Genetic Mineralogy and Metamorphic Evolution of Al-Rich Gneisses in the Shiguai Area, Daqingshan-Wulashan Netamorphic Complex Belt
详细信息
- 责任者：Cai Jia (Institute of Geology ; Chinese Academy of Geological Sciences ; Beijing 100037 ; China) ; Liu Pinghua
- 刊名：Acta Petrologica Sinica
- 出版年：2013
- 卷期：29(2)
- 关键词：片麻岩 ; gneisses ; 大青山 ; Daqing Mountains
- 页码：p.437-461
- 图表：illus., 6 tables, 102 refs.
- 分类号：0802
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
Al-rich gneisses as interlayers within mafic granulites are widespread in the Shiguai area, Daqingshan-Wulashan metamorphic complex belt which is belong to the central part of the Khondalite Belt of the North China Craton. Shiguai Al-rich gneisses consist mainly of sillimanite-garnet-cordierite gneiss, hypersthene-garnet gneiss and sillimanite-garnet gneiss. Based on integrated structural, petrographic, mineral compositional features, geothermobarometric estimations and P-T pseudosection modelling in the system NCKFMASHTO, the metamorphic evolution for the Shiguai Al-rich gneisses could be subdivided into four metamorphic stages. Thereinto, early prograde metamorphic stage (M1) is characterized by garnet cores and the mineral inclusions of biotite+quartz+plagioclase±sillimanite ±K-feldspar±spinel. In contrast, mineral assemblage at the peak metamorphic stage (M2) is interpreted to be matrix garnet and coarse-grained sillimanite+biotite+quartz+plagioclase + K-feldspar±magnetite±ilmenite, which formed at P-T conditions of 840～860℃ and 10.0～10.5kbar. Typical decompressional reactions, such as Grt+Sil+Qz→Crd、Grt+Melt→Crd+Bt+Pl and Grt+Melt→Crd+Qz±Pl have been identified at the post-peak metamorphic stage (M3), and new mineral assemblage of garnet+cordierite+biotite+plagioclase+quartz±sillimanite±hypersthene was formed at this stage with P-T conditions of 720～800℃ and 5.6～6.1kbar. The late cooling stage (M4) is characterized by a retrogressive mineral assemblage of garnet+biotite+plagioclase+quartz+magnetite ±K-feldspar±ilmenite, which formed at P-T conditions of 616～661℃ and 3.4～5.2kbar. This indicates that the Shiguai Al-rich gneisses recorded a clockwise near-isothermal decompression (ITD) P-T path following by a near-isobaric cooling (IBC) stage. It can be concluded that the Shiguai Al-rich gneisses within the Daqingshan-Wulashan metamorphic complex belt was indeed involved in the subduction-collision orogenic event between Yinshan block and Ordos block at Paleoproterozoic.
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