scholarly journals Structural assemblage of high-pressure mantle and crustal rocks in a subduction channel (Cabo Ortegal, NW Spain)

Tectonics ◽  
2003 ◽  
Vol 22 (2) ◽  
pp. n/a-n/a ◽  
Author(s):  
B. Ábalos ◽  
P. Puelles ◽  
J. I. Gil Ibarguchi
Keyword(s):  
High Pressure ◽  
Nw Spain ◽  
Subduction Channel ◽  
Crustal Rocks

U-Pb, Hf isotope and REE constraints on high-pressure acid migmatites from the Cabo Ortegal Complex (NW Spain): New evidence of short-duration metamorphism in a Variscan subduction channel

Lithos ◽  
2020 ◽  
Vol 372-373 ◽  
pp. 105660
Author(s):  
A. Beranoaguirre ◽  
S. García de Madinabeitia ◽  
M.E. Sanchez Lorda ◽  
P. Puelles ◽  
B. Ábalos ◽  
...  
Keyword(s):  
High Pressure ◽  
Short Duration ◽  
Hf Isotope ◽  
Nw Spain ◽  
Subduction Channel ◽  
New Evidence

scholarly journals Subduction of trench-fill sediments beneath an accretionary wedge: Insights from sandbox analogue experiments

Geosphere ◽  
2020 ◽  
Vol 16 (4) ◽  
pp. 953-968 ◽  
Author(s):  
Atsushi Noda ◽  
Hiroaki Koge ◽  
Yasuhiro Yamada ◽  
Ayumu Miyakawa ◽  
Juichiro Ashi
Keyword(s):  
High Pressure ◽  
Side Wall ◽  
Metamorphic Rocks ◽  
Accretionary Wedge ◽  
Seafloor Topography ◽  
Subduction Channel ◽  
Hp Metamorphism ◽  
Analogue Experiments ◽  
Topographic High

Abstract Sandy trench-fill sediments at accretionary margins are commonly scraped off at the frontal wedge and rarely subducted to the depth of high-pressure (HP) metamorphism. However, some ancient exhumed accretionary complexes are associated with high-pressure–low-temperature (HP-LT) metamorphic rocks, such as psammitic schists, which are derived from sandy trench-fill sediments. This study used sandbox analogue experiments to investigate the role of seafloor topography in the transport of trench-fill sediments to depth during subduction. We conducted two different types of experiments, with or without a rigid topographic high (representing a seamount). We used an undeformable backstop that was unfixed to the side wall of the apparatus to allow a seamount to be subducted beneath the overriding plate. In experiments without a seamount, progressive thickening of the accretionary wedge pushed the backstop down, leading to a stepping down of the décollement, narrowing of the subduction channel, and underplating of the wedge with subducting sediment. In contrast, in experiments with a topographic high, the subduction of the topographic high raised the backstop, leading to a stepping up of the décollement and widening of the subduction channel. These results suggest that the subduction of stiff topographic relief beneath an inflexible overriding plate might enable trench-fill sediments to be deeply subducted and to become the protoliths of HP-LT metamorphic rocks.

Metamorphic evolution of Raspas complex (Ecuador) and its relation with a J-K belt of melanges in NW of the South American plate.

2020 ◽  
Author(s):  
Mayda Arrieta-Prieto ◽  
Carlos Zuluaga-Castrillón ◽  
Oscar Castellanos-Alarcón ◽  
Carlos Ríos-Reyes
Keyword(s):  
High Pressure ◽  
Subduction Zones ◽  
Mineral Chemistry ◽  
White Mica ◽  
Petrographic Analysis ◽  
South American ◽  
The South ◽  
South American Plate ◽  
Subduction Channel ◽  
Southern Ecuador

<p>High-pressure complexes along the Earth's surface provide evidence of the processes involved in both the crystallization of rocks in the subduction channel and its exhumation. Such processes are key to understand the dynamics and evolution of subduction zones and to try to reconstruct P-T trajectories for these complexes.</p><p>Previous studies on the Raspas complex (southern Ecuador) agree to state that it is composed of metamorphic rocks, mainly blueschists and eclogites, containing the mineral assemblage: glaucophane + garnet + epidote + omphacite + white mica + rutile ± quartz ± apatite ± pyrite ± calcite; which stabilized in metamorphic conditions of high pressure and low temperature. Additionally, the Raspas Complex has been genetically related to accretion and subduction processes of seamounts, which occurred in South America during the Late Jurassic - Early Cretaceous interval; and the exhumation of the complex was related to subduction channels. However, the evidence presented in the existing literature makes little emphasis on the reconstruction of thermobarometric models for the rocks of this complex.</p><p>By combining petrographic observations, whole-rock chemistry, and mineral chemistry in this work; it was possible to determine that pressure values of 10 ± 3 Kbar and temperature values of 630 ± 30 ° C, (obtained by simulations with THERMOCALC®) correspond to an event of retrograde metamorphism, suffered by the complex during its exhumation. This theory is complemented by the specific textures (that suggest this retrograde process) observed during petrographic analysis, such as amphibole replacing pyroxene, garnet chloritization, plagioclase crystallization and rutile replacement by titanite.</p><p>The results obtained, together with the thermobarometry data published for the Arquía complex in Colombia, allow us to establish a P-T trajectory, that may suggest a genetic relationship between these two complexes as a result of the tectonic processes associated with an active subduction margin that affected the NW margin of the South American plate at the end of the Jurassic.</p><p> </p>

A new model for brittle failure at depth involving high-pressure metamorphism

2020 ◽  
Author(s):  
Philippe Yamato ◽  
Marie Baïsset
Keyword(s):  
High Pressure ◽  
Host Rock ◽  
Continuous Process ◽  
Shear Zones ◽  
Brittle Deformation ◽  
Local Pressure ◽  
Intermediate Depth ◽  
Crustal Rocks ◽  
High Pressure Metamorphism ◽  
Convergence Zones

<p>Intermediate-depth earthquakes are registered in convergence zones where crustal rocks are expected to deform by ductile flow. This paradox is also evidenced in exhumed crustal rocks where brittle structures (e.g., pseudotachylytes and breccias) associated to high-pressure metamorphism have been documented. If the link between brittle deformation and metamorphic reactions appears obvious today, the mechanism involved is still a burning issue. We propose that the initial heterogeneity of rocks, by itself, is sufficient to trigger both metamorphic reaction and brittle deformation. Based on a mechanically consistent dynamic model, we show that local pressure variations due to pre-existing heterogeneities can be high enough to reach the thermodynamic conditions required for reaction initiation. Brittle behaviour is then controlled by the strength difference between the untransformed host rock and its reaction product. This continuous process also explains the higher pressures recorded in eclogite facies rocks of ductile shear zones compared to their brittle host rock. Our results, constraint by natural data, have therefore significant implications for intermediate-depth seismicity.</p>

scholarly journals The role of buoyancy in the fate of ultra-high-pressure eclogite

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Timothy Chapman ◽  
Geoffrey L. Clarke ◽  
Nathan R. Daczko
Keyword(s):  
High Pressure ◽  
Continental Crust ◽  
Upper Mantle ◽  
Crustal Rocks ◽  
Ultra High Pressure ◽  
Rock Types ◽  
Mineral Assemblages ◽  
Facies Metamorphism ◽  
Point Of No Return

AbstractEclogite facies metamorphism of the lithosphere forms dense mineral assemblages at high- (1.6–2.4 GPa) to ultra-high-pressure (>2.4–12 GPa: UHP) conditions that drive slab-pull forces during its subduction to lower mantle conditions. The relative densities of mantle and lithospheric components places theoretical limits for the re-exposure, and peak conditions expected, of subducted lithosphere. Exposed eclogite terranes dominated by rock denser than the upper mantle are problematic, as are interpretations of UHP conditions in buoyant rock types. Their subduction and exposure require processes that overcame predicted buoyancy forces. Phase equilibria modelling indicates that depths of 50–60 km (P = 1.4–1.8 GPa) and 85–160 km (P = 2.6–5 GPa) present thresholds for pull force in end-member oceanic and continental lithosphere, respectively. The point of no-return for subducted silicic crustal rocks is between 160 and 260 km (P = 5.5–9 GPa), limiting the likelihood of stishovite–wadeite–K-hollandite-bearing assemblages being preserved in equilibrated assemblages. The subduction of buoyant continental crust requires its anchoring to denser mafic and ultramafic lithosphere in ratios below 1:3 for the continental crust to reach depths of UHP conditions (85–160 km), and above 2:3 for it to reach extreme depths (>160 km). The buoyant escape of continental crust following its detachment from an anchored situation could carry minor proportions of other rocks that are denser than the upper mantle. However, instances of rocks returned from well-beyond these limits require exceptional exhumation dynamics, plausibly coupled with the effects of incomplete metamorphism to retain less dense low-P phases.

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

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

<p>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 (<em>P</em>) in the wedge as a function of subduction velocity (<em>u<sub>s</sub></em>), convergence angle (<em>α</em>) and wedge viscosity (<em>µ</em>). 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 <em>u</em><sub><em>s</em>  </sub>and <em>µ</em>, 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–Apennine and Aegean belts) and Western Alps.</p>

scholarly journals Clockwise and Anticlockwise P–T Paths of High-pressure Rocks from the ‘La Pioza’ Eclogite Body of the Malpica–Tuy Complex, NW Spain

2017 ◽  
Vol 58 (7) ◽  
pp. 1363-1392 ◽  
Author(s):  
Botao Li ◽  
Hans-Joachim Massonne ◽  
Joachim Opitz
Keyword(s):  
High Pressure ◽  
Nw Spain

High-pressure ultramafics in the lower crustal rocks of the Pekul’ney complex, central Chukchi Peninsula. 1. Petrography and mineralogy

Petrology ◽  
2013 ◽  
Vol 21 (3) ◽  
pp. 221-248 ◽  
Author(s):  
B. A. Bazylev ◽  
G. V. Ledneva ◽  
N. N. Kononkova ◽  
A. Ishiwatari
Keyword(s):  
High Pressure ◽  
Chukchi Peninsula ◽  
Crustal Rocks ◽  
Lower Crustal
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