现代地质2024，Vol.38Issue(4)：1147-1161,15.DOI:10.19657/j.geoscience.1000-8527.2023.074
柴达木盆地东北部拉合根地区中生代火山岩的发现及其地质意义:来自地球化学与锆石年代学证据
Discovery of the Mesozoic Volcanic Rocks in Lahegen Area of the Eastern North Qaidam Tectonic Belt,and Its Geological Implications:Evidence from Geochemistry and Zircon Geochronology
摘要
Abstract
The stratigraphic attribution of volcanic rocks in the eastern area of the northern margin of the Qaidam Basin is difficult to determine due to a lack of geochronological data.These rocks are located between the Wa-hongshan-Wenquan Fault and the southern margin of the Zongwulong Mountain Fault.This also leads to signifi-cant disputes over the division of geotectonic units in this area,as no Mesozoic volcanic rocks have been found here before.In this study,a set of Mesozoic volcanic rocks consisting of rhyolite,intermediate-acid brecciate lava and dacite was newly confirmed in the Lahegen area.Zircon U-Pb dating was performed on the rhyolite samples using the LA-ICP-MS technique with weighted mean age of 248.3±1.2 Ma,indicating an Early Trias-sic age.The geochemical data show that the volcanic rock is a metaluminous high-potassium calc-alkaline rock with clear fractionation of light rare earth elements,enrichment of light rare earth elements and depletion of heavy rare earth elements.The mean δEu value is 0.63,indicating a weak negative anomaly.The rocks are relatively enriched in large ion lithophile elements(e.g.,Rb and Ba)and high field strength elements(e.g.,Th,U,Pb,and Zr),and are significantly depleted in Sr,Ta,and Nb.These are typical geochemical charac-teristics of continental island arc volcanic rocks.Zircon Hf isotope compositions show εHf(t)values of～-19.62 to-3.07 and tDM2values of～1,639 Ma to 2,421 Ma,indicating that the volcanic rocks are derived from the partial melting of Paleoproterozoic crustal materials.Based on geochronology and geochemical charac-teristics,the volcanic rocks are attributed to the anatexis of crustal materials(the Darken Daban Group)caused by the northward subduction of the Anemaqen Ocean to the East Kunlun block in the Early Triassic.The vol-canic rocks of the Hongshuichuan Formation are similar to those in the magma arc of Olashan,according to the regional correlation.Therefore,these rocks are identified as Early Triassic Hongshuichuan Formation volcanic rocks.The confirmation of the studied volcanic rocks indicates that the Lahegen area has a close tectonic affini-ty with the Olashan magmatic arc of the East Kunlun orogenic belt.This study provides new evidence for the tectonic division of the eastern area of the northern margin of Qaidam Basin.关键词
拉合根/火山岩/锆石U-Pb定年/Hf同位素/构造环境Key words
Lahegen area/volcanic rock/zircon U-Pb dating/Hf isotope/tectonic environment分类
天文与地球科学引用本文复制引用
郑英,韩杰,张小永,缑明亮,王明,袁博武..柴达木盆地东北部拉合根地区中生代火山岩的发现及其地质意义:来自地球化学与锆石年代学证据[J].现代地质,2024,38(4):1147-1161,15.基金项目
青海省地质调查局地质调查项目(2019048021jc013,2020021022jc013) （2019048021jc013,2020021022jc013）
青海省地质矿产勘查开发局项目(青地矿[2021]61号) （青地矿[2021]61号）
青海省地质矿产开发局项目(青地矿科[2023]33号). （青地矿科[2023]33号）
