松潘—甘孜造山带南缘青海省秋智地区晚三叠世花岗岩体成因及构造背景  

Petrogenesis and Tectonic Setting of Late Triassic Granites in Qiuzhi Area,Qinghai Province,Southern Margin of Songpan-Garze Orogenic Belt

作　　者：曹锦山 张新远[1] 欧阳光文[1] 王春涛[1] 刘建栋[1] 李五福[1] Cao Jinshan;Zhang Xinyuan;Ouyang Guangwen;Wang Chuntao;Liu Jiandong;Li Wufu(Laboratory of Geological Process and Mineral Resources in Northern Qinghai-Tibet Plateau/Qinghai Institute of Geological Survey,Xining 810012,China)

机构地区：[1]青海省青藏高原北部地质过程与矿产资源重点实验室/青海省地质调查院,西宁810012

出　　处：《吉林大学学报(地球科学版)》2025年第2期483-502,共20页Journal of Jilin University:Earth Science Edition

基　　金：国家自然科学基金项目(42362006);中国科学院广州地球化学研究所委托项目(2019QZKK0702)。

摘　　要：松潘—甘孜造山带内广泛发育印支期花岗岩小岩体或岩株。本文以松潘—甘孜造山带南缘青海省秋智地区花岗岩体为研究对象,通过岩相学、锆石U-Pb年代学、锆石Lu-Hf同位素、全岩Sr-Nd同位素及全岩地球化学研究,探讨了岩石成因及构造背景。结果表明:秋智地区花岗岩体主要为花岗闪长岩,具弱富钠(Na_(2)O/K_(2)O=0.97~1.34)、低铝饱和指数(A/CNK=0.99~1.08)的特征,属弱过铝质钙碱性系列花岗岩;稀土元素图解具有轻稀土元素富集、重稀土元素亏损的右倾特征;富集Rb、K、U、Th、La、Ce、Nd、Zr、Hf、Y,亏损Ba、Sr、Ta、Nb、P、Ti;花岗闪长岩锆石^(206)Pb/^(238)U加权平均年龄为(215.4±1.4)Ma(MSWD=1.05,n=23),代表成岩时代为晚三叠世;锆石Hf同位素初始值(^(176)Hf/^(177)Hf)_(i)介于0.282377~0.282437之间,ε_(Hf)(t)值为-9.44~-7.19,二阶段模式年龄(T_(DM2))为1840~1702 Ma;全岩Sr同位素初始值(^(87)Sr/^(86)Sr)_(i)为0.709783~0.710530,ε_(Nd)(t)为-8.2~-7.8,二阶段模式年龄(T_(DM2))介于1659~1630 Ma之间,显示岩浆源区为古老地壳物质的部分熔融,具有钙碱性I型花岗岩特征。综合区域地质资料及岩石球化学特征等研究,认为秋智花岗岩体是晚三叠世后碰撞构造背景下,岩石圈拆沉、软流圈物质上涌导致下地壳部分熔融的产物。During the Indosinian period,small granitic bodies or stocks were wildly developed in the Songpan-Garze orogenic belt.This study focuses on the granitic body in Qiuzhi area of Qinghai Province,located along the southern margin of Songpan-Garze orogenic belt.The petrogenesis and tectonic setting of the granitic body are discussed through petrography,zircon U-Pb chronology,zircon Lu-Hf isotope,Sr-Nd isotope of whole rock and whole rock geochemistry.The results show that the granites in Qiuzhi area are mainly granodiorite,characterized by weak sodium enrichment(Na_(2)O/K_(2)O=0.97-1.34)and a low aluminum saturation index(A/CNK=0.99-1.08),thus classified as weak peraluminous calc-alkaline series granites.Rare earth element patterns show enrichment of light rare earth elements and depletion of heavy rare earth elements,along with a right-leaning distribution.The rocks are enriched in Rb,K,U,Th,La,Ce,Nd,Zr,Hf and Y,while being depleted in Ba,Sr,Ta,Nb,P and Ti.The weighted average age of granodiorite zircon^(206)Pb/^(238)U is(215.4±1.4)Ma(MSWD=1.05,n=23),indicating a Late Triassic diagenetic age.Zircon Hf isotopic values(^(176)Hf/^(177)Hf)i range from 0.282377 to 0.282437,withε_(Hf)(t)between-9.44 and-7.19,and two-stage model ages(T_(DM2))from 1840 to 1702 Ma.The initial Sr isotope values(^(87)Sr/^(86)Sr)i of whole rock range from 0.709783 to 0.710530,ε_(Nd)(t)ranges from-8.2 to-7.8,and the two-stage model ages(T_(DM2))range from 1659 to 1630 Ma.These findings suggest that the magma source is the partial melting of the ancient crust material,exhibiting characteristics of calc-alkaline I type granite.By correlating regional geological data with the geochemical characteristics of the petrosphere,it is concluded that Qiuzhi granitic body is a product of lithospheric delamination,asthenosphere material upwelling,and lower crustal partial melting within the background of Late Triassic post-collision environment.

关 键 词：松潘-甘孜造山带 后碰撞 锆石U-Pb年代学 锆石Lu-Hf同位素 SR-ND同位素 晚三叠世 Ⅰ型花岗岩 地球化学 

分 类 号：P571[天文地球—矿物学] P597[天文地球—地质学]