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Formation and metamorphism of sedimentary rocks beneath the Dingxi Basin: Record of the evolution from subduction to collision in the North Qilian Orogen
Author(s) -
Wang Bin,
Wang WeiRZ,
Tian Zuoling,
Wei Chunjing,
Zhao Yue
Publication year - 2020
Publication title -
terra nova
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.353
H-Index - 89
eISSN - 1365-3121
pISSN - 0954-4879
DOI - 10.1111/ter.12447
Subject(s) - geology , metamorphism , geochemistry , protolith , continental collision , kyanite , sedimentary rock , metamorphic rock , terrane , subduction , zircon , continental crust , petrology , paleontology , tectonics , crust
The North Qilian Orogen (NQO) in northwest China underwent oceanic subduction and subsequent continental collision. Metasedimentary rocks from a deep borehole in the Dingxi Basin, NQO, contain garnet, biotite, plagioclase, quartz and minor cummingtonite and chlorite in the matrix, with inclusions of kyanite and staurolite in garnet. The mineral textures and compositions define clockwise pressure–temperature evolution with peak conditions of ~10.5 kbar and ~670°C, followed by isothermal decompression down to ~6.5 kbar. Age and Hf isotope data of detrital zircon support the formation of the sedimentary protolith in an arc setting at ~460 Ma, and the age and rare earth element characteristics of metamorphic monazite reflect exhumation at ~425 Ma. These results indicate a complete cycle of deposition – burial – exhumation for the sedimentary rocks, and directly constrain the continental collision process in NQO to yield a geotherm of ~21°C/km and to culminate before 425 Ma.