赣杭构造带中段岩石圈电性结构研究

Study on the Lithospheric Electrical Structure of Beneath the Central Segment of the Gan-Hang Tectonic Belt

赣杭构造带(简称赣杭带)位于扬子板块和华夏板块的结合部,是中国重要的铀多金属矿成矿带,发育一系列中酸性火山—侵入杂岩;前人对岩浆喷发和侵入的地球动力学背景仍然存在诸多争议。文章对赣杭带中段(盛源盆地)及邻区收集的大地电磁测深(MT)数据,利用MT相位张量分解技术、二维非线性共轭梯度法(NLCG)等技术手段进行处理和反演获得到了研究区可靠的岩石圈电性结构。结合已有资料分析表明:赣杭带中段浅部火山—侵入杂岩带存在东南方向下倾的高导带和深部软流圈高导区且相连,揭示了该地区中酸性岩浆活动受区域江绍深断裂控制,在晚中生代岩石圈伸展作用下沿着区域深断裂上升侵入和喷发形成火山—侵入杂岩;该岩浆活动处在伸展构造环境与同期Izanagi板块俯冲后撤有关。

The Gan-Hang tectonic belt(GHB)is an important uranium polymetallic ore belt,which is located at the junction of the Yangtze plate and the Cathaysia plate.A series of intermediate-felsic volcano-intrusive rocks are developed in the belt.There are still many controversies about the geodynamic backgrounds of magmatic eruption and intrusion in the belt.Therefore,the magnetotelluric(MT)data collected in the middle part of the Gan-Hang Belt(Shengyuan Basin)and its adjacent areas are processed and inverted by MT phase tensor decomposition technique,two-dimensional nonlinear conjugate gradient method(NLCG),and other technical means to obtain reliable lithospheric electrical structures in the area.The analysis reveals that the shallow volcano-intrusive hybrid rocks in the middle part of the GHB is connected with the southeast downdipping highconductivity band and the deep asthenosphere area,suggesting that the felsic magmatism in the region was controlled by the regional Jiang-Shao deep fracture.In the late Mesozoic lithospheric stretching led to magma rise along the regional deep fracture under the action of intrusion and eruption,forming the volcano-intrusive complexes;The magmatism in the extensional tectonic regime was related to the coeval retreat of the subducting Pacific plate.