哀牢山构造带新元古代双峰式岩浆岩的锆石U-Pb年代学、元素-同位素地球化学特征及构造意义  

Neoproterozoic Bimodal Magmatism in the Ailaoshan Tectonic Belt:New Zircon U-Pb Geochronology,Whole-rock Geochemistry,and Tectonic Implications

作　　者：苏路路 魏月华 杨朝 刘桂春 刘嵘[3] 訾建威 SU Lulu;WEI Yuehua;YANG Zhao;LIU Guichun;LIU Rong;ZI Jianwei(State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences(Wuhan),Wuhan 430074,Hubei,China;Yunnan Institute of Geological Survey,Kunming 650216,Yunnan,China;School of Earth Sciences,China University of Geosciences(Wuhan),Wuhan 430074,Hubei,China;John de Laeter Centre,Curtin University,Bentley WA 6102,Australia)

机构地区：[1]中国地质大学(武汉)地质过程与矿产资源国家重点实验室,湖北武汉430074 [2]云南省地质调查院,云南昆明650216 [3]中国地质大学(武汉)地球科学学院,湖北武汉430074 [4]John de Laeter Centre,Curtin University,Bentley WA 6102,Australia

出　　处：《大地构造与成矿学》2024年第5期1148-1166,共19页Geotectonica et Metallogenia

基　　金：国家自然科学基金项目(41873062,42162020)资助。

摘　　要：分布于扬子克拉通西缘的新元古代岩浆岩对研究华南陆块的前寒武纪演化及其与Rodinia超大陆的关系意义重大,但由于该区域后期构造-热历史的复杂性,关于一些重要岩石单元的时代、属性和构造背景仍存在诸多争议。本文聚焦哀牢山构造带南段的桃家寨岩体,报道了来自该岩体的一套变基性岩和钠长花岗岩组合的年代学和地球化学组成,以期为解决现存争议提供新的证据和约束。SHRIMP原位锆石U-Pb同位素测年表明变基性岩和钠长花岗岩的结晶年龄分别为756±9 Ma和763±23 Ma,表明二者为同期岩浆作用的产物,其合并加权平均年龄759±7 Ma(MSWD=0.88,n=8)代表了岩浆事件年龄;同时,来自两件样品的锆石都记录了~730 Ma的岩浆后热扰动事件。变基性岩具有低碱(Na2O+K2O=0.17%~0.36%),高Mg#(76~79)的地球化学特征,略富集轻稀土元素(LREEs),并具有弱的Nb-Ta负异常和正的ε_(Nd)(t)值(+2.67~+3.10),表明其来自E-MORB型富集地幔岩浆源区,可能经历了俯冲板片流体或者熔体的改造。钠长花岗岩显示高碱(Na_(2)O+K_(2)O=6.70%~8.30%)、富集LREEs和大离子亲石元素(LILEs)、亏损重稀土元素(HREEs)等特点,具有负的ε_(Nd)(t)值(-2.43~-1.26),表明其母岩浆可能源自下地壳物质部分熔融与基性熔体的混合。综合前人研究,发现桃家寨岩体的岩石组合具有双峰式特点,并在地球化学特征上显示典型的弧-弧后盆地属性;岩浆作用峰期~760 Ma,指示其为新元古代扬子克拉通西缘的洋陆俯冲构造体系的一部分,从而为将华南陆块置于Rodinia外围的超大陆重建模式提供了新的证据。Neoproterozoic magmatic rocks distributed within the western margin of the Yangtze Craton are of great importance for understanding the Precambrian evolution of South China and its position within the Rodinia configuration.However,due to repeated tectono-thermal overprinting and modification of the region by later geological events,the age,petrogenesis,and tectonic properties of some of the rock units remain contentious.In this study,we focus on the Taojiazhai pluton,the most prominent igneous feature in the southern part of the Ailaoshan belt.We present zircon U-Pb geochronology and geochemistry data for a suite of meta-mafic and granitic rocks newly identified in the pluton,and offer new insights into the nature and geodynamic setting of the pluton.SHRIMP U-Pb dating of zircon from meta-mafic and granite samples yielded weighted mean_(2)06Pb/238U ages of 756±9 Ma and 763±23 Ma,respectively,with a combined mean age at 759±7 Ma(MSWD=0.88,n=8),confirming the emplacement of the pluton at ca.760 Ma.In addition,zircon crystals from both samples recorded younger concordant ages at ca.730 Ma(726±10 Ma,MSWD=0.36,n=4),indicating Pb loss shortly after crystallization.The meta-mafic rocks are characterized by low SiO_(2)(44.34%-45.01%),low alkalis(Na_(2)O+K_(2)O=0.17%-0.36%),high Na_(2)O/K_(2)O(3.33-6.10),and high Mg#(76-79).They have slightly enriched light rare earth elements(LREEs),large-ion lithophile elements(LILEs),and weakly negative Nb-Ta anomalies.These features,together with their positiveε_(Nd)(t)(+2.67-+3.10)and low(87 Sr/86 Sr)i(0.7046-0.7067),indicate an E-MORB-type mantle source.Multi-element discrimination diagrams suggest that the meta-mafic rocks were formed in a back-arc basin setting.The albite-granite samples have high SiO_(2)(71.81%-74.92%)and Na_(2)O/K_(2)O(3.35-10.25),and are peraluminous in composition(A/CNK=1.00-1.30).They show pronounced Nb-Ta depletion,enrichment of LREEs relative to HREEs,and slightly enriched Nd isotopic signatures(ε_(Nd)(t)=−2.43-−1.26),indicating that the granite w

关 键 词：哀牢山构造带 桃家寨岩体 新元古代 双峰式岩浆岩 SHRIMP锆石U-PB年代学 地球化学 

分 类 号：P595[天文地球—地球化学] P597[天文地球—地质学]