桃山—诸广—贵东地区基性岩脉岩石化学特征及其地质意义

Petrochemical characteristics of basic dikes and its geological significance in Taoshan-Zhuguang-Guidong area

桃山—诸广—贵东地区基性岩脉广泛发育,桃山地区以煌斑岩为主,诸广和贵东地区以辉绿岩为主。煌斑岩和辉绿玢岩以高SiO2、K2O含量,低TiO2、∑FeO含量为特征,辉绿岩则相对富钛、富铁、贫硅、贫钾。本区基性岩脉除个别类似于碱性玄武岩外,大多数属亚碱性系列玄武岩。诸广南部和贵东地区的辉绿岩表现出板内拉斑玄武岩特征,桃山和鹿井地区基性岩脉、贵东地区辉绿玢岩、闪长玢岩表现出大陆边缘弧钙碱性玄武岩特征。导致本区基性岩脉两种岩石系列差异的原因可能是由于岩石圈地幔组成不同、不同深度的基性岩浆源区或俯冲带流体交代作用的程度不同等因素造成的。

Basic dikes are well developed in Taoshan-Zhuguang-Guidong area. Lamprophyre is the main rock in Taoshan area, while diabase is dominating in Zhuguang and Guidong areas. The lamprophyre and diabase porphyrite are characterized by high contents of SiO2 and K2O and low contents of TiO2 and ∑FeO. The diabase shows the depletion in SiO2 and K2O, enrichment in TiO2 and ∑FeO. Most basic dikes are similar to subalkaline basalt while very few are similar to alkaline basalt. Diabase in the southern Zhuguang and Guidong areas bears the features of intraplate tholeiite, while basic dikes in Taoshan, diabase porphyrite and diorite porphyrite in Guidong area and diabase in Dajishan area have the features of continental margin arc calc-alkaline basalt. Differences of the two kinds of basic dikes are probably attributed to the differences of the mantle composition of lithosphere and the depth of magma recourse or the grade of liquid metasomatism in subduction zone.