西秦岭凤县北部罗汉寺岩组沉积时代和源区特征:来自LA-ICP-MS锆石U-Pb年龄证据  

A study of the provenance and sedimentary age of the Luohansi Formation in the Fengxian County, eastern part of West Qinling orogenic belt: evidence from LA-ICP-MS zircon U-Pb ages

作　　者：张亚峰 陈国超[2,3] 杨玲 易鹏飞 姚征 赵端昌 杨涛 张振凯 杜彪 ZHANG Yafengn;CHEN Guochao;YANG Ling;YI Pengfei;YAO Zheng;ZHAO Duanchang;YANG Tao;ZHANG Zhenkai;DU Biao(Shaanxi Mineral Resources and Geological Survey Xi'an,Shannxi 710068,China;Key Laboratory of Western China's Mineral Resources and Geological Engineering,Ministry of Education,Xi'an,Shannxi 710054,China;School of Civil Engineering Nanyang Institute of Technology,Nanyangy Henan 473000,China;Shaanxi geological survey experiment center,Xi'an,Shannxi 710054,China;Shaanxi satellite application center for Natural Resources,Xi'an,Shannxi 710119,China)

机构地区：[1]陕西省矿产地质调查中心,陕西西安710068 [2]长安大学西部矿产资源与地质工程教育部重点实验室,陕西西安710054 [3]南阳理工学院土木工程学院,河南南阳473000 [4]陕西省地质调查实验中心,陕西西安710054 [5]自然资源陕西省卫星应用技术中心,陕西西安710119

出　　处：《地质学报》2022年第3期805-823,共19页Acta Geologica Sinica

基　　金：陕西省地质调查财政专项(编号20150101和201918);自然资源部成矿作用与资源评价重点实验室开放基金项目(编号ZS006);自然资源部东北亚矿产资源评价重点实验室开放课题基金项目(编号DBY-KF-19-10)联合资助的成果。

摘　　要：秦岭造山带罗汉寺岩组的形成时代长期存在争议。选择西秦岭东段凤县北部罗汉寺岩组凝灰岩和浅变质碎屑岩为研究对象,运用LA-ICP-MS锆石U-Pb同位素年代学方法,探讨罗汉寺岩组的形成时代和物源特征。结果显示,罗汉寺岩组下部a岩段中凝灰岩结晶年龄为407±10 Ma;上部碎屑岩段(c岩段)中千枚岩碎屑锆石年龄介于2658-420 Ma之间,主要包括490-420 Ma和997-639 Ma两个区间峰值年龄,其次为1557-1318 Ma、2484-1745 Ma,另有少量2650 Ma左右年龄值。结合区域地质资料,限定罗汉寺岩组主体形成时代为早—中泥盆世。研究同时表明,罗汉寺岩组物源具有明显的多元性,490-420 Ma年龄组的锆石主体来自于商丹洋俯冲作用形成的弧岩浆岩;997-639 Ma年龄组可进一步细分为843-639 Ma和997-867 Ma,前者主要来自于南秦岭构造带,后者主要来自于北秦岭构造带;2658-1318 Ma的中元古代—新太古代年龄组与北秦岭构造带、华北板块和扬子板块的岩浆活动相关。综合分析认为南秦岭和北秦岭地块早—中泥盆世时期尚未全面碰撞成陆,商丹洋为残留洋(海)盆。There has been considerable controversy over the formation age of the Luohansi Formation in Qinling orogenic belt. Based on the LA-ICP-MS zircon U-Pb isotopic dating, the formation age and material source of the Luohansi Formation have been analyzed from tuff and epi-metamorphic detrital rocks, in the eastern part of West Qinling orogenic belt. The results show that the crystallization age of the tuff in Member a of the Luohansi Formation is 407±10 Ma. The captured zircon ages of phyllite detrital zircon in upper clastic member(Member c) range from 2658 to 420 Ma, mainly including the peak ages of 490-420 Ma and 997-639 Ma, followed by 1557-1318 Ma and 2484-1745 Ma, and a small amount of about 2650 Ma. Combined with the regional geological data, the primary formation age of the Luohansi Formation is defined as Early―Middle Devonian. The study also shows that the material source of the Luohansi Formation is diverse. The age group from 490-420 Ma comes from magmatic arc rocks formed by the Shangdan ocean subduction;the 997-639 Ma age group can be further subdivided into 843-639 Ma and 997-867 Ma, the former mainly comes from the South Qinling tectonic belt, the latter mainly comes from the North Qinling tectonic belt. The 2658-1318 Ma age group of the middle Proterozoic Neoarchean is related to magmatic activities in the North Qinling tectonic belt, North China plate and Yangtze plate. Comprehensive analysis shows that the South Qinling and North Qinling blocks did not ultimately collide into land during the Early-Middle Devonian, and the Shangdan ocean is a residual ocean basin.

关 键 词：锆石U-Pb定年 物源分析 罗汉寺岩组 凤县 西秦岭造山带 

分 类 号：P597.3[天文地球—地球化学] P542[天文地球—地质学]