| Petrochemistry,Age and Petrogenesis of the Shexian Pluton in Southern Anhui |
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| 摘 要： |
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| 关 键 词： | 安徽 岩石成因 岩石化学 深成岩体 示踪元素 硬绿泥石 稀土元素 地球化学 |
Petrochemistry,age and petrogenesis of the Shexian pluton in southern Anhui |
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| Authors: | Xing Fengming Xu Xiang Ren Siming Li Yingyun |
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| Institution: | (1) Institute of Geological Sciences of Anhui Province, 230001 Hefei |
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| Abstract: | The Shexian gneissic granodiorite in southern Anhui trends NE 55° from Shexian in the west to Guitoujian in the east with
a length of 22 km and an outcrop area of 32 km. It was considered formerly to be Caledonian on the basis of a biotite K-Ar
age of 474 Ma (1982). However, new evidence indicates that it may be Early Jinning in age as shown by: (1) it is found intruding
into the Mid-Proterozoic Shangxi Group and is unconformably overlain by the Sinian Xiuning Formation, and (2) a zircon U-Th-Pb
age of 928 Ma is obtained for the pluton.
The pluton is composed of plagioclase (An=27.37%), K-feldspar(14%), biotite(16%) and quartz(32%). Accessory minerals are ilmenite
(150g/T), xenotime (15g/T). garnet(25g/T), monazite(10g/T), zircon (20g/T) and apatite (104g/T). Petrochemical characteristics
of the intrusion are:(l) Al-enrichment (A/NKC=1.30); (2) H2O enrichment (H2O= 1.74%); and (3) low oxidation index (f ’=0.10). It belongs to the continental crust transformation type as evidenced by: (1) MF and Mg/Y values of biotite are 0.41
and 0.31 respectively; (2) (87Sr/86Sr)=0.71119; (3) δ Eu=0.52; and (4) A/NKC=130. The Shexian pluton is therefore considered as a product of melting of phyllite
at depth in the light of similarities in trace element and REE contents with the phyllite of the Banxi Group. Calculations
of REE batch partial melting indicate that it may have resulted from 75% melting of the Banxi phyllite. |
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