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

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.

Fabrication of fine grained molybdenum by fast resistance sintering under ultra-high pressure

2019 ◽  
Vol 782 ◽  
pp. 899-904 ◽  
Author(s):  
Zhangjian Zhou ◽  
Nan Deng ◽  
Hui Wang ◽  
Juan Du
Keyword(s):  
High Pressure ◽  
Fine Grained ◽  
Ultra High Pressure

Transient high heat load tests on pure ultra-fine grained tungsten fabricated by resistance sintering under ultra-high pressure

2010 ◽  
Vol 85 (1) ◽  
pp. 115-121 ◽  
Author(s):  
Zhangjian Zhou ◽  
Gerald Pintsuk ◽  
Jochen Linke ◽  
Takeshi Hirai ◽  
Manfred Rödig ◽  
...  
Keyword(s):  
High Pressure ◽  
Heat Load ◽  
High Heat ◽  
Fine Grained ◽  
Ultra High Pressure ◽  
Load Tests ◽  
High Heat Load

Possibly diamond-bearing mantle peridotites and podiform chromitites in the Luobusa and Donqiao ophiolites, Tibet

1993 ◽  
Vol 30 (8) ◽  
pp. 1650-1659 ◽  
Author(s):  
Wen-Ji Bai ◽  
Mei-Fu Zhou ◽  
Paul T. Robinson
Keyword(s):  
High Pressure ◽  
Subduction Zone ◽  
Suture Zone ◽  
Ultramafic Rocks ◽  
Eurasian Plate ◽  
Southern Tibet ◽  
Suprasubduction Zone ◽  
Mantle Peridotites ◽  
Podiform Chromitites ◽  
Reducing Environment

The Luobusa ophiolite of the Yarlung–Zangbo (southern Tibet) suture zone and the Donqiao ophiolite of the Bangong–Nujiang (northern Tibet) suture zone are allochthonous bodies that contain possibly diamond-bearing mantle peridotites and podiform chromitites. The mantle sections in both massifs consist chiefly of harzburgite and diopside-bearing harzburgite with abundant lenses of dunite and chromitite. These ultramafic rocks are more strongly depleted than typical abyssal peridotites and their whole-rock and mineral chemistries suggest formation above a subduction zone. An unusual mineral association (diamond, SiC, graphite, native chromium, Ni–Fe alloy, Cr2+-bearing chromite), indicating a high-pressure, reducing environment, occurs in both the peridotites and chromitites. We suggest that these ophiolites were generated originally in a suprasubduction zone environment and were later carried deep into the mantle along a second subduction zone, at which time the diamonds and other high-pressure minerals were formed. It is not yet clear whether the diamonds formed by high-pressure metamorphism of the oceanic crust or by crystallization from mantle melts, but their occurrence in chromitites and harzburgites suggests a metamorphic origin. During the collision of India with the Eurasian plate, the mantle sections were tectonically emplaced at shallow crustal levels rapidly enough to preserve the diamonds.

scholarly journals Dating of ultramafic rocks from the Western Alps ophiolites discloses Late Cretaceous subduction ages in the Zermatt-Saas Zone

2017 ◽  
Vol 155 (2) ◽  
pp. 298-315 ◽  
Author(s):  
GISELLA REBAY ◽  
DAVIDE ZANONI ◽  
ANTONIO LANGONE ◽  
PIETRO LUONI ◽  
MASSIMO TIEPOLO ◽  
...  
Keyword(s):  
High Pressure ◽  
Late Cretaceous ◽  
Middle Jurassic ◽  
Late Jurassic ◽  
Western Alps ◽  
Ultramafic Rocks ◽  
Uhp Metamorphism ◽  
Ultra High Pressure ◽  
Cretaceous Subduction

AbstractThe Zermatt-Saas Zone was part of the Middle to Late Jurassic Tethyan lithosphere that underwent oceanic metamorphism during Mesozoic time and subduction during Eocene time (HP to UHP metamorphism). In upper Valtournanche, serpentinite, metarodingite and eclogite record a dominant S2 foliation that developed under 2.5±0.3 GPa and 600±20°C during Alpine subduction. Serpentinites contain clinopyroxene and rare zircon porphyroclasts. Clinopyroxene porphyroclasts show fringes within S2 with similar compositions to that of grains defining S2. Zircon cores show zoning typical of magmatic growth and thin fringes parallel to the S2 foliation. These features indicate crystallization of clinopyroxene and zircon fringes during HP syn-D2 metamorphism, related to the Alpine subduction. The U–Pb zircon dates for cores and fringes reveal crystallization at 165±3.2 Ma and 65.5±5.6 Ma, respectively. The Middle Jurassic dates are in agreement with the known ages for the oceanic accretion of the Tethyan lithosphere. The Late Cretaceaous - Paleocene dates suggest that the Zermatt-Saas Zone experienced high-pressure to ultra-high-pressure (HP–UHP) metamorphism at c. 16 Ma earlier than previously reported. This result is in agreement with the evidence that in the Western Alps the continental Sesia-Lanzo Zone reached the subduction climax at least from 70 Ma and was exhumed during ongoing oceanic subduction. Our results are further evidence that the Zermatt-Saas ophiolites diachronically recorded heterogeneous HP–UHP metamorphism.

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