Lubrication Dynamics for Exhumation of high-pressure Rocks in Subduction Zones

Mapping Intimacies ◽

10.5194/egusphere-egu2020-314 ◽

2020 ◽

Author(s):

Giridas Maiti ◽

Joyjeet Sen ◽

Nibir Mandal

Keyword(s):

High Pressure ◽

Subduction Zones ◽

Earth Science ◽

Dynamic Pressure ◽

Threshold Value ◽

Western Alps ◽

Plate Motion ◽

Gravitational Potential Energy ◽

Crustal Rocks ◽

Subduction Wedge

Subduction zones witness exhumation of deep crustal rocks metamorphosed under high pressure (HP) and ultra-high pressure (UHP) conditions, following burial to depths of 100 km or more. The exhumation dynamics of HP and UHP rocks still remains a lively issue of research in the Earth science community. We develop a new tectonic model based on the lubrication dynamics to show the exhumation mechanism of such deep crustal rocks in convergent tectonic settings. Our model suggests subducting plate motion produces a dynamic pressure in the subduction wedge, which supports the excess gravitational potential energy of the thicker and relatively denser overriding plate partly lying over the buoyant subduction wedge. A drop in the dynamic pressure causes the overriding plate to undergo gravitational collapse and forces the wedge materials to return to the surface. Using lubrication theory we estimate the magnitude of dynamic pressure (P) in the wedge as a function of subduction velocity (us), convergence angle (&#945;) and wedge viscosity (&#181;). We also conduct thermo-mechanical numerical experiments to implement the lubrication model in subduction zones on a real scale. Our analysis suggests that drop in wedge dynamic pressure below a threshold value due to decease in us&#160; and &#181;, or by other processes, such as slab rollback and trench retreat facilitate exhumation of deep crustal rocks. Finally we discuss their implications for the exhumation of deep crustal rocks in different subduction setups such as the Himalayan continental subduction, the Mediterranean realm (Calabria&#8211;Apennine and Aegean belts) and Western Alps.

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Synconvergent and coherent (ultra)high-pressure crustal rock exhumation

10.5194/egusphere-egu21-11119 ◽

2021 ◽

Author(s):

Lorenzo G. Candioti ◽

Joshua D. Vaughan-Hammon ◽

Thibault Duretz ◽

Stefan M. Schmalholz

Keyword(s):

Numerical Models ◽

A Priori ◽

Western Alps ◽

Ultrahigh Pressure ◽

Plate Motion ◽

Crustal Rock ◽

Plate Boundaries ◽

Crustal Rocks ◽

Natural Data ◽

The Alps

Ultrahigh-pressure (UHP) continental crustal rocks were first discovered in the Western Alps in 1984 and have since then been observed at many convergent plate boundaries worldwide. Unveiling the processes leading to the formation and exhumation of (U)HP metamorphic crustal rocks is key to understand the geodynamic evolution of orogens such as the Alps.&#160;Previous numerical studies investigating (U)HP rock exhumation in the Alps predicted deep (>80 km) subduction of crustal rocks and rapid buoyancy-driven exhumation of mainly incoherent (U)HP units, involving significant tectonic mixing forming so-called m&#233;langes. Furthermore, these predictions often rely on excessive erosion or periods of divergent plate motion as important exhumation mechanism. Inconsistent with field observations and natural data, application of these models to the Western Alps was recently criticised.&#160;Here, we present models with continuous plate convergence, which exhibit local tectonic-driven upper plate extension enabling compressive- and buoyancy-driven exhumation of coherent (U)HP units along the subduction interface, involving feasible erosion.&#160;The two-dimensional petrological-thermo-mechanical numerical models presented here predict both subduction initiation and serpentinite channel formation without any a priori prescription of these two features. The (U)HP units are exhumed coherently, without significant internal deformation. Modelled pressure and temperature trajectories and exhumation velocities of selected crustal units agree with estimates for the Western Alps. The presented models support previous hypotheses of synconvergent exhumation, but do not rely on excessive erosion or divergent plate motion. Thus, our predictions provide new insights into processes leading to the exhumation of coherent (U)HP crustal units consistent with observations and natural data from the Western Alps.

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Divergence in subduction zones and exhumation of high pressure rocks (Eocene Western Alps)

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2011.08.002 ◽

2011 ◽

Vol 310 (1-2) ◽

pp. 21-32 ◽

Cited By ~ 82

Author(s):

Marco G. Malusà ◽

Claudio Faccenna ◽

Eduardo Garzanti ◽

Riccardo Polino

Keyword(s):

High Pressure ◽

Subduction Zones ◽

Western Alps

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Deciphering the coupling between tectonic and metamorphic processes in the Monte Rosa nappe (Western Alps)

10.5194/egusphere-egu21-11159 ◽

2021 ◽

Author(s):

Joshua D Vaughan Hammon ◽

Cindy Luisier ◽

Lorenzo G Candioti ◽

Stefan M Schmalholz ◽

Lukas P Baumgartner

Keyword(s):

Subduction Zones ◽

Numerical Models ◽

Western Alps ◽

Gravitational Potential Energy ◽

Lithostatic Pressure ◽

Burial Depth ◽

Differential Stress ◽

Metamorphic History ◽

Monte Rosa ◽

Metamorphic Facies

Our refined ability to estimate metamorphic conditions incurred by rocks has increased our understanding of the dynamic earth. Calculating pressure (P), temperature (T) and time (t) histories of these rocks is vital for reconstructing tectonic movements within subduction zones. However, large disparities in peak P within a structurally coherent tectonic unit poses difficulties when attempting to resolve a tectono-metamorphic history, if a depth dependant lithostatic P is assumed. However, what is clear is that pressure, or mean stress, in a rock cannot exactly be lithostatic during an orogeny due to differential stress, required to drive rock deformation or to balance lateral variations in gravitational potential energy. Deviations from lithostatic P is commonly termed tectonic pressure, and both its magnitude and impact on metamorphic reactions in disputed.For the &#8216;Queen of the Alps&#8217; (the Monte Rosa massif), estimates for the maximum P recorded during Alpine orogenesis remain enigmatic. Large disparities in published estimates for peak P exist, ranging between 1.2 and 2.7 GPa. Moreover, the highest P estimates (2.2 - 2.7 GPa) are for rocks that comprise only a small percentage (< 1%) of the total volume of the nappe (whiteschist bodies and eclogitic mafic boudins). We present newly discovered whiteschist lithologies that persistently exhibit higher P conditions (c. 2.2 GPa) compared to metagranitic and metapelitic lithologies (c. 1.4 - 1.6 GPa). Detailed mapping and structural analysis in these regions lack evidence for tectonic mixing. Therefore, we suggest that a &#916;P 0.6 &#177; 0.2 GPa during peak Alpine metamorphism could potentially represent tectonic pressure. Furthermore, we outline possible mechanisms that facilitate &#916;P, namely mechanically- and/or reaction-induced. We present data from numerical models that exhibit significant &#916;P (c. 0.4 GPa) during a transient period of high differential stress prior to buckling and subsequent exhumation of viscous fold nappes, similar to exhumation mechanisms suggested for the Monte Rosa nappe. As well as this, we present new routines for calculating metamorphic facies distribution within numerical models of subduction zones that agree with natural distributions within orogens.The maximum burial depth of the Monte Rosa unit was likely significantly less than 80 km (based on the lithostatic pressure assumption and minor volumes of whiteschist at c. 2.2 GPa). Rather, the maximum burial depth of the Monte Rosa unit was presumably equal to or less than c. 60 km, estimated from pressures of 1.4 - 1.6 GPa recorded frequently in metagranite and metapelitic lithologies. In order to understanding, more completely, a rocks metamorphic history, consideration of the interplay between tectonic and metamorphic processes should not be overlooked.

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Metasediments Covering Ophiolites in the HP Internal Belt of the Western Alps: Review of Tectono-Stratigraphic Successions and Constraints for the Alpine Evolution

Minerals ◽

10.3390/min11040411 ◽

2021 ◽

Vol 11 (4) ◽

pp. 411

Author(s):

Paola Tartarotti ◽

Silvana Martin ◽

Andrea Festa ◽

Gianni Balestro

Keyword(s):

High Pressure ◽

Western Alps ◽

Metamorphic Evolution ◽

Alpine Orogeny ◽

Sedimentary Evolution ◽

Hp Metamorphism ◽

Tethys Ocean ◽

Depositional Setting ◽

Oceanic Rocks ◽

Outer Band

Ophiolites of the Alpine belt derive from the closure of the Mesozoic Tethys Ocean that was interposed between the palaeo-Europe and palaeo-Adria continental plates. The Alpine orogeny has intensely reworked the oceanic rocks into metaophiolites with various metamorphic imprints. In the Western Alps, metaophiolites and continental-derived units are distributed within two paired bands: An inner band where Alpine subduction-related high-pressure (HP) metamorphism is preserved, and an outer band where blueschist to greenschist facies recrystallisation due to the decompression path prevails. The metaophiolites of the inner band are hugely important not just because they provide records of the prograde tectonic and metamorphic evolution of the Western Alps, but also because they retain the signature of the intra-oceanic tectono-sedimentary evolution. Lithostratigraphic and petrographic criteria applied to metasediments associated with HP metaophiolites reveal the occurrence of distinct tectono-stratigraphic successions including quartzites with marbles, chaotic rock units, and layered calc schists. These successions, although sliced, deformed, and superposed in complex ways during the orogenic stage, preserve remnants of their primary depositional setting constraining the pre-orogenic evolution of the Jurassic Tethys Ocean.

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Roles of vanes in diffuser on stability of centrifugal compressor

Proceedings of the Institution of Mechanical Engineers Part G Journal of Aerospace Engineering ◽

10.1177/0954410019844433 ◽

2019 ◽

Vol 233 (14) ◽

pp. 5380-5392

Author(s):

Wangzhi Zou ◽

Xiao He ◽

Wenchao Zhang ◽

Zitian Niu ◽

Xinqian Zheng

Keyword(s):

High Pressure ◽

Centrifugal Compressor ◽

Dynamic Pressure ◽

Pressure Ratio ◽

Pressure Rise ◽

Rotating Stall ◽

Centrifugal Compressors ◽

Compression System ◽

The Stability ◽

Rotating Instability

The stability considerations of centrifugal compressors become increasingly severe with the high pressure ratios, especially in aero-engines. Diffuser is the major subcomponent of centrifugal compressor, and its performance greatly influences the stability of compressor. This paper experimentally investigates the roles of vanes in diffuser on component instability and compression system instability. High pressure ratio centrifugal compressors with and without vanes in diffuser are tested and analyzed. Rig tests are carried out to obtain the compressor performance map. Dynamic pressure measurements and relevant Fourier analysis are performed to identify complex instability phenomena in the time domain and frequency domain, including rotating instability, stall, and surge. For component instability, vanes in diffuser are capable of suppressing the emergence of rotating stall in the diffuser at full speeds, but barely affect the characteristics of rotating instability in the impeller at low and middle speeds. For compression system instability, it is shown that the use of vanes in diffuser can effectively postpone the occurrence of compression system surge at full speeds. According to the experimental results and the one-dimensional flow theory, vanes in diffuser turn the diffuser pressure rise slope more negative and thus improve the stability of compressor stage, which means lower surge mass flow rate.

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Up the down escalator: the exhumation of (ultra)-high pressure terranes during on-going subduction

Solid Earth Discussions ◽

10.5194/sed-4-745-2012 ◽

2012 ◽

Vol 4 (1) ◽

pp. 745-781 ◽

Cited By ~ 5

Author(s):

C. J. Warren

Keyword(s):

High Pressure ◽

Subduction Zone ◽

Continental Crust ◽

Subduction Zones ◽

Crustal Material ◽

Time And Space ◽

Ultra High Pressure ◽

Tectonic Environment ◽

Tectonic Style ◽

Weak Material

Abstract. The exhumation of high and ultra-high pressure rocks is ubiquitous in Phanerozoic orogens created during continental collisions, and is common in many ocean-ocean and ocean-continent subduction zone environments. Three different tectonic environments have previously been reported, which exhume deeply buried material by different mechanisms and at different rates. However it is becoming increasingly clear that no single mechanism dominates in any particular tectonic environment, and the mechanism may change in time and space within the same subduction zone. In order for buoyant continental crust to subduct, it must remain attached to a stronger and denser substrate, but in order to exhume, it must detach (and therefore at least locally weaken) and be initially buoyant. Denser oceanic crust subducts more readily than more buoyant continental crust but exhumation must be assisted by entrainment within more buoyant and weak material such as serpentinite or driven by the exhumation of structurally lower continental crustal material. Weakening mechanisms responsible for the detachment of crust at depth include strain, hydration, melting, grain size reduction and the development of foliation. These may act locally or may act on the bulk of the subducted material. Metamorphic reactions, metastability and the composition of the subducted crust all affect buoyancy and overall strength. Subduction zones change in style both in time and space, and exhumation mechanisms change to reflect the tectonic style and overall force regime within the subduction zone. Exhumation events may be transient and occur only once in a particular subduction zone or orogen, or may be more continuous or occur multiple times.

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Magnetite (U-Th-Sm)/He dating: analytical challenges and application

10.5194/egusphere-egu21-16379 ◽

2021 ◽

Author(s):

Marianna Corre ◽

Martine Lanson ◽

Arnaud Agranier ◽

Stephane Schwartz ◽

Fabrice Brunet ◽

...

Keyword(s):

Laser Ablation ◽

Subduction Zones ◽

Major Elements ◽

Western Alps ◽

Planetary Science ◽

Mantle Xenoliths ◽

Transform Faults ◽

Geological Processes ◽

History Of ◽

Geochronological Constraints

Magnetite (U-Th-Sm)/He dating method has a strong geodynamic significance, since it provides geochronological constraints on serpentinization episodes, which are associated to important geological processes such as ophiolite obductions, subduction zones, transform faults and fluid circulations. Although helium content that range from 0.1 pmol/g to 20 pmol/g can routinely be measured, the application of this dating technique however is still limited due to major analytical obstacles. The dissolution of a single magnetite crystal and the measurement of the U, Th and Sm present at the ppb level in the corresponding solution, remains highly challenging, especially because of the absence of magnetite standard. In order to overcome these analytical issues, two strategies have been followed, and tested on magnetite from high-pressure rocks from the Western Alps (Schwartz et al., 2020). Firstly, we purified U, Th and Sm (removing Fe and other major elements) using ion exchange columns in order to analyze samples, using smaller dilution. Secondly, we performed in-situ analyzes by laser-ablation-ICPMS. Since no solid magnetite certified standard is yet available, we synthetized our own by precipitating magnetite nanocrystals. The first quantitative results obtained by LA-ICP-MS using this synthetic material along with international glass standards, are promising. The laser-ablation technique overcomes the analytical difficulties related to sample dissolution and purification. It thus opens the path to the dating of magnetite (and also spinels) in various ultramafic rocks such as mantle xenoliths or serpentinized peridotites in ophiolites.Schwartz S., Gautheron C., Ketcham R.A., Brunet F., Corre M., Agranier A., Pinna-Jamme R., Haurine F., Monvoin G., Riel N., 2020, Unraveling the exhumation history of high-press ure ophiolites using magnetite (U-Th-Sm)/He thermochronometry. Earth and Planetary Science Letters 543 (2020) 116359.

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Opening and closure of Iranian back-arc basins: A seismic tomography view

10.5194/egusphere-egu21-5209 ◽

2021 ◽

Author(s):

Nalan Lom ◽

Abdul Qayyum ◽

Derya Gürer ◽

Douwe G. van der Meer ◽

Wim Spakman ◽

...

Keyword(s):

Seismic Tomography ◽

Subduction Zones ◽

Three Dimensional ◽

Plate Motion ◽

Limited Information ◽

Three Dimensional Model ◽

Slab Geometry ◽

Novel Approach ◽

Sanandaj Sirjan Zone ◽

Back Arc

Iran is a mosaic of continental blocks that are surrounded by Tethyan oceanic relics. Remnants of these oceanic rock assemblages are exposed around the Central Iranian Microcontinent (CIM), discretely along the Sanandaj-Sirjan Zone and in Jaz-Murian. The ophiolite belts surrounding the CIM are mainly assumed to represent narrow back-arc basins that opened in Cretaceous and closed before the Eocene. Although these ophiolites are exposed as small pieces on continental crust today, they represent oceans wide enough to form supra-subduction ophiolites and arc-related magmatic rocks which suggest that their palaeogeographic width was at least some hundreds of kilometers. Current models for the palaeogeographic dimension, opening and closure of these basins are highly schematic. They usually seem plausible in two-dimensional reconstructions, however a single three-dimensional model explaining whole Iran and its surrounding regions has not been fully accomplished.&#160; This is mostly because while the geological record provides constraints on the origin and ages of the subducted ocean floor, it provides limited information about onset and cessation of the subduction and almost no constraints on the dimension of these oceans and the subduction zones that consumed them.In this study, we follow a novel approach in estimating the dimension and evolution of these back-arc basin by using seismic tomography. Seismic tomography has revealed that we can image and trace subducted lithosphere relics. Imaged mantle structure is now being used to link sinking slabs with sutures and to define shape of a slab. Systematic comparison of regions where the timing of subduction is reasonably well constrained by geological data showed that slabs sink gradually through the mantle at rates more or less the same. This perspective enabled us to study slab shape as a function of absolute trench motion. While mantle stationary trenches tend to create steep slabs or slab walls, the flat-lying segments are formed where the overlying trenches are mobile relative to the mantle, normal facing during roll-back, overturned during slab advance. &#160;Under the assumption of vertical sinking after break-off, it is also possible to locate the palaeo-trenches. &#160;When combined with absolute plate motion reconstructions, tomographically determined volume and size of the subducted lithosphere can also be used to estimate the size/width of the prehistoric oceans. To this end, we build on and further develop concepts that relate absolute trench motion during subduction to modern slab geometry to evaluate the possible range of dimensions associated with opening and closure of the Iranian back-arc basins.

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