摘要
金沙江缝合带内地质构造单元组成多样,岩浆作用复杂,关于其初始碰撞时间和碰撞后伸展时限还存在较大的争议。本文利用锆石U-Pb年代学和岩石地球化学分析方法,选取金沙江缝合带中北段贡觉地区二长岩和花岗斑岩进行研究,分析岩体的形成时代、岩石成因、物质来源以及构造背景。研究表明,贡觉二长岩属于钾玄岩系列的I型花岗岩,成岩年龄为(250±1)Ma;岩体富集轻稀土元素,Mg#值为28~30,Rb/Sr比值为0.07~0.11,Nb/La比值为0.43~0.49,为下地壳基性变火成岩物质发生部分熔融形成的产物;成岩环境为俯冲末期至碰撞早期地壳隆升增厚的环境。贡觉花岗斑岩属于中钾钙碱性系列的S型花岗岩,成岩年龄为(244±2)Ma;岩体Mg#值介于26~29,FeO^(T)/MgO比值为4.43~4.98,Al_(2)O_(3)/TiO_(2)比值为47.57~51.12,CaO/Na_(2)O比值为0.28~0.49,为地壳变杂砂岩部分熔融形成的产物;成岩环境为碰撞后的伸展环境。综合分析金沙江缝合带内二叠纪—中三叠世的花岗岩类的年代学、Hf同位素及地球化学数据,并结合前人研究成果,认为金沙江缝合带俯冲—碰撞—伸展的构造–岩浆作用过程中,地壳物质越来越多地参与到了岩浆源区。
The Jinsha River suture zone is characterized by diverse geological structures and complex magmatic processes.There are considerable controversies about the timing of its initial collision and subsequent extension time limit.This paper uses zircon U-Pb dating and rock geochemical analysis methods to study the monzonite and granite porphyry in the Gonjo area in the mid-north section of the Jinsha River suture zone,analyzing the formation age,rock origin,material source,and tectonic setting of the rock mass.Research shows that Gonjo monzonite belongs to the shoshonite series and is classified as I-type granite,with a diagenetic age of(250±1)Ma.The rock mass is enriched in light rare earth elements,with Mg#values ranging from 28 to 30,Rb/Sr ratios from 0.07 to 0.11,and Nb/La ratios from 0.43 to 0.49,indicating that it is the product of partial melting of basic metavolcanic materials in the lower crust.The diagenetic environment is a tectonic environment in which the crust uplifts and thickens during the end of subduction to the early collision period.Gonjo granite porphyry belongs to the medium-potassium calc-alkaline series of S-type granite,with a crystallization age of(244±2)Ma.The Mg#values of the rock range from 26 to 29,with FeO^(T)/MgO ratios between 4.43 and 4.98,Al_(2)O_(3)/TiO_(2) ratios of 47.57~51.12,and CaO/Na_(2)O ratios between 0.28 and 0.49,indicating that it is the product of partial melting of the crustal metasandstone.The diagenetic environment is an extensional tectonic environment after collision.Based on the geochronological data,Hf isotope,and geochemical data of the Permian–Middle Triassic granitic rocks within the Jinsha River suture zone,and in combination with previous research results,it is believed that during the process of subduction,collision,and extension of the Jinsha River orogenic belt,more and more crustal materials participated in the magma source region.
作者
杨礼创
唐渊
祝向平
李勇
吴昊
吴波
YANG Lichuang;TANG Yuan;ZHU Xiangping;LI Yong;WU Hao;WU Bo(College of Earth and Planetary Sciences,Chengdu University of Technology,Chengdu 610059,China;Chengdu Center,China Geological Survey(Geosciences Innovation Center of Southwest China),Chengdu 610218,China)
出处
《沉积与特提斯地质》
北大核心
2025年第1期168-186,共19页
Sedimentary Geology and Tethyan Geology
基金
中国地质调查局项目(DD20240026,DD20221635)。
关键词
金沙江缝合带
初始碰撞
碰撞后伸展
I型花岗岩
S型花岗岩
Jinsha River suture zone
initial collision
post-collision extension
I-type granite
S-type granite
作者简介
杨礼创(1997-),男,矿物学、岩石学、矿床学专业硕士研究生。E-mail:903646335@qq.com;通信作者:唐渊(1985-),女,正高级工程师,主要从事构造地质学研究。E-mail:tyvienna@163.com。
