吉林珲春地区大荒沟花岗岩岩基的岩浆演化和构造环境

MAGMATIC EVOLUTION AND STRUCTURAL ENVIRONMENT OF THE DAHUANGGOU GRANITOID BATHOLITH IN THE HUNCHUN AREA,JIL.IN PROVINCE

大荒沟岩基形成于242—220Ma间,为晚海西—早印支期花岗质岩石系列。岩石类型为花岗闪长岩—二长花岗岩—钾长花岗岩,岩系具有酸度高,富Na、Fe,相对贫Mg、K、Rb和REE的特点,属于铝弱过饱和的钙碱性岩系。岩源物质可能为具拉斑玄武质特征的火成岩。花岗闪长岩和二长花岗岩形成于造山运动旋回的早期阶段,而钾长花岗岩属于造山运动晚期阶段的产物,整个岩系的形成反映了一个造山旋回的深成岩浆作用过程。

A comprehensive study of the regional sedimentary cycles, rock body geologyand isotope chronology shows that a granitic rook series was developed in thisarea in the late Hercynian to early Indosinian. The rock types of this graniticseries are: granodiorite, monzonitic granite and K-feldspar granite, and their iso-topic ages range between 242 to 220± Ma. The granitic rock series is generally characterized by high acidity(SiO_2 70%-79% mostly), enrichment in Na and Fe and relative depletion in K, Mg, Rb andREE. Al_2O_3/(Na_2O+K_2O+CaO) values (molecule ratio) are mainly in the range of1.0--1.1, which indicates that the rock series is a weakly peraluminous, calc-alkaline rock series. The source material of the rock series is probably igneous rocks with highcontents of Na and Fe and low Rb/Sr ratios, showing some features of tholeiites.The rock series was formed in an orogenic belt. Granodiorite and monzonitic gra-nite were formed in the early stage of the orogeny, while K-feldspar granite wasrelated to the late orogeny. The granitic rock series as a whole reflects the plutoniccharacteristics of an orogenic cycle.