苏鲁地区地壳岩浆底侵的地球物理判识

Geophysical Evidences for Magmatic Underplating in the Sulu Area, East China

底侵作用是研究壳幔物质交换与大陆增生演化的重要机制之一,但是对岩浆底侵作用的判识是十分困难的科学问题。中国大陆科学钻探先行项目在苏鲁地区积累的地震学、地热学及地电学资料表明,在苏鲁地区发生过与大陆裂谷同期的地幔岩浆底侵作用,发生的时段主要为始新世,它的发育与沿嘉山—响水大陆裂谷带在时空上有密切联系。这里的壳幔过渡带厚度可达3 km,推测为橄榄岩与基性麻粒岩互层。结合岩石学资料可以推算出由岩浆底侵作用造成大陆地壳增厚的平均速率约为0.1 mm/a。

Magmatic underplating is an important process in the interaction between the crust and mantle and for un-derstanding continental accretion. However, identification of underplating process is a very difficult task. Based on seismic, geothermal and geoelectrical data collected during the site-selection investigations for the Chinese continental scientific drilling project, it is inferred that an event of magmatic underplating occurred accompany-ing the Jiashan-Xiangshui continental rift system in the Eogene Period. This magmatic underplating process had the same heat origin with the rift system. The thickness of the transition zone between the crust and the mantle is about 3 km and composition of the zone might be the interbed of peridotite and basic granulites. To-gether with the data of basalts in the area, it is estimated that the average rate of vertical thickening of the con-tinental crust owing to the magmatic underplating is about 0. 1 mm/year.