伊犁地块北缘早志留世辉绿岩脉岩石成因与构造启示:年代学与地球化学制约  

Petrogenesis and tectonic implications of Early Silurian diabasic dikes in the northern margin of the Yili Block:Constraints from geochronology and geochemistry

作　　者：陈有炘[1] 王盟 马晓伟 魏星 裴先治[1] 朱生强 曹明 布龙巴特 CHEN YouXin;WANG Meng;MA XiaoWei;WEI Xin;PEI XianZhi;ZHU ShengQiang;CAO Ming;BULONG BaTe(School of Earth Science and Resources,Chang an University,MOE Key Laboratory of Western China's Mineral Resources and Geological Engineering,Xi'an 710054,China;The Fifth Oil Production Plant,Changqing Oilfield Company,PetroChina,Xi'an 710200,China;Center of Urumqi Natural Resources Comprehensive Survey,CGS,Urumqi 830057,China)

机构地区：[1]长安大学地球科学与资源学院,西部矿产资源与地质工程教育部重点实验室,西安710054 [2]中国石油长庆油田第五采油厂,西安710200 [3]中国地质调查局乌鲁木齐自然资源综合调查中心,乌鲁木齐830057

出　　处：《岩石学报》2023年第8期2429-2444,共16页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41802234、42072267);陕西省自然科学基础研究计划项目(2023-JC-YB-237);中央高校基本科研业务费专项资金项目(300102271207);陕西高校青年创新团队和中国地质调查局项目(12120115041301)联合资助。

摘　　要：伊犁地块北缘发育新元古代、石炭纪等多期基性岩脉,记录了区域构造体制转换过程的重要信息。本文报道了在伊犁地块北缘温泉县乌斯图一带出露的前寒武纪变质岩系中新识别出早志留世辉绿岩脉及其围岩锆石U-Pb年龄与Hf同位素、岩石地球化学及全岩Sr-Nd同位素组成,并探讨了岩石成因及其构造意义。辉绿岩锆石U-Pb年龄为442±7Ma,形成于早志留世;围岩(淡色花岗岩)锆石U-Pb年龄为901±3Ma,形成于新元古代早期。辉绿岩样品具有较高的Fe_(2)O_(3)T(8.34%~9.81%)、全碱含量(K_(2)O+Na_(2)O=5.72%~6.86%)和较低的MgO(3.69%~4.38%)和TiO2(1.69%~2.00%)含量,属于高钾钙碱性系列岩石。岩石富集大离子亲石元素(LILEs,如Rb、Th、U、K),亏损高场强元素(HFSEs,如Nb、Ta、Ti),具有较低的Nb/Th比值(0.13~1.16)、Nb/La比值(0.42~0.45)及较高的Zr/Hf比值(39.6~42.2),锆石εHf(t)值介于+3.0~+9.1,全岩εNd(t)值介于+1.9~+3.6,暗示其来源于受俯冲流体改造的岩石圈地幔,源区岩石主要为尖晶石二辉橄榄岩和石榴石二辉橄榄岩。同时,岩石具有较低的Mg#值(49.6~52.5)和Cr(39.8×10^(-6))、Ni(17.1×10^(-6))含量,表明岩浆的演化过程中经历了镁铁质矿物的分离结晶,受地壳混染作用不明显。岩石Zr(212×10^(-6)~242×10^(-6))、Hf(5.16×10^(-6)~6.02×10^(-6))、Nb(6.69×10^(-6)~9.24×10^(-6))、Ta(0.60×10^(-6)~0.81×10^(-6))元素含量及Zr/Y(5.21~6.82)、Hf/Th(0.69~0.91)比值等指示辉绿岩脉形成于伸展环境,可能与奥陶纪末阿克陶-温泉微地块拼贴到伊犁地块后诱发的俯冲板片角度变化或构造体制转换而导致的伸展构造背景有关。Multi-period basic dikes,including Neoproterozoic and Carboniferous ones,are exposed in the northern margin of the Yili Block,which provide important information for revealing the transformation process of regional tectonic system.Recently,we have identified several Early Silurian diabasic dikes in the Precambrian metamorphic rocks outcropped in the northern margin of the Yili Block in Wustu area,Wenquan County.This paper reports the zircon U-Pb ages and Lu-Hf isotopic compositions and the whole-rock geochemical and Sr-Nd isotopic compositions of these diabasic dikes and their surrounding rocks,from which the genesis of the diabase and their tectonic significance are also discussed.One diabase sample yielded a mean zircon U-Pb age of 442±7Ma and positive zirconεHf(t)values of+3.0~+9.1,while a leucogranite sample in its surrounding area yielded a mean zircon U-Pb age of 901±3Ma.Geochemically,the diabase samples have high Fe 2O 3 T(8.34%~9.81%)and K 2O+Na 2O(5.72%~6.86%)contents,low MgO(3.69%~4.38%)and TiO 2(1.69%~2.00%)contents,demonstrating that they belong to the high-K calc-alkaline series.Furthermore,they are enriched in large ion lithophile elements(LILEs,such as Rb,Th,U and K),and have negative anomalies in the high-field-strength elements(HFSEs,such as Nb,Ta and Ti)with low Nb/Th(0.13~1.16)and Nb/La(0.42~0.45)and high Zr/Hf(39.6~42.2)ratios.They also have high initial 87 Sr/86 Sr ratios(0.707369~0.708637)and positiveεNd(t)values(+1.9~+3.6).The analysis results indicate that they were sourced from a metasomatic sub-continental lithospheric mantle,and the mineralogical assemblage of their primary rocks is mainly composed of spinel iherzolite and garnet iherzolite.Simultaneously,they have low Mg#value(49.6~52.5),Cr(39.8×10^(-6))and Ni(17.1×10^(-6))content,which indicate that the magma has undergone the crystal fractionation of mafic minerals during their ascent towards surface or accumulation in magma chambers,and negligible effects from crustal contamination.The characteristics of the trace element cont

关 键 词：温泉县 基性岩脉 早古生代 锆石U-Pb年龄 Hf同位素 岩石地球化学 全岩Sr-Nd同位素 板内伸展环境 

分 类 号：P588.124[天文地球—岩石学] P597.3[天文地球—地质学]