Geochronology and Geochemical Characteristics of the Laojunshan Granites in Maguan County , Yunnan
详细信息
- 责任者：Zhang Binhui (Chengdu Center ; China Geological Survey ; Chengdu 610082 ; China) ; Ding Jun
- 刊名：Acta Geologica Sinica
- 出版年：2012
- 卷期：86(4)
- 关键词：花岗岩 ; granite ; 云南 ; Yunnan Province
- 页码：p.587-601
- 图表：9 illus., 2 tables, 64 refs.
- 分类号：0801
- issnNo：ISSN0001-5717
- isbnNo：CN11-1951/P
摘要
The Maguan Laojunshan granites are located in the Sn-W metallogenic belt trending from southeastern Yunnan Province to western Guangxi Province.To limit the precise age of the Late Mesozoic magmatic mineralization in the Maguan area,the Laojunshan granites have been analyzed using LA-ICP-MS zircon U-Pb techniques and geochemical methods,producing an age of 96 2Ma for the early stage.This suggests a late Cretaceous age for the Laojunshan granite,coupled with Late Cretaceous diagenesis-mineralization in western South China.The Laojunshan granites are geochemcially characterized by medium content of SiO2(69.6% ~ 73.6%),high alkali(K2O+Na2O=6.56%~8.66%),high-K(K2O>Na2O),and peraluminous ratio(A/CNK>1.1).Low contents of Na2O,CaO and Sr(<50×10-6),high abundances of Rb(>270×10-6),and P2O5-Rb and Y-Rb change trends indicate that the Laojunshan granites are fractioned S-type granites.Low CaO/Na2O ratios(<0.3),high Rb/Sr and Rb/Ba ratios suggest a plagioclase-poor,clay-rich pelites source.Combined with regional tectonic setting,the Laojunshan granites formed at the same geodynamic setting as the Late Cretaceous diagenesis-mineralization belt from southeastern Yunnan Province to western Guangxi Province,i.e.Late Cretaceous lithospheric extension in western South China.Basing on the analysis of regional geochemical anomalies and geological setting,we outline that the contact zones of the granites(and concealed granites) and the faulting system in sedimentary covers are the significant ore prospecting direction in this area.