武夷山成矿带及邻区上地幔速度结构及其对燕山期岩浆-成矿活动的启示

The upper mantle velocity structure beneath the Wuyishan metallogenic belt and its adjacent areas:Implications for the Yanshanian magmatism and mineralization

武夷山成矿带燕山期岩浆-成矿活动的深部动力学机制一直是学者们研究的热点。已有的研究结果表明,武夷山成矿带及邻区的上地幔存在着显著的低速异常,可能与地表的岩浆-成矿活动存在着密切的联系。本研究利用分布在华夏地块98个固定地震台站以及59个流动地震台站所记录到的278个远震事件,采用远震层析成像方法构建了武夷山成矿带及邻区上地幔三维P波速度结构模型。成像结果表明,武夷山成矿带及其东侧的上地幔存在着显著的低速异常,代表了热物质富集的地幔楔,且上地幔的热物质在这些地幔楔间进行着横向流动。东南沿海的地幔过渡带存在着一个显著的低速异常,推测为新生代欧亚板块与菲律宾海板块碰撞俯冲的产物。南岭成矿带下方的低速异常从上地幔一直向上延伸到上地壳,可能指示了一个热物质上涌的通道。结合已有的研究结果,本研究认为武夷山成矿带燕山期岩浆-成矿活动可能与古太平洋板块的俯冲和后撤所引起的热物质上涌有关。

The deep dynamic process of the Yanshanian magmatism and mineralization in the Wuyishan metallogenic belt is always a research hotspot among scholars.Previous studies have shown that there exist prominent low-Vp anomalies in the upper mantle beneath the Wuyishan metallogenic belt and its adjacent areas,which may be closely related to the magmatism and mineralization at the surface.In this study,we apply the teleseismic tomography method and present a three-dimensional P-wave velocity model of the upper mantle beneath the Wuyishan metallogenic belt and its adjacent areas by using 278 teleseismic events recorded by 98 permanent seismic stations as well as 59 temporary seismic stations in the Cathaysia Block.Our model shows prominent low-Vp anomalies do exist in the upper mantle beneath the Wuyishan metallogenic belt and its eastern adjacent areas,which may represent mantle wedges with rich thermal materials.Furthermore,the thermal materials revealed by our results flow laterally between these mantle wedges.A prominent low-Vp anomaly also exists in the Mantle Transition Zone beneath the southeastern coastal area,which may be caused by the collision between the Eurasian Plate and the Philippine Sea Plate in the Cenozoic.And a low-Vp anomaly beneath the Nanling metallogenic belt extends upward from the upper mantle to the upper crust,which perhaps indicates an upwelling channel for thermal materials.Based on previous studies,we suggest that the Yanshanian magmatism and mineralization in the Wuyishan metallogenic belt could be related to the upwelling of thermal materials caused by the Paleo-Pacific Plate subduction and rollback.