期刊
GONDWANA RESEARCH
卷 30, 期 -, 页码 48-64出版社
ELSEVIER SCIENCE BV
DOI: 10.1016/j.gr.2014.10.006
关键词
High pressure metamorphism; Geochemistry; Phase equilibria modeling; Zircon geochronology; North Qinling belt
资金
- Open Fund of SKLCD of the Northwest University, China
- Talent Award under the 1000 Talents Plan of the Chinese Government
- NSFC [41225008, 41190074]
- Japan Society for the Promotion of Science (JSPS) [26302009]
- Grants-in-Aid for Scientific Research [26302009] Funding Source: KAKEN
The Shangdan suture zone (SSZ) is the main collisional boundary between the North China Craton and the South China Craton, along which discontinuous Paleozoic ophiolites and subduction-accretion related volcanic arc assemblages occur. Here we report the petrology, geochemistry, geochronology and phase equilibria modeling of garnet amphibolite from the Songshugou ophiolite which is one of the largest ophiolite outcrops in the northern side of the SSZ. From petrological studies, we identify: (1) prograde stage, defined by garnet + clinopyroxene + calcic amphibole + ilmenite + rutile + epidote + plagioclase + quartz; (2) peak stage with garnet + clinopyroxene + ilmenite + rutile + quartz; and (3) retrograde stage with amphibole + plagioclase + titanite + ilmenite. Our pseudosection analysis defines stability of the peak assemblage at 750-850 degrees C, 15-19 kbar and traces a clockwise P-T path in the system Na2O-CaO-FeO-MgO-Al2O3-SiO2-H2O-TiO2-Fe2O3 (NCFMASHTO), suggesting high pressure (HP) metamorphism. Subsequently, the rocks experienced rapid decompression and cooling. LA-ICP-MS U-Pb analyses of zircons from the garnet amphibolite yield a weighted mean Pb-206/U-238 age of 515 +/- 12 Ma. This Early Paleozoic metamorphic age represents the emplacement time of the Songshugou ophiolite, and suggests that the HP metamorphism is possibly related to the northward deep subduction of the Shangdan oceanic crust in Early Paleozoic. (C) 2014 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
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