摘要
对出露于冈底斯西部地区措勤北部达瓦错东侧的达雄岩体进行了锆石U-Pb定年、全岩主量元素、微量元素、Sr-Nd同位素和锆石Hf同位素研究,以约束其岩石成因。达雄岩体的主体岩性为花岗闪长岩,其中发育大量闪长质包体。花岗闪长岩的锆石LA-ICP MS年龄为107±1Ma,该年龄代表了岩体结晶年龄。花岗闪长岩锆石ε_(Hf)(t)值变化于-1.0～3.0,两阶段模式年龄变化于974～1226Ma。花岗闪长岩富硅(SiO_2=70.65%～71.10%),富钙(CaO=3.21%-3.26%)、贫钾(K_2O= 2.81%～2.99%)、低P_2O_5(0.09%),铝饱和指数(A/CNK)为1.01～1.02,属于偏铝质花岗岩或弱过铝质花岗岩。闪长质包体Sio_2含量为57.84%,与寄主岩相比,闪长质包体更富CaO、MgO、TFe_2O_3和TiO_2。花岗闪长岩和闪长质包体均属中钾钙碱性系列,ε_(Nd)(t)值分别为-4.6和-3.2,两阶段模式年龄(t_(DM2))相近(分别为1277Ma和1166Ma),并与锆石Hf同位素模式年龄一致。岩相学、年代学和地球化学研究表明闪长质包体可能是由岩浆混合作用形成的镁铁质微粒包体。我们的初步研究成果似乎表明,冈底斯中西部地区在早白垩世晚期(～110Na)很可能存在一次重要的岩浆混合作用,这一初步认识对研究冈底斯中北部地区规模宏大的白垩纪岩浆作用的深部动力学过程具有重要意义。
LA-ICP-MS zircon U-Pb age, whole-rock major and trace element, Sr-Nd and zircon Hf isotopic compositions from the Daxiong pluton, western Gangdese are used to constrain its origin. The predominant lithology observed in Daxiong pluton is granodiorite, in which dioritic enclaves are well developed. Zircon U-Pb dating for one granodiorite sample yields an emplacement age of 107 ± 1Ma. Zircon Hf isotopic analysis yields εHf （ t ） values of - 1.0 to ＋ 3. 0, with two-stage model age ranging from 974 to 1226Ma. Granodiorites are silica enriched in composition （ SiO2 = 70.65% - 71. 10% ）, with high contents of CaO （3.21% 3.26% ） and low contents of K2O （2.81 - 2.99% ） and P2O5 （0.09%）. Both granodiorite and dioritic enclave are medium-K calcalkaline, and exhibit similar εNa （t） values （ -4.6, and -3, 2, respectively）. Their two-stage model ages are identical, consistent with the zircon Fir isotope model age. Geochemical characteristics combined with field and petrographic observations show that the dioritic enclave can be considered as the marie microgranular enclave. Our data indicate that an important magmatic mixing event probably occurred in middle-western Gangdese belt during the late of Early Cretaceous time.
出处
《岩石学报》
SCIE
CAS
CSCD
北大核心
2008年第2期348-358,共11页
Acta Petrologica Sinica
基金
国家重点基础研究发展规划项目(2002CB412603)
中国科学院同位素年代学和地球化学重点实验室开放课题
国家自然科学基金(40503005，40473020，40572051，40672044，40572048)
国土资源部百名优秀青年科技人才计划联合资助
