江苏东海大陆钻址区层析成像

Tomography in the Chinese Continental Scientific Drilling Area of Donghai County, Jiangsu Province, China

苏鲁大别造山带是出露榴辉岩典型的超高压变质带,大陆科学钻选择东海县榴辉岩大片覆盖区作为址区,对揭示碰撞造山和后期变形及折返等动力学过程有重要意义。但该地区缺少深部地质资料和数据,层析成像作为深部速度扰动分析的主要手段之一,可以作为这个地区的深部探测的先导工作。以钻址为中心布置了N340W和N70E的十字测线。层析反演结果第3层与重力异常变化一致,和Moho面变化有关,高速体和高重力都在中心出现,而郯庐断裂和嘉山-响水断裂均为高低速体变化的界线。NS剖面垂直于构造走向可分为三个部分,可能分别代表扬子板块、苏鲁地体和华北板块及它们之间界线的特征。南部断裂产状较陡,在其北侧隐约有不连续倾斜的高速体,北部断裂的产状比较一致的北倾,受郯庐断裂控制明显。200km深度以上的高速体与低速体发生突变的地带,分别处于30km、80km、130km的深度上,相当于Moho面、岩石圈、软流圈的大致深度。这种格局反映了苏鲁地区在断裂控制下岩石圈活动的特征。

The Sulu-Dabie erogenic belt is a typical UHP zone with outcropping of eclogites. The CCSD (Chinese Continental Scientific Drilling) project chose Donghai County which is covered by widespread eclogites as the first site for deep drilling, because this will be of great significance in disclosing the geodynamic processes of the post-collisional orogeny and later deformation and exhumation. However, the lack in data for the deep geology of this area makes tomography one of the most important methods for velocity perturbation analysis of deep materials, and it may serve as a guide for deep surveys of the area. We arranged a crossed profile at the center of the drilling site at N340°W and N70°E. The results of the tomography show that the 3rd layer is consistent with the variations of the Bouguer anomaly, and related to the Moho. Both the high velocity perturbation and high gravity appear at the center, and the Tanlu and Jiashan-Xiangshui faults both show as boundaries between high and low velocities and gravities. The NS section perpendicular to the structural strike can be divided into three parts, which represent the Yangtze, Sulu and North China plates respectively. The fault in the southern part is steeper with discontinuous dipping high-velocity bodies, while the faults in the northern part are all dipping north, obviously controlled by the Tanlu fault. There are three zones of abrupt changes for high- and low-velocity bodies at depths below 200 km, which are at 30 km, 80 km and 130 km, corresponding to the depths of the Moho, the lithosphere and the asthenosphere, respectively. This framework reflects the features of lithosphere activity controlled by deep faults in the Sulu area.