摘要
乌本迪带位于坦桑尼亚西南缘,具有多阶段的构造演化历史。相比其他演化阶段,有关中元古代的岩浆作用研究相对较少,从而制约了乌本迪带中元古代构造演化历史的研究。基于此,笔者选择坦桑尼亚姆贝亚(Mbeya)地区发现的中元古代辉长岩和正长花岗岩进行岩石学、地质年代学和地球化学研究。结果表明,辉长岩和正长花岗岩的锆石结晶年龄分别为(1433±9)Ma和(1428±11)Ma,为中元古代岩浆活动的产物。辉长岩具有高的TiO_(2)含量(最高可达2.6%)和Ti/Y值(最高可达601),轻稀土元素(LREE)富集,(La/Yb)N值为4.85;Eu具轻微正异常,δEu值为1.02;富集大离子亲石元素(LILEs,如Rb、Ba、Sr、K),亏损高场强元素(HFSEs,如Nb、Ta、Zr),其微量元素组成与大陆溢流玄武岩(CFB)类似,推测为富集大陆岩石圈地幔发生低程度部分熔融的产物。正长花岗岩具高的SiO_(2)含量(71.59%~75.08%)和Ga/Al值(Ga/Al×10^(4)值为2.98~3.11),Zr+Nb+Ce+Y远大于350×10^(-6);LREE富集,(La/Yb)N值为22.86~28.51;Eu具明显负异常,δEu值为0.12~0.34,显示A型花岗岩特征,较低的Mg#值(6~10)和Sr/Y值(0.17~0.65),表明其可能为中–下地壳基性岩石部分熔融的产物。辉长岩和正长花岗岩的构造环境研究显示,两者均形成于板内拉张环境,与全球该时期构造演化体制相吻合,为Columbia超大陆裂解事件的岩浆产物。
The Ubendian Belt,which is situated on Tanzania’s southwest border,has undergone a multi-stage tectonic evolution history.Compared with other stages,there has been comparatively little research on the Meso-proterozoic Mag Matism,which restricts the study on the Mesoproterozoic tectonic evolution history of Ubendi-an Belt.Based on this,the Mesoproterozoic gabbro and syenite are selected for petrological,geochronology and geochemistry studies.The results show that the crystallization ages of the gabbro and syenogranite are(1433±9)Ma and(1428±11)Ma,respectively,indicating they are Mesoproterozoic.The gabbro is characterized by high content of TiO_(2)(2.6%)and Ti/Y ratio(601),enriched in LREE with(La/Yb)N of 4.85,and slightly positive Eu ano Malies(δEu=1.02).The LILEs(Rb,Ba,Sr,K)are enriched and HFSEs(Nb,Ta,Zr)are depleted,the geochemical features of the gabbro are consistent with continental flood basalts(CFB),indicating that it May be the production of a low degree partial melting of the enriched continental lithospheric Mantle.The syenites have high contents of SiO_(2)(71.59%~75.08%),they are characterized by enrichment in LREE with(La/Yb)N of 22.86~28.51,significant negative Eu ano Malies(δEu=0.12~0.34).Their values of Ga/Al are high(Ga/Al×104=2.98~3.11)and the content of Zr+Nb+Ce+Y is much larger than 350×10^(-6),indicating that they are A-type#granites.The lower Mg values(6~10)and Sr/Y ratios(0.17~0.65),indicating that they are the production of partial melting of basaltic rocks in the middle-lower crust.Both of the gabbro and syenite originated within an intra-plate rifting enviroment,which is consistent with the global tectonic regime of the Columbia Superconti-nent rifting event.
作者
许康康
谢薇
刘晓阳
赵晓博
顾延景
XU Kangkang;XIE Wei;LIU Xiaoyang;ZHAO Xiaobo;GU Yanjing(China Geological Survey,Tianjin Centre/North China Center for Geoscience Innovation,Tianjin 300170,China;Tianjin Geological Mineral Testing Center,Tianjin 300191,China;Geological Exploration Institute of Shandong Zhengyuan,China Metallurgical Geology Bureau,Jinan 250013,Shandong,China)
出处
《西北地质》
CAS
CSCD
北大核心
2024年第3期209-222,共14页
Northwestern Geology
基金
国家重点研发计划课题“辽东/胶东矿集区深部矿产勘查与增储示范”(2018YFC0603805)
中国地质调查局项目(DD20160108
DD20190439
DD20551801)联合资助。
