地质科学2026，Vol.61Issue(2)：402-414,13.DOI:10.12017.dzkx.2026.028
拉脊山西段扎巧合晚寒武世火山岩的地球化学、锆石U-Pb年龄及其构造意义
Geochemistry,zircon U-Pb age,and tectonic implications of the Late Cambrian volcanic rocks in the Zhaqiaohe area,western segment of the Lajishan structural belt
摘要
Abstract
As a suture zone where the central Qilian and southern Qilian blocks converge within the Qilian orogenic belt,the Lajishan tectonic belt has long been subject to controversies regarding the formation age and tectonic setting of its Early Paleozoic volcanic rock series.This paper conducts petrological,geochemical,and chronological studies on the intermediate-basic volcanic rocks in the Zhaqiaohe area to clarify their formation age,tectonic background,and relationship with the evolution of the Proto-Tethys Ocean.LA-ICP-MS zircon U-Pb dating yields a weighted mean age of 496±5 Ma for the andesites,providing isotopic chronological data for the formation age of volcanic rocks in this region.Geochemical analyses indicate that the volcanic rocks belong to the medium to high-k calc-alkaline series,characterized by strongly enriched light rare earth elements((La/Yb)N=15.55～26.60)and weak negative Eu anomalies(δEu=0.89～1.03).The trace elements show significant enrichment in Rb,Ba and Th,along with obvious depletion in Nb,Ta and Ti.Tectonic setting discrimination diagrams consistently suggest that these rocks formed in an island arc environment.Based on a comprehensive study of regional tectonic evolution,it is proposed that the Late Cambrian volcanic rocks in Zhaqiaohe record the products of intra-oceanic subduction within the southern Qilian Ocean,forming in an intra-oceanic arc setting.Combined with the ages of contemporaneous volcanic rocks(523～506 Ma)in the central and eastern segments of the Lajishan belt and the age of ophiolites(～524 Ma),this study constrains the time range of intra-oceanic subduction activities in the Lajishan tectonic belt to 523～496 Ma.This further confirms the existence of the southern Qilian paleo-ocean basin,improves the understanding of intra-oceanic subduction evolution of the Proto-Tethys Ocean,and provides an important geological basis for reconstructing the Early Paleozoic plate tectonic framework of the Qilian region.关键词
拉脊山构造带/寒武纪火山岩/锆石U-Pb年龄/地球化学/祁连洋俯冲Key words
Lajishan tectonic belt/Cambrian volcanic rocks/Zircon U-Pb age/Geochemistry/Qilian Ocean subduction分类
天文与地球科学引用本文复制引用
许海全,严玉峰,袁锦鹏,陈光庭..拉脊山西段扎巧合晚寒武世火山岩的地球化学、锆石U-Pb年龄及其构造意义[J].地质科学,2026,61(2):402-414,13.基金项目
青海省天峻县苏里地区1∶5万五幅区域地质调查项目(编号:1212011140088)和青海省科学技术厅重点研发与转化计划项目"柴北缘全吉地块沉积变质型铁矿成矿环境与找矿方向研究"(编号:2023-QY-212)资助 （编号:1212011140088）
