南岭万洋山加里东期花岗岩地球化学特征、成因与构造意义

Geochemical Characteristics,Petrogenesis and Tectonic Implication of the Caledonian Wanyangshan Granite in the Nanling Range,South China

万洋山岩体位于湘赣两省交界地带,为加里东期多阶段岩浆活动的复式岩体,其主要岩石类型有英云闪长岩、花岗闪长岩、黑云母二长花岗岩和二云母二长花岗岩,以黑云母二长花岗岩分布面积最广。岩石样品SiO2含量为63.94~74.8 wt%,ALK含量为5.89~7.88 wt%,属高钾钙碱性系列。A/CNK=0.99~1.23,涵盖准铝质到强过铝质。微量元素富集Rb、K、Th、U,相对亏损Sr、P、Ti,ΣREE=19.0~274.6μg/g,(La/Yb)N=0.93~14.74,δEu=0.13~0.72。岩体源区成分不均一,包含变质玄武岩、变质杂砂岩和变质泥质岩石。综合前人研究,将英云闪长岩、花岗闪长岩划入HSS型花岗岩,黑云母二长花岗岩划入HS型花岗岩,二云母二长花岗岩划入S型花岗岩。基于上述岩石成因并结合区域构造演化过程,推断万洋山岩体形成于华南加里东造山带从挤压向伸展转换阶段,南北两条断层控制了岩体的上升通道和就位空间。

Wanyangshan batholith is an important part of Caledonian magmatism in south China,which is mainly composed of tonalite,granodiorite,biotite monzogranite and two-mica monzogranite,and biotite monzogranite is the most widely distributed.Geochemical analyses showed that:the Wanyangshan granite has a SiO2 content of 63.94 to 74.8 wt%,and ALK content of 5.89 to 7.88 wt%,Which indicates Wanyangshan is high-K calc-alkaline granitic batholith.A/CNK=0.99~1.23,shows the characteristics of quasi-aluminous to strongly peraluminous.The granite is enriched in Rb,K,Th and U,but depleted in Sr,P and Ti;ΣREE=19~274.6 ppm,(La/Yb)N=0.93~14.74,δEu=0.13~0.72.Its primitive magma could be mainly sourced from melting of metamorphic basalt,metamorphic graywacke and metamorphic mudstone.Considering previous studies,the tonalite and granodiorite shows HSS-type granite attribution,biotite monzogranite shows HS-type granite attribution,and the two-mica monzogranite shows S-type granite attribution.Based on petrogenesis and combined with regional tectonic evolutional setting analysis,the Wanyangshan granites might formed under the conditions of transition from collision to extension,be dominated by two faults which located on the north and south.