龙门山深部结构的三维视密度成像技术解析

Delineating deep structures of the Longmen mountains using apparent density imaging technology

为描述和解析龙门山深部地质构造特征,结合模型试算和效果分析,利用一种基于多空间异常分离的三维快速视密度反演成像技术,处理并得到了龙门山地区多空间多尺度源的视密度分布。视密度成像结果表明:松潘-甘孜地块地壳低密度物质流在向东推进时,受到扬子地块冷硬高密度物质的阻挡,导致沿龙门山形成高密度老变质基底物质逆冲倒转的推覆体弧形构造,中下地壳伴有大规模低密度中酸性热岩浆活动。这种三维空间密度信息的物质展布特征,在展示深浅部构造的差异性与继承性特征的同时,也较好地刻画了龙门山不同深度区域构造边界,为深入研究该地区地壳结构、深部构造演化、地震孕育动力等方面提供了依据。

Deep geological tectonic features of the Longmen mountains were described using a fast 3D apparent density imaging technology.This technology,based on multiple spatial anomaly separation with model test and effect analysis,was applied to the Longmen mountains area to obtain lateral apparent density distributions corresponding to sources of multiple scales.Results of apparent density imaging show that crustal low-density material flow of the Songpan-Ganzi fold belt is moving eastward,and it is blocked by cold high-density material of the Yangtze plate.High density,old metamorphic basement material thrust nappe arc structures along the Longmen mountains,with massive low density acidic hot magma activity between middle and lower crusts. The material distribution characteristics of 3D space density information shows differences and inheritance characteristics between deep and shallow structures,delineating structural boundaries of Longmen mountains in different depths,which could provide some insights for research of deep structure evolution,seismogenic mechanism,and crustal structure in this area.