关键词: 郯庐断裂带, 挤压活动, 深部过程, 玄武岩喷发

Abstract: Thrusting time of the Tan Lu fault zone has been a controversial issue for long. Recently, many lines of evidence has proved that wide spread compression initiated on the fault zone between Eogene and Neogene, which has given rise to the uplift and consumption of many previous large faulted basins. Since Neogene period the fault zone has continued to suffer from compression, which resulted in many times of thrusting on the fault. The fault zone is currently the largest seismically active belt in eastern China. The compressive activities on the fault zone were dominated by thrusting with small amount of right lateral displacement sometimes and were often associated with the development of NW striking left lateral wrench faults. Margins of basins on the fault zone were intensely involved in the thrusting which caused the formation of shuttered zone and folds. Measurements of paleostress and present stress fields show that the fault zone has suffered nearly E W compression since Neogene due to the back arc spreading of the west Pacific Ocean and tectonic extrusion produced by the northward collision of the Indian Plate. Basalt eruption extensively occurred along the fault zone in Cenozoic, indicating that the fault zone cuts deeply into the upper mantle. Lithological character of the Cenozoic basalts demonstrates that the cutting depth of the fault increased from Paleogene to Quaternary gradually. Geoscience transects reveal obvious intensification of asthenoshperic upwelling beneath the Tan Lu fault zone, which demonstrates that the fault zone cut through the entire lithosphere. Deformed mantle derived xenoliths, such as mylonitic peridotite xenolith, in the basalts reflect that mantle shearing appeared in mantle involved by the fault. Metasomatic minerals in the xenoliths as well as geochemical features of the basalts and xenoliths all suggest that the involved mantle experienced extensive metasomatism. The mantle shearing and metasomatism are related closely and help each other. They also help partial melting in the involved mantle. Under these backgrounds, large scale partial melting appeared in the upper mantle involved by the fault zone. At last, large scale basalt eruption took place along the intracontinental fault zone under the compressive setting. Therefore, integrate active processes of the fault zone since Neogene consist of the thrusting, basin inversion and basalt eruption near the surface as well as the upper mantle shearing, metasomatism and partial melting at deeps.

Key words: Tan Lu fault zone, Compressive activities, Deep processes, Basalt eruption