长江中下游成矿带三维S波速度结构及对深部过程的约束

S-wave velocity structure beneath the Middle-Lower Yangtze River Metallogenic Belt and the constraints on the deep dynamic processes

利用73个固定台站记录的163个远震事件数据,采用多道互相关技术挑选了5524条S波到时数据,并对S波到时数据进行地壳校正,在此基础上采用天然地震层析成像方法和远震S波到时信息,获得了长江中下游成矿带上地幔的三维S波速度结构模型.研究结果表明:(1)研究区域上地幔存在着明显的低速异常,且走向与成矿带相同,可能为上涌的软流圈热物质;(2)研究区域地幔过渡带和上地幔底部存在着明显的高速异常,可能为俯冲的古太平洋板块和拆沉的岩石圈;(3)成矿带上地幔的低速异常呈现由南向北逐渐变浅的空间分布特征,该特征表明软流圈热物质由南向北上涌.综合分析认为,成矿带中生代大规模岩浆活动和成矿作用的深部过程主要与岩石圈的拆沉密切相关.

The Middle-Lower Yangtze River Metallogenic Belt（MLYRMB）is one of the most important metallogenic belts in China and plenty of researches have done in this belt.In this paper,we determined a 3-D S-wave velocity structure of the mantle down to 600 km depthbeneath the MLYRMB by using 5524S-wave relative travel times collected from 163 teleseismic events recorded by 73 static seismic stations located within this belt and its adjacent areas.The tomography method used in our study is the TOMOG3 D,which has been widely used in a lot of tomography studies and gained a lot of achievements.In the data processing,we chose the data with high signal to noise ratio according to 3criteria and used an automatic method called MMCC to pick up the relative travel times precisely.Besides that,we have also applied the crust correction method to reduce the effect caused by the crustal inhomogeneity,in order to make the final result more accurate.Our result shows：（1）there exist a low velocity anomaly in the upper mantle and the trend of the anomaly is consist with MLYRMB,which maybe the upwelling of asthenosphere;（2）there exist a high velocity anomaly in the mantle transition zone and the bottom of upper mantle which maybe the subduction of paleo-Pacific plate and the delaminated lithosphere;（3）the low velocity anomaly beneath the belt has a trend that is gradually shallower from the south to the north,which means the up welling of asthenosphere start from south to north.Combining a lot of studies about geophysics,geochemistry,geology and so on,we assumed that the formation of the MLYRMB in Mesozoic was mainly caused by the delamination of lithosphere.