南天山早二叠世Ⅰ型花岗岩Sr-Nd-Hf同位素特征：岩石成因和大陆地壳增长的意义  

Sr-Nd-Hf Isotopic Characteristics of Early Permian Ⅰ-Type Granites in Southern Tianshan: Petrogenesis and Implications for Continental Crustal Growth

作　　者：陶再礼 尹继元[1] 陈文[1] 李大鹏[2] 徐志华 杜秋怡 Tao Zaili;Yin Jiyuan;Chen Wen;Li Dapeng;Xu Zhihua;Du Qiuyi(Key Laboratory of Deep Earth Dynamics,Ministry of Natural Resources,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;School of Earth Sciences and Resources,China University of Geosciences,Beijing 100083,China)

机构地区：[1]中国地质科学院地质研究所自然资源部深地动力学重点实验室,北京100037 [2]中国地质大学地球科学与资源学院,北京100083

出　　处：《地球科学》2019年第10期3565-3582,共18页Earth Science

基　　金：国家重点研发计划项目(No.2017YFC0601301);中国地质调查项目(Nos.DD20190001,DD20190004);自然资源部深地动力学重点实验室开放课题基金(No.J1901-5);国家自然科学基金项目(Nos.41573045,41873060,41830216);IGCP 662资助成果

摘　　要：新疆南天山地区发育大量晚石炭世-早二叠世的花岗质侵入岩,然而这些花岗岩的岩石成因和形成构造背景仍然存在着较大的争议.对南天山黑云母二长花岗岩进行了锆石U-Pb年代学、岩石地球化学以及Sr-Nd-Hf同位素研究.LA-ICP-MS锆石U-Pb定年结果显示,其形成年龄为295.8±1.7 Ma.地球化学特征表明,该花岗岩具有弱过铝质(A/CNK=1.02~1.04)、富碱(K2O+Na2O=7.49%~8.78%)、富钾(K2O/Na2O=1.05~1.53)特征,属于高钾钙碱性Ⅰ型花岗岩;微量元素富集大离子亲石元素和轻稀土元素,亏损高场强元素(Nb、Ta、Ti),具有中等的负铕异常(δEu=0.38~0.57),且Sr、Ba也显示明显的亏损特征.该花岗岩具有较高的(87Sr/86Sr)i值(0.709 2~0.714 2),其εNd(t)与εHf(t)以负值为主,个别样品εNd(t)和εHf(t)值显示较低的正值.这些特征表明其源自古-中元古代地壳的长英质岩浆与地幔的镁铁质岩浆混合而成,且少量新元古代地壳物质也参与了成岩过程,其母岩浆就位前发生了斜长石分离结晶作用.综合前人研究,认为南天山地区晚石炭世-早二叠世花岗质岩石可能是南天山洋板片回撤、软流圈上涌诱发前寒武基底组分发生部分熔融并与幔源岩浆混合作用形成.显生宙以来南天山造山带花岗岩源区主要为古老地壳重熔,与中亚造山带其他地区相比,南天山新生地壳增长并不明显.The Late Carboniferous-Early Permian granitic intrusions extensively occur in the southern Tianshan block,whereas the petrogenesis of these granites and their tectonic setting remain controversial.In this paper,it reports new zircon U-Pb age,and geochemical and Sr-Nd compositions and zircon Hf isotopic compositions of the biotite monzonitic granites in the southern Tianshan block.Based on LA-ICP-MS U-Pb zircon dating,the biotite monzonitic granites were emplaced at 295.8±1.7 Ma.They are characterized by slightly peraluminous(A/CNK=1.02-1.04),rich alkali(K2O+Na2O=7.49%-8.78%)and potassium-rich(K2O/Na2O=1.05-1.53),belonging to high potassium calc-alkaline affinity,consistent with the geochemical features of I-type granites.They are enriched in LILEs and LREEs,depleted in HFSEs(e.g.,Nb,Ta,Ti),medium-negative Eu anomalies(δEu=0.38-0.57),and predominately negative Sr,Ba anomalies.In addition,most of the biotite monzonitic granites show high initial(87Sr/86Sr)i ratios,negativeεNd(t)andεHf(t)values and few samples with low and positiveεNd(t)andεHf(t)values,suggesting that they were produced by mixing of mafic melt-derived mantle and felsic melt derived ancient(Paleo-Mesoproterozoic)crust,with minor involvement of the Neoproterozoic crustal material,and that the crystal fractionation of plagioclase could have occurred before the parental magma emplaced.In association with previous analysis,it is proposed that the Late Carboniferous–Early Permian magmatism in the southern Tianshan block might be related to mixing of melt-derived Precambrian basement and melt-derived mantle induced by the slab roll-back of the subducted southern Tianshan oceanic lithosphere and asthenosphere upwelling.The Phanerozoic magmatic source of the southern Tianshan block is mainly characterized by the reworking of ancient crust.Compared to other regions of CAOB,there is no excessive juvenile crustal growth in the southern Tianshan.

关 键 词：南天山 Ⅰ型花岗岩 构造背景 板片回撤 岩浆混合 岩石学 

分 类 号：P581[天文地球—岩石学]