摘要
近年研究显示，古元古代晚期，扬子陆块西南缘发生了大规模的地幔物质上涌事件。本文系统报道了康滇地区中部东川铜矿因民一落雪矿区古元古代辉绿岩的地球化学特征。主量元素中MgO含量较高，为6．16％～9．65％，Mg2＋平均为72．2；富Na20，Na20／K20为1．3～9．8；低Si02，45．61％～49．34％；低TiOz，0．74％～2．74％；FeO／MgO小于1，表明本区辉绿岩初始岩浆相对较原始，MgO与主要组分的相关性表明岩浆早期出现过轻微的橄榄石、斜方辉石及铬铁矿、钛铁矿结晶分异。（La／Yb）。为1．66～4．37，8Eu为1．04～1．22，稀土元素球粒陨石的配分呈平缓右倾模式，出现Eu的弱正异常。富集Rb、Ba等大离子半径元素，MORB配分为向右陡倾模式，出现突出的Rb、Ba峰，Zr、Hf弱负异常，多数样品没有明显的Nb、Ta异常。eNd，为一0．2～3．8，初始87Sr／86Sr。值为0．7055-0．7084。东川地区辉绿岩的源区为尖晶石二辉橄榄岩相，为较亏损的过渡型地幔部分熔融的产物，轻度混染主要源于陆下岩石圈地幔及少量的下地壳物质。东川古元古代辉绿岩地球化学表现为明显的板内玄武岩、E—MORB和0IB的特征，表明古元古代末期，扬子陆块西南缘发生了大规模的陆内裂谷拉张事件，与全球性Columbia超级大陆裂解同步，可能与地幔柱活动密切相关。
There exists a large scale upwelling event of mantle source materials during late Paleoproterozoic in southwestern Yangtze block, China, and the detailed geochemistry of Paleoproterozoic diabase at the Yimin- Luoxue mine of the Dongchuan copper deposit in the central Kangdian area is reported in this paper. The results show that the major elements of diabase have the characteristics of high MgO, 6.16~ ~9.65% （mean Mg~ of 72.2）, low SiO2 （45.61%~49.34~）, low TiO2 （0.74%~2.74%）, and FeO/MgO%l, implying that the initial magma of the diabase was relatively primitive. The correlations between MgO and the main major components and trace elements reflect that the primitive magma have experienced fractional crystallization of olinve, orthopyroxenite, chromite, and ilmenite in early stage. The diabse has （La/Yb）N of 1. 66~4. 37, and 8Eu of 1.04 1. 22, and the chondrite normalized REE pattern slightly tilt to the right. The diahase enriches in large-ion lithophile elements（LILE）, such as Rb, Ba, U, etc. , and the MORB normalized trace elements pattern steeply tilt to the right, with obviously positive anomaly of Rb, Ba, and slightly negative anomaly of Zr, Hf, and without obvious anomaly of Nb, Ta except few samples. The Paleoproterozoic diabase in the Dongchuan area displays --0.2~3.8 of eNd, and 0. 7055~0. 7084 of initial 87 Sr/a6 Sr~. The source area of the Dongchuan diahase exhibits the spinel lherzolite facies, indicating a product of partial melting of relatively deplete transitional mantle, and the slight contamination is derived from sub-continental lithospheric mantle and little lower crust materials. The geochemical characteristics of intraplate basalt（WPB）, E-MORB, and OIB of Dongchuan diabase imply that a large scale intracontinental rift extensional event may occur contemporaneously with the breakup of the global Columbia supercontinent in the southwest of Yangtze block during late Paleopoterozoic, and may be caused by the mantle plume activity.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2013年第12期1834-1852,共19页
Acta Geologica Sinica
基金
国土资源大调查(编号1212010911064
1212010813066)
国家重点基础研究发展规划(973)项目(2009CB421006)
国家自然科学基金(编号40173025)联合资助的成果
