江南造山带东部旌德高Sr／Y花岗闪长岩的形成机制及其构造意义  

High Sr/Y Jingde Pluton in the Eastern Jiangnan Orogen,South China: Formation Mechanism and Tectonic Implications

作　　者：周洁[1,2] 姜耀辉[1] 葛伟亚[2] 

机构地区：[1]南京大学内生金属矿床成矿机制研究国家重点实验室,地球科学与工程学院,南京210093 [2]中国地质调查局南京地质调查中心,南京210016

出　　处：《地质学报》2014年第1期53-62,共10页Acta Geologica Sinica

基　　金：国家自然科学青年基金项目(编号41002017)资助的成果

摘　　要：旌德岩体是江南造山带东部一个典型的高Sr/Y岩体。锆石的原位U-Pb定年表明,该岩体侵位于141±1Ma。岩体由花岗闪长岩和二长花岗岩组成。全岩地球化学表明,高的碱(K2O+Na2O=6.64%~8.01%),K2O/Na2O值(变化范围在0.78~1.04),Sr(189×10-6~452×10-6)和LREE;低的HREE和HFSE含量,Eu有轻微的负异常到弱的正异常(δEu=0.81~1.18)。岩体具有高的Sr/Y值(23~66)和(La/Yb)N值(13~58),低Y(6.03×10-6~14.5×10-6)、Yb(0.36×10-6~1.17×10-6),且MgO、Cr、Ni含量较低,与中国东部中生代埃达克质岩的地球化学特征相似。岩体中黑云母为镁质黑云母,显示寄主岩为壳幔混合来源。斜长石主要为奥长石、中长石。初始87Sr/86Sr为0.7096~0.7101,εNd(t)值为-12.92^-6.28,二阶段Nd模式年龄tDM2=1.4~1.9Ga。岩体中发育有岩浆混合成因的暗色包体,指示有幔源岩浆参与。结合前人研究成果,早白垩世,先前(新元古代)发生交代的岩石圈地幔发生部分熔融,岩浆底侵到壳幔过渡带附近,导致下地壳发生部分熔融形成了旌德岩体,且发生了岩浆混合作用。江南造山带东段上发育独特的150~135 Ma的岩浆活动和成矿作用,可能与江南造山带新元古代华夏陆块与扬子陆块发生拼合形成初生地壳物质的中生代再造有关。高Sr/Y比值的旌德岩体可能代表晚侏罗世—早白垩世挤压增厚事件的结束,指示了江南造山带东部从造山增厚向伸展垮塌的转折时期的岩浆活动。Jingde pluton is a typical high Sr/Y granodiorite emplaced in the eastern Jiangnan Orogen, China. New LA-ICPM zircon U-Pb dating for one diorite yields an emplacement age of 141±1Ma. The pluton is composed of monozograntie and granodiorite. The pluton possesses high total alkalinity（K2O ＋ Na2O = 6.64%-8.01%）,high K2O/Na2O ratio（0.78-1. 04）,high Sr（189 X10-6-452X10-6 ）and LREE,low HREE and HFSE contents, and slightly negligible to positive Eu anomalies （3Eu = 0. 81- 1. 18）. Consequencely, the samples have high Sr/Y（23-66）and （La/Yh）N （13-58）ratios, low Y（6.03 X 10-6- 14.5×10.6） and Yb （0.36X10-6-1.17X10-6）, low MgO （or Mg^#）, Cr and Ni contents, show that they have the characteristics similar to the Mesozoic adakitoid in eastern China. The biotite in the pluton is classified into high Mg-type, and is plotted in the crust-mantle zone on the material source discrimination diagram. Plagioclase is mainly oligoclase and andesine. The initial 8rSr/86Sr ratios of the pluton is 0. 7096 N0. 7101 ,variable end （t） （-12. 92- 6. 28）, and tDMz model ages（1.4-1.9 Ga）. Mafic microgranular enclaves （MMEs） distriduted in the host granodiorite, suggest the importance of mantle material in the magma source. Combined with previous research, we suggest that mafic magmas ascended from the metasomatized lithospheric mantle and heated the lower crust, triggering partial melting to form the Jingde pluton, with input of mantle-derived materials. Special magmatism and metallization （150 - 135 Ma） developed in eastern Jiangnan orogen have relationship with reworking of Neoproterozoic juvenile crust. Jingde high Sr/Y pluton represent the end of late Jurassic-Early Cretaceous crust thickening event, and suggest the magmatic activity in the tectonic setting changing from thicken to extension stage.

关 键 词：高Sr Y旌德岩体 形成机制 构造意义 江南造山带 

分 类 号：P588.121[天文地球—岩石学]