桂北新寨强过铝质花岗岩的岩石成因及其构造意义--来自年代学、地球化学及Sr-Nd-Hf同位素的制约  

Constraints of geochemistry,geochronology and Sr-Nd-Hf isotopes on the Xinzhai peraluminous granite in northern Guangxi:implications for petrogenesis and tectonic significance

作　　者：贾小辉[1,2] 王晓地[1,2] 杨文强[1] JIA Xiaohui;WANG Xiaodi;YANG Wenqiang(Wuhan Center of Geological Survey, CGS, Wuhan 430223, Hubei, China;Research Center for Petrogenesis and Mineralization of Granitoid Rocks, CGS, Wuhan 430223, Hubei, China)

机构地区：[1]中国地质调查局武汉地质调查中心,湖北武汉430223 [2]中国地质调查局花岗岩成岩成矿地质研究中心,湖北武汉430223

出　　处：《地质通报》2017年第5期738-749,共12页Geological Bulletin of China

基　　金：国家自然科学基金项目《粤北罗岗钾玄质侵入岩的岩石成因及其动力学意义》(批准号:41302046);中国地质调查局项目《南岭关键地区区域地质调查》(编号:12120113063600)和《国家地质数据库建设与整合》(编号:1212011220512)

摘　　要：LA-ICP-MS锆石U-Pb定年结果显示,桂北新寨花岗岩形成于中奥陶世(465±2Ma)。该花岗岩的地球化学特征表现为化学成分较均一,具有高硅(SiO_2=68.54%~74.57%)、富碱(K_2O+Na_2O=7.61%~8.31%)、更富钾(K_2O/Na_2O=1.77~2.35)、强过铝质(A/CNK=1.09~2.39)和富集大离子亲石元素而亏损高场强元素等特征,属于S型花岗岩。新寨花岗岩具有比较均一的Sr、Nd同位素组成(I_(Sr)=0.71137~0.71328,ε_(Nd)(t)=-7.89^-7.26)。锆石Hf同位素组成为:(^(176)Hf/^(177)Hf)_i=0.28232~0.28252,ε_(Hf)(t)=-6.18^+0.61,Hf同位素两阶段模式年龄TDM2变化于1.67~2.11Ga之间。元素及Nd-Sr-Hf同位素分析结果显示,新寨花岗岩可能源自古元古代地壳变质泥岩的部分熔融,在成岩过程中有少量幔源组分的参与。新寨S型花岗岩可能是广西运动第二幕在桂北地区的岩石学响应,为早古生代构造-岩浆群事件的建立提供了新证据。LA-ICP-MS zircon U-Pb dating shows that the Xinzhai granites,emplaced in northern Guangxi,were generated in Mid?dle Ordovician(465±2Ma).These granites are characterized by uniform silicon content(SiO2=68.54%~4.57%),enrichment of alkali val?ues and considerable enrichment of K values(K2O+Na2O=7.61%~8.31%,K2O/Na2O=1.77~2.35),concentration of peraluminous(A/CNK=1.09~2.39)and high large ion lithophile elements(LILE)(e.g.,Rb,K,Th)but relative depletion of high field-strength el?ements(HFSE)(e.g.,Nb,Ta,P,Ti)and Sr.They belong to S-type granite.Granitic samples have homogeneous Sr-Nd isotopecompositions(ISr=0.71137~0.71328,εNd(t)=-7.89^-7.26).Zircon Hf isotope compositions of the Xinzhai granites have relativelywide ranges(176Hf/177Hf=0.28232~0.28252,εHf(t)=-6.18^+0.61,TDM2=1.67~2.11Ga).The authors hold that the Xinzhai granites werelikely generated by partial melting of Paleoproterozoic metapelite,with the addition of small amounts of mafic magma mantle-derivedmaterial.The Xinzhai S-type granites might have been the petrological response to the second activity of the Kwangsian orogen innorthern Guangxi,which provided new evidence for the establishment of the Early Paleozoic tectonic-magma events in South China.

关 键 词：中奥陶世 S型花岗岩 SR-ND-HF同位素 广西运动 桂北 

分 类 号：P534.42[天文地球—古生物学与地层学] P588.121[天文地球—地质学]