摘要:
毕机沟钒钛磁铁矿位于扬子板块北缘汉南杂岩的西北部,是基性-超基性杂岩体分异演化的产物.矿区范围出露的岩石主要包括橄长岩、辉长岩、辉长闪长岩和闪长岩,具有明显岩相分带和韵律旋回特征.目前,已发现的多个钒钛磁铁矿体均位于基性岩-超基性杂岩体的辉长岩相带内.本次研究对毕机沟矿区的含矿辉长岩和穿切含矿辉长岩的花岗岩脉进行了原位微区LA-MC-ICPMS锆石U-Pb定年,获得两者的侵位时间分别为(783±4)Ma(MSWD=0.09)和(759±4)Ma(MSWD=1.50),结果表明毕机沟钒钛磁铁矿的成矿时代大约为783 Ma,但不晚于759 Ma.结合前人区域成果资料,毕机沟含钒钛磁铁矿的基性-超基性杂岩体与该区新元古代大规模具岛弧性质的基性-超基性杂岩体的形成时代相近,我们认为毕机沟钒-钛磁铁矿可能形成于活动型大陆边缘环境.
Abstract:
Situated in the northwest of the Hannan complex on the northern margin of the Yangtze Plate, the Bijigou V-Ti magnetite deposit is a product of the mafic-ultramafic magma differentiation. It consists mainly of olivine gabbro, gabbro, gabbro diorite and diorite, and exhibits clear lithofacies belts and rhythmicity. Several V-Ti magnetite bodies have been found in the gabbro lithofacies belt of mafic-ultramafic complex. In order to find out the metallogenic epoch of the Bijigou V-Ti magnetite deposit, the authors present new laser ablation–multicollector–inductively coupled plasma–mass spectrometry (LA-MC-ICP-MS) U-Pb data for zircons from mineralized gabbro and granite dike in the Bijigou V-Ti magnetite deposit, with the emplacement ages being (783±4) Ma (MSWD=0.09) and (759±4) Ma (MSWD=1.50), respectively. These new ages suggest that the mineralization of the Bijigou V-Ti magnetite deposit occurred at 783 Ma and was not later than 759 Ma. Coupled with previous regional data, the age of the Bijigou mafic-ultramafic rock-containing V-Ti magnetite deposit is similar to that of Neoproterozoic large scale mafic-ultramafic complex with arc properties. It is therefore held that the Bijigou V-Ti magnetite deposit might have been formed on the active continental margin.
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