江南造山带东段九岭新元古代复式花岗岩源区性质的差异:来自地球化学及锆石Hf同位素的制约  

Compositional difference from the sources of Jiuling Neoproterozoic granite complex in Eastern Segment of the Jiangnan Orogen: Constraints from geochemistry and Hf isotope of zircons

作　　者：段政[1] 邢光福[1] 廖圣兵[1] 褚平利[1] 黄文成[1] 朱延辉 

机构地区：[1]中国地质调查局南京地质调查中心,南京210016

出　　处：《岩石学报》2017年第11期3610-3634,共25页Acta Petrologica Sinica

基　　金：国家重点研发计划(2016YFC0600206);中国地质调查局基础地质综合研究项目(12120113064800;121201008000160902;12121008000150004)联合资助

摘　　要：江南造山带东段九岭新元古代花岗岩据其岩石学及野外产出特征可分为3个序次的侵入体,由早到晚依次为黑云母花岗闪长岩、英云闪长岩及黑云母二长花岗岩。本次研究的黑云母花岗闪长岩和英云闪长岩中等富硅(SiO_2分别为66.05%~75.78%和67.36%~73.94%),而黑云母二长花岗岩极富硅(SiO_2为73.96%~77.83%)。三者铝饱和指数A/CNK分别为1.53、1.71和1.32,A/NK分别为2.04、2.0和1.39,均显示典型过铝质花岗岩特征;三类岩石单元主体属高钾钙碱性系列。黑云母花岗闪长岩和英云闪长岩SiO_2与MgO、TiO_2、CaO、Fe_2O_3T、Al_2O_3、MnO、V成负相关,但黑云母二长花岗岩这种相关性不明显。黑云母花岗闪长岩和英云闪长岩均富轻稀土元素,(La/Yb)N分别平均为10.1和18.7,具弱Eu负异常(δEu分别为0.11～0.88和0.30～0.72),而黑云母二长花岗岩轻重稀土分馏弱((La/Yb)N=4.70),强烈Eu负异常(δEu=0.18～0.61)。三类岩石均富集大离子亲石元素Cs、Rb、Th、U、K、Pb,明显亏损高场强元素Nb、Ta、Sr、Ti,且锆石εHf(t)变化范围极大,分别介于-6.76～9.22、-1.08～6.63和-0.64～7.96之间。研究区北西侧和南东侧岩体锆石Hf同位素组成存在明显差异,表现为岩体北西部的锆石εHf(t)变化范围高于南东部,锆石tDM2模式年龄多集中在1.6～1.8Ga。综合研究推断本区黑云母花岗闪长岩、黑云母二长花岗岩的源区分别为砂质上地壳和泥质上地壳部分熔融产物,而英云闪长岩则为砂泥质源区部分熔融产物。同时,SE侧岩浆起源深度和岩体剥蚀程度均高于NW侧,且SE侧岩体的成岩时代也略早于NW侧,这暗示了新元古代华夏板块和扬子板块碰撞后的伸展过程中,研究区SE侧岩浆起源深度较深,且形成时代较早,并逐渐向NW侧迁移。另外,花岗质岩石源区由砂质向泥质转变的过程可能也是区域陆壳伸展作用逐渐增大的结果。The Jiuling Pluton in Estern Segment of the Jiangnan Orogen can be divided into three stage intrusion according their petrology and outcrops in the field, which are biotite-granodiorite, tonalite and biotite-monzogranite respectively from early to late. The biotite-granodiorite and tonalite are medium enrichment of silica （SiO2 is 66.05%~75.78% and 67.36%~73.94% respectively）, while the biotite-monzogranite strong enrichment of silica （SiO2 is 73.96%~77.83%）. The A/CNK aluminium saturation index value of them are 1.53, 1.71 and 1.32, A/NK are 2.04, 2.0 and 1.39 respectively, which show typical characteristics of the peraluminous granites; All of them are manily high-K calc-alkaline series. The biotite-granodiorite and tonalite show negative correlation relationship between SiO2 and MgO, TiO2, CaO, Fe2O3T, Al2O3, MnO, V, while such correlation above didn＇t emerge in the biotite-monzogranite from their Harker diagram. Both of biotite-granodiorite and tonalite are enrichment of LREE but present weak Eu negative anomaly, the （La/Yb）N of them with an average of 10.1 and 18.7 and δEu are 0.11~0.88 and 0.30~0.72, respectively. Unlike that though, biotite-monzogranite show weak fractionation between the light and heavy rare earth element （（La/Yb）N=4.70） with strong Eu negative anomaly （δEu=0.18~0.61）. Besides, the biotite-monzogranite＇ REE distribution diagrams present ＂M＂-type tetrad effect, which implied that biotite-monzogranite experienced stronger crystallization differentiation. All of them are enrichment of Cs, Rb, Th, U, K and Pb, while deplete in Nb, Ta, Sr, Ti obviously. Their εHf（t） of zircons range wildly, which are -6.76~9.22, -1.08~6.63 and -0.64~7.96, respectively. There are significant differences in the Hf isotopic composition of zircons between the northwest and southeast of the studied area, which shows that the variation range of zircons εHf（t） from the northwestern is more widely than that from the southeastern pluton, the zircon model ages （tDM2） are c

关 键 词：岩石成因 S型花岗岩 新元古代 九岭岩体 江南造山带 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]