Spinifex‐like textured metaperidotites from the Higo Metamorphic Rocks, Japan, a possible high‐pressure dehydration product of antigorite serpentinite

Island Arc ◽  
2020 ◽  
Vol 30 (1) ◽  
Author(s):  
Tadao Nishiyama ◽  
Hibiki Eguchi ◽  
Dai Shiosaki ◽  
Akira Yoshiasa ◽  
Nobutatsu Mochizuki ◽  
...  
Keyword(s):  
High Pressure ◽  
Metamorphic Rocks ◽  
Dehydration Product

Under Pressure: High-Pressure Metamorphism in the Alps

Elements ◽  
2021 ◽  
Vol 17 (1) ◽  
pp. 17-22 ◽  
Author(s):  
Lucie Tajčmanová ◽  
Paola Manzotti ◽  
Matteo Alvaro
Keyword(s):  
High Pressure ◽  
Structural Data ◽  
Metamorphic Rocks ◽  
Lithostatic Pressure ◽  
Mineral Inclusion ◽  
Crustal Material ◽  
Local Pressure ◽  
Ultra High Pressure ◽  
Mechanical Models ◽  
The Alps

The mechanisms attending the burial of crustal material and its exhumation before and during the Alpine orogeny are controversial. New mechanical models propose local pressure perturbations deviating from lithostatic pressure as a possible mechanism for creating (ultra-)high-pressure rocks in the Alps. These models challenge the assumption that metamorphic pressure can be used as a measure of depth, in this case implying deep subduction of metamorphic rocks beneath the Alpine orogen. We summarize petro-logical, geochronological and structural data to assess two fundamentally distinct mechanisms of forming (ultra-)high-pressure rocks: deep subduction; or anomalous, non-lithostatic pressure variation. Furthermore, we explore mineral-inclusion barometry to assess the relationship between pressure and depth in metamorphic rocks.

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.

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