大别造山带肖畈钼矿床花岗岩岩石成因

摘要

The Mesozoic granitoids in the Dabie Orogen are of particular geological interest as indicators for Mesozoic lithospheric evolution because of their close association with porphyry Mo mineralization. Here, we present a study using petrogeochemistry data to constrain the petrogenesis of the Xiaofan granites in the Dabie Mo mineralization belt (DMB), Henan Province, China. Field investigations show that the Xiaofan pluton mainly consists of porphyritic granite. The Xiaofan granites have high SiO2contents of 74.29 wt%-76.07 wt% (average: 75.18 wt%), Al2O3contents of 11.66 wt%-12.83 wt% (average: 12.13 wt%), and K2O contents of 5.37 wt%-7.90 wt% (average: 6.86 wt%) and low MgO (0.06 wt%-0.16 wt%), TiO2(0.09 wt%-0.10 wt%), and P2O5(0.047 wt%-0.103 wt%) contents. They are enriched in Rb, U, K and Hf but depleted in Ba, Nb, Ta, Sr and Ti. By geochemical and mineralogical features, we propose that the Xiaofan granites belong to A-type type granite and dominantly sourced from the crust. The granites from the Xiaofan Mo deposit may have formed in a post-collision extensional setting.%大别造山带中生代花岗岩类岩石不仅能够提供中生代岩石圈演化信息,而且该类岩石往往与斑岩型钼矿床的形成有着密切的联系.本文选择大别钼成矿带上肖畈钼矿床花岗岩,开展岩石地球化学特征研究,岩相学特征表明肖畈花岗岩体属斑岩花岗岩.岩石地球化学结果显示,花岗岩具有高SiO2含量(74.29 wt%~76.07wt%,平均值 75.18 wt%),高 Al2O3含量(11.66 wt%~12.83 wt%,平均值12.13 wt%)和高K2O含量(5.37 wt%~7.90 wt%,平均值6.86 wt%),以及低 MgO含量 (0.06 wt%~0.16 wt%),低TiO2含量(0.09 wt%~0.10 wt%)和低P2O5含量(0.047 wt%~0.103 wt%),岩石富集Rb, U,K和Hf,亏损Ba,Nb,Ta,Sr和Ti.结合岩石产出地质背景和矿物学特征,认为肖畈花岗岩属于源于下地壳的A型花岗岩,形成于后碰撞伸展环境.