Yanjing Gr

Central Sichuan (Ya'an). The Yanjing Gr was named by the No. 2 Party of Regional Geological Survey, Sichuan Bureau of Geology in 1976. The naming locality is Yanjing, Baoxing County, Sichuan Province. The reference section is at Yanjing- Yaside- Huangdianzi, Baoxing County, Sichuan Province.

The Yanjing Gr is a metamorphosed series of low greenschist facies; and, owing to lack any isotopic data, both its age attribution and its relation with the Huangshuihe Gr have not been completely resolved. As a result, the formation-level stratigraphic units within the group (in ascending order into Yaside Fm, Shimenkan Fm, Fengtongzhai Fm and Huangdianzi Fm) are only described briefly in this entry, rather than as separate Lexicon entries.

Synonym: （盐井群）

The Yanjing Gr is composed of two series of meta-sedimentary rocks and two series of metavolcanic rocks (acid and intermediate-basic). Yaside Fm, the lowest unit, 1980 m thick, is a series of meta-sedimentary clastic rocks, mainly composed of sericite-quartz schist, metamorphosed quartz sandstone accompanied with phyllite. Shimenkan Fm, 892 m thick, consists of meta-rhyolite, rhyolite-porphyry, rhyolitic tuff and rhyolitic volcanic breccia. Fengtongzhai Fm, varying from 142 to 1287 m thick, is carbonaceous slate, phyllite sandwiched with thin- to medium-bedded limestone, with quartzite and sericite schist in lower part and with crystalline limestone in middle and upper part. Huangdianzi Fm, the highest unit, varying from 54 m to 3891 m thick, is massive trachyte accompanied with trachyte porphyry and minor sericite quartz schist, carbonaceous phyllite and slate.