摘要
古太古代(约4.0Ga)时地球上可能只有一个超级大陆,它的岩石圈厚度高达400km。在早元古代,这个超级大陆减薄、裂解成十几块,每块中心是太古宙岩石,边缘是元古宙岩石,且各块厚度不等(150～350km)。从元古宙之后这些被称之为稳定克拉通的大陆岩石圈就一直漂游在地幔软流圈之上。中国华北地块就是这些克拉通之一,与众不同的是它在中生代时遭受了第二次破坏,岩石圈厚度从古生代时的180～200km减少到现今的80～100km。本文作者从流变学的视角出发,围绕华北克拉通破坏和岩石圈减薄这一核心问题,从岩石圈厚度的定义、应变弱化及其机理、岩石圈减薄的时空不均一性、岩石圈减薄的构造模型、郯庐深大断裂的作用以及地幔热转流的效应等6个方面分别阐明一些自己的观点,希望能与华北克拉通研究的同行们讨论。
A supercontinent with a keel down to the mantle transition zone （～400 km） is assumed to have existed during the early Archean （～4.0 Ga）. The supercontinent （Rodinia？） was thinned and finally split into fragments with highly variable thicknesses （150～350 kin） and sizes （1 ×10^6～17 × 10^6 km^2） during the early and middle Proterozoic. Each fragment or craton is characterized by a thick Archean lithosphere surrounded by thin Proterozoic mobile belts. Since the late Proterozoic, these cratons have been stable without notable deformation and moved around Earth＇s surface. Unlike most of the cratons such as the Canadian and African ones, the North China craton （NCC） was re-activated during the Mesozoic and reduced its lithospheric thickness from 180～200 km in the Paleozoic to 80～100 km in the Cenozoic. The critical problems associated with the break-up and lithospheric thinning of the NCC are discussed in terms of rheology, with special focuses on the effects of various strain softening mechanisms （e. g. , water weakening, reaction weakening, melt-induced weakening, structural layering weakening, recrystallization weakening, geometrical weakening, and superplasticity）, heat deflection, and trans-lithospheric shear zones （e. g. , Tan-Lu fault zone）. The lithosphere beneath the Qinling-Dabie-Sulu orogenic belt, thickened by the Triassic collision between the NCC and Yangtze block, diverted heat coming vertically from the deep mantle away from the thickened southern margin of the NCC into the lithosphere beneath the Bohai Gulf and the Song-Liao basins. It is emphasized that the lithospheric thickness is a more complicated concept than has been generally considered. The lithospheric thicknesses determined using different techniques （e. g., petrology, geochemistry, S-wave tomography, wave receiver functions, low velocity zone, geothermal data, rheology, electrical conductivity, and water content） can contradict each other. Any conclusion about the lithospheric thinning obtained from a single technique should be cross-checked by other methods.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2008年第2期174-193,共20页
Acta Geologica Sinica
基金
中国国家自然科学基金海外青年合作基金
中国科学院杰出海外青年学者基金
加拿大自然科学和工程研究基金联合资助
关键词
华北克拉通
岩石圈减薄
流变学
应变弱化
郯庐断裂
地幔热转流
North China craton
lithospheric thinning
rheology
strain softening
Tanlu fault zone
mantle heat flow diverting
