| Characteristics of Lower Crustal Granulite Xenoliths from the East Qinling Orogenic Belt and Their Tectonic Significance |
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| 摘 要： |
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| 关 键 词： | 麻粒岩 捕虏体 河南 秦岭地区 花岗粒玄岩 |
Characteristics of lower crustal granulite xenoliths from the east Qinling orogenic belt and their tectonic significance |
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| Authors: | Sun Yong Yu Zaiping A Kröner |
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| Institution: | (1) Department of Geology, Northwest University, 710069 Xi’an;(2) Department of Geology, Mainz University, Germany |
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| Abstract: | The Tongbai granulites are present mainly as xenoliths in granodioritic gneisses. The xenoliths with a zircon age of 470Ma
are older than the host rocks of granodioritic gneisses which yield a zircon age of 435Ma. It is suggested that the granulites
were transported from the lower crust to the upper level along with granodioritic magma. Geothermometrical and geobarometrical
studies based on the coexisting minerals (Opx-Cpx and Opx-Gar) show that the granulites were crystallized at 818 –840 °C and
9.5−9.8 × 108 Pa corresponding to the lower crust. Tectonically, the Shangdan suture zone constitutes the boundary between the North China
and Yangtze plates. The zone is char acterized by the occurrence of ophiolites in the western part and by that of granulites
in the eastern part. So the western part marks the upper crustal level of the Qinling belt, while the eastern part represents
the exposure of a deeper level. The results of isotopic dating and the geochemical characteristics of the xenoliths are consistent
with those of metatholeiites of the ophiolites in the western part. Therefore, it is assumed that both ophiolites found in
the west and granulites found in the east all represent the remnants of the ancient Qinling ocean plate. The difference is
that the ophiolites are pieces of obducted fragments from the ocean floor during the subduction in the Early Palaeozoic. However,
in the Tongbai area, when the ocean floor was subducting towards the lower crust, it underwent a granulite fades metamorphism.
Subsequently, granodioritic magma formed by partial melting trapped some fragments of granulite upwards.
This project was jointly granted by the National Natural Science Foundation of China and Stiftung Volkswagenwerk of Germany |
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| Keywords: | Qinling granulite xenolith |
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