西秦岭党川花岗岩基的岩石化学特征

党川花岗岩基产于祁连与北秦岭造山带结合部位,由9个岩体组成,岩石普遍富K2O。志留纪为闪长岩-石英闪长岩,显著贫SiO2、Na2O,显著富MgO、CaO、TFeO、MnO、P2O5。泥盆纪-侏罗纪岩体为二长-正长花岗岩类,各岩体岩石化学特征较相似,高TiO2、K2O、Na2O,贫MgO、CaO,显示继承性演化规律。志留纪岩体的岩石化学构造环境判别及与其共生的早古生代火山岩相配套,是俯冲造山过程中的岛弧闪长岩类,而泥盆纪熊山沟岩体则是与之密切有关的造山期后陆缘或弧后花岗岩类。其余各岩体是本区造山后与大陆抬升作用以及大陆裂谷作用有关的花岗岩类。

The Petrochemical Characteristics of the Dangchuan Granitic Batholith in the Western Qinling

The Dangchuan granitic batholith, which is located in the conjunction area of the Qilian and the North Qinling orogenic belts, is composed of 9 granitic intrusive bodies, whose rocks are rich in K2O generally. The Silurian intrusive bodies are diorite-quartz diorite which are obviously poor in SiO2, Na2O, but rich in MgO, CaO, FeOt, MnO and P2O5. The Devonian-Jurassic intrusive bodies are composed of monzonitic granite -syenitic granite which have common petrochemical characteristics of high contents of TiO2. K2O. Na2 O and low contents of MgO and CaO, with inherited evolutionary regularity. The petrochemical plots for diagnosing tectonic environments of rocks indicated that the Silurian intrusive rocks and the coexisted Lower Palaeozoic volcanics were a series of island arc dioritoid formed in the process of subduction orogenesis. However, the Devonian Xiongshangou body of granit- oid was composed of post-orogenic continental or back arc granitoid. The other intrusive bodies are post-orogenic granitoid in association with the continental uplifting and rifting.