柴北缘尕海南山晚志留世—晚泥盆世火山岩浆组合对早古生代造山后伸展时限的约束  

Constraints for post-orogenic extension of the northern margin of the Qaidam Basin from the Late Silurian–Late Devonian igneous rocks in the Gahai–Nanshan area

作　　者：高万里[1,2] 王宗秀 吴林[1,2] 江万 钱涛[1,2] GAO Wanli;WANG Zongxiu;WU Lin;JIANG Wan;QIAN Tao(Institute of Geomechanics,Chinese Academy of Geological Science,Beijing 100081,China;Key Lab of Paleomagnetism and Tectonic Reconstruction of Ministry of Natural Resources,Beijing 100081,China)

机构地区：[1]中国地质科学院地质力学研究所,北京100081 [2]自然资源部古地磁与古构造重建重点实验室,北京100081

出　　处：《地质力学学报》2024年第3期506-518,共13页Journal of Geomechanics

基　　金：国家自然科学基金项目(42372179,41702204)。

摘　　要：柴达木盆地北缘(柴北缘)构造带经历了早古生代的大洋俯冲到大陆俯冲,形成了广为人知的柴北缘超高压变质带。早古生代造山带何时开始垮塌一直存在争论,火山岩和侵入岩作为深地岩石探针能为约束地壳活动提供关键制约。应用锆石LA–ICP–MS U–Pb年代学和Lu–Hf同位素方法对柴北缘东段尕海南山地区出露的牦牛山组火山碎屑岩和侵入其中的花岗岩开展研究。锆石U–Pb年代学结果显示,牦牛山组火山碎屑岩的形成时代约为423 Ma,侵入其中的花岗岩的形成时代为370 Ma,表明火山岩喷发的年龄在晚志留世,后期侵入的花岗岩结晶年龄为晚泥盆世;锆石Lu–Hf同位素结果显示,晚志留世熔结凝灰岩ε_(Hf)(t)值集中在–11.5~–8.3,其两阶段Hf模式年龄集中在1945~2133 Ma,显示火山岩主要源于古老地壳物质熔融;而晚泥盆世侵入的花岗岩的ε_(Hf)(t)值分布在3.9~9.1,其两阶段的Hf模式年龄集中在792~1118 Ma,显示花岗岩主要源于中—新元古代地壳物质的部分熔融。结合对区域地质、岩石学等资料的综合分析认为,晚志留世—早泥盆世时期,大陆深俯冲导致的强烈造山作用造成柴北缘地壳发生明显加厚,加厚的欧龙布鲁克地壳基底发生部分熔融,形成了该时期的火山岩;晚泥盆世时期,加厚地壳的拆沉作用导致软流圈地幔上涌,引发区域地壳伸展,上涌的软流圈物质与地壳相互作用并发生部分熔融作用。因此区域牦牛山组形成时代跨度较大,不能笼统地用牦牛山组代表造山结束的时限,晚泥盆世岩浆岩的出现才预示着柴北缘地区进入显著的地壳伸展状态。[Objective]The northern margin tectonic zone of the Qaidam Basin underwent a transition from oceanic subduction to continental subduction during the Early Paleozoic,resulting in the formation of the ultrahigh-pressure metamorphic zone known as the northern Qaidam tectonic zone(NQTZ).There has been a longstanding debate regarding the collapse time of the NQTZ.The Maoniushan Formation has long been regarded as a sign of the end of orogeny;however,recent studies show that the Maoniushan Formation has spanned a long time,and it is controversial when the orogenic belt began to collapse.This study aims to determine the age and genetic background of the Maoniushan Formation and to understand the tectonic transition process of the northern Qinghai–Tibet Plateau from the Proto-Tethys to the Paleo-Tethys.[Methods]Deep-earth samples,including volcanic and intrusive rocks,offer valuable insights into the activity of the crust during this period.In order to investigate the volcaniclastic rocks and granites in the Gahai–Nanshan area,located in the eastern section of the NQTZ,zircon LA–ICP–MS U–Pb chronology and Lu–Hf isotope methods were employed to explore the formation age of igneous rocks and the characteristics of source rocks.[Results]The zircon U–Pb chronology reveals that the volcaniclastic rocks of the Maoniushan Formation originated approximately 423 Ma.Furthermore,the intrusive granite was formed at 370 Ma,indicating that the volcanic eruption occurred during the Late Silurian,while the subsequent intrusion and crystallization of the granites occurred during the Late Devonian.The zircon Lu–Hf isotope data reveals that theε_(Hf)(t)values of the Late Silurian tuffs are concentrated within the range of–11.5 to–8.3,and the corresponding two-stage Hf model ages are primarily between 1945–2133 Ma.These results indicate that the volcanic rocks predominantly originated from partially melting ancient crustal materials.In contrast,theε_(Hf)(t)values of the Late Devonian intrusive granites exhibit a dist

关 键 词：青藏高原 晚古生代 柴达木盆地北缘 火山-侵入岩 构造背景 

分 类 号：P574[天文地球—矿物学] P611[天文地球—地质学]