Tectonic Geomorphology - Science topic

Dear Mr. Ahmad,

you are completely right as you state that such giant streams are governed in their river-run by deep-seated lineamentary fault zones within and at the edge active fold belts.

HGD

Dear Atul Singh many thanks for posting this important technical question which is certainly of broad general interest to many other RG members. In addition to the useful links which have already been suggested, I recommend thet you also search the "Questions" section of RG to find questions about the same topic. For example, please have a look at the answers given to the following closely related question which has been posted earlier on RG:

(29 answers)

Good luck with your work and best wishes!

Dear Ahmed Morad: I understand perfectly what is your proposal. The best way to show how marine sediments get into a subduction zone is to draw a detail of the hinge zone where the oceanic plate bends when foundering inside the mantle. In this hinge zone stretching occurs, and some expansive graben structures are formed (normal faults parallel to the trench), which trap sediments and lead them to subduction. Then those sediments are metamorphosed under high P/T conditions and become phyllites and schists, usually white schists, and even metacherts and fine grained marbles. There is a quite accesible outcrop in a main freeway near the city of Puerto Cabello (north-central Venezuela) of eclogite knockers inside a relatively monotonous micaschist. A close look at thin sections of this schist shows the presence of kyanite, garnet, white mica, and Mg-glaucophane, these are usually called white schists, since the glaucophane is almost colorless and retrogradly altered to talc! Some have carbonate too, and in nearby localities of this same high P terrane there are also metacherts and marbles. So, there's no doubt that some marine sediments are indeed subducted and transformed to high P metamorphic rocks in the subduction complex. Regards, Sebastian.

One option would be to use the ChiProfiler tool that integrates with TopoToolbox that Sean Gallen (Colorado State University) created. It is available from his Zenodo site for download at https://zenodo.org/record/321868#.YCV91WhKg2w or on Github at https://github.com/sfgallen/ChiProfiler.

Article to reference for use of ChiProfiler is:

Gallen, S.F., Wegmann, K.W.: River profile response to normal fault growth and linkage: An example from the Hellenic forearc of south-central Crete, Greece, Earth Surf. Dynam., 2017, http://www.earth-surf-dynam.net/5/161/2017/.

Dear Sebastian,

The informal methodological guidelines we have used to compile hazardous faults in South America may partially meet your question, particularly for putting the outcome data in a friendly formal for SHA requirements:

More info will be available late this year in an upcoming special issue of the Journ. South. Am. Earth Sc.

Best,

Carlos

I think you find parallels with the question in the paper of Iván Almár and coauthor: the London scale. The authors try to formulate the impact of a discovery which is complex enough (for example: to find life somewhere in the Solar System). Earlier other scales were also used by I. Almár in connection with the CETI researcg.

It has come to my understanding.

Bedrock landslides (rockfall, rock avalanche) are found to be more sensitive to the change in area and hence their scaling exponent lie close to self similar exponent (1.5). Therefore, s can be considered to be controlled by size in this case. 

In case of debris (rock+soil) slides, varied material is found to be less effective to change in area and hence lies far below self similar exponent (1.5). Thus, in this case, material controls exponent.

However, a common relationship still seems rare.

Dear Dr. Ahmad Ali,

you can use these types of tectonics in soft and hard rocks. There are many examples of them in loess, e.g., Hungary and several in crystalline (hard) rocks as well.

I can give you one example from the Dead Sea Transform Fault below:

DILL, H.G., HAHNE, K. and SHAQOUR, F. (2012) Anatomy of landslides along the Dead-Sea-Transform Fault System in NW Jordan.- Geomorphology, 141-142: 134-149.

Best regards

H.G.Dill

Hello,

Please plot your data using the freely available software (see below).

Once you plot, it is easy to measure a range of things. Possibly all that you are asking for, though, you may need more than one software for your work, and  luckily all is free.

Enjoy plotting 

Regards

Shah

Dear all,

Thanks a lot for your response and catering me some good literature. However, my question was related to the project "Understanding Proterozoic Chert" posted by Dr. Linda Kah, University of Tennessee. I am interested to get associated with that project and wish to listen from Dr. Kah.

Regards,

Himadri

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...

You can find in the RG Data Base the following papers reflecting the deep structure of the Eastern Mediterranean:

Ben-Avraham, Z., Ginzburg, A., Makris, J. and Eppelbaum, L., 2002. Crustal structure of the Levant basin, Eastern Mediterranean. Tectonophysics, 346, 23-43.

Eppelbaum, L.V., Katz, Y.I. and Ben-Avraham, Z., 2012. Israel – Petroleum Geology and Prospective Provinces. AAPG European Newsletter, No. 4, 4-9.

Eppelbaum, L.V., Nikolaev, A.V. and Katz, Y.I., 2014. Space location of the Kiama paleomagnetic hyperzone of inverse polarity in the crust of the eastern Mediterranean. Doklady Earth Sciences (Springer), 457, No. 6, 710-714.

Eppelbaum, L.V. and Katz, Yu.I., 2015. Newly Developed Paleomagnetic Map of the Easternmost Mediterranean Unmasks Geodynamic History of this Region. Central European Jour. of Geosciences (Open Geosciences), 7, No. 1, 95-117.

Eppelbaum, L.V. and Katz, Yu.I., 2015. Eastern Mediterranean: Combined geological-geophysical zonation and paleogeodynamics of the Mesozoic and Cenozoic structural-sedimentation stages. Marine and Petroleum Geology, 65, 198-216.

Best regards,

Dear Miroslav,

I am afraid it's just sandstone concrections - no fossils, sorry.

thomas

Dear colleagues,

I would like to draw your attention to a sanidine-bearing diamontiferous igneous rock in Mongolia. Sanidine is a common constituent in the Tertiary to Quaternary volcanic rocks and recovered as a by-product besides garnet and olivine: The economic figures for garnet are 1764 gr/m3, peridot 80 gr/m3 and for sanidine 4 gr/m3. The gemstones are accommodated by dark tuffaceous breccias representative of the diatreme pipe facies. Olivine, plagioclase, clinopyroxene and magnetite are rather fine-grained. Accessory minerals are ilmenite, apatite, zircon, chromium spinel, graphite. Inclusions may reach a size of as much as 3 cm and contain garnet, pyroxene, olivine, biotite and sanidine. The host rock was identified as a lamproite rather  than a kimberlite. The overall features of the basic source rocks are moderate trace element contents of Cr and Ni, presence of sanidine instead of leucite and a K2O/Na2O of far below 5.

You can dowload the paper from my list of publications from the RG server:

DILL H.G. , KHISHIGSUREN S., MAJIGSUREN Yo. BULGAMAA J., HONGOR O. and HOFMEISTER, W. (2004) The diamondiferous peridote (olivine)-garnet deposit Shavryn Tsaram, Central Mongolia, with special reference to its placer deposits.- Gemmologie, 53: 87-104.

I wish you much success

H.G.Dill

Bonjour,

En espérant que votre question soit toujours d'actualité... Voici ce qu je peux répondre pour alimenter le débat.

Est-il possible de corréler l'existence de karsts profonds jurassiens à la crise de salinité messinienne ?

Pour répondre à cette question, il nous faudrait connaitre entre autre 1/ la profondeur à laquelle ont été identités ces karsts et 2/ la profondeur d'incision du canyon du Rhône et de ses affluents à de telles latitudes. En lisant la réponse formulée par M Bakalowicz je me rends compte que les impacts de l’événement messinien sont encore assez mal compris. En effet, la vague d'érosion régressive provoqué par le Rhône ne s'est jamais arrêtée au niveau de la localité de Lyon mais est allée bien au delà (jusqu'en Suisse selon G. Clauzon). En revanche, c'est la transgression méditerranéenne au lendemain du refooding qui s'est stoppée au sud de Lyon. Cet amalgame est souvent commis, celui d'assimiler la surface d'érosion immergée au lendemain de la crise à l'érosion totale provoquée par le réseau hydrographique. 

A ma connaissance, peu ou pas d'études ont été réalisées dans cette partie du territoire sur la profondeur exacte de l'incision messinienne, ce qui laisse une partie de la question ouverte.

Concernant, la corrélation de la formation de ces karsts avec un paléo-niveau niveau de base (tel que le fond d'un canyon messinien), il nous faut disposer de davantage d'informations, notamment sur la géométrie de ces objets. En effet, la mise en place d'un karst profond en rapport avec un niveau de base déprimé (comme se fût le cas au Messinien dans la partie aval de la vallée du Rhône) répond à une structuration d'un karst dit "épigène" sous l'influence d'un gradient topographique. Ce type de réseau à une signature morphologique particulière correspondant à un drainage des eaux d'infiltration vers un point d'émergence, selon un dispositif de drains plus ou moins bien hiérarchisés d'amont vers l'aval.

La seule découverte de karsts profonds très en contre bas du niveau actuel des vallées ne peut suffire à envisager des périodes durant lesquelles le niveau de base fût très en dessous de l'actuel. En effet, certains processus de cavernement peuvent être tout ou partie découplés de l'influence du niveau de base, c'est notamment le cas des karsts dits "hypogènes"  ou encore des phénomènes de fantomisation des carbonates pouvant atteindre plusieurs centaines de m de profondeur sous le niveau de base (voir à ce sujet les travaux de l'école Belge dirigée par Quinif).

Donc, en ce qui me concerne et bien qu'étant un fervent défenseur du modèle profond promu par Hsü et al. 1970 et de ses conséquences morphologiques, la découverte de karsts profonds peut faire référence à plusieurs processus de karstification qu'il convient de soumettre aux données disponibles.

En résumé : 

- Oui, les impacts morphologiques de la crise de salinité ont largement dépassés la latitude du Jura. Je ne connais pas en revanche de travaux autres que ceux de Gorges Clauzon dans la région (qui sont toutefois relativement succincts).

- La présence de karsts profonds peut renvoyer à plusieurs processus. Sans informations supplémentaires (nature des remplissages...), il me semble difficile de discriminer le processus ayant été en jeu.

Enfin, si vous avez des informations supplémentaires, je serai très intéressé d'en rediscuter !

Cordialement, L Mocochain

Hola, notros datamos arenas de playa, de ambiente de berma y dunas, a >50 m, yo  recomiendo IRSL acoplado con sedimentologia y estratigrafia in situ para  muestrear depositos de bermas o dunas que generalmente son homogeneas y un poco lixiviadas, por eso parecen paleosuelos, pero en contraste no tienen matriz fina.

Thanks Kenneth. Very helpful paper.

Hi Almaz

I came across a paper from Chinese authors who described block movement on continental slopes, published in English on an Asian journal. They have modelled some of your parameters in the lab, so scholar.google should be of use to you. See also Alves (2015) Marine and Petroleum Geology. All the best,

Tiago

Regional groundwater U-turns, rejected recharge and hydraulically perched groundwater sapping beneath divides may all be pieces of the peneplain puzzle (Elfrink, 2009).  Drainage basin disruption can create conditions favorable for the formation of low relief landscapes.  Migrating regional groundwater drainage divides tend to reject deep recharge and focus groundwater sapping into relatively shallow stress-relief fractures.   The concentrated flow can help explain why in situ peneplain development (Yang et al., 2015; Brocard et al., 2012) and intense stream incision (Yanites et al, 2013) are associated with drainage reorganization. Relatively recent river network disruptions (Conti, 2012) may be a plausible explanation for East African peneplain development.  The same long-wavelength crustal tilting (Moucha & Forte, 2011) that disrupts river networks can also add an upwelling discharge component to the sapping system. This increase in subsurface erosion efficiency is not directly related to atmospheric recharge or local topography.  Upwelling groundwater from distal sources tends to create sparsely dissected landscapes (Marra, et al. 2015). I suspect planation in Malawi is related to the northward migration of the growing Zambezi Basin catchment divide.

Peneplains evolve by seepage-induced cliff recession and “..spatially averaged lowering of the surface by chemical denudation” (Higgins, 1990).  Subsurface erosion causes “surface lowering following volume decrease and compaction in the regolith …as vast quantities of dissolved minerals are carried in rivers and groundwaters”  (Twidale & Romani, 2005). 

REFERENCES

Brocard et al, 2012,

Conti, 2012.  Paleodrainage Systems.

Elfrink, 2009

Higgins, 1990, page 166 and page 291

Marra et al., 2015

Moucha & Forte, 2011

Yang et al., 2015

Yanites et al, 2013 https://www.researchgate.net/publication/256475092_High_magnitude_and_rapid_incision_from_river_capture_Rhine_River_Switzerland

Many examples are given within the semail ophiolite of Oman

Thanks to Scott Edmund Kelsey Bennett!

NAVDAT is an excellent resource for igneous rock data of all kinds. I suggest you use their excellent search tools.

Best of luck,

Scott Bennett

USGS

This is a bit of a cryptic question without further background...

It does have some interesting aspects to it though. Plagioclase fractionation is typically suppressed in water-rich magmas, and that is the reason why arc magmas (which typically have appreciable H2O-contents) can evolve to high-Al basalts: as long as plagioclase doesn't fractionate, Al is an incompatible element, and is enriched in the melt. There are two ways to have plagioclase crystallising: just continue crystallisation, and in the end, plagioclase will become a stable phase; or decrease the pressure, whereby the maximum amount of water that can be dissolved in the silicate melt decreases, and this will also cause plagioclase crystallisation. The latter mechanism is the reason why arc lavas that have erupted on the surface are nearly always full of plagioclase crystals: to reach the surface, the magma would have had to undergo a reduction in pressure.

Probably your best bet is to look at the isotopic signature, because the Rb/Sr, Sm/Nd, U/Pb etc ratios of arc rocks are different from mantle rocks. So over time a different isotopic signature should develop. There is still a chance that the answer will be ambiguous, as many arc magmas contain a contribution from subducted sediments. For a 'recycled' arc signature, I would not expect to see too many mafic rocks - unless of course the 'recycled' arc signature comes from the mantle rather than from remelting crustal materials. Perhaps the attached publication can give you some ideas...

I can suggest this other paper, based on the evolution of Caribbean Large Igneous Province (CLIP), and Central American and West Caribbean subduction zones, giving indications of how this slab avalanche can happen, related to a mantle plume, such as the one which originated the CLIP - or a similar process that could have started subduction in the Archean. It has excellent cartoons depicting their new model.

Scott A. Whattam &,Robert J. Stern (2105). Late Cretaceous plume-induced subduction initiation along the southern margin of the Caribbean and NW South America: The first documented example with implications for the onset of plate tectonics, Gondwana Research 27(2015): 38-63.

 

Dear Dr. Xie,

a simple pattern showing the different features of Cu and Au skarn deposits may hard to be given. The two distinct types are described below with some literature.

Cu skarn deposit are co-magmatic to porphyry-type deposits. Bornite-chalcocite mineral associations are the dominant Cu-Fe sulfides rather than pyrite-chalcopyrite assemblages in the skarn deposit such as at Ertsberg-Irian Jaya, Indonesia, and Maid of Erin, Canada (Kyle et al., 1991). The world’s largest Cu-Zn skarn is located at Antamina, Peru. Cu skarns commonly are zoned with respect to alteration and ore minerals with garnetite near the pluton and pyroxene, vesuvianite and/or wollastonite near the marble contact. Pyrite and chalcopyrite are most abundant near the pluton with increasing chalcopyrite and finally bornite near the marble contact in copper skarns (Ripley and Ohmoto, 1977). Skarn-type mineralization with ilvaite, hedenbergite, epidote, garnet and johannsenite evolved in Liassic limestones in the surroundings of Campiglia Marittima-Tuscan, Italy (Brandi et al. 1968). Metasomatic deposits at the contact of diorites and monzonites developed within the Precambrian Chidué Group at Chidué in Mozambique. Copper minerals occur in fissures and faults as well as in skarnoid rocks bearing actinolite-tremolite s.s.s., andradite, grossularite and epidote (Steiner 1992).

The term "gold skarn" in the economic sense was suggested by Einaudi et al. (1981) in that they are mined exclusively or predominantly for gold and exhibit calc-silicate alteration, dominated by garnet and pyroxene genetically related to the gold mineralization. See gold skarn deposit in the Hedley district, British Columbia, Canada (Ettlinger et al. 1992, Ettlinger and Ray 1993), in Andorra, Spain, at Junction Reefs, Australia, at Crown Jewel, Elkhorn, Redline USA, Nambija District, Ecuador, (Theodore and Hammarstrom 1991, Hickey 1992, Everson and Read 1992, Gray et al. 1995, Fontboté et al. 2004). The Au skarn deposits were emplaced within carbonates, calcareous clastics, volcaniclastics, volcanites intrusions of calc-alkaline, less frequently of alkalic composition in orogenic belts at convergent plate margins and arc or back-arc environments. The mineralogy is highly variable and depends on the type of skarn deposit: (1) Mg skarns: gold, pyrrhotite, pyrite, magnetite, Cu-Pb sulfides, (2) pyroxene skarn: gold, pyrrhotite, arsenopyrite, Cu-Zn-Co-Bi sulfide and ± Au tellurides with high sulfide contents and pyrrhotite: pyrite ratios, (3) garnet and (4) epidote skarns resembling pyroxene skarn with respect to mineralogy but minor sulfide and low pyrrhotite: pyrite ratios. Mueller (1997) described the Nevoria gold skarn deposit of the Archean Yilgarn craton, Western Australia occurring in amphibolite facies greenstones between two dome-shaped granitoid batholiths. The gangue is calcic, highly reduced, with accessory arsenopyrite-loellingite, and chalcopyrite. Native gold is enclosed in hedenbergite, actinolite, almandine, and quartz and occurs together with the alloy maldonite and a suite of bismuth tellurides. This skarn formed in a deep midcrustal environment (10-15 km) during late Archean magmatism very much distinct from the copper-gold skarns in Cenozoic continental margins and from gold-rich iron-copper skarns in Cenozoic to Mesozoic island-arc terranes, which all formed at much shallower depths of 2 to 5 km. In contrast to the reduced or typical skarn deposits also reported from the Sn-W camp, that are characterized by low garnet: pyroxene ratios, hedenbergite, abundant sulfides and dominated by pyrrhotite and arsenopyrite, there are gold skarn deposits named as oxidized gold skarns by Brooks et al. (1991).

Best regards

H.G.Dill

Dear Christian !

Kindly find attached the papers related to tectonics of the northern alps. May be, you find them helpful.

All the best !

 Many thanks to all of you about your carefull answers

Thanks for reply, Numan, Reza and Sissakian sir. Is there any possibility to get a range of GSI and RMR value based on empirical formula given by different researchers. The most of empirical formula applicable to determine the rock mass parameters in combination of lab results such as UCS (intact rock). Here we can assume the intact rock parameters are higher than rock mass parameters and similarly we can get the range of GSI and RMR values for the particular type of rock mass. Is it right way to determine the range of GSI and RMR values based on lab test. If you are agree, please suggest any reference paper and comments.  

there are many forces on the slab while subducting. driving forces include negative buoyancy which is the primary driving force and ridge push, resistance forces include bending force at the trench, viscous shear. when slab reaches 660km, lower mantle is usually regarded as a higher viscosity zone, then viscous shear increases which makes slab much more difficult to subducts.

Moreover, if slab is too weak, slab is difficult to subduct, and it may breakoff somehow. 

The classic model defined by Davies and Blanckenburg (1995) assumes that slab break off occurs during continental collision.

Dear NKosilathi

With cooling the Earth, the hotter mantle construct the mid oceanic ridge. Generally tectonic regime of the Archean eon is controlled by volcanism and plotunism. thickness distribution of lithosphere and natural buoyancy  took place during Archean. The subduction may took place in this time (Condie, 1997) 

link: https://books.google.com/books?id=SsZR_zsqQWsC&pg=PA176&lpg=PA176&dq=Tectonic+activity+in+Archean&source=bl&ots=REsZl-tYsa&sig=vI9Cd2wcMyPe9L21k348nMp3x7I&hl=en&sa=X&ei=wUqJVeCVB4e1sQSBuLywDA&ved=0CCUQ6AEwATgK#v=onepage&q=Tectonic%20activity%20in%20Archean&f=false

 Many mountain belts formed during the Proterozoic, in particular during the intervals between 2.1 and 1.8 billion, 1.3 and 1.0 billion, and 800 and 500 million years ago, associated with the breakup of supercontinents and the subsequent collision of their fragments. New ocean basins were created by the rifting apart of the continents and were subsequently destroyed in subduction zones similar to those under modern-day Japan. The closure of these oceans enabled continental blocks to collide, giving rise to major mountain belts such as the Grenville belt in eastern North America. This belt, which is 1.3 to 1.0 billion years old and 4,000 km (about 2,500 miles) long, was very similar in origin to the Himalayan Mountains that formed in recent geological time. Other major Proterozoic mountain belts created by continental collisions include the Wopmay Orogen in northwest Canada (2.1 billion years old), the Trans-Hudson in Canada (1.8 billion years old), the Svecofennian in Finland (1.9 to 1.8 billion years old), the Ketilidian orogen (1.8 billion years old) in southwestern Greenland, and the Braziliano, Namibian, and Mozambique belts, which are all about 900 to 500 million years old. In contrast, mountain belts such as the 2.1-billion-year-old Birimian in West Africa and the 1-billion-year-old to 500-million-year-old belts of the Arabian-Nubian Shield developed by the addition of new material largely derived from Earth’s mantle. Thus, they include many island arcs similar to those found in modern-day Japan as well as many ophiolite sequences.

Related links:

1-Erickson and Hathaway Muller (2009)

  https://books.google.com/books?id=g0SY7j3iGHsC&pg=PA31&lpg=PA31&dq=Tectonic+activity+in+Proterozoic+eon&source=bl&ots=itCY2oN1bs&sig=aZkUaJa-MrbPElFU1LNbNsLE2bI&hl=en&sa=X&ei=RU-JVZOiHeaBywPd87uAAw&ved=0CD0Q6AEwBTgK#v=onepage&q=Tectonic%20activity%20in%20Proterozoic%20eon&f=false

2- Malcuit (2014)

Regards

Massih

If by "restite" you mean the residual from mantle melting, the easiest is to look at the Magnesium number (Mg#): highly residual would probably be between 92-94% (or 0.92-0.94 in non-%). If by "from partial melt of peridotite" you mean crystallized from a partially melted peridotite (=basaltic melt), it will usually have a lower Mg# than 90.

See Figure DR5 (from the data repository) from Blum and Pecha 2014-this is an excellent, up to date summary map, although there are smaller plutons, igneous suites, and terranes that are missing from this map (they are too small to effectively show on a continental scale map).

Zircon fertility is much trickier. Moecher and Samson (http://www.sciencedirect.com/science/article/pii/S0012821X06003396) is a good start, but zircon fertility can change abruptly across small spatial or temporal spans.

Dear Professors, 

I'm sure that these zircons come from sedimentary rocks according to other evidence. My question  in fact lies in that I don't know whether the angular shape is caused by the short-distance transportation or mechanical crushing during the zircon separation.I am sorry for the ambiguity of the question .

Dear All,

Apologies for the late reply. We were busy getting some more field evidences. Please have a look at the attached photographs from the same structure, but taken from much shorter distance. In several boudins the quartz veins, at the neck  demosntrate the so called "fish-mouth"  structure. Thus proving that the structures are boudins and the layers had very large competency contrast.

To answer Prof. Dill, the structure is in viscinity of South Almora Thrust in Kumaun Lesser Himaya. The rocks belong to Ramgarh Group. The quartzite can be refereed as quartz arenite with more than 90% quartz. The phyllites are meta-sedimentary and are derived from argellecious rocks. We do not have the precise minerology of the rocks, however visually there are only minor differences. The depositional environment is still not well established. 

If the boudins were initially Hummocky cross-beds. Does it imply that there was a cyclic change in the depostional environment, from stormy to calm/deep sea, and visa-versa. The stormy conditions formed hummocky cross bed and the argilleceous layers were depostied in the calm/deep sea condition ?

Many Thanks for the reply!

Amar

While this is a contentious subject, most researchers in the field would agree that "hotspot" volcanism results from the intersection of a plate with a mantle plume.  However some folks would like it to be driven by lithospheric cracking or edge driven convection.  Whether plumes originate from the core mantle boundary (CMB) or elsewhere in the mantle remains somewhat controversial. 

Plume generation requires a significant thermal boundary layer, and the only one we know of within the deep earth is the CMB.  Recently we have identified low shear wave velocity provinces (LSVPs) on the CMB, the edges of which have been shown to lie vertically below hotspots at the time of their eruption.  Leading to the hypothesis that the intersection of the LSVPs with the outer core and the lower mantle creates conditions favorable to plume generation.

For more info see:  Burke, K., Plate Tectonics, the Wilson Cycle, and Mantle Plumes: Geodynamics from the Top, Annual Review of Earth and Planetary Sciences, Vol. 39: 1-29, May 2011

Burke, K., Cannon, J., Plume-Plate Interaction, Canadian Journal of Earth Sciences, 2014, 51(3): 208-221, 10.1139/cjes-2013-0115

Marcos,

one valid criterion, in the lack of clear kinematic indicators, is to look for possible pre-faulting/fracturing features that could be used as markers. In the case of a strike-slip fault, the marker appears truncated, offset and displaced.In the case of a large fracture, the marker is truncated, but not offset and displaced. I hope this could be a simple criterion to answer your question.

Best wishes,

Enrico

Pablo,

Your is a primary question in earth sciences and I think that it is rather difficult, or even impossible, to reply with a more or less composite answer, since, as evidenced also by David, several constraints should be considered before trying to reply to your question.

And, first of all, I guess that you should take into consideration whole lithosphere extension, and not simply “crustal stretching”, and the evidence that slow-ultraslow rift systems are characterized by magmatic activity that is stored into the shallow mantle lithosphere without giving rise to subaerial volcanic activity.

But to obtain appropriated answers, the question should be posed with more precision. In fact, you write of “decompression melting (of the upwelling asthenosphere?) and recall that “such decompression results from the crustal stretching related with rifting”. Are you referring to a mechanism of passive rifting (driven by far field tectonic forces) with almost passive asthenosphere upwelling, without any active upwelling of deep/hot asthenosphere, as it happens in the case of asthenosphere diapirs or mantle plumes?

Your question (“how much of this crustal extension is needed for triggering the magmatic activity observed in rift settings”) is apparently simple, but it is solely posed in an oversimplified way. It needs that the estimates evidenced by David and, moreover, the driving forces of rifting and the geodynamic context are constrained.

Rift formation has long been the focus of attention for researchers, and an enormous number of studies have been carried out in order to understand causes and modes of whole lithospheric extension (e.g., Brun, 1999; Corti et al., 2003; Dewey and Hancock, 1987; Illies, 1981; Keen et al., 1987; Khain, 1992; Morgan and Baker, 1983; Neugebauer, 1983; Neumann and Ramberg, 1978; Palmason,1982; Ruppel, 1995; Whitmarsh et al., 2001; Ziegler, 1992; and many others).

Just as an example suggested by my personal experience, I can recall that in the case of passive rifting (where asthenosphere is considered to play no active role in passive lithosphere extension) experimental investigations evidenced that the lithosphere must be thinned to about half of its original thickness (i.e., thinned by a factor β≃2: Foucher et al., 1982; Corti et al., 2007; Ranalli et al., 2007) (considering a lithosphere away from mid-ocean ridges, mantle plumes and subduction settings), in order that the near-adiabatically upwelling asthenosphere undergo decompression melting under spinel-peridotite facies conditions.

FOUCHER, J.P., LE PICHON, X., SIBUET, J.C., ROBERTS, D.G., CHENET, P.Y., BALLY, A.W., OXBURGH, E.R., KENT, P., DEWEY, J.F., BOTT, M.H.P., JACKSON, J.A., OSMASTON, M.F. & TURCOTTE, D.L., 1982. The Ocean-Continent Transition in the Uniform Lithospheric Stretching Model: Role of Partial Melting in the Mantle [and Discussion]. Philosophical Transactions of the Royal Society A, 305, 27-43.

CORTI, G., BONINI, M., INNOCENTI, F., MANETTI, P., PICCARDO, G.B. & RANALLI, G., 2007. Experimental models of extension of continental lithosphere weakened by percolation of asthenospheric melts. Journal of Geodynamics, 43, 465-483.

RANALLI, G., PICCARDO, G.B. & CORONA-CHAVEZ, P., 2007. Softening of the subcontinental lithospheric mantle by asthenosphere melts and the continental extension/oceanic spreading transition. Journal of Geodynamics, 43, 450-464.

In conclusion, my suggestion is that you have to explore fundamental references on rifting, easily found in the international bibliography, and try to make your own understanding of the primary process you are interested in, on the basis of a good knowledge of the present state of art of researches on rifting.

Ciao

Giovanni

Thanks Stephen. I have already gone through it but it doesn't satisfy my interest.

Appreciating the explanation given by Ahmad Nourbakhsh, it will be good to say that there is a fine line of demarcation. In 'Tectonic Geomorphology', we are essentially interested in understanding the existing geomorphic features as well as changing landforms in the light of tectonic forcings. On the other hand if from seismological data or some other geophysical evidences, we are having a structural model of a particular study area and some of the geomorphic features are used to validate(or question) those models, it will be treated under 'morphotectonics'.

I would like to request Meelad to go through two of our recent publications on these issues.

doi:10.1016/j.geomorph.2012.04.012

Nature always tries to spend the less possible amount of energy. Due to this consideration, you won't be wrong if you say that the water will follow the path of a fault (or will dig a valley) which is much easier to erode because of the overworked rocks.

Of course this doesn't mean that all the branches of a drainage system can only be driven by faults. Water can also follow the pattern of discontinuities such as cracks.

In the extreme case where a rock formation is absolutely homogeneous, water will just be driven by gravity.

Kind regards

Ioannis Alexandrides

Hello Shi-Yong Yu,

It looks to me like you are asking about the onset of the Quaternary glaciations in general, in which case I recommend you read Cane and Molnar (2001) (http://rainbow.ldgo.columbia.edu/papers/canemolnar.pdf). They concluded that the change resulted from diversion of West Pacific Warm Pool water following uplift of Halmahera. I think they are correct that the closure of the Indonesian Gateway was critical but their detailed model is inconsistent with Karas et al. (2009) (http://www.nature.com/ngeo/journal/v2/n6/full/ngeo520.html). The timing and nature of events recorded by Karas is more consistent with a change caused by the uplift of Timor in the Banda Arc, which caused major changes in the regional oceanography.

Some researchers suggest there are also other contributions to plates motions.

You can find some of these in the following papers:

Riguzzi F., Panza G., Varga P. & Doglioni C. (2009): Can Earth's rotation and tidal despinning drive plate tectonics? Tectonophysics, doi:10.1016/j.tecto.2009.06.012.

Doglioni C., Tonarini S. and Innocenti F., (2009), Mantle wedge asymmetries and geochemical signatures along W- and E-NE-directed subduction zones. Lithos, doi:10.1016/j.lithos.2009.01.012

To monitor the tectonic influence on river dynamics, temporal changes are very important elements. Older the topographic maps and satellite images are there better it is. Bigger rivers may not have appreciable change in their median path. Monitor the smaller channels. There might be certain trend.

Secondly, If you have Bouguer anomaly map for the area, put those stuff on the GIS and try to locate the probable places where the possibilities of accommodation space generation is more. Try to relate the fluvial dynamics with the tectono-geomorphic zonation of the study area.

Thirdly, you can investigate lateral P-wave velocity variability by conducting shallow refraction studies. Besides sedimentological reasons, tectonic activities influence the degree of lateral compaction of the 'Low velocity layer' as well as the sub-weathered zone.

Collate your findings( if necessary, raise a rational scheme of weightage for different parameters) to strengthen your model.

There is also plenty of literature on alluvial fans offset by the Dead Sea Fault or one of its branches:

Klinger et al., 2000: Slip rate on the Dead Sea transform fault in northern Araba valley (Jordan). http://gji.oxfordjournals.org/content/142/3/755.full

Ginat et al., 1998: Translocated Plio-Pleistocene drainage systems along the Arava fault of the Dead Sea Transform. http://earth.huji.ac.il/data/pics/RP28.pdf

Niemi et al., 2001: Late Pleistocene and Holocene slip rate of the Northern Wadi Araba fault, Dead Sea Transform, Jordan. http://link.springer.com/article/10.1023/A:1011487912054

Braided streams occur in many environments, from foothills to deltas.

Rosanna,

I suggest that you compile historical earthquake data and recorded measurements of seiche waves on Lago di Bolsena for those events. Didn't some one note the seiche amplitude for the 1980 earthquake? If not, then perhaps historical photos will show the water line? This may be a question that is easiest to answer with a day or two spent in the library, followed by interviews with residents at the lake.

Dinoflagellate cysts - some indicators as warm/cold, oceanic/neritic, etc… on parle au télephone si tu veut plus d'info

Too bad I don't have a proper answer, since I can only think of shakemaps for earthquakes occurring near the coastline - i.e. estimates are automatically computed anyway in those cases, although I doubt those estimates can take different attenuation models in account.. It'a fascinating issue..