华北地台东部古生代与新生代岩石圈地幔特征及其演化

Comparison between Palaeozoic and Cenozoic Lithospheric Mantle in the Eastern Part of the North China Block——With a Discussion of Mantle Evolution

古生代含金刚石及捕虏体的金伯利岩和新生代含捕虏体的玄武岩先后共同侵位于华北地台东部,提供了研究自古生代以来板内岩石圈地幔特征及其演化的深源岩石探针。通过对古生代与新生代、新生代时郯庐断裂带内与带外岩石圈地幔物质之间岩相学,岩石和矿物的主元素、微量元素,地幔热状态的对比研究,结合现代地球物理资料,建立了以新生地幔物质对古老岩石圈置换作用为主的华北地台东部地幔减薄模型。该模型强调,古老岩石圈地幔业已存在的幔内薄弱带及郯庐断裂带为新生地幔物质和流体提供了通道。

Palaeozoic diamond-and xenolith-bearing kimberlites and Cenozoic xenolith-bearing basalts, erupted in the eastern part of the North China Block (NCB), provide excellent mantle probes for research on intraplate processes and the Phanerozoic evolution of the subcontinental lithospheric mantle (SCLM). In this study, the mineral inclusions in diamond and xenoliths from Mengyin (Shandong province) and Fuxian (Liaoning province) kimberlites were chosen for constraining the nature of Palaeozoic SCLM. while xenoliths from the Shanwang and Qixia basalts (in Shandong province) were chosen for constraining the natures of Cenozoic SCLM. Shanwang lies astride the Tancheng-Lujiang (Tanlu) fault zone, a major lithospheric fault in eastern China, and Qixia lies east of the fault zone. Based on the research on the petrography of mantle xenoliths , petrochemistry, major and trace element geochemistry of mantle minerals, mantle heat state, combined with the modern geophysical data, it is concluded that the attenuation and replacement of the Palaeozoic SCLM by upwelling asthenospheric materials through thermal erosion and possibly delamination resulted in the formation of irregular-shaped hot bodies, mainly along weakness zones within the mantle. The Tanlu fault played an important role in the Cenozoic replacement of the pre-existing lithospheric mantle.