The suggested mechanisms for recrystallization correspond with border migration and migration of intracrystalline defects (Hoskin & Black, 2000).
References cited: 
ROBERTS, M.P., FINGER, F., 1997. Do U–Pb zircon ages from granulites reflect peak metamorphic conditions? Geology 25 (4), 319–322.
HOSKIN, P.W.O., BLACK, L.P., 2000. Metamorphic zircon formation by solid-state recrystallization of protolith igneous zircon. Journal of Metamorphic Geology 18, 423–439.
PIDGEON, R. T., 1992, Recrystallization of oscillatory zoned zircon: Some geochronological and petrological implications: Contributions to Mineralogy and Petrology, v. 110, p. 463–472.
You can also look the review of zircons textures made by Corfu et al 2003. 
CORFU, F., HANCHAR, J. M., HOSKIN, P.W.O., KINNY, P., 2003. Atlas of zircon textures. In: Hanchar, J. M, Hoskin, P. W. O (eds) Zircon. Mineralogical Society of America and Geochemical Society, Reviews in Mineralogy and Geochemistry 53: 469-500.
I hope this information could help you with your research. 
If you need the cited articles please tell me and I can send them to your email. 
Regards
Cesar
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 Everybody,
    I'm studying a Late Cretaceous (~68 Ma) opx-bearing granite in the Qiangtang Terrane, Tibetan Plateau. The two-pyroxene barametry indicates that the melt-formation of the this pluton require pressure ≥ 14.2–18.1 kbar and temperature ≥ 900–1000 ℃. When plotted on the P-T diagram illustrating the partial melting of mafic lower crust and phase relationship, this P-T range corresponds to the “amphibole and plagioclase-out” and “garnet-in” field, implying the breakdown of amphiboles and plagioclases and occurrence of garnets in the source region. 
    In combination of chemical compositions, we suggest that partial melting of mafic lower continental crust in the stability of garnet (e.g., garnet-granulites or eclogites) was the most plausible scenario for the genesis of the pluton. High Sr and Ba, low Y and heavy rare earth elements (REEs), strong depletion of high-field-strength elements (HFSEs) such as Nb, Ta and Ti, and lack of negative Sr and Eu anomalies (Martin 1986, 1999; Defant and Drummond 1990; Martin et al. 2005) in the rocks indicate that the pluton closely resembles adakites in element compositions. However, peculiarly, it exhibits higher Yb and Y concentrations as well as lower Sr/Y and (La/Yb)N ratios relative to the typical adakites.
 It is so peculiar. So, I want to ask partial melting of garnet-granulites or eclogites necessarily produces adakites with high Sr/Y and (La/Yb)n ratios? If not, what geological processes would result into the decrease of these two ratios in the partial melts from the eclogites or garnrt-bearing granulites?
Thanks.
Lu
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Dear Lu-Lu: for some srange reason I haven't been able to unload the photomicrographs you attached, a message saying "Netwok error" appears all the time. Perhaps the file is too heavy (21 MB) and doesn't come through. Any way, pyroxenes, both ortho and clino, are silica saturated minerals, so they should be stable in a granitic melt, unlike olivine, for example. The possibility that these minerals could be restites is also quite likely, I've found similar examples in Venezuelan and Colombian granitoid rocks. But eclogites don't contain orthopyroxene, only granulites, so the source rock of the magma should have been granulites, not eclogites. Regards. Sebastian. 
P.D.: try to send the pictures one by one, and not as an attached, and heavy, file...
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Hello all,
I read this paper from Butler and Paton (Butler R.W.H., Paton D.A., 2010. Evaluating lateral compaction in deepwater fold and thrust belts: How much are we missing from “nature’s sandbox”?, GSA today, v.2 , n° 3, 7pp, 4-10, doi : 10.1130/GSATG77A.1) that shows on the Namibian margin how shortening related to gravity gliding can be accommodated by direct lateral compaction within the sedimentary layers. Lateral compaction could thus accommodate 18 to 25% of the shortening and then the amount of shortening evidenced by the reverse faults is lower than the true shortening. 
Do you know other examples/references concerning lateral compaction process?
Does a low amount of shortening (say less than 25%) could be entirely accommodated by lateral compaction within the sedimentary layer, then without any reverse fault?
Many thanks in advance!
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Hello Gaël,
Layer-parallel compaction (LPC) or tectonic compaction is a significant component of shortening. In couple of papers we quantified LPC in sand models it to "lithology", basal friction, stratigraphic location, and amount of bulk shortening. This is easy to quantify in models where the initial dimensions and boundary conditions are better known. We have also compared LPC in models to that in Pyrenees where we measured 16-23% depending in different sections. If you are interested, send me your email address and I will send the PDF of those articles.
Cheers,
Hemin
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Hi,
This picture is published in the web site of the Amazing Geologist. Can any one reconstitute the paleohistoir of this region?
Best,
Hakima
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Hi Hakima,
Such patterns were admired even 100 years ago of visitors and miners underground of the salt mine Marosujvar in Romania (see images attached). The original alternation of flat layers of pure rock salt (light) and clay impurities (dark) was bent and erected steep by salt tectonics. The photographs are printed on historic picture postcards (out of my collection).
Best regards,
Guenter
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A 1.9 Ga metamorphism existed in North China. In the khodalite belt, there is a consensus that the metamorphism is a product of subduction. But for the middle and east part, why people say when metamorphism happened, the orogeny process initiated? So, I am confused and wondered other cases. Welcome to any idea. Thank you in advance.
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Dear Mrs. Xinping,
the correlation of metamorphism, excluding shock metamorphism related to impact processes, to orogeny is common sense. I would like to refer to the eclogite and glaucophane facies coming in place as oceanic crust is involved in subduction processes, The alteration of rocks is characterized by high pressure and a wide range of temperature from rather low to very high. You can correlate the various metamoprhic facies types from the classical Abukuma through Barrow types with the architectural elements of plate tectonic (see also paired belts). Textbooks on metamorphism offer a wealth of nice examples on a global basis.
Best regards
H.G.Dill
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Climate and geological faults
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Dear David Garcia
I exactly do not have the paper this time in which the author tried to describe the precipitation along geological fault lines known as MBT/HFT, MCT AND MMT from north tto south on windward side of great himalayas in Nepal, India and Pakistan. I am in search of papers describing this relationship. Welcome for all for co-operation in this regard.
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Where can i find a paper about bioenvironmental problems caused by serpantine?
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Please see the journal of geology department of university of peshawar, peshawar, Pakistan.
Regards
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We Know Nb and Ta are usually coupled in most geological processes. However, in my a recent study on a granitoid, I observe the decoupling between elements Nb and Ta. In the samples, element Nb is obviously depleted whereas Ta is variable in content from highly depleted to slightly enriched. I want to ask what geological process leads to Ta decoupled from Nb in granitoid? Fluid contamination or fractional crystallization of both major phases and accessory phases?
A spider diagram is attached here.
Thanks. With regards.
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Hi Lu Lu,
The subject is also treated in this paper:
Green, T. H. (1995) Significance of Nb/Ta as an indicator of geochemical processes in the crust-mantle system. Chemical Geology 120(3–4):347-359.
Regards,
Antoine Caté
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basaltic melt production from metasomatized mantle is common feature of subduction zones. I want to know if high degree partial melting has occured in Deep Crustal Hot Zones, the basaltic melt likewise can be produced?
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Leonid's comment is very useful. Basalt magmas are commonly believed to originate by partial melting of the upper mantle peridotites. The lower continental crust is generally no more mafic than basalt. It would require unrealistic amount of heat supply to cause high degree of melting to produce basaltic magma. 
Regards,
Qasim
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I am doing a Project based on xenoliths and megacrysts in kimberlites based on the Monastery mine and other mines in the Free State, South Africa; and would like to know if there are any journals, books, any research work available to look at. I have realized that most research work on acquiring information about the crust and mantle has been mainly focused on using mantle xenoliths as compared to crustal xenoliths. If any, i would love to acquire more information about crustal xenoliths in general as this is also part of my project.
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Thank you very much.
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Can melting fraction of lower crust (SiO2 of 58%) reach to 40%-50%, when the mantle-derived activities are extensive?
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Although I assume it's a possibility to have such a high degree of partial melting, I wonder about Sobhi Nasir's answer that one would expect to get melts with over 80% SiO2. What is that number based on, experimental work? It sounds rather high to me.
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zambezi belt
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Probably this article DOI: 10.1016/0899-5362(94)90061-2 and the citing articles will be a good start
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I need a sampling device to get relatively undisturbed samples from soft sediment habitats in fjords, which can be operated from a relatively small vessel (multicorer is too large). The Gemini corer seems to be suitable, but I cannot find a supplier. I think it was often used in Russia and Finland. Thanks for your help!
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check alibaba.com website. i am sure u can get it there.
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Dear all, what I whant to know is - if a herbivorous mammal species crossed the area of modern Sea of Marmara, would this species face something new? I mean, the distance is not so long... Could there be more or less significant differences? To make such a comparison myself using different articles of different authors seems to me unreliable. Different authors use different approaches...
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 I asked about Last glacial maximum...
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What are the effects of these fluids on partial melting degree of rocks? Why do the rocks' partial melting degree decrease? 
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Hi Mustafa,
Fluids, whether slab-derived or not, and even any additional phases, thermodynamically tend to lower the temperatures at which partial melting (and also crystallisation) is commenced. This is a result of depressing of the liquidus and solidus with the eutectic points. In subduction zones, this is typically driven by addition of the H2O- and CO2-rich fluids which are released from the descending hydrated crust at ~100 km (amphibole breakdown to prx). This is the basic of the subduction magmatism. This process do not require any reasonable increasing in the temperature of the mantle wedge. Also, when any mineral phase in the source (e.g., cpx) is consumed, melting may be ceased in response to re-increased melting points. You can find further in some books. Anyway, I will send you some lecture notes. 
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I would like to ask that is there any quantitative index to describe the complexity of geological conditions for the purpose of risk assessment in mining or construction.
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The complexity of geological conditions must be described in numerous quantitative parameters.
The most important parameters of geological processes (genesis and formation conditions of rocks) are:
Pressure (P)
Temperature (T)
Composition of the fluid phase (X-fluid)
Time (t) (time of the rock formation)
Formation age
Deformation (brittle, ductile) (d)
Relations between crystallization and deformation
Furthermore: all technical properties of the respective rocks of the study area (stress, strain, compressive strength, porosity, permeability, water saturation, tensile stress, etc. etc.).
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I  am looking to find  a relation between  potential source rock thickness and the migration path of  Hydrocarbon and volume in reservoir Rock.
Regards
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Dear Sir,
The thickness of the source rock has no relation to hydrocarbon generation. The hydrocarbon generation is depended on TOC, maturity, enough maturity from depth of burial and thermal point of view, and reservoir rock associated with source rock. The thickness of source rock is important from the amount generated and expelled hydrocarbon.
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Flow of rivers are not only affected by the size and slopes but also of its geometry. Used several software but most do not consider river sinuosity in the calculation.
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Dear Ronald,
FLDWAV can model single channel or dendritic systems, straight or meandering channels, or divided channels.
You can download it at the following site
 
With my best regards
Prof. Bachir ACHOUR
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The O18 isotopic equilibrium temperature (between biotite-muscovite) in a metapelitic mylonite is 300 deg C. However, the stable paragenesis of these metapelites includes garnet, staurolite. The Ar-Ar age of recrystallized muscovite is 11-13 Ma. Can we say that ductile deformation related to mylonitization occurred 11-13 Ma?..Or is it the just the cooling age of the pelites which have undergone garnet and staurolite stable metamorphism earlier? What are the constraints??
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Dear Nirmalya,
deformation conditions seem to be thus well constrained. Consequently, I think grain size could be a possible explanation to understand the obtained ages. One interesting point that you could evaluate is whether the so called "closure temperatures" are valid, specially for mylonitic rocks (e.g., have a look on Igor Villa´s papers). I´ve been working on this topic for the last year and I think it´s not as easy as it´s thought due to the complexity and interaction of different processes during mylonitization (deformation, metamorphism, magmatism, fluids).
In any case, I am still not pretty sure whether both micas are contemporaneous or not. For example, the biotites >400 microns, do they represent the grain-size reducted biotites or the remnants of "underformed" biotites? Based on what you mention, I would still think that biotite nucleated prior to muscovite, although both could be afterwards homogeneised in terms of 18O. In that case, this event shouldn´t have affected K-Ar isotopy. 
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Hi, I am working with pull apart basins and I would like to know if there is any work that relates the size of the basin with the offset of the transform plate boundary. For example, offset vs basin length.
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Be careful trying to extrapolate plate boundary offset from basin length.  Pull apart basins are typically short lived features which form in response to bends or step-overs in strike slip systems.  As such they are generally not active for the entire "lifespan" of the fault system and do not record the entire slip history.  
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For Na-montmorillonite, experiment has not detected cation solvation by CO2 in the interlayer, even for dry Na-montmorillonite. Why? It happens in dry zeolites, why not montmorillonite?
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Unfortunately I am not very familiar with the montmorillonite structure. But I had a look to this interesting clay structure and there are two obvious differences to zeolites, as far as I can see.
On the one hand zeolites provide a defined pore/channel opening in every state dry or wet, while the layer distance of the montmorillonite structure is strongly dependent from the swelling ( and so from wetness). Could the small layer distance in your dry clay hinder the solvation?
On the other hand the montmorillonite structure has a neutral surface, while zeolites are acidic. Sodium cations in zeolites are bound to the negatively charged Brønsted-sites of the structure (Zeo- Na+). For montmorillonite sodium cations are intercalated between the layers of the structure. Could this different surrounding of the cations influence the solvation?   
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I am planing to evaluation my fault data so i use and try diffrent software  but i want to get your advice.
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Why don´t you try this website http://app.visiblegeology.com/ It has some structural geology software that you can use for free online
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What is the typical angle of inclination for dunes formed by fluvial processes? And is there any reference discusses that.
Is there any reference explains the difference between aeolian dunes and fluvial dunes in term of the angle of repose and inclination. Thanks.
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Apparently the difference between the angle of reponse of sand in a subaerial case and in a subaqueous case (sand saturated in water) is given by a difference in the effective stress between the grains.  The effective stress is the force that prevents the movement between particles (related to friction) and in turn is related to the gravitational force of the grains. Once the grains are saturated by water, they "weight less" and both the frictional force and the effective stress between them is smaller. The smaller the effective stress, smaller the angle of repose. For this reason the angle of repose of dry sand is around 34° and of 30° for saturated sand.
A final comment: A different scenario comes with sand filled with capillary water! in that case your angle of repose increases! but i think your question was oriented towards the angle of repose of sand in the lee faces of subaqueous and subareal dunes!
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Hey guys,
I would like to kindly have your opinion on this matter. Here is a couple of polarization microscope snaps (scale is on the snaps). Does any of these qualify as a planar deformation feature (PDF)? Thank you for your ongoing support. I am sorry for the bad quality. It is the best the camera can do.
Why I do not think they are PDFs:
- Some of them cross several grains
- They might be preparation artifacts
Why I think they might be PDFs:
- They only occur in a small region near the crater
- They have different orientations
- They only occur in the highest shocked sample (the other less shocked samples were prepared in the same exact manner)
Thank you in advance, looking forward to your replies! :D
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Nothing to add to the previous collegues. I do feel you are observing PDFs due to shock in quartz.
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Can the following processes happen?
1 Long term of oceanic subduction took place at first.
2 Afterwards, due to slab roll-back or slab breakoff, the tectonic setting switch from compression to extension. 
3 After a period, the subduction cease. 
If it is not feasible, can you give me some other possibilities that active continental margin can be transformed to passive continental margin?
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Dear Mr. Rurui.
the answer is simply yes. It is only a question of time which lies between the formation  of these very contrasting geodynamic settings. There are numerous crustal sections where you can find interlocked with each other lithologies indicative of both settings.
Best regards
H.G.Dill
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please can you help me to know about this bioturbation which I found it in lower callovien of algeria
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Dear all,
what do you think about marks created by rolling ammonidea?
Similar traces where found in the quarries of Solnhofen in a micritic limestone.......
best regards
Andreas
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Absolute dating is necessary for knowing specific time e.g. by isotope K/Ar in mica, especially in the crystalline rock: igneous and metamorphic rock. On the other hand, the sedimentary rock (as I know) usually provide the time of formation by age range of fossil e.g. Upper Miocene - Piocene. Is there any method to make it more specific like the crystalline one?
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The best way to obtain a numerical age for a sedimentary rock – other than through comparison of fossil content or magnetopolarity reversals with the geological timescale – is through the direct dating of volcanic ash layers (U-Pb and Ar-Ar techniques on mineral separates). The main difficulties with this approach relate to the mixing of grains of different age and significance, and alteration of the dated minerals. An approach that works really well in marine deposits of Oligocene-Miocene age is to measure Sr isotope ratios in microfossils and macrofossils. The seawater ratio is well established for that interval, and more or less linear. Glauconite dating is mostly a mess. Poor resolution.
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This article published (where?) by Stanislaw Halas et al, 2013, discusses stable isotopic values in authigenic quartz crystals that are supposedly co-precipitated in halite crystals. However, to me, it looks as if the researchers forget that authigenic quartz precipitates from hydrothermal liquids at higher temperatures (200 - 400 C). If they are found inside halite crystals, it means that also these crystals likely precipitated at high temperatures, such as is documented in the Afar region, see attached article.
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one can have liquid water at -70 ° C and solid water (ice) to + 80 ° C, and it is the game of pressure that makes the difference !
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Are Recent geological processes like they were millions and hundreds of millions of years ago. Can  you give some examples.
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See perhaps criticism of Lyell's original meaning of uniformitarianism in Steve Gould's book "Time's arrow - time's cycle": Lyell himself included distinct concepts which are not necessarily related, among others:
(1) idea that the same natural laws we observe today were at work in earth history (usually not disputed today, only for the earliest history of the universe exceptions are plausible);
(2) the idea that (only) geological processes observed today shall be taken into account for explaining traces of processes in earth history (= actualism(?); a bit like the geological version of Occam's razor; today only regarded as heuristic principle but not necessarily applicable for most past processes);
(3) the idea that geologically (as well as biological evolutionary) processes run slowly and always at the same rate (problematic in contemporary view);
(4) the idea that certain developmental stages of the earth and life on earth re-occur periodically (only some modern concepts like supercontinent cycles and icehouse-hothouse changes are reminiscient of this idea).
(So discussing Lyell's uniformitarianism it is difficult not to mix up concepts.)
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This thin section is stained by alizarin red, the calcite is probably a late stage pore filling, but why the unstained dolomite prior to the calcite? what a process would be prefered? Thanks!
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Dear Mrs. Sun,
A mixture of adjacent dolomite ooids and botryoidal lumps are interconnected by an early diagenetic dolomite cement. These connecting 'bridges' consist of a so-called meniscus cement in the form of concave dolomite fiber cement perpendicular to the grain surface. The red-colored calcite forms a late diagenetic granular cement and also fills (includes) the pore spaces in some hollow dolomite grains.
That's my interpretation.
Best regards and greetings to my birthplace Berlin.
Guenter Grundmann
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Highly matured Permian sediments (0.6%vro) occurr at shallow depth(~300m). Why is that? How is the tectonic history related to thermal history in these basins?  What are the geological ages of different tectonic phases?
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Hi
The vitrinite reflectance shows that the coals may have been formed at a depth and lately uplifted to a shallower depth.
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The Trans-Mexican volcanic belt is a very irregular and wide (100-500 km) active magmatic arc, but I am not sure where does it actually end. In the backarc or in the rear arc?
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I restrict the term "Backarc" to be followed by "Basin"; a backarc basin is a region of seafloor spreading or at least strong extension. "Reararc" I use for everything else, including rear arc alkaline volcanism, rear arc cross-chains, and rear arc fold-and-thrust belts. For the eastern TMVB I would use term "rear arc"
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The late Prof. Dr. Antonio de Barros Machado, Director of the Dundo Museum of Zoology and Anthropology in Angola (1947-1974) studied during more than 30 years of intense work (until 2003 in Portugal, Oeiras)  a great number of laterite and bauxite rock samples, in his opinion molded by termite activity in geologic times. He analyzed laterite and bauxite rocks  from many places on Earth. His results were only partially recognized because they put into question the "sedimentary origin" of theses formations. I have been dealing with his heritage and am ready to bridge important data for interested colleagues.   Grasset mentions in his double volumed encyclopedia part, dedicated to termites, that he never had met more convincing arguments as to the origin of these rocks then those of Barros Machado, though in his first approach, documented in the earlier Zoology encyclopedia, he was not yet convinced, but then surrendered to the smashing amount of proof, proposed by Barros Machado.
In the collection of private letters, there were more geology scientists to accept this innovating idea, but it still remains controverse. 
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I salute your dedication to the work, certainly the legacy which has been  left by late Prof. Dr. Antonio de Barros Machado should be maintained. If it losts it will be a great loss to entomologists about evolutionary significance of termites. In future certainly it will provide new directions to the experts in the field of geology and geochemistry and entomology.
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The figure shows EPMA data of clinopyroxene fragments in a subaqueous basaltic tuff. The tuff, as interlayer of radiolarian chert, is part of the circum-Pacific accretionary complex. It mainly consists of well-sorted angular vitreous and crystal (mostly clinopyroxene) fragments and geochemically belongs to OIB type. The analytical sites are on different clinopyroxene fragments located at a small area about 2cm*2cm.
The linear trends of MgO, TiO2, FeO, Mg#, Al2O3 vs. SiO2 of clinopyroxenes are very well. Based on Kushiro, 1960 and LeBAS, 1962, these trends are likely related to fractionation. However, the Al-Si trend in LeBAS, 1962 is from data of different rocks whereas here we have non-alkaline (possibly tholeiite), alkaline, and peralkaline clinopyroxenes from one tuff (one-time eruption).
What is the controlling factor of the chemical variations of clinopyroxene fragments in subaqueous basaltic tuff? What's the geological processes behind the fractionation?
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Hello Mingdao,
You could compare your cpx data to published analyses that may be slightly more recent than 1962, for instance by using the GeoRoc (http://georoc.mpch-mainz.gwdg.de/georoc/ ) website. However, if I remember correctly (I don't have the paper handy here), Ewart (Ewart, A., 1976. A petrological study of the younger Tongan andesites and dacites, and the olivine tholeiites of Niua Fo'ou Island, S.W. Pacific. Contrib. Mineral. Petrol. 58, 1-21; I hope this is the correct reference) demonstrated that quench crystallisation of pyroxene could increase their Al content to higher values than expected from equilibrium crystallisation. Perhaps something similar is at work here.
Marlina
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This granular (Fig. 1) is found in a shard of subaqueous basaltic tuff (Fig. 2). The tuff mainly consists of clinopyroxene and chlorite mineral clasts and shard. As shown in Fig. 1 and Fig. 3, the granular has three part: the darkest rim and core is chlorite, with low SiO2, low CaO, high MgO and Fe2O3. The gray part is epidote, with high Al2O3, high CaO, and low MgO. The light ring is likely sphene, with ~30% TiO2, ~30% CaO, and ~30% SiO2.
There is a small high CaO grain in the right like a door of the high Ti-Ca ring (See the CaO distribution map), possibly calcite. Some small sphene globules ejected through the door (Fig. 1).  
I am trying to explain this geological process:
The three-part chemical association was formed by chloritization of basaltic magma. The chloritization was faster than magma coolling because the seawater was heated to a very high temperature. When the chloritization (explosion and seawater-magma interact) occured, the melt was separated into chlorite, epidote, sphene and calcite, however, the granular was still hot that the core was still in liquid state. Then the sphene globules ejected into the core because of pressure difference...
Does anyone believe this? I am interested to hear your interpretations!
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Dear Mr. Sun,
the growth textures of concentric morphology are numerous and run the gamut from pegmatitic zonation through vesicles in basalts like that. They cover the supercritical and subcritical fluids. It is fundamental to know exactly what the different zones are made up mineralogically, and then take a look at the direction of growth (is it unidirectional...). Also keep in mind the size of the rings and zones, it will show you the quantity of the various components involved and last but not least are there breaks or hiatuses in the formation of the concentric shells which may direct your thoughts to different pulses. I know similar textures but feel unable of giving you a good explanation at this stage of investigation. It will only end up in a back- and-fro of speculations. The step "description" has not yet been solved to the extent to allow for a passage into interpretation. A cartoon showing all your information with regard to my recommendations will minimize the field of speculation.
Best regards
Harald G. Dill
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I am doing research in volcano sedimentary terrain of Precambrian period. I am unable to differentiate shale and tuff because of metamorphism of these rocks.     
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Dear Ajay,
As promised, I am sending you a few photomicrographs of shale, tuff and the metamorphosed equivalents from my own thin section collection. In addition, I have included some captions.
If you still have any further questions, do not hesitate to tell me about it.
Best regards,
Guenter
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Thank you very much in advance
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Hi, the following article might be useful for you.
1. Interpreting magmatic processes from accessory phases: titanite—a small-scale recorder of large-scale processes.
2. DISTRIBUTION OF TRACE AND RARE EARTH ELEMENTS IN TITANITE FROM TUNGSTEN AND MOLYBDENUM DEPOSITS IN YUKON AND BRITISH COLUMBIA, CANADA.
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At the end of the 1990's, we compiled and published comprehensive data on the trace-element composition of trioctahedral micas (i.e., TISCHENDORF, G., FÖRSTER, H.-J. and GOTTESMANN, B. (2001a) Minor- and trace-element composition of trioctahedral micas: a review. – Mineral. Mag., vol. 64, No. 2, p. 249–276.). Unfortunately, respective data on dioctahedral micas is largely missing.
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Hi Rongqing,
thanks for this valuable information. Rolf Romer is particularly interested in this subject, and I will forward to him your reference.
Have fun,
Hans
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I want to apply this calibration to some granulites I'm working with.
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SOLVCALC might do the job:
Wen, S.and Nekvasil, H. (1994) SOLVCALC: An interactive graphics program package for calculating the ternary feldspar solvus and for two-feldspar geothermometry. Computers & Geosciences 20, No. 6, 1025-1040.
it is, for example, in ther list of software linked below.
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I'm working with granulites and I applied the thermometer of Ti-in-Biotite in my samples, the problem is that this is calibrated for 4-6 kbar rocks and T<800°C and I'm working with granulites of 7 Kbar and >800°C. The results I got from this thermometer are similiar with others thermometers as Ti-in-Quartz and Zr-in-Rt. 
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The criteria for using the thermometer are detailed on Henry's website at the link below. Here it states:
"Pressure range of the rocks should be 4-6 kbar - this is the P range of the calibration data set. (Based on evidence from a number of biotite experiments, samples equilibrated at lower P will have higher Ti and yield higher TIB temperatures whereas samples equilibrated at P>6 kbar will have lower Ti and will yield low TIB temperatures.)"
There is no information (there) on what the results will mean if T>800C. Providing the system is saturated in Ti (sounds like you have rutile present) it may be fine.
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I'm looking for some information about fault/fracture network created in the host rock by the stresses induced from the intrusion of a magma body in the crust.
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Stress Pulse Migration by Viscoelastic Process for Long-Distance Delayed Triggering of Shocks in Gujarat, India, After the 2001 Mw 7.7 Bhuj Earthquake,  American Geophysical Union Geophysical Monograph Series 01/2012; DOI: 10.1029/2011GM001061
may be helpful to you.
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Explosive volcanic eruptions occurred throughout Palaeozoic time.  Under the right set of circumastances they can be preserved in the sedimentary record.
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Ken Towe has indicated the presence of pumice is a way of recognizing air-fall volacanic ash deposits  Although very rare, this phenomenon has been reported in the cinerites of France (see Bouroz et al;. 1983, Review of the formation and evolution of pegtrographic markers in coal basins, Societe Geologique du Norld, Memoires, Tome XVI ( Pl. III,  Fig. 4). Thank you Ken. Best wishes, Paul.
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The age of my metavolcanic rocks is about 2.5Ga, some of the samples have too low trace element concerntrations especially the HREE, they are even lower than the chondrite, I want to figure out what geological processes have happened? 
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Dear Mr. Ge Songsheng,
I feel fine with the gradual unraveling of the details and it is good to see that you try and constrain the origin of this rock. The basic of all that is, that we have to follow up a clear pathway: (1) Geology (in the field and study) including , in places, geophysics, (2) Mineralogy, (3) Chemistry (4)-if necessary more advanced and more highly-sophisticated methods. And then discussion and interpretation. Otherwise we end up into speculation and the outcome is a matter of conjecture. This is not to complain about your doing; it is my simple attempt to get much of what we are faced with in RG Q&A back on track. Please apologize for that philosophical side leap. I can´t get out of my suit that I had on for 40 years.
I wish all the best
Harald G. Dill
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Is there any other comprehensive work which is dealing with the terminology of layered intrusions apart from the classical paper of T. N.Irvine (1982). Terminology for layered intrusions. Journal of Petrology, 23(2), 127-162.
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Hi Gönenç,
You can also have a look at John Winter 'Principles of igneous and metamorphic petrology'. You can download the book for free. Chapter 12 is about Layered mafic intrusions. Publication is 2009, not so old. Have a look.
Cheers.
Michel
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It seems that in a fossil orogenic belt, like the famous Sulu-Dabie orogenic belt, both orogenic delamination and slab breakoff have proposed to them. Which one is more plausible?  How can we tell which process might have been responsible for a specific fossil orogenic belt if both HP-UHP metamorphic rocks and syn- and post-orogenic magmatic rocks occur there?
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The difference lies in the nature of the lithosphere. In breakoff, the subducted oceanic lithosphere is fragmented and falls into the asthenosphere, whereas in orogenic delamination, the base of the continental lithosphere is laminated and falls into the asthenosphere. The first is at the end of the subduction while the latter usually happens at the end of the collision.
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I am trying to reduce a wealth of crystallographically determined vorticity vector orientations from some sample suites, some of which are known to have been deformed in a triclinic system. For some of the samples (deformation geometry is not known for all of them), the vorticity vector does not lie in the foliation plane (I am inferring that the foliation approximates the flow plane, which may not be the case). I understand that is predicted (and observed) that vorticity vectors can be oblique to lineation orientations in triclinic deformation. However, is it permissible that the vorticity vector lie outside of the foliation plane in certain deformations?
thanks.
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see Talbot C.J., 2014b Empirical Paths of Poles to Planes (eppps) in shear zones. Journal of Structural Geology, 66, 309-333
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The picture is taken from non-metamorphic limestones of the Ionian zone (NW Greece). Information provided within it. Any thought - possible explanation about the origin of the structure is more than welcome.
Thank you
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Dear Ioannis,
from your descriptions I assume that the structure under consideration occurs within a normal (i.e. not inverted and not otherwise folded or thrusted) stratigraphic section. Hence I would rather assume that the structure is indeed a slump fold that formed shortly after sedimentation and before the overlying sediments were deposited. Otherwise it would be difficult to explain why only a certain level of the sequence has been subjected to folding. You mention also monomictic limestone breccias; such breccias may also develop by means of slump movements and other kinds of soft-sediment deformation shortly after sedimentation. What is a little bit confusing for me are the boudinaged layers which you indicated on the photograph: are they really boudins (i.e. a tectonically stretched competent layer within a less competent country rock)? If they were indeed boudins, this could be an indication for real tectonic deformation. On the other hand, the supposed boudins could also be just sedimentary concretions.
To sum up: it's difficult to judge from a photo alone, but taking into account your additional comments, I would suggest that the structure is a slump fold.
With best regards from Switzerland
Dominik 
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Estimada Mirta,
en las roccas piroclasticas la situacion no es muy diferente del ambiente volcanico, donde se encuentran la esfalerita y la calcopirita como las principales materias de indio. Los contenidos de indio normalmente son muy bajos fuera de las roccas formando en un regimen de alta temperatura.
Deme mas informacion sobre el estado de la alteracion supergeno y el lugar de origin de las roccas piroclasticas considerando en sus estudios. Necesito mas datos para darle a usted una respuesta mas profunda. Pienso tambien en diversos minerales arcillosos.
En espera de su respuesta a proposito de su asunto.
Con saludos cordiales
Harald
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Can wind and/or water (marine environment) transport produce a mineralogical selection on volcanic tuffs deposits? Do you know any example?
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Have a look at the paper of M.G. Stamatakis et al. (1998): Mineralogy, origin and commercial value of the zeolithe-rich tuffs in the Petrota-Pentalofos area, Evros County, Greece.-- It might be useful for you.
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Recently there are reports on xenocrystic zircons found within chromite-deposits in peridotites. Any idea how they may have survived the mantle conditions?
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As briefly mentioned in Zheng and Hermann (2014), both newly grown and relict zircon domains have been found in orogenic peridotites from continental subduction zones. These relict zircons exhibit older U-Pb ages than the subduction-zone metamorphic ages. They were erratically interpreted as xenocrysts in some publications, but substantially they were inherited from the metasomatized mantle wedge peridotites and thus eventually derived from subducted crust-derived fluids/melts. In this process, there are both the chemical transport of dissolved Zr and the physical transport of crustal zircon xenocrysts by either metamorphic fluids or anatectic melts at the slab-mantle interface in subduction channels (Zheng, 2012). While U-Pb ages for the newly grown zircon directly date the metasomatic event, its Lu-Hf isotope composition is primarily inherited from the metasomatic agent and thus has little to do with the composition of the overlying lithosphere. The survival of subducted crust-derived zircon in the orogenic peridotites suggests that the crustal metasomatism beneath the mantle wedge would have proceeded at kinetically limited conditions, and thus it did not achieve the thermodynamic equilibrium between crustal and mantle components.
Zheng Y.-F. (2012) Metamorphic chemical geodynamics in continental subduction zones. Chem. Geol. 328, 5-48.
Zheng Y.-F., Hermann J., 2014. Geochemistry of continental subduction-zone fluids. Earth, Planets and Space 66, 93.
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Many minerals like spinel, phlogpite, olivine etc. crystallize records the magma evolutionary trends forming zoning trends; but simultaneously similar phases may give zoning due secondary or interaction with the late stage magma.
Is there any clear discrimination for these?
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Aside from some minerals where it is visible because the chemical change causes a visible difference, the chemistry in zoned minerals usually changes going more towards one end member then in another direction or to a completely different but related species. This must be determined via probe by measuring points at various places in the sample to determine chemical variance (if there is one).
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My problem is that clay can undergo compaction without any true crystallographic change. In consequence, how can I reliably attribute any concentration change (major or trace elements) to the smectite-to-illite transition ?
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I agree with Glonaz, the smectite is an expandable clay and the XRD peaks will shift while the illite peaks will not.  In addition, illites usually incorporate 5-10% NH4 in the interlayer sites instead of K+.  So nitrogen content is a useful elemental parameter.
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There have been many studies in recent years showing that granitoid intrusions can be built through several pulses of melt. A lot of these focus on the internal structure and timing of emplacement. Does anyone know of studies that examine the relative volumes of individual melt pulses within composition intrusions?
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Hi Colin,
we tried to interpret something along the lines of what you are asking about in the Memeti et al. 2010 paper http://gsabulletin.gsapubs.org/content/122/11-12/1912.abstract
Check out also Economos et al. 2009: Causes of compositional diversity in a lobe of
the Half Dome granodiorite, Tuolumne Batholith, Central Sierra Nevada, California.
We argued in both papers that the lobes are potentially representing the maximum size of a magma batch that intruded into the Tuolumne intrusion. We suggest that since what we are observing is the final stage of the intrusive history, it is not clear if it took one large batch (3x10km) to form the Half Dome lobe or multiple smaller batches that amalgamated very quickly to produce the interconnected magma mush in the lobe. And we extrapolate this to the overall 1000km2 Tuolumne Intrusion.
Jean-Francois, please note that Scott Paterson is a co-author on both of these papers, and that he would agree that it is possible that lots of smaller batches may produce one big unit in the Tuolumne (it could be 10, 100 or 10000 pulses), however, the important point is that they will have to come in quite frequently to produce interconnected magma mush - we see lots of evidence for that at the emplacement level. Personally, I think it is just difficult to find the evidence for an individual pulse at the emplacement level since typically any magma batch appears to be interacting (above the solidus) with whatever magma is already there (mix and mingle) and continue to differentiate. I am working on going after this issue now with crystal scale geochemistry.
Cheers
Vali