西藏措勤尼雄岩体的岩石成因及其对富Fe成矿作用的潜在意义  

Petrogenesis of the Nixiong pluton in Coqen,Tibet and its potential significance for the Nixiong Fe-rich mineralization

作　　者：张晓倩[1] 朱弟成[1] 赵志丹[1] 王立全[2] 黄建村 莫宣学[1] 

机构地区：[1]地质过程与矿产资源国家重点实验室中国地质大学地球科学与资源学院,北京100083 [2]成都地质矿产研究所,成都610082 [3]江西地质调查院,南昌330201

出　　处：《岩石学报》2010年第6期1793-1804,共12页Acta Petrologica Sinica

基　　金：国家973项目(2009CB421002);国家自然科学基金重点项目(40830317);教育部新世纪优秀人才项目(NCET-10-0711);111计划(B07011);国家自然科学基金面上项目(40973062;40873023);中国地质调查局综合研究项目(1212010610104)资助

摘　　要：西藏措勤尼雄岩体是冈底斯造山带白垩纪大规模酸性岩浆活动的代表之一,著名的尼雄富铁矿体就主要赋存在发育闪长质包体的尼雄岩体外接触带上。因此要探讨此富铁矿体的成因机制,就需要对邻近的尼雄岩体进行研究。本文报道了尼雄岩体的寄主岩石(～116Ma和～110Ma)和闪长质包体(～110Ma)的岩石学、全岩主量、微量元素和Sr-Nd同位素数据,以约束其岩石成因,并通过与南美智利安第斯铁成矿作用的对比,初步探讨了尼雄岩浆活动与富铁成矿作用的可能联系。尼雄岩体寄主岩石富硅(SiO2=67.52%～76.39%),铝饱和指数(A/CNK)为0.96～1.05,属偏铝质中-高钾钙碱性系列的花岗闪长岩到二长花岗岩。闪长质包体属偏铝质(A/CNK=0.82)中钾钙碱系列岩石。寄主岩石与闪长质包体具相似的稀土元素配分模式和微量元素蜘蛛图型式,如均富集大离子亲石元素(如Rb、Ba、K、U和Th)、亏损高场强元素(如Nb、Ta、Ti、P和Zr)。寄主岩石中约116Ma的样品具高的(87Sr/86Sr)i值(0.7145和0.7156)、负的全岩εNd(t)(-8.9和-7.8)和锆石εHf(t)(-7.1～-3.0),对应古老的Nd同位素二阶段模式年龄(1.55～1.60Ga)和锆石Hf同位素地壳模式年龄(1.40～1.60Ga);约110Ma的寄主花岗岩和闪长质包体具偏低的(87Sr/86Sr)i值(0.7066～0.7095和0.7088)、负的全岩εNd(t)(-8.1～-5.2和-7.8)和锆石εHf(t)(-6.2～-2.1和-6.8～-0.2),对应的Nd同位素二阶段模式年龄和锆石Hf同位素地壳模式年龄分别为1.34～1.56Ga和1.20～1.60Ga。结合文献数据提出,尼雄岩体很可能是中上地壳来源的壳源熔体和古老岩石圈地幔来源的幔源熔体不同比例混合而成,并且幔源物质的混入量随时间有增加的趋势(即从约116Ma的50%到约110Ma的65%～75%)。初步认为尼雄岩体可能处于与班公湖-怒江洋壳岩石圈南向俯冲有关的俯冲板片角度变陡并断离(约110Ma)的伸展背景。尼雄岩体在岩浆作用成因、构�The Nixiong Fe-rich deposits mainly grown in the external contact zone of Nixiong pluton in Coqen,Tibet,which is one of the representative Cretaceous plutons widely distributed in Gangdese Orogenic Belt. In order to explore the mineralization mechanism of the Fe-rich deposits,it is vital to understand the petrogenesis of Nixiong pluton nearby. Here we reported petrology,whole-rock major and trace elements,Sr-Nd isotopic data of Nixiong pluton that consists predominantly of granites (~116Ma,110Ma) with dioritic enclaves (~110Ma),to constrain its petrogenesis and to explore possible link between the Nixiong plutonism and Fe-rich mineralization by comparing with the iron mineralization in Chile Andean,South American. The host granites of Nixiong pluton are enriched in silica (SiO2=67.52%~76.39%) with aluminum saturation index (A/CNK) of 0.96~1.05,and are metaluminous,medium-high K calc-alkaline,ranging from granodiorite to monzogranite in rock type. Dioritic enclaves are metaluminous (A/CNK=0.82) and medium K calc-alkaline. Both host granites and dioritic enclaves have similar chondrite-normalized REE patterns and primitive mantle normalized trace element spectrum,e.g. enriched in LILEs (Rb,Ba,K,U and Th),depleted in HFSEs (Nb,Ta,Ti,P and Zr). The ~116Ma host granites show high initial87Sr/86Sr (0.7145 and 0.7156),negative whole-rock εNd(t) (-8.9 and-7.8) with old two-stage Nd model ages of 1.55~1.60Ga,and negative zircon εHf(t) (-7.1^-3.0) with Hf crustal model ages of 1.40~1.60Ga; the ~110 Ma host granites and dioritic enclaves are characterized by relatively low initial 87Sr/86Sr (0.7066~0.7095 and 0.7088),and enhanced whole-rock εNd(t) (-8.1^-5.2 and-7.8) and zircon εHf(t) (-6.2^-2.1 and-6.8^-0.2),corresponding to two-stage Nd model ages of 1.34~1.56Ga and zircon Hf crustal model ages of 1.20~1.60Ga,respectively. The data reported here,combined with the data in the literature,allow us to propose that the Nixiong pluton is probably the product of varying extents of magma mixing between middle to upper crust-d

关 键 词：闪长质包体 岩浆混合 富Fe成矿作用 尼雄岩体 西藏措勤 

分 类 号：P588.121[天文地球—岩石学]