Zircon SHRIMP U-Pb dating of basalt from Huangshuihe Group on the western margin of the Yangtze block and its geological significance

Abstract：The structural clip of Huangshuihe Group, distributed along Longmenshan thrust nappe belt, is one of the typical low-grade metamorphic rock series, and some metamorphism could reach amphibolite facies, with the wide distribution of volcanic rocks. Based on field geological survey in combination with petrologic and petrographic analysis, the authors collected a sample of basalt from Ganheba Formation for zircon SHRIMP U-Pb dating, and obtained two U-Pb 206Pb/238U weighted average ages of (799±8) Ma (MSWD=0.96) and (875± 12) Ma (MSWD=0.38). The former age of (799±8)Ma represents the crystallization age of the basalt, suggesting Mid-Neoproterozoic, whereas the latter represents the age of captured zircon, signifying a tectonic-magmatic event of Jinning movement. Combined with the results of data obtained from the region, the authors hold that Huangshuihe Group, Yanjing Group, and Suxiong Formation were contemporary sedimentary strata formed in the late Qingbaikou period.