拉萨地块扎扛地区晚寒武世—早奥陶世流纹岩锆石U-Pb定年、岩石成因及其对原特提斯洋俯冲的启示  

Zircon U-Pb age,petrogenesis and the revelation to the Proto-Tethyan ocean of the Late Cambrian-Early Ordovician rhyolite from Zhakang area in the Lhasa terrane

作　　者：陈红灿 解超明[1,2,3] 张家俊 白希泰 段梦龙 CHEN Hongcan;XIE Chaoming;ZHANG Jiajun;BAI Xitai;DUAN Menglong(College of Earth Science,Jilin University,Changchun 130061,Jilin,China;Key Laboratory of Mineral Resources Evaluation in Northeast Asia,Ministry of Land and Resources of China,Changchun 130061,Jilin,China;Research Center for Qinghai-Tibetan Plateau,Jilin University,Changchun 130061,Jilin,China)

机构地区：[1]吉林大学地球科学学院,吉林长春130061 [2]东北亚矿产资源评价自然资源部重点实验室,吉林长春130061 [3]吉林大学青藏高原地质研究中心,吉林长春130061

出　　处：《地质通报》2025年第2期441-458,共18页Geological Bulletin of China

基　　金：国家自然科学基金项目《唐加-松多蛇绿岩及对青藏高原古特提斯洋演化制约》(批准号:42172226)。

摘　　要：【研究目的】青藏高原南部早古生代岩浆作用对于揭示冈瓦纳大陆北缘的大陆边缘性质及原特提斯洋的俯冲过程具有重要的研究意义,通过对拉萨地块申扎县北部扎扛地区发现的晚寒武世—早奥陶世流纹岩进行研究,探讨该流纹岩的岩石成因及地质意义,为进一步约束申扎地区扎扛不整合时限,并为认识冈瓦纳大陆北缘在早古生代的地质演化过程提供依据。【研究方法】对青藏高原北拉萨地块申扎县北部扎扛地区流纹岩的LA-ICP-MS锆石U-Pb年龄、锆石Hf同位素及地球化学进行研究。【研究结果】流纹岩的锆石^(206)Pb/^(238)U年龄加权平均值为485±5 Ma,样品显示出高硅、富碱、富铝、低磷、低镁等地球化学特征,SiO_(2)含量为75.10%~77.39%,Al_(2)O_(3)含量为10.74%~12.90%,K_(2)O+Na_(2)O为6.65%~7.99%,P2O5含量介于0.03%~0.11%之间,MgO含量为0.27%~0.35%,A/CNK值为1.20~1.61,大于1.1,为强过铝质钾玄岩岩石系列。扎扛流纹岩表现出轻稀土元素富集,重稀土元素元素相对平坦的特征,有较明显的轻、重稀土元素分馏,并伴随强烈的负Eu异常(δEu=0.44~0.48),扎扛流纹岩具有较高的Rb(368.43×10^(-6)~489.42×10^(-6))含量,Zr/Hf(31.97~37.35)、Nb/Ta(12.17~15.32)值较低,指示其在形成过程中发生了强烈的结晶分异作用,在SiO_(2)-Zr图解及ACF图解中,样品落入S型花岗岩区域,显示出高分异S型花岗岩的特征;锆石ε_(Hf)(t)值变化范围较小,介于-2.0~-5.5之间,平均为-3.7,均为负值,指示其可能是地壳部分熔融的产物,Hf同位素二阶段模式年龄为1581~1752 Ma,表明中元古代地壳物质可能为其岩浆源区。【结论】综合前人研究资料及样品特征,扎扛地区晚寒武世—早奥陶世流纹岩可能形成于原特提斯洋洋壳向冈瓦纳大陆北缘俯冲的构造背景之下。[Objective]The Early Paleozoic magmatisms in the southern Qinghai-Tibet Plateau are important for researching the nature of the continental margin of the northern margin of the Gondwana continent and the subduction process of the Proto-Tethys Ocean.Based on the reaserch of the Late Cambrian-Early Ordovician rhyolite found in the Zhakang area in the northern part of Xainza County,Lhasa block,this paper discusses the petrogenesis and geological significance of the rhyolite,so as to further constrain the time limit of the Zhakang unconformity in the Xainza area,and provide a basis for understanding the geological evolution process of the northern margin of the Gondwana continent in the Early Paleozoic.[Methods]In this study,we report the zircon U-Pb age,rock geochemistry and zircon Hf isotope analysis of rhyolites in Zhakang area,northern Xainza County,Lhasa Block,Qinghai-Tibet Plateau.[Results]The results show that the weighted average age of zircon ^(206)Pb/^(238)U of rhyolite is 485±5 Ma.The rock geochemistry shows high silicon,rich alkali,rich aluminum,low phosphorus and low magnesium.The content of SiO_(2) is 75.10%~77.39%,the content of Al2O3 is 10.74%~12.90%,the content of K_(2)O+Na_(2)O is 6.65%~7.99%,the content of P2O5 is 0.03%~0.11%,the content of MgO is 0.27%~0.35% and the A/CNK is 1.20~1.61,which is greater than 1.1.It belongs to a set of strongly peraluminous shoshonite series.The character in rare earth elements of the rhyolite is enrichment of light rare earth elements and relatively flat right-inclined curve of heavy rare earth elements.The fractionation of light and heavy rare earth elements is obvious,accompanied by obvious negative Eu anomalies(δEu=0.44~0.48).The Zhakang rhyolite has high Rb(368.43×10^(-6)~489.42×10^(-6))content,low Zr/Hf(31.97~37.35)and Nb/Ta(12.17~15.32)values,indicating that strong crystallization differentiation occurred during its formation.In the SiO_(2)-Zr diagram and ACF diagram,the samples fell into the S-type granite area,showing the characteristics of highly differ

关 键 词：青藏高原 扎扛地区 流纹岩 地球化学 锆石U-Pb年龄 

分 类 号：P534.4[天文地球—古生物学与地层学] P588.141[天文地球—地质学] P597.3