Structural and Geochronological Study of High‐Pressure Metamorphic Rocks in the Kekesu Section (Northwestern China): Implications for the Late Paleozoic Tectonics of the Southern Tianshan

Abstract —Coal fires are a phenomenon that can be observed worldwide in areas where rocks containing coal seams are exposed and can pose major environmental threats. A coal fire can begin through spontaneous combustion when coals are exposed to dry and oxygen-rich near-surface conditions. Burning, depending on the temperature of heating, causes baking or even melting of the surrounding rocks and the formation of different types of combustion metamorphic rocks. In Northwestern China, coal fire occurrences are concentrated at the edges of the sedimentary basins or at the margins of orogenic belts, where coalrich units were exposed owing to the Indo-Eurasian collision. On the northern margin of the Tianshan range, evidence of coal fires is widespread in the Jurassic sedimentary units containing coal seams which outcrop along the Central Asian Orogenic Belt. In some cases, coal fires are active and can be linked to ongoing mining activity, but outcrops of combustion metamorphic rocks not associated with fires are also found and are indicative of past burning events. We examine combustion metamorphic rocks outcropping in the Toutunhe River valley (Liuhuangou area, Xinjiang, Northwestern China). Combustion metamorphic rocks in the study area were mapped and classified according to their morphological and mineralogical characteristics. Outcrops are exposed at various heights on the valley flanks, which are characterized by the presence of multiple levels of fluvial terraces. These terraces are indicative of the phases of erosion and deposition of the Toutunhe River and testify to tectonic uplift. The investigation of the stratigraphic and crosscutting relationship of combustion metamorphic rocks with terrace deposits and apatite fissiontrack dating made it possible to determine that at least four phases of coal fire activity occurred from late Miocene to Quaternary. The first and oldest burning phase dates back to 10 ± 1.3 Ma and terminated prior to 2–3 Ma; the second was active before ~550 ka; the third had terminated by ~140 ka; the fourth began later than ~5.7 ka. The relationships between combustion metamorphic rocks and fluvial terraces further suggest that coal fire ignition/extinction in the area since the Miocene have been linked to the interplay between the uplift of the Central Asian Orogenic Belt and the phases of fluvial erosion and deposition in interglacial periods.

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Mineral ages and P-T conditions of Late Paleozoic high-pressure eclogite and provenance of melange sediments from Atbashi in the south Tianshan orogen of Kyrgyzstan

American Journal of Science ◽

10.2475/09.2010.07 ◽

2010 ◽

Vol 310 (9) ◽

pp. 916-950 ◽

Cited By ~ 156

Author(s):

E. Hegner ◽

R. Klemd ◽

A. Kroner ◽

M. Corsini ◽

D. V. Alexeiev ◽

...

Keyword(s):

High Pressure ◽

Late Paleozoic ◽

The South ◽

South Tianshan

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Kinematic analysis of ultrahigh-pressure-high-pressure metamorphic rocks in the Chaglinka-Kulet area of the Kokchetav Massif, Kazakhstan

Island Arc ◽

10.1046/j.1440-1738.2000.00280.x ◽

2000 ◽

Vol 9 (3) ◽

pp. 304-316 ◽

Cited By ~ 11

Author(s):

Hiroshi Yamamoto ◽

Masahiro Ishikawa ◽

Ryo Anma ◽

Yoshiyuki Kaneko

Keyword(s):

High Pressure ◽

Kinematic Analysis ◽

Ultrahigh Pressure ◽

Metamorphic Rocks ◽

Kokchetav Massif

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Eclogitic rocks in the St. Cyr klippe, Yukon, and their tectonic significance

Canadian Journal of Earth Sciences ◽

10.1139/e92-103 ◽

1992 ◽

Vol 29 (6) ◽

pp. 1296-1304 ◽

Cited By ~ 11

Author(s):

Philippe Erdmer

Keyword(s):

High Pressure ◽

Oceanic Crust ◽

North American ◽

Suture Zone ◽

Late Paleozoic ◽

The North ◽

Tectonic Significance ◽

Subducted Oceanic Crust ◽

Ophiolitic Rocks ◽

Subducting Slab

Until recently, the Nisutlin allochthonous assemblage, a part of the Yukon–Tanana composite terrane interpreted as trench mélange from a late Paleozoic – Mesozoic arc system, was the only tectonic assemblage known to include subducted material in the northern Cordillera. The discovery of eclogitic rocks in two parts of a klippe of the Anvil allochthonous assemblage, which comprises mafic ophiolitic rocks, above the Cassiar terrane west of the Tintina fault confirms other evidence that subducted oceanic crust was also returned to the surface. The eclogitic rocks have been largely retrograded by postsubduction metamorphism. Their existence is interpreted as additional evidence of the link between nappes above the Cassiar terrane and their inferred root, the Teslin suture zone. The Nisutlin and Anvil allochthonous assemblages can now be interpreted, not simply as crustally metamorphosed assemblages with minor, structurally interleaved high-pressure components, but as deeply metamorphosed and intensely strained slices of continental and oceanic crust switched from subducting slab to overriding plate and returned to the surface during collision of the arc with the North American margin.

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Under Pressure: High-Pressure Metamorphism in the Alps

Elements ◽

10.2138/gselements.17.1.17 ◽

2021 ◽

Vol 17 (1) ◽

pp. 17-22 ◽

Cited By ~ 1

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.

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

Geosphere ◽

10.1130/ges02212.1 ◽

2020 ◽

Vol 16 (4) ◽

pp. 953-968 ◽

Cited By ~ 1

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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