西大别造山带大磊山地区早志留世基性侵入岩的岩石成因及其构造背景  

Petrogenesis and Tectonic Significances of Early Silurian Mafic Intrusion in the Daleishan Area,Western Dabie Orogenic Belt,Centeral China

作　　者：金鑫镖 徐扬 刘浩[1,2] 邓新 张维峰[1,2] JIN Xin-Biao;XU Yang;LIU Hao;DENG Xin;ZHANG Wei-Feng(Research Center for Petrogenesis and Mineralization of Granitoid Rocks,China Geological Survey,Wuhan 430205,Hubei,China;Wuhan Center of China Geological Survey(Central South China Innovation Center of Geosciences),Wuhan 430205,Hubei,China)

机构地区：[1]中国地质调查局花岗岩成岩成矿地质研究中心,武汉4300205 [2]中国地质调查局武汉地质调查中心(中南地质科技创新中心),武汉430205

出　　处：《华南地质》2022年第1期94-109,共16页South China Geology

基　　金：中国地质调查局花岗岩成岩成矿地质研究中心开放基金课题(PMGR202016);湖北省自然科学基金项目(2020CFB344);中国地质调查局基础地质调查项目(DD20190050、DD20221634)。

摘　　要：武当-随枣地区普遍发育的早古生代北西西向延伸的碱性-基性岩墙群和火山岩,记录了秦岭-大别早古生代构造演化的重要信息。在西大别造山带南缘新识别出的傅家河基性岩侵位于新元古代大磊山岩体内部,其岩性以辉绿岩为主,局部相变为辉绿玢岩。SIMS锆石U-Pb法定年结果表明,其形成年龄为439±3 Ma(MSWD=0.08),时代为早志留世。地球化学组成上,傅家河基性岩具变化的SiO_(2)含量(44.00~55.82 wt%),高的总碱含量(K_(2)O+Na_(2)O=1.61~5.20 wt%),相对富集轻稀土和大离子元素(如Rb、Ba、Pb)、而亏损重稀土和高场强元素(如Nb、Ta、Ti);这样的弧型地球化学特征可能是其母岩浆上侵过程中吸收了围岩物质造成的,岩石中高Zr、Ti含量和Zr/Y比值指示傅家河基性岩形成于大陆裂谷环境。本文新发现的傅家河基性岩证实了南秦岭450-400 Ma大陆裂谷岩浆活动向东可延伸至大别造山带大磊山地区,这为进一步研究南秦岭-大别造山带早古生代构造演化提供了新的制约信息。Mafic dike swarms and alkaline volcanic rocks,trending in NW-SE direction,are widely distributed in the Wudang-Suizao areas,Central China,providing important information of the early Paleozoic tectonic evolution of the Qinling-Dabie-orogenic belt.New identification of the Fujiahe mafic intrusion,rocks of which are mainly diabase with minor diabase prophyrite,is located in the southern Western Dabie orogenic belt.SIMS(Secondary Ion Mass Spectrum)zircon U–Pb dating suggests that this intrusion was emplaced at 439±3 Ma(MSWD=0.08)from early Silurian.They have variable SiO_(2)(44.00~55.82 wt.%),and high alkalis(K_(2)O+Na_(2)O=1.61~5.20 wt.%)contents.They are generally characterized by arc-like trace-element patterns such as enrichment of large-ion lithophile elements(i.e.,Rb,Ba,Pb)and light rare earth elements(REEs),and depletion of high-field-strength elements(i.e.,Nb,Ta,Ti)and heavy REEs.Arc-like geochemical signatures in this mafic rock was the result of assimilation of wall-rocks during their parental magma ascent.High contents of Ti,Zr yielding high Zr/Y ratios suggest Fujiahe intrusion were formed in a continental rift setting.The new identification of the Fujiahe intrusion proved that the proposed 450~400 Ma continental rift magma in the South Qinling tectonic belt extended eastward to Daleishan area in the Dabie orogenic belt,which provides new constrains on the early Paleozoic tectonic evolution of the Dabie orogenic belt.

关 键 词：基性岩 早志留世 大陆裂谷岩浆岩 西大别造山带 

分 类 号：P534.43[天文地球—古生物学与地层学] P581[天文地球—地质学]