Yunxi Gr

Hubei-Henan border region. The Yunxi Gr was named by the Qinling Party of Regional Geological Survey of the Shaanxi Bureau of Geology (1961). The type section is located in Yunxi County, Hubei Province. The reference section is located in Neixiang area, Henan Province.

Synonym: （郧西群）

The Yunxi Gr is a series of marine acidic volcanic rocks, volcaniclastic rocks and minor ordinary sedimentary rocks. The Yunxi Group includes two parts. Lower part is mainly composed of gray white acidic volcanic lava (quartz keratophyre and acid brecciated tuff) and tuff. Upper part consists of coarse-grained acidic volcaniclastic rocks, acid or alkaline lava and volcanic agglomerate.

The thickness, lithology and metamorphism grade of the Yunxi Group are quite variable. Around Zhaochuan of Shangnan County, it is metamorphosed into higher grade of various schists with dolomitic limestone in upper part, over 1696 m thick. Around Xixia and Xichuan in Henan Province there are mainly metamorphosed feldspathic quartz sandstone and sericite phyllite, with quartz keratophyre and keratophyre, volcanic breccia and agglomerate in upper part, 2000 m thick. In Yunxi area, Hubei Province, the Yunxi Group consists of crysto-blastic tuff, micaceous quartz schist and rhyolite, felsite and acidic tuff, 5000 m thick. Around Pingli in Shaanxi Province, it developed into feldspathic quartz schist, 2500 m thick; and in Niushan, acidic volcaniclastic rocks and volcanic lava are interbedded with ordinary sedimentary rocks (metamorphosed grit). Therefore, the Group ranges from 1696 m to 5000 m in thickness.