Geodynamics - Science topic

Dear Maksim Kuznetsov

Yes, Basaltic rocks can be formed in fore arc settings without boninite. Specifically in the embryonic stage of arc development. In this case Peperites ( an erupted basaltic lava in to wet sediments ) can be formed also. For further information I recommend you to read this paper.

Regards

Abdelfattah El Boustani

Very interesting discussion, and congratulations on the responses. I knew nothing about this, so am learning from all your knowledge! Thank you ResearchGate members who are involved.

That is a really interesting question. I am sure that these terminologies are all widely used in the literature to kinematically describe complex slip behaviors along the fault. These words are not exclusive and can be the same thing sometimes, such as the aseismic transient creep.

In my understanding, slow slip is mentioned as the counterpart of the fast slip. Slow or fast slip is the kinematic description in terms of the speed of the slip. For example, slow slip corresponds to a velocity of several orders of magnitude less than several meters per second (i.e., seismic ruptures).

Aseismic slip is used as the counterpart of the seismic slip. It means that the slip does not generate seismic waves, like common earthquakes. As a result, aseismic slip can be detected only by geodetic observations or indirectly by the accompanied seismic events, such as tremors.

Transient slip is used as the counterpart of the steady slip. It means the slip is transient regarding the time scale, not a long-term steady slip behavior. It can refer to the postseismic transients, transient creep, or triggered slip.

Creep is an important slip behavior in the whole modes of fault slip, including fault locking, creep, slow earthquakes, usual earthquakes and so on.

I had data for observations from 1990 to 2007. With this, I completed my research and published a monograph. Until 2005, I identified geodynamic epochs No. 1 (1990-1995); No. 2 (1995-1998); No. 3 (1998-2002); No. 4 (2002-2005); No. 5 (2005...). Each geodynamic epoch was homogeneous in terms of characteristics (rotational processes, seismicity, aseismic deformations, natural anomalies). Changes from one geodynamic epoch to another occurred abruptly (the transition from quantity to quality occurs abruptly - the law of dialectics). With each geodynamic epoch, the dispersion of all indicators increased exponentially. The peak came in early 2006. After that, the reversal started.

Felipe,

Nothing is ever going to drip into the mantle unless it is denser than the mantle. So, we all know that eclogitised mafic crust can sink into the mantle, but what about "huge packs of chlorite-schists and serpentinites"?! What are the density contrasts here with ambient mantle, with TTGs, and with the unaltered mafic crust?

Food for thought...

In my article on RG 'The driving forces of tectonic activity' I propose a mechanism that can explain an oscillatory motion of moving plates.

It is well documented that tectonic activity has a seasonal variation. The article gives a mechansm based on the axis tilt of the earth with a different velocity ( and centr@ifugal force) of the earth hemispheres in the rotation around the sun according to the seasons.

How about ASPECT(https://aspect.geodynamics.org/), which is supported by CIG (Computational Infrastructure for Geodynamics). It's easy to get started , but I haven't use ASPECT for subduction initiation. And I think you could have a brief look about it , I hope it's useful to you (https://github.com/geodynamics/aspect).

There is not a straightforward answer to your question. The abundance relates to the temperatures reached, the compositions of the source rocks (metaseds, metaigneous, mantle or a mixture of all three, and the amount of volatiles, particularly water. There are some general patterns that one may see in specific settings e.g., Pearse and others or Frost et al. (2001).

Arcs tend to have calcic magnesian compositions, becoming more ferroan as melts differentiate, generally I-type. Continental collisional granites tend to be more S and A-types.

Dear Sandu,

You have right, In the zone happened three earthquakes around 'M: 7.4' onto the base of Google map see the attached file.

Regards,

Laszlo

Hello dear;

I didn't research on Paleomagnetic studies, but i know 2 methods in order to behavioral study between two things. K-means clustering and Artificial Neural Network (ANN). you can read this combination method in this paper :

good luck

Dear Afshin Majidi

Please refer to the following trademark paper.

1. https://www.tandfonline.com/doi/abs/10.1080/00206814.2021.1972352?journalCode=tigr20

2. https://onlinelibrary.wiley.com/doi/10.1002/gj.4236?af=R

3. https://personal.utdallas.edu/~rjstern/pdfs/Moghadam%20Early%20Paleozoic%20Lithos%2017.pdf

I hope this helps.

Best Wishes,

Haroon

Siwana Ring Complex (SRC) is most spectacular and spatially related Ring Complex of Neoproterozoic Malani Igneous Suite (MIS) . Basically, there are two accepted and Preferred model for the geodynamic system of MIS, one is plume related extensional model and another is subduction related model. The high concentration of REE-Nb-U in Siwana granitoids is due to crustal assimilation of Protolith melt that was generated through a mantle plume. The anorogenic character of rock-types of SRC ruled out any External fluid role in the enrichment of these incompatible elements. Therefore, to understand the magmatic evolution, tectonic affinity and geodynamic of SRC, the plume related extensional model should be very preferable.

"Capella makes a portion of its historical archived imagery available through the Open Data Program".

Hi There! You should try the Andino, one of the most powerful modeling softwares, and it is available in full for free academic use,

info@lateandes.com

Yes it does. You can read more about crustal thickness beneath 90⁰East ridge (Indian Ocean), Walvis ridge (Atlantic Ocean), Shatsky rise (Pacific Ocean) etc.

Oceanic crust under the influence of plumes may get thickened by magmatic addition at the base of the crust. Processes of such 'underplating' may depend upon prevailing tectonics. I suggest you read more about oceanic plateaus and aseismic ridges to discover more.

Dear Mulugeta Chanie Fenta, nice to meet you.

There are a lot of programs to help the students and professors, I know by myself about that due that I was professor / teacher in Applied Geophysics as the same time I was (I still on activity) working in the E&P research and development for Oil and Gas industry (Exploration and Production), not only with the most advances technologies in 3D seismic tools, but also with the latest advances in 3D grav/mag modeling and inversion.

I can say you by my own experience, that there are a lot / several companies that try to help students, not only with datasets such as seismic or well-logs or geological data, but also with software’s and with programs of scholarship and training. It is a natural process to sign an agreement between the universities and the oil companies, under a confidentiality’s umbrella, it is a win-to-win scenario, particularly in the case of 3D seismic data that it is the hard data to get, and also because in case of seismic, you must - additionally - need the dataset from well-logs to work in the interpretation.

On the other hand, organizations such as AAPG; SEG; EAGE, AGU, in this COVID-19 pandemic’s time offer a lot of webinars and presentations / virtual events, free. If you chek the web, upcoming free online webinars, just you do have to be registered for the webinars and that´s all!!!

Visit please for example:

Please, let me know if my answer satisfied your expectations, I try to help you.

Best wishes, Mario E. Sigismondi

read Roy Lindholm book to know about tilt correction in paleocurrent database

Hi, I think this is one of the best resources that can point you in the right direction. At the end of the book, you will find some code. Mignan, A., and J. Woessner (2012). Estimating the magnitude of complete- ness in earthquake catalogs, Community Online Resource for Statistical Seismicity Analysis, 1–32, doi: 10.5078/corssa-00180805.

Earthquake or what I sometimes call geo-quake builds up becuse of stored energy that is lurking within the subsurface. The position of the epicenter, earth's surface above the focus of an earthquake where this energy lurks does not depend on the shape of the earth nether can the shape of the earth be used to predict, but it relates to the mobile plates, which create disequillibrium above, below and around the position of the lurking energy. The resuling disequilibrium causes the sudden release of energy, which is disastrous whenever it occurs. Its prediction can be achieved by assessing the seismogenic activities few hours before and few hours after the earthquake/geo-quake.

this paper is a good place to start:

Martin, H., Smithies, R. H., Rapp, R., Moyen, J. F., & Champion, D. (2005). An overview of adakite, tonalite–trondhjemite–granodiorite (TTG), and sanukitoid: relationships and some implications for crustal evolution. Lithos, 79(1-2), 1-24.

Dear Sunjay²: Usually geologists and other earth scientists make very concrete questions in this page, but you make none, so what is there to answer?

Regards, Sebastian

Dear colleagues and Vinicius:

My ideas about your questions:

Vinicius ask:

1. Could I calculate in Oasis Montaj the power spectrum for RTP-TMI grid or is it recommended to TMI grid only? Spector & Grant (1970) had calculated the power spectrum using total magnetic intensity maps.

Mario´s answer:

My answer is: you can use the RTP data, the result should be similar to TMI only, since the solution of sources is an average depth for the whole grid, and not a point solution of each source.

That is: each line segment you choose in your crossplot is an average depth´s solution for sources at deep, intermediate and shallow relative depth of your work area / grid.

In any case, the recommendation would be to know first, comparing the TMI and RTP outputs, how far the anomaly locations are displaced in one map and in the other, and of course it is according your region of research.

Vinicius ask:

2. In Spector & Grant (1970, p.295) it is written:

“The postulate states that the mathematical expectation of the value of the power density function is equal to the ensemble average of E. It is strictly valid only for large samples, but in fact works very well even if the number of bodies present is as small as 5 or 6.”

This means that the RAPS method cannot be used for studies of less than 5 bodies? I am asking this because I am pretending to use this method for 2 alkaline bodies close to each other.

Mario´s answer:

This question is related to the first in the sense that the most important thing to apply the solution of Spector and Grant is the size of your area of ​​work, and not the number of anomalies present. You should also be in mind that 50 years have passed since this breakthrough publication, and the authors did not have the computational tools that we have today. On the other hand: your RAPS solutions would be your first step in order to understand your research, in order to interpret your dataset. This solution is only one, maybe the first, maybe the most robust, maybe the most quickly for us, but it has limitations. You must be careful about the theory and assumptions of the Spector and Grant´s paper. If you are working with magnetic data, the first inspection is the RAPS, but you must try an extra step to get, e.g. the AS and SPI solutions, and compare to arrive a valid geological interpretation.

Vinicius ask:

3. Could I use the RAPS method for low magnetic latitudes or close to the geomagnetic equator?

In Spector & Grant 1970 work (p.295) it is written:

“...Care must be taken in low magnetic latitudes, however, and close to the geomagnetic equator.”

Mario´s answer:

Thinking about the first and second ideas. I am not original if I said that you are trying, such as Geophysicist Interpreter of Potential methods, to estimate parameters of the sources, but you must integrate geologic information, or seismic data, for a realistic solution.

Again: If you are working with magnetic data, the first inspection is the RAPS, but you must try an extra step to get, e.g. the AS and SPI solutions, and compare to arrive a valid geological interpretation.

I hope this words help to you, please, let me know if I can do anymore else.

Best wishes, Mario

Your email

Pankaj, if you send to me a map with the coordinates, I can try your ZOI with WDMAM.

Whenever you want, Mario

Hi,

I recently have made these tutorial videos on youtube...how install and test gamit-globk...hope will help you...

cheers,

A. Fadil

If you need to determine WGS 84 geoid then you shall compute the standard gravity (Latitude) on WGS84, otherwise for local geoids you have to use your local ellipsoid parameters

Wish you all the success

Dr. Lotfollah Emadali,

In Sigma/w, you can check "Coupled Stress/PWP" or "Volume Change" analysis. However, the problem here is your period of consideration (15 years), it is too long. You can convert your hydraulic conductivity into m/day, and choose the time steps to be "a week or half a month (as small as possible).... , increase the Number of Iterations, ...Just check the outcome if it is ok?

Hi, from my point of view, and some might have mentioned this already in the discussion, continental breakup is not the separation of the crust, but the entire continental lithosphere. This can get complicated and depends on inheritance, magmatism, extension rate and thermal state of the lithosphere. In Petersen & Schiffer (2016) we have explored and discussed this. You can find also a number of relevant references. When your crust/lith is warm, you can create highly thinned (hyperextended) margins, before breakup. Vice versa, a cold crust/lith. will "snap" and create abrupt, only minorly thinned margins. It's the interplay of crustal vs. mantle rheology, leading to depth dependent extension. cheers, Christian

Dear Sir

I think the following links will benefit you in your search

Best Regards

Ok.

The anticyclonic type of weather is high atmospheric pressure.

  The level of groundwater depends very much on geo-information. Much more than from other factors.

Borys.

Dear Mario, Before determining the origin of any phenomenon, it is good to understand what kind of phenomenon it is. In the case of subduction, everything is complicated due to the fact that it has been tied for a very long time to the unconfirmed idea of ​​the infinite sinking of the oceanic crust, which constantly draws down the descending movement of the mantle convective cell. If we look at "subduction" soberly, we can say that it is most likely a zone of interaction between oceanic and continental slabs with predominant compression, an analog of a collision, or obduction, but with a predominant under-thrust component. Now in the zones of "subduction" compression and underlay predominate, later in the framework of the oscillatory process they can be replaced by stretching and spreading. Infinite podviganie plates on the outer part of the descending convection cell is unlikely by the elementary laws of physics. The geometric impossibility of this is proved among other authors and by me. Below is a reference of my abstracts on EGU-13 and mu presentation on EGU-14 on this topic.

Geophysical Research Abstracts

Vol. 15, EGU2013-6448, 2013

EGU General Assembly 2013

© Author(s) 2013. CC Attribution 3.0 License.

Unfortunately, all these publications are on Russian.

A. Buslovich "Мезозойские трубки взрыва Вологодской области" (Mesozoic explosive pipes of Vologodskaya oblast')

Also, there is another author V. Tret'yachenko "Перспективы мезозойского кимберлитового вулканизма юго-восточной части Архангельской алмазоносной провинции" (Perspectives of mesozoic kimberlite magmatism of the southeastern part of Arkhangel'sk diamond province)

Here is a link on the latest Sablukov's presentation (June 2017) about "highly perspective" Ust'yanskaya area where he propose mesozoic kimberlites:

Regards Alexander

If was aware about. It seems that you have enough knowledge, Your polite comportment its reflect well...

I think we do not know to give such a response: which you do not aware it.

If you practice an examination procedure, its better to do with your students

The simple answer to get to strain from displacements is to find the deformation matrix that connects initial to final positions. If you are working in 3D that would be a 3D tensor. If you could assume plane strain the matrix would be simpler. Basically the displacements would be longitudinal and angular and you could go about quantifying those depending on your problem. If your data consist of GPS displacements, it is the longitudinal strain (typically N and E) that is significant and you can look at "baselines" that shorten or extend in the direction that is most important to you. As Stress and Strain tensors are connected through the Rheology tensor, you would need to have information about the rheology of the deforming material to be able to go from strain to stress (as Martijn correctly pointed out above). If the deformation is near surface then elastico-frictional laws typically apply. Other wise you could opt for quasi-plastic or viscoelastic rheologies.

Yes Geodynamics have indirect relation with agroecology or rather say cultivation of crops. The any dynamism on soil either on surface or inner layers bound to impact by changes which ultimately link to rhizopspheric interaction in crops.

A specific plate velocity, described by an Euler vector, results from an equilibrium equation between active and passive torques exerted on a tectonic plate. An example of this equation can be found in:

Schettino, A. & Macchiavelli, C., 2016. Plate kinematics of the central Atlantic during the Oligocene and Early Miocene, Geophysical Journal International, 205, 395–413, DOI: 10.1093/gji/ggw022.

Passive torques arise from passive asthenosphere drag. Active torques are associated with 1. active asthenosphere drag when lateral changes of pressure occur in the upper mantle, 2. lateral changes in the age of the lithosphere, which generates the so-called ridge push, 3. slab pull when the tectonic plate is subducting beneath another plate.

You could also give a look at chapter 13 of my book Quantitative Plate Tectonics.

The most fundamental property is likely to be the composition of the nebula the planetary system and star formed from. The ratios and abundances of certain elements from the nebula they all formed from will dictate the end composition of all the planets and the star itself.  All other variables are going to be influenced by the initial composition.

you may find this article useful

Munazzam Hello

Your question is not simple. At the same time, I propose that our paper (you can find it in RG DataBase) will be useful for you:

Eppelbaum, L.V. and Katz, Yu.I., 2016. Tectono-Geophysical Zonation of the Near and Middle East and Eastern Africa. International Journal of Geology, 10, 1-10.

Best

Lev

I recommend reviewing the equations of the following topics:

a) A spherical expansion source at depth can simulate the change in storage of a magma chamber and account for deformation caused by magma intrusion events [Mogi, 1958].

b) Finite Element Models

c) Inverse analyses

d) 3-D visco-elasto-plastic numerical models of rock intrusion emplacement incorporating in particular the temperature-sensitive properties of both magma and country rocks. Thermomechanical modelling of magma intrusion involves simultaneous and intense deformation of materials with very contrasting rheological properties:

1.- the country

2.- crustal rocks

3.- visco-elasto-plastic while the intruding magma is a low viscosity

4.-complex fluid

Reference: Burg, J.P. & Gerya, T.V. (2008)

 Dear Zehra,

I understand that the separation of minerals is not the most important of your business.

The simplest method of separation - manual separation of minerals during irradiation with UV radiation. Zircon will luminesce green-yellow light color (see answers to Petra Vesela). Pyrite is not luminescent.

If you have a lot of minerals, I recommend using the automatic X-ray luminescent separators, which are used for diamond industry. In the diamond industry zircon is a poor mineral which is extracted together with diamond and clogs concentrate.

But if you do not afraid some change the characteristics of zircon, it is possible to heat a mixture of pyrite + zircon at 200 -300C for 10 - 15 minutes. After that, zircon becomes lighter, but they restore color later. The pyrite becomes magnetic. After the procedures ferropirite is removed by magnetic fild.

Vasily

Dear Sumanta: the question you posed is a very complex one! The supercontinent cycle has been operating since at least the Paleoproterozoic or Neoarchean, assembling and disrupting continental masses, creating -and destroying- orogenic belts and ocean basins, volcanic belts, and the like. So it is unquestionable that such tectonic variarions had a strong influence on past climate, just as they have been doing since the Pangea disruption in the Jurassic. The problem is relatively easy to resolve in Mesozoic terrains, a bit more difficult in Paleozoic, and really a hard one in the Precambrian. Conditions for deposition of evaporitic basins were widespread during the Permian, but also in the Devonian and Proterozoic, where large evaporitic basins are found, also aeolian sandstones are frequent in this very dry period, and in older times too. Climate changes so profound as to be unimaginable to us happened when continental blocks collided to form supercontinents. Pangea was covered possibly by a desert three times larger that the actual Sahara, and by an enormous ice cover in its southern parts. The uplift of the Appalachian-Caledonian belt surely had a profound effect in the climate of this supercontinent and global Earth. Before this, in the Neoproterozoic, the uplift of the world-wide Greenvillian system of orogenic belts, which was probably even higher than the Himalaya and longer than the Andes..., due to the assembly of Rodinia, certainly had a marked influence in atmospheric and oceanic circulation, as to eventually lead he planet to the "Snow-ball Earth" global glaciation, just as the uplift of the Andes and Himalaya has done in more recent times, creating large deserts in South America and Central Asia. The problem in older terrains is the large uncertainties in the relative shape, positions and paleolatitudes adquired by land masses, this is relatively easy to solve during the Jurassic, but increasingly difficult to ascertain in older times. With regards, Sebastian.

There are no standard curves dedicated or specialized for faults detection using HEP in ground resistivity survey. The HEP could only detect fractures which are usually characterised by relatively low resistivity. However, you can obtain a large data set of HEP and carry out deep vertical electrical soundings (VES) at the delineated fracture points using current electrodes spacing ranging from 2 metres to greater than 300 metres and construct geoelectric sections along the appropriate traverses. This would reveal network of fractures and possibly faults could be delineated if present.

Good luck.

Many thanks for the answer. I am working on stichtite and pyroaurite, and have not found much information on these relatively rare (in the natural world) minerals. I work at a smaller CSU campus and don't have access to much research instrumentation. Just got back from sabbatical with more questions than answers.

Do you know of a lab that could do this work, and what the cost might be? I am worried about doing just a theoretical estimate of interlayer spacing, as these natural samples have non-endmember compositions.

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If you have a segmentation of the pores you can use connected component labeling (http://www.mathworks.com/help/images/ref/bwconncomp.html) and regioprops (http://www.mathworks.com/help/images/ref/regionprops.html) and than for each pore you can find the 'Orientation' property of the pore which is the best ellipse that is fitted to the connected component. 

Dear Dr. Jan:

Let me add a general statement. I also was fond of using discrimination diagrams like those mentioned in this Q&A relation. It makes you think you have an ideal and efficient tool passing a lot of samples through an analytical device which does not only  provide us with read-outs of chemical data but delivers straight ahead the geodynamic setting in a way which can be satirized as "Mountain building out of the test tube". We are creating a plethora of results which having a closer look at the geology as it is in the field are in no way related to the real geology. Geoscientific work takes time and needs substituting the swivel chair for the campstool, at least from time to time. For those who are riding only the paper tiger it may be sufficient but those who also want to deal with earth in an extractive way or want to know more about only the interplay of mineralogical and chemical in-house studies with field work will provide us with lasting results.

Sorry for this comment. But from time to time I feel it is necessary to put in order the system and champion the cause of this unprivileged discipline "field geology", which cannot be underrated.

With kind regards

Harald G. Dill

Your welcome.

There are many things that are unknown. But the temperature in the outer core is not a big deal. The Earth is not a magnet, the Earth is an electromagnet, is the circulation of electrons in the outer core which produced the magnetic field and not a remanence in the core.

Regards

Dear Nagarayu, there is no special method of locating earthquakes with linear arrays, any localization program will work. A linear array, however, will always produce large localization errors for events lateral from the line, simply caused by the small differences of the arrival times. Why don't you shift 1 station  to get an areal array.

Kind regards

Rainer

Such texture occur in "eutectoids". I would call it symplectite in preference to myrmekite, The orthopyroxene and feldspar may have grown simultaneously.

Dear All

I will try yo locate and make a pdf of this paper, but it will take a couple of weeks as I am travelling at the moment. Incidentally, I wrote and presented this paper, not apparent from the author list !!

If you want to convert ellipsoidal heights to orthometric you can use the PROJ libraries with the geoidgrids for height conversion.  In python you'll need to get pyproj

https://pypi.python.org/pypi/pyproj?

<code snippet>

WGS84=pyproj.Proj(init="EPSG:4326") #WGS84 datum ellipsoid height

UTM19S=pyproj.Proj(init="EPSG:32719", geoidgrids='egm08_25.gtx') #Chile UTM coords, zone 19S, orthometric heights(masl)

 east, north, masl = pyproj.transform(WGS84,UTM19S, data.LONGITUDE.values, data.LATITUDE.values, data.ELEVATION.values)

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.

Vagif salam!

Without hesitation, geodynamic situation strongly influences to hydrocarbon deposit generation and its preservation. For instance, geological conditions in the Dead Sea Basin are very favorable for large oil deposits accumulation. At the same time non-stable geodynamic pattern and active seismology do not assist to hydrocarbon deposit safety. Therefore, several drilled boreholes in this area discovered only signatures of hydrocarbons.

Dear madam,

Actually, my research is on river morphology. Which means, it will consider the river will be migrated in such a time

Dear Gerhard,  Thanks a lot for all these info. Regarding the large Laacher See zircons, I fully agree with your pegmatite hypothesis and I have scanned a photo of a zircon that supports this - indeed you have already suggested similar observations you have made yourself. On the other hand for the large zircons in the older tephrite lavas I am less convinced that the same process could work (no obvious resorbption features). I'll attach the two scans to illustrate the contrast asap, in the coming days most probably.

Thanks again for the discussion and for the ref.

Beste Grüsse,

Gerald

Characteristic of eclogites is the absence of plagioclase, whose albite-component is incorporated as jadeite in the omphacite. The anorthite-component is incorporated in the form of grossular-component in garnet. The transition from the loose framework structure of plagioclase (tectosilicate) changes into the close-packed structure of the chainsilicate omphacite and the nesosilicate garnet, with an eclogite-density of about 3.5. Each aluminum oversaturation in the eclogite protolith, which can not be incorporated in garnet and omphacite, crystallized in the eclogite as kyanite (nesosilicate).

Tyrone,

I have been writing lots of XOJO code now that I got the I/O problem figured out.

There is one other thing that I appreciate your help with.  I can use the dialog method to open and save files interactively.  But I'd also like to open and save files directly to a folder without going through the dialogue box.  How do I tell my program (in code) to go to a specific folder and open or save a file there?  In old VB,  I simply entered all the directory routing info, but am not sure what that would look like in XOJO (for a Mac running OSX).

Thanks for any advice you can give.

Best Wishes for the holidays,     Chris

Thank You very much Marwan Wartes

Though I have not looked at the specific area you are referring to the changes in the lithologies in layered intrusions result from fractionation where the magma becomes  gradually depleted in mafic minerals and enriched in silicate minerals. if in the system you still had the hydrothermal fluids that form complexes with the Cr that would form the stringers which would settle at the bottom of the each  cyclic unit.

Dear Nirmalya,

S and C planes (or shear bands as they used to be called) may display variable angles to one another, especially as they are traced into areas of higher strain. The intersection of s and C planes may also rotate into higher strain areas (perhaps producing some of the relationships you describe). In addition, new sets of shear bands develop that overprint the older rotated sets. I wrote a paper many years ago looking at geometric relationships between S-C fabrics (shear bands), mineral lineations, and rotation of c intersections (see attachment).

Note also that layer-normal differential shearing may cause extensional structures (including S-C fabrics) to develop obliquely to the overall transport direction marked by the mineral lineations (Check out Fig. 2 of the attached Alsop & Holdsworth 2007 paper)

I hope this may help.

Ian

Dear Longgang,

The formation of a foreland basin starts during the continent-continent collision when one of the two continental plates starts to be subducted by the obducted plate. The continent-continent collision starts after closure of the remnant ocean. Accordingly, the foreland basin develops not before or after, but during the collison. The sedimentation into the foreland basin occurs during the rise of the newly forming mountain range. The reasons for intense sedimentation into the forelland basin are the intense erosion in the rising mountains and the increasing relief between the rising mountains and the descending foreland basin. If marin or terrestrial sedimentation occurs in the foreland basin is controlled by the relative sea-level and the tectonic conditions. If the grade of mountain rise is high, the subsidence in the foreland bain is also high and marin transgression into the foreland basin may occur if the relative sea-level is high.

The sedimentation in the closing but stll deep ocean before the collision is dominated by deep-marin deposits ("Flysch") whereas sedimentation into the foreland basin is dominated by shallow marine conditions. Characteristic for marine foreland basin deposist are shallow marine siliciclastic deposits in the basin and deltaic fan conglomerates around the rims of the basin.

All the best,

Elmar

Dear Xiaojun Feng. We consider the weakening ratio by calculating strain softening for the undeformed rock (peak friction - dynamic friction) and for reactivation of the shear zone (stable friction - dynamic friction). I expect this is describing the same parameters you suggested. You can see our workflow for frictional parameters ingranular materials in Lohrmann et al. 2003. Do you consider the weaking ratio as similar parameter or a different one?

Dear Parkash

The Euler Pole estimation correspond to the Helmert-type velocity transformation model using only rotational rates. Euler Pole Parameters have one-by-one dependency to rotational rates about the three axes.

In my opinion, use the Helmert type transformation model using shift and rotational rates (not scale).

Regards!

The NUMERICAL problem is that the "reduction to pole" filter has a divisor which gets smaller as you get nearer to zero magnetic inclination (i.e. near the geomagnetic equator), and becomes zero at zero inclination. So RTP is unstable at inclinations less than about 20 degrees and infinite at zero inclination. Some commercial software has a stabilisation technique which is somewhat effective, but there's no TRUE solution.

The PHYSICAL problem is that 2D source bodies with strike exactly aligned N-S have zero induced magnetic anomaly at zero geomagnetic inclination. And there's no filter that can make "something" out of "nothing".

The PHYSICAL and NUMERICAL descriptions are really different ways if stating the same thing.

         

I think you should read a text book. These things are explained. The corner frequency is important because this is the peak of energy radiated (you see this when you consider the power spectrum) and like an antenna radiates best at is own dimension the wave length corresponding the the corner frequency is approximately equal to the source dimension.

The moment can be estimated from the low frequency constant amplitude of the displacement spectrum from the amplitude of any frequency because at these long wavelength the source can be modeled as a point.

Of course you can estimated the energy radiated seismically by integrating first the energy at one station in the spectrum and then integrate in space considering the variations of amplitudes according to the fault plane solution, and then you need to add the energy in the P and the S-waves. After that you would have the energy radiated, but would know nothing about the energy that went into heating the fault plane by friction and the energy possibly used to break rocks, plus there is also the potential energy stored by uplift,

As I said, it's best to study a text book, perhaps Aki and Richard.

Dear Mr. Ze-Zhou Wang,

I think this is a very ambitious project and I agree with you that with regard to the derivation of rare elements there is still room for a lot of work. So far, the studies using Zn, Cu, and Ba isotopes are already at the beginning and many aspects obviously have not fully been understood. I would like to give you a piece of advice, try and keep in touch from the early beginning with the geology. I saw too many projects and papers ending up as a "flying carpet" . A highly sophisticated method well done but its data fraught with difficulties when in comes to the interpretation is not unsusual. I wish you all the best. Feel free to contact me through RG.

I hope my piec of  advice will help you better find your way.

Harald G. Dill

I have found accumulation of olivine and pyroxene from a high-Mg basaltic magma (12-13% MgO) in sills as thin as 4m. However, these are not true ultramafic rocks, they are olivine-chromite-enriched melagabbronorites. They also contain minor disseminated sulphides (pyrrhotite-pentlandite-chalcopyrite) which probably formed by contamination of the magma at an earlier stage. These sulphides could possibly contain trace amounts of Pt-Pd sulphides or other PG minerals.

To consider the question of whether the sills nearby to your hydrothermal Pt-Pd deposits could have provided the initial concentration of PGE, there are many things to consider along with the thickness. There is also the stage at which S-saturation occurred (early or late), the sequence of mineral crystallization (olivine-pyroxene-plagioclase, or olivine-plagioclase-pyroxene) and the temperature of magma emplacement (supraliquidus, liquidus, or as a cool, crystal-charged mush).

In order to provide a source for the hydrothermal enrichments, I think that these sills would have to have been emplaced in either a S-undersaturated state, in which case the PGE would have been widely distributed throughout the sill and only weakly concentrated in any mafic-ultramafic cumulate basal layer, or that they were emplaced in a sulphur saturated state, but with the immiscible sulphide droplets still entrained with the magma. In that case, the PGE would all be concentrated into the sulphide droplets, which would be themselves concentrated towards the base of the sills together with olivine-chromite-pyroxene cumulates. The worst case (for pre-enrichment of the PGE in the sills) would be if the magma was already S-saturated, but it had left all or most of the sulphides behind at a deeper level. In that case, the sills would be depleted in the PGE, and would be no better as a source rock for the hydrothermal Pt-Pd than any other crustal rocks like granites, granite-gneisses etc.

Another thing to consider would be the hydrothermal pathways - are the sills themselves or their basal contacts a locus for shearing or any other type of structure permitting fluid ingress?

Wall et al. 2010 from Basin research

Cheers

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.