Eclogites and other high-pressure rocks in the Himalaya: a review

AbstractHimalayan high-pressure metamorphic rocks are restricted to three environments: the suture zone; close to the suture zone; and (mostly) far (>100 km) from the suture zone. In the NW Himalaya and South Tibet, Cretaceous-age blueschists (glaucophane-, lawsonite- or carpholite-bearing schists) formed in the accretionary wedge of the subducting Neo-Tethys. Microdiamond and associated phases from suture-zone ophiolites (Luobusa and Nidar) are, however, unrelated to Himalayan subduction–collision processes. Deeply subducted and rapidly exhumed Indian Plate basement and cover rocks directly adjacent to the suture zone enclose eclogites of Eocene age, some coesite-bearing (Kaghan/Neelum and Tso Morari), formed from Permian Panjal Trap, continental-type, basaltic magmatic rocks. Eclogites with a granulite-facies overprint, yielding Oligocene–Miocene ages, occur in the anatectic cordierite ± sillimanite-grade Indian Plate mostly significantly south of the suture zone (Kharta/Ama Drime/Arun, north Sikkim and NW Bhutan) but also directly at the suture zone at Namche Barwa. The sequence carpholite-, coesite-, kyanite- and cordierite-bearing rocks of these different units demonstrates the transition from oceanic subduction to continental collision via continental subduction. The granulitized eclogites in anatectic gneisses preserve evidence of former thick crust as in other wide hot orogens, such as the European Variscides.

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Fluids in coesite-bearing rocks of the Tso Morari Complex, NW Himalaya: evidence for entrapment during peak metamorphism and subsequent uplift

Geological Magazine ◽

10.1017/s0016756809990069 ◽

2009 ◽

Vol 146 (6) ◽

pp. 876-889 ◽

Cited By ~ 19

Author(s):

BARUN K. MUKHERJEE ◽

HIMANSHU K. SACHAN

Keyword(s):

High Salinity ◽

Granulite Facies ◽

Ultrahigh Pressure ◽

Nw Himalaya ◽

Rock Interaction ◽

Low Salinity ◽

Ultrahigh Pressure Metamorphism ◽

Indian Lithosphere ◽

External Sources ◽

Tso Morari

AbstractFluid inclusions trapped in coesite-bearing rocks provide important information on the fluid phases present during ultrahigh-pressure metamorphism. The subduction-related coesite-bearing eclogites of the Tso Morari Complex, Himalaya, contain five major types of fluids identified by microthermometry and Raman spectroscopy. These are: (1) high-salinity brine, (2) N2, (3) CH4, (4) CO2and (5) low-salinity aqueous fluids. These fluids were trapped during both deep subduction and exhumation processes. The coesite-bearing rocks are inferred to have been buried to a depth of >120 km, where they experienced ultrahigh-pressure metamorphism. The fluid–rock interaction provides direct evidence for fluid derivation during a deep subduction process as demonstrated by silica–carbonate assemblages in eclogite. High salinity brine, N2and CH4inclusions are remnants of prograde and peak metamorphic fluids, whereas CO2and low-salinity aqueous fluids appear to have been trapped late, during uplift. The high-salinity brine was possibly derived from subducted ancient metasedimentary rocks, whereas the N2and CH4fluids were likely generated through chemical breakdown of NH3-bearing K minerals and graphite. Alternatively, CH4might have been formed by a mixed fluid that was released from calcareous sediments during subduction or supplied through subducted oceanic metabasic rocks. High density CO2is associated with matrix minerals formed during granulite-facies overprinting of the ultrahigh-pressure eclogite. During retrogression to amphibolite-facies conditions, low-salinity fluids were introduced from external sources, probably the enclosing gneisses. This source enhances salinity differences as compared to primary saline inclusions. The subducting Indian lithosphere produced brines prior to achieving maximal depths of >120 km, where fluids were instead dominated by gaseous phases. Subsequently, the Indian lithosphere released CO2-rich fluids during fast exhumation and was then infiltrated by the low-salinity aqueous fluids near the surface through external sources. Elemental modelling may improve quantitative understanding of the complexity of fluids and their reactions.

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A Discussion on the evolution of the Precambrian crust - Geochemistry of granulite facies rocks and problems of their origin

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1973.0009 ◽

1973 ◽

Vol 273 (1235) ◽

pp. 429-442 ◽

Cited By ~ 182

Keyword(s):

High Pressure ◽

Continental Crust ◽

Major Element ◽

Granulite Facies ◽

Sr Isotope ◽

Average Surface ◽

Magmatic Rocks ◽

Mineral Associations ◽

High Pressure Granulite ◽

Critical Mineral

Occurrences of granulite facies rocks are widespread in continental regions where they mostly are parts of stable shield areas. Granulite facies terrains are classified as low-, medium- or high-pressure terrains on the basis of critical mineral associations. Special interest is attached to the medium- and highpressure terrains, as they are representative of the deepest crustal levels available for study in any areal extent on the surface, and may give information about the composition of the lower continental crust. Granulite facies terrains are mainly composed of metamorphic and metasomatic rocks, but magmatic rocks with primary igneous textures interpreted as formed by crystallization of magmas under granulite facies conditions are frequent in some areas. Examples of such rocks are anorthosites, gabbros and mangerites. The low-pressure—high-temperature granulite facies rocks are chemically indistinguishable from the amphibolite facies gneisses with which they characteristically occur. It is therefore important to make a distinction between these and the higher pressure types. The medium- to high-pressure granulite facies terrains are characterized by a less ‘acidic’ average major element compositions, and significant depletions in Rb, Cs, Th and U compared with average surface shield compositions. Available data also indicate low initial Sr isotope ratios, even in the gneissic types. In the author’s opinion the important problem associated with granulite facies rocks is not that of their origin, but rather of their importance as constituents of the continental crust, and how they attained their present chemistry.

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High-Pressure Granulite Facies Overprinting During the Exhumation of Eclogites in the Bangong-Nujiang Suture Zone, Central Tibet: Link to Flat-Slab Subduction

Tectonics ◽

10.1002/2017tc004774 ◽

2017 ◽

Vol 36 (12) ◽

pp. 2918-2935 ◽

Cited By ~ 25

Author(s):

Xiu-Zheng Zhang ◽

Qiang Wang ◽

Yong-Sheng Dong ◽

Chunfu Zhang ◽

Qing-Yun Li ◽

...

Keyword(s):

High Pressure ◽

Granulite Facies ◽

Suture Zone ◽

Flat Slab ◽

High Pressure Granulite ◽

Flat Slab Subduction ◽

Central Tibet

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High-Pressure Fault Tectonites of the Yenisei Ridge as Result of Ductile Shear Deformations in the Suture Zone

Доклады Академии наук ◽

10.31857/s086956520003279-9 ◽

2018 ◽

Vol 483 (4) ◽

pp. 417-421

Author(s):

I. Likhanov ◽

◽

P. Kozlov ◽

K. Ivanov ◽

S. Zinov'ev ◽

...

Keyword(s):

High Pressure ◽

Suture Zone ◽

Yenisei Ridge ◽

Shear Deformations ◽

Ductile Shear

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Comment on “Middle Cretaceous back-arc formation and arc evolution along the Asia margin: the Shyok Suture Zone in northern Ladakh (NW Himalaya)” by Rolland and Pêcher

Tectonophysics ◽

10.1016/s0040-1951(01)00183-4 ◽

2001 ◽

Vol 340 (3-4) ◽

pp. 265-268 ◽

Cited By ~ 3

Author(s):

R.F Weinberg ◽

W.J Dunlap

Keyword(s):

Suture Zone ◽

Nw Himalaya ◽

Back Arc

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High-pressure granulite-facies metamorphism and anatexis of deep continental crust: new insights from the Cenozoic Ailao Shan–Red River shear zone, Southeast Asia

Gondwana Research ◽

10.1016/j.gr.2021.10.010 ◽

2021 ◽

Author(s):

Haobo Wang ◽

Shuyun Cao ◽

Junyu Li ◽

Xuemei Cheng ◽

Franz Neubauer ◽

...

Keyword(s):

High Pressure ◽

Southeast Asia ◽

Shear Zone ◽

Continental Crust ◽

Granulite Facies ◽

Red River ◽

Granulite Facies Metamorphism ◽

High Pressure Granulite ◽

Facies Metamorphism

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Exsolution Lamellae in Orthopyroxene of Lherzolite from the Pauza Ultramafic Rocks, Ne Iraq: Evidence of Deep Mantle Signature in the Zagros Suture Zone

International Journal of Geography and Geology ◽

10.18488/journal.10/2013.2.9/10.9.102.115 ◽

2013 ◽

Vol 2 (9) ◽

pp. 102-115

Author(s):

Yousif Osman Mohammad ◽

Nabaz Rashid Hama Aziz

Keyword(s):

High Pressure ◽

Upper Cretaceous ◽

Suture Zone ◽

Ultramafic Rocks ◽

Chromian Spinel ◽

Spinel Peridotite ◽

Incongruent Melting ◽

Fine Grained ◽

Ultra High Pressure ◽

Deep Mantle

The Pauza ultramafic body is part of Upper Cretaceous Ophiolitic massifs of the Zagros Suture Zone, NE Iraq. The present study reveals evidence of Ultra-high pressure (UHP), and deep mantle signature of these peridotites in the Zagros Suture Zone throughout the observation of backscattered images and micro analyses which have been performed on orthopyroxen crystals in lherzolite of Pauza ultramafic rocks.Theorthopyroxen shows abundant exsolution lamellae of coarse unevenly distributed clinopyroxene coupled with the submicron uniformly distributed needles of Cr-spinel. The observed clusters of Opx–Cpx–Spl represent the decompression products of pyrope-rich garnet produced as a result of the transition from ultra-high pressure garnet peridotite to low-pressure spinel peridotite (LP). Neoblastic olivine (Fo92 – 93) with abundant multi-form Cr- spinel inclusions occurs as a fine-grained aggregate around orthopyroxene, whereas coarse olivine (Fo90-91) free from chromian-spinel is found in matrix. The similarity of the Cr-spinel lamellae orientations in both olivine and orthopyroxene, moreover, the enrichments of both Cr and Fe3+ in the Cr-spinel inclusions in neoblastic olivine relative to Cr-spinel lamellae in orthopyroxene, suggest that spinel inclusions in olivine have been derived from former Cr-spinel lamellae in orthopyroxene. Neoblastic olivine is formed by reaction of silica-poor ascending melt and orthopyroxene. It is inferred that the olivines with multi-form spinel inclusions has been formed by incongruent melting of pre-existing spinel lamellae-rich orthopyroxene.

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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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