Petrography, Mineral Chemistry and Implications of the A’re Porphyry of Shangri-La, Western Yunnan
详细信息
- 责任者：Dong Yi (Institute of Earth Science ; Chengdu University of Technology ; Chengdu 610059 ; China) ; Liu Xianfan
- 刊名：Acta Geologica Sinica
- 出版年：2013
- 卷期：87(4)
- 页码：p.498-514
- issnNo：ISSN0001-5717
- isbnNo：CN11-1951/P
摘要
The A’re porphyry is located at the north end of the Zhongdian Arc, which is consistent with the direction of the Geza Fault (NNE). It is composed mainly of amphibole diorite porphyry, clinopyroxene diorite porphyry, clinopyroxene amphibole diorite porphyry and qaurtz diorite porphyry. According to the distribution features of phenocrysts in the A’re porphyry, we studied the petrography and mineral chemistry of the amphibole diorite porphyry, clinopyroxene diorite porphyry, clinopyroxene amphibole diorite porphyry and the schlieren. The results show that both amphibole and clinopyroxene can be divided into two types: high Mg# and low Mg#. The disequilibrium textures related to magmatic mixing are found to occur in amphibole and pyroxene, suggesting mixing of homologous heterogeneous magma (without obvious crystallization fraction). Diagenetic magmas might be related to the subducting Ganze-Litang ocean slab of Late Triassic. Metasomatism of fluid derived from dehydration due to plate subduction and melt from partial melting with the mantle wedge is the important mechanism for formation of magma. The magma process was controlled by tectonic stress and magma was changing from poor in water or local water to water rich magmas, characterized by high MgO and SiO2/Al2O3 ratio to the low MgO and SiO2/Al2O3. The results from estimation of amphibole geothermobarometry exhibits low Mg #amphiboles formed at much higher pressure than high Mg# amphibole did. Based on the structure, stress and dynamic backgrounds of magma emplacement, it can be concluded that during the westward subduction of the Ganze-Litang Ocean slab, the ocean slab might break-off due to eastward extrusion of the Qiangtang Block to the south of the Zongzai Block in ~230Ma, and thus the tectonic stress in the research area decreased after short increasing during 228~219Ma.