扬子地块西缘中元古代晚期辉长岩成因及地质意义:来自锆石U-Pb-Hf同位素和全岩地球化学的约束  

Petrogenesis and geological significance of Late Mesoproterozoic gabbro in the western Yangtze Block:Constrains from zircon U-Pb-Hf isotopes and whole-rock geochemistry

作　　者：薛文斌 赖绍聪[1] 朱毓 秦江锋[1] 朱韧之 刘敏 杨航 XUE Wenbin;LAI Shaocong;ZHU Yu;QIN Jiangfeng;ZHU Renzhi;LIU Min;YANG Hang(State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi’an 710069,China)

机构地区：[1]西北大学地质学系/大陆动力学国家重点实验室,陕西西安710069

出　　处：《西北大学学报（自然科学版）》2024年第4期696-714,共19页Journal of Northwest University（Natural Science Edition）

基　　金：国家自然科学基金(42172056);国家自然科学基金青年基金(42202048);陕西省自然科学基金(2024JC-YBMS-235)。

摘　　要：对扬子地块西缘锦川地区辉长岩进行系统的锆石U-Pb-Hf同位素、全岩主微量元素和Sr-Nd同位素分析,旨在探讨其岩石成因及地质意义。年代学分析结果表明,锦川辉长岩的锆石U-Pb年龄为(1041.1±1.1)Ma。全岩地球化学特征显示,锦川辉长岩具有较低的SiO_(2)(50.26%~51.16%)、CaO(6.59%~7.64%)、K_(2)O(1.22%~1.96%)质量分数以及较高的Al_(2)O_(3)(16.38%~17.15%)和TiO_(2)(2.61%~2.80%)质量分数,属于低钾拉斑玄武质岩石系列。岩石总体上相对富集轻稀土元素和大离子亲石元素(如Ba、Sr),亏损重稀土元素和高场强元素(如Nb、Ta和Th),并且显示弱的Eu异常(δEu=0.99~1.11)。同时,锦川辉长岩具有低的全岩εNd(t)值(-3.61~-2.75)和正的锆石εHf(t)值(+1.62~+7.58)。上述特征表明,锦川辉长岩应起源于已保存在岩石圈地幔中的先期(中元古代中期)俯冲流体交代过的富集地幔源区。结合扬子地块西缘同期广泛发育的A型花岗岩和板内玄武质岩浆作用,认为锦川辉长岩应形成于被动大陆边缘背景下的陆内裂谷环境,代表了Rodinia超大陆在中元古代晚期局部拉张构造体制下的岩浆响应。This study presents systematic analysis of zircon U-Pb-Hf isotopes,whole-rock major and trace elements,and Sr-Nd isotopes of the Jinchuan gabbros,aiming to explore its petrogenesis and geological significance.The Jinchuan gabbros has Zircon U-Pb age of 1041.1±1.1 Ma,it has moderate SiO_(2)(50.26%to 51.16%),CaO(6.59%to 7.64%),K_(2)O(1.22%to 1.96%)contents,with high Al_(2)O_(3)(16.38%to 17.15%)and TiO_(2)(2.61%to 2.80%)contents,belonging to low-K tholeiite rocks.These gabbros were enriched in light rare earth elements and large ionic lithophile elements(e.g.,Ba,Sr),as well as depleted in heavy rare earth elements and high field strength elements(e.g.,Nb,Ta,Th),with weak Eu anomalies(δEu=0.99 to 1.11).They have negativeεNd(t)values(-3.61 to-2.75)and positive zirconεHf(t)(+1.62 to+7.58)contents.These geochemical features indicate the Jinchuan gabbros were originated from the enriched mantle source that metasomatized by middle Mesoproterozoic subduction fluids preserved in the lithosphere mantle.Combined with the coeval A-type granites and intra-plate basaltic magmatism,the Jinchuan gabbros formed in an intracontinental rift environment under a passive continental margin,representing the magmatic response of the Rodinia supercontinent under local extensional tectonic mechanism during the late Mesoproterozoic.

关 键 词：扬子地块西缘 中元古代晚期 辉长岩 岩石成因 地质意义 

分 类 号：P588.1[天文地球—岩石学]