关键词: 金水口群, 斜长角闪岩, 锆石UPb定年, 锆石LuHf同位素分析, 东昆仑造山带

Abstract:  The sedimentary and metamorphic ages of the Jinshuikou Group in the East Kunlun orogenic belt has been controversial. In this paper, the zircon UPb geochronology and LuHf isotope of amphibolite in Jinshuikou Group in Gouli area, Dulan County, Qinghai Province were studied by LAICPMS technique. The results  show that the ages of detrital zircons in amphiboliterange from 2.1 to 2.0 Ga, with the youngest detrital zircons dating to 1 829 Ma；The upper intersection age of metamorphic zircons is (1 905±300) Ma, although with a large error. However, this implies a lengthy deposition time for the Jinshuikou Group, not extending beyond the Early Mesoproterozoic. Therefore, this study proposes a deposition time of about 1 800 Ma for the Jinshuikou Group. The detrital zircons with ages of 2 100 Ma are characterized by granulite facies metamorphic zircon. Metamorphic zircon ages are concentrated between 450 and 420 Ma, with a weighted average age of 12 points is (444.3±5.3) Ma (Early Paleozoic), consistent with the age of regional anatexis in the East Kunlun orogenic belt in response to the subduction and amalgamation of the ProtoTethys Ocean. The zircon 176Lu/177Hf values are low, the εHf (t) values of metamorphic zircons are -35.41-3.75, and the TDM2 is between 3 6411 666 Ma. The source rock materials are the product of ancient crustal recycling. The εHf (t) values of the Proterozoic detrital zircons are -2.9825.58, and the TDM2 is between 2 833920 Ma. The source area is the continental crust from the depleted mantle, which is similar to the Archean TTG rock series, suggesting that the TTG rock series of Altyn block provides some material sources to Jinshuikou Group. The Jinshuikou Group was deposited on the active continental margin or the initial rift basin, while the Binggou Group and Wanbaogou Group, the upper sedimentary cover, were deposited on the shallow sea shelf, with a continuous deposition process.

Key words: Jinshuikou Group, amphibolite, zircon UPb dating, zircon LuHf isotope analysis, East Kunlun orogenic belt