Anatectic record and P-T path evolution of metapelites from the Wulashan Complex, Khondalite Belt, North China Craton

作者：Cai, Jia^*; Liu, Fulai^*; Liu, Pinghua; Wang, Fang; Liu, Chaohui; Shi, Jianrong

来源：Precambrian Research, 2017, 303: 10-29.

DOI：10.1016/j.precamres.2016.09.007

• Metapelitic rocks
• Partial melting
• Phase equilibria modeling
• P-T path
• Khondalite Belt

The Wulashan Complex in the Khondalite Belt, the North China Craton contains high-grade garnet-cordierite-sillimanite metapelitic rocks with anatectic record. The rocks preserve representative metamorphic assemblages of peak, post-peak near-isothermal decompression, and decompressional cooling stages. Combined with petrographic observation and P-T pseudosections of residual bulk compositions, a clockwise P-T path was inferred involving near-isothermal decompression and decompressional cooling that followed the peak metamorphism. Furthermore, based on phase equilibria modeling for the melt-reintegrated composition, a whole, clockwise P-T path with a possible pre-peak segment was inferred. In the pre-peak field of garnet + biotite + K-feldspar + plagioclase + sillimanite + quartz + magnetite + liquid, garnet was first introduced by consuming biotite, quartz, and plagioclase via the biotite dehydration melting reaction of Bt + Sil + Qz +/- Pl -> Grt + Kfs + Melt. The peak metamorphic assemblage was interpreted to be garnet + biotite + K-feldspar + plagioclase + sillimanite + quartz+ ilmenite + magnetite + liquid at 830-860 degrees C and 9.5-11 kbar. The following post-peak near-isothermal decompressional assemblage is garnet + biotite + cordierite + K-feldspar + plagioclase + quartz + magnetite + ilmenite + liquid at 840-880 degrees C and 6.0-7.5 kbar, resulting in matrix cordierite isolated from garnet due to the biotite decompressional dehydration melting reaction of Bt + Sil + Qz +/- Pl -> Crd + Kfs +/- Ilm + Melt. Furthermore, subsequent decompressional cooling processes resulted in symplectites of cordierite and biotite + plagioclase mantling garnet due to the breakdown reactions: Grt + Sil + Melt -> Crd + Bt + Fe-oxide, and Grt + Melt -> Bt + Qz +/- Pl. Melt that remained in the host rocks formed thin films of plagioclase or K-feldspar distributed along plagioclase, quartz, and sillimanite grain boundaries. The results indicate that the Khondalite Belt experienced continent-continent subduction and collision followed by exhumation and cooling between the Yinshan and Ordos Blocks in the Western Block of the North China Craton, and the rocks of the Wulashan Complex were subjected to granulite-facies metamorphism accompanied by partial melting events.

• 出版日期2017-12
• 单位中国地质科学院