粤西北印支期太保岩体的锆石U-Pb年代学、地球化学及岩石成因  

Zircon Geochronology, Geochemistry and Petrogenesis of the Taibao Pluton in Northwest Guangdong Province

作　　者：李响[1,2] 王令占[1,2] 涂兵[1,2] 田洋[1,2] 谢国刚[1] 张楗钰[1] 张宗言[1] Li Xiang;Wang Lingzhan;Tu Bing;TianYang-;Xie Guogang;Zhang Jianyu;Zhang Zongyan(Wuhan Center of China Geological Survey,Wuhan 430205,China;Research Center for Petrogenesis and Mineralization of Granitoids Rocks,China Geological Survey,Wuhan 430205,China)

机构地区：[1]中国地质调查局武汉地质调查中心,湖北武汉430205 [2]中国地质调查局花岗岩成岩成矿研究中心,湖北武汉430205

出　　处：《地球科学》2021年第4期1199-1216,共18页Earth Science

基　　金：中国地质调查局项目(Nos.12120113063200,DD20201121)。

摘　　要：华南早中生代构造-岩浆演化还存在不同的争议.以广东西北部连山地区晚三叠世含暗色微粒包体(MMEs)的太保岩体为研究对象,进行了岩石学、锆石U-Pb年代学、地球化学和Sr-Nd-Hf同位素组成研究.4个花岗岩样品的锆石^(206)Pb/^(238)U加权平均年龄分别为219.8±1.8 Ma、220.5±1.0 Ma、221.5±1.7 Ma和220.2±1.1 Ma,为印支晚期岩浆作用的产物.地球化学分析显示,寄主花岗岩为高钾钙碱性花岗岩,低硅、高碱,铝饱和指数A/CNK值为0.79~1.16.包体SiO_(2)含量为55.13%~62.56%,铁、镁含量明显高于寄主花岗岩,MgO和FeO^(T)含量分别为2.31%~4.60%和5.53%~6.63%.包体与寄主花岗岩均富集轻稀土,并表现出显著的Ba、Sr、Ti负异常.寄主花岗岩和包体均具有较高的ε_(Nd)(t)值(-3.42~-2.60和-0.90~-0.52)和较小的二阶段Nd模式年龄(T_(DM2)分别为1.30~1.35 Ga、1.10~1.13 Ga).寄主花岗岩具有较宽泛的εHf(t)值(-2.6~+4.3,平均值为+0.7)和两阶段Hf模式年龄(0.95~1.39 Ga)变化范围,指示太保岩体形成于中元古代下地壳变基性岩物质的熔融,并与亏损地幔物质发生岩浆混合作用.基于以上数据,笔者认为太保岩体是印支晚期伸展条件下亏损地幔和下地壳物质混合的产物.结合近年来报道的邻近区域的基性岩浆活动,认为华南古特提斯构造域向古太平洋构造域的转换可能开始于晚三叠世(233 Ma).The tectono-magmatic evolution of the South China block during Early Mesozoic remains controversial.In this paper,it conducts the comprehensive study of petrology,zircon U-Pb geochronology,whole-rock element and Sr-Nd-Hf isotopic geochemistry for Late Triassic Taibao pluton with mafic microgranular enclaves (MMEs) in the Lianshan area,located in the northwest Guangdong Province.LA-ICP-MS U-Pb zircon analysis yielded^(206)Pb/^(238)U weighted mean ages of 219.8±1.8 Ma,220.5±1.0 Ma,221.5±1.7 Ma and 220.2±1.1 Ma for four granite samples respectively,indicating that the pluton was formed during the Late Indosinian period.The host rocks are high K calc-alkaline granite,with lower SiO_(2),higher total alkalis and A/CNK values ranging in 0.79-1.16.The mafic microgranular enclaves show lower SiO_(2),higher FeO,MgO with contents of55.13%-62.56%,2.31%-4.60%and 5.53%-6.63%,respectively.Both of them show enrichment in light rare earth elements,and depletion in Ba,Sr,and Ti.They have relatively low ε_(Nd)(t) values(-3.42 to-2.60 and-0.90 to-0.52)and younger Nd model ages (T_(DM2)=1.30-1.35 Ga and 1.10-1.13 Ga,respectively).Zircon ε_(Hf)(t) values of the host rocks are scattered (-2.6-+4.3,with average value of+0.7) and the corresponding two-stage model ages are 0.95-1.39 Ga.The results suggest that the Taibao host granodioritic rocks and the MMEs were likely produced by mixing of depleted mantle and lower crust-derived magmas,under the post-orogenic (Indosinian) extensional tectonic setting.These results,considered with the coetaneous basic magmatic activities in the adjacent area,indicate that the transition from the Paleo-Tethys to the Paleo-Pacific tectonic regimes of the South China block occurred during the Late Triassic (233 Ma).

关 键 词：太保岩体 闪长质包体 年代学 SR-ND-HF同位素 中生代构造转换 华南板块 

分 类 号：P597[天文地球—地球化学]