Granulite relics and pyroxene-facies ductile deformation in the northern boundary of the southern Tien Shan

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Authors:Shu Liangshu; Wang Ciyin; Ma Ruishi
Author Affiliations:Primary:
Nanjing University, Department of Earth Sciences, Nanjing, China
Volume Title:Dizhi Kexue Scientia Geologica Sinica
Source:Dizhi Kexue = Scientia Geologica Sinica, 31(4), p.375-383. Publisher: Zhongguo Kexueyuan Dizhi Yanjiusuo, Beijing, China. ISSN: 0563-5020
Publication Date:1996
Note:In Chinese with English summary. 14 refs.; illus., incl. 3 tables, geol. sketch maps
Summary:This paper reported the latest research results on the granulite relics and pyroxene-facies ductile deformation that occur in the early Paleozoic ophiolitic melange blocks along the northern boundary of the Southern Tianshan belt, Xinjiang. Studies on Yushugou granulite from field geology, crystal optics, petrochemistry, mineral chemistry and REE geochemistry suggest that the Yushugou granulite is composed of diopsite, salite, hypersthene, garnet and plagioclase and is named as garnet websterite granulite or basic rock-type granulite, which is characterized by lower SiO2 (45.54%), higher CaO (14.83%), lower REE content (65×10-6-90×10-6), LREE/HREE 0.66-0.91, Eu/Sm 0.34-0.35 and weakly depletion in Eu, showing a formation environment in lower crust with higher pressure (1.5GPa), higher temperature (813°C) and lower magmatic differentiation. All the granulites are bordered by faults. Our works found that ductile shear structures occur commonly in the pyroxenes of granulite and ultramafic rock, including core-mantle structure, flatten and elongated structure, dynamic recrystallised pyroxene subgrains with orientated arrangement, asymmetric pyroxene porphyroclast system, fish-tail structure, pyroxene pressure shadow and deformed twinning striation, and so on. So, these deformed rocks can be called as pyroxene-facies mylonitic ones. Kinematic analysis indicates a thrust ductile deformation from south to north. The authors propose that the Yushugou granulite formed about 420 Ma in the lower crust was resulted from the early Paleozoic crustal rifting to form the Southern Tianshan marginal sea, and pyroxene-facies ductile deformation that took place about 402 Ma was related to thrusting from deep to shallow due to closure of the marginal sea during the end stage of early Paleozoic, leading to rising of granulite toward upper crust. [R.E.S.]
Subjects:Complexes; Deformation; Ductile deformation; Facies; Faults; Fold and thrust belts; Geochemistry; Granulite facies; Granulites; Lithogeochemistry; Lower Paleozoic; Melange; Metals; Metamorphic rocks; Nappes; Ophiolite complexes; P-T-t paths; Paleozoic; Pyroxene granulite; Rare earths; Tectonics; Thrust faults; Trace elements; Asia; China; Far East; Tien Shan; Xinjiang China; Yushugou Formation
Coordinates:N410000 N430000 E0920000 E0900000
Abstract Numbers:97M/4491
Record ID:1998005883
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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