长江中下游成矿带九瑞矿集区(北部)含矿岩体的锆石U-Pb定年及其地质意义

Zircon U-Pb Ages of Ore-bearing Granitic Bodies in Northern Jiujiang-Ruichang Metallogenic District of the Mineralization Belt of the Middle-Lower Reaches of the Yangtze River,and Its Geological Significance

江西九(江)-瑞(昌)地区是长江中下游铜-铁-金(硫)成矿带的一个重要的矿集区,位于成矿带的西段。本文选取了区内研究程度相对薄弱的丁家山、洋鸡山、宝山、铜岭和大浪等5个与Cu-Au成矿作用密切相关的花岗质岩体,首次进行了锆石LA-ICP-MS U-Pb年龄测定,并讨论其地质意义。测年结果显示,上述岩体分别形成于145.4±1.2 Ma、144.8±1.3 Ma、143.6±1.2 Ma、141.2±1.3 Ma和146.4±1.2 Ma,为晚侏罗世-早白垩世岩浆活动的产物。结合区域地质资料,认为九瑞矿集区内这一成岩-成矿地质事件可能与古太平洋板块俯冲挤压造山作用后期整体向弧后伸展环境过渡的地球动力学机制有关。是否为区域性加厚下地壳、拆沉下地壳部分熔融或洋脊俯冲作用的产物,还有待进一步研究。

The Jiujiang-Ruichang area is an important ore concentrated district in the western section of the Cu-Fe-Au（S） mineralization belt of the Middle-Lower Reaches of the Yangtze River.Five poorly-stuided granitic rocks at Dingjiashan,Yangjisha,Baoshan,Tongling,and Daliang,which are closely related to Cu-Au mineralization,were selected to conduct zircon LA-ICP-MS U-Pb dating and explore its geological significance.Zircon U-Pb dating results indicate that these granitic rocks formed in Late Jurassic to Early Cretaceous at 145.4±1.2 Ma,144.8±1.3 Ma,143.6±1.2 Ma,141.2±1.3 Ma and 146.4±1.2 Ma,respectively,and may be the product of the Createcous magmatic activity.In combination to regional geological data,it is believed that the petrogenetic and metallogenic event in the Jiujiang-Ruichang ore concentrated district may occur in a transitional environment from the early orogeny stage of the paleo-Pacific plate subduction to the subsequent back-arc extensional environment.However,much research is necessary to study whether they were formed by partial melting of overthickened or delaminated lower crust,or resulted from the oceanic ridge subduction along the lower Yangtze River area.