长江中下游成矿带及邻区三维Moho面结构:来自人工源宽角地震资料的约束

为深入理解长江中下游地区在中生代成矿的深部动力学过程,对跨越宁芜矿集区地质廊带内的非纵剖面反射/折射地震数据进行动校正和时深转换处理,获得了非纵方向的Moho面深度;联合纵测线和非纵测线上Moho面深度数据,获得了长江中下游成矿带及邻区的三维Moho面深度结构.结果显示宁芜矿集区下方的Moho面整体较浅,约32~34 km,华北块体合肥盆地内Moho面整体较深,约34~35 km.Moho面深度和区域布格重力异常变化趋势对应良好.宁芜矿集区下方Moho面呈上隆特征,支持长江中下游地区成矿模式中增厚岩石圈发生拆沉、软流圈的上隆及底侵作用等动力学过程.Moho面平行于成矿带走向的变化趋势,预示长江中下游成矿带地壳和上地幔在板块边界发生了NE-SW向的切向流动变形.郯庐断裂带两侧,Moho面深度变化较大,表明地表近陡立的郯庐断裂为深大断裂,深部可能切穿Moho面并延伸至上地幔.

3D Moho depth beneath the middle-lower Yangtze metallogenic belt and its surrounding areas: Insight from the wide angle seismic data

To understand the formation and the tectonic processes of the Mesozoic Middle Lower Yangtze metallogenic belt(MLYMB), the SinoProbe-03-02 program conducted a 450 km long in-line controlled-source seismic experiment with a 400 km long off-line data collection across the Ning-wu ore-district. We deal with the off-line seismic data using normal moveout correction and time-depth conversion in order to obtain the off-line Moho depth. Using the Moho depth derived both from in-line and off-line seismic data, we construct a Moho depth map in the Middle-Lower Yangtze metallogenic belt and its surrounding areas. The results show that the Moho depth is about 32~34 km beneath the Ning-Wu ore-district, shallower than that beneath the Hefei basin in North China which is about 34~35 km. The variation tendency of Moho depth coincides with the Bouguer gravity anomaly well. The uplifting characteristic of Moho depth in Ning-Wu ore-district supports the model of lithosphere delamination, asthenosphere welling, and mantle-derived magmatic underplating during the formation of MLYMB. The variation of Moho beneath metallogenic belt parallels the strike of the MLYMB. It supports the tangential flow deformation in NE-SW direction in the plate boundary of the crust and mantle. On both sides of Tanlu fault zone, the depth of the Moho changes greatly, which indicates that the Tanlu fault may extend to the mantle.