西准噶尔乌尔禾地区哈拉阿拉特组富斑碱性玄武岩年代学、地球化学及地质意义  

Geochronology,geochemistry and geological significance of multi-porphyritic alkaline basalt from Hala alate Formation in Urho area,West Junggar,Xinjiang

作　　者：李永军[1,2] 王盼龙 支倩 黄家瑄 张新远 李伟 段丰浩 LI YongJun;WANG PanLong;ZHI Qian;HUANG JiaXuan;ZHANG XinYuan;LI Wei;DUAN FengHao(School of Earth Science and Resources,Chang an University,Xi'an 710054,China;Key Laboratory of Western China s Mineral Resources and Geological Engineering,Ministry of Education,Xi'an 710054,China;Shaanxi Institute of Geological Survey,Shaanxi Hydrogeological,Engineering and Environment Geological Survey Center,Xi'an 710068,China)

机构地区：[1]长安大学地球科学与资源学院,西安710054 [2]西部矿产资源与地质工程教育部重点实验室,西安710054 [3]陕西省地质调查院,陕西省水工环地质调查中心,西安710068

出　　处：《岩石学报》2024年第7期2037-2055,共19页Acta Petrologica Sinica

基　　金：国家科技重大专项(2017ZX05008-006-003-001);国家重点研发计划(2018YFC060400);陕西省自然科学基础研究计划项目(2024JC-YBQN-0292、2024JC-YBQN-0324);中国博士后科学基金项目(2022M710479)联合资助.

摘　　要：新近于新疆乌尔禾之北的哈拉阿拉特组(后文简称“哈山组”)最底部发现的一套富斑玄武岩,斑晶含量高达30%~40%,成分全为斜长石,晶形粗大完好,聚片双晶发育,粒径8×0.3mm~18×3 mm。该富斑玄武岩总厚大于90m。如此厚度大、层位稳定且组构特殊的玄武岩在本区乃至整个新疆北部地区极为罕见,鲜有报道。本文研究表明,哈山组富斑玄武岩斑晶主要为浅红褐色、灰白色长石,其中浅红褐色长石电子探针分析其属钠长石和中长石;LA-ICP-MS锆石U-Pb年龄为306±2Ma,属晚石炭世晚期;地球化学显示属碱性钠质系列,岩石具低的SiO_( 2)含量(48.84%~49.63%),较高的Al _(2)O_( 3)(17.78%~18.78%)、MgO(4.59%~9.29%)和全碱(6.62%~7.11%)含量,富钠贫钾(K _(2)O/Na _(2)O比=0.16~0.20)。相对富集轻稀土而亏损重稀土;富集Rb、Ba、K、Sr等大离子亲石元素,亏损Th、U、Nb、Ta等高场强元素。具正的ε_(Hf)(t)值(9.94~14.86)和较年轻的二阶段Hf模式年龄(t _(DM2)=0.37~0.68Ga)。综上认为该富斑玄武岩具有N-MORB和弧岩浆系列的双重地球化学特征,是流体交代的亏损地幔源石榴石+尖晶石二辉橄榄岩部分熔融形成。富斑碱性玄武岩所具有的“Nb、Ta亏损Ti不亏损”这一“初始岛弧”的地球化学特征,表明包古图构造带进入晚石炭世后开启了一个新生弧-盆构造体系。哈山组最底部的新生初始弧富斑玄武岩与其之上的成熟弧埃达克质火山岩,记录了一个相对完整的增生弧火山岩形成与演化历史。A suite of porphyritic-rich basalt recently unearthed at the base of the Hala alate Formation to the north of Urho Town in Xinjiang.It exhibits phenocryst predominantly composed of plagioclase,whose contents occupy the total of the basalt of 30%~40%.The crystals display a robust,coarse structure with well-preserved cluster twin-crystals,showcasing a particle size range of 8×0.3mm~18×3mm.The overall thickness of this porphyritic-rich basalt exceeds 90m.Basalts of such considerable thickness,characterized by stability and distinctive lithological features,are exceedingly uncommon in this region and even throughout the northern Xinjiang,with scant documented occurrences.The findings indicate that the porphyry in the porphyritic-rich basalt of the Hala alate Formation primarily consists of light reddish-brown and grayish-white feldspar.Electron microprobe analysis identifies the light reddish-brown feldspar as albite and andesine.LA-ICP-MS zircon U-Pb dating places the rocks in the Late Carboniferous Epoch at 306±2Ma.Geochemical analyses reveal their classification in the alkaline sodium series,showing low SiO_( 2) content(48.84%~49.63%),high Al _(2)O_( 3)(17.78%~18.78%),MgO(4.59%~9.29%),and total alkali content(6.62%~7.11%).They are sodium-rich and potassium-poor(K _(2)O/Na _(2)O ratio=0.16~0.20).There is a relative enrichment of light rare earth elements and a depletion of heavy rare earth elements.Large ion lithophile elements such as Rb,Ba,K and Sr are enriched,while high field strength elements such as Th,U,Nb and Ta are depleted.The rocks exhibit a positiveε_(Hf)(t)value range of 9.94~14.86 and a younger two-stage Hf model t _(DM2) age range of 0.37~0.68Ga.In summary,the porphyritic-rich basalt is considered to possess dual geochemical characteristics of N-MORB and arc magmatic series,formed through partial melting of garnet and spinel lherzolite from the depleted mantle source with fluid metasomatism.The geochemical characteristics of“proto-arc”of“Nb,Ta depletion but Ti non-depletion”exhibited by t

关 键 词：富斑碱性玄武岩 地球化学 初始岛弧 增生弧火山岩 晚石炭世 新疆西准噶尔 

分 类 号：P588.145[天文地球—岩石学] P597.3[天文地球—地质学]