辽宁凤城大堡—五龙背岩体特征与侵入机制

Rock mass features and emplacement mechanism of Fengcheng Dapu-Wulongbei

凤城大堡—五龙背岩体由花岗闪长岩、中细粒二长花岗岩、中细粒似斑状二长花岗岩组成。岩体呈小岩基状产出,空间上侵入中侏罗世大堡组,并被117Ma早白垩世石英闪长岩和石英二长岩所侵,SHRIMP年龄为126.2 Ma,时代为早白垩世。岩石地球化学特征说明,岩浆演化由中酸性→酸性,由钠质→钾质,属钙碱系列过铝质岩石。稀土和微量元素参数及岩石化学特点均说明该岩体源区性质以壳源为主,成因类型为I型与S型过渡。其形成构造背景是在太平洋板块向欧亚板块俯冲,受其影响,中国东部大陆处于地幔软流圈上涌,拉张减薄与挤压双重作用下,壳熔岩浆沿北东向基底断裂上侵,形成的花岗闪长岩-二长花岗岩造山型侵入岩组合。侵位机制为气球膨胀式主动就位。

Fengcheng Dapu-Wulongbei pluton consists of grmaodiorite, medium fine-grained monzonitic granite, medium fine-grained porphyritic monzonitic granite. The intrusive bodies occur as small basement rocks and intrude into the Dabao Formation of Middle Jurassic in space. They are intruded by quartz diorite and quartz monzonite of 117 Ma early Cretaceous. The SHRIMP age is 126.2 Ma and the age is Early Cretaceous. That rock geochemistry characteristics show that magma evolved from intermediate-acidic to acidic, from sodium to potassium, belonging to calc alkaline series peraluminous rocks. REE, trace element parameters and petrochemistry characteristics indicate that the nature of the source region of the rock in crust, genesis type is type I mad S. The tectonic setting is rushed to the Eurasia plate palace in the Pacific Plate, the eastern part of the continent China in the circle of upwelling mantle, under the dual role of extensional thinning and extrusion, The crustal magma intruded along the NE trending basement fault and formed the granodiorite-monzonite orogenic intrusive rock association.. The emplacement mechanism is balloon expmasion active positining.