黄陵地区基性岩墙群的地球化学特征及其地质意义

Geochemistry of Mafic Dykes in Huangling Area and Its Tectonic Implications

黄陵地区的基性岩墙群主要由辉绿岩脉和辉绿玢岩脉组成 ,走向主要为NEE向 ,少量为NNW向 .元素地球化学显示其为形成于板内拉张环境下的亚碱性玄武岩特征 ,其很低的Mg# 指示为岩浆高度演化的产物 ,同时Nb、Ta的亏损和Pb的富集表明其受到地壳物质的混染 ,这说明可能是在拉张环境下由先前被俯冲带流体交代的地幔源重熔的结果 .根据前人的年代学研究结果 ,它形成于 770Ma左右 ,可能跟Rodinia超级古陆裂解构造背景相关 .

According to the geological characteristics, the mafic dykes in Huangling area mainly include diabase and diabase-prophyrite, with nearly NEE trend and NNW trend. Geochemical characteristics of the dykes indicate that they are sub-alkaline basalt formed in WPB. The low Mg~#(Mg~#=100×MgO/(MgO+0.9×TFe_2O_3))shows the magma for the dykes was highly evolutionary. The depletion in Nb and Ta, and the enrichment in Pb indicate that the mafic dykes are contaminated by crustal material. All these suggest that it may be the product of remelted materials from mantle source, which had been metasomatismed by the fluid in subduction zone, under the extensional circumstance. Based on the previous geochronological researches, it is concluded that the mafic dyke swarms intruded at about 770 Ma and may be related to the breakup of the Rodinia supercontinent.