Isostatic state and crustal structure of North China Craton derived from GOCE gravity data
Isostatic state and crustal structure of North China Craton derived from GOCE gravity data
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DOI：
10.1016/j.tecto.2020.228475
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发表时间：
2020-07
期刊：
影响因子：
2.9
通讯作者：
Yuan-yuan Li;Yu-shan Yang
中科院分区：
文献类型：
--
作者：
Yuan-yuan Li;Yu-shan Yang
华北克拉通不同亚区之间的地壳结构对加深对克拉通演化的认识起着重要作用。本文给出了由GO_CONS_GCF_2_TIM_R3模型导出的NCC挠曲莫霍面图和均衡剩余重力场，首先研究了附加源对挠曲计算的影响，特别是岩石圈厚度自西向东明显减薄的影响。在消除LAB起伏的重力影响后，利用Vening-Meinesz区域等重力场模型计算了NCC的弯曲莫霍面和均衡剩余重力场。东部块体和横贯华北造山带下方存在高-中等正剩余异常，阴山块体、鄂尔多斯高原和孔兹岩带为负剩余异常。这种明显的差异与弯曲莫霍面深度自西向东逐渐减小的趋势是一致的。利用一条横跨东部地块、华北造山带和西部地块的剖面，建立了地壳和上地幔的密度结构。通过对比地表地形、布格重力、均衡莫霍面和地震莫霍面的起伏，发现鄂尔多斯地块北方边缘的挠曲莫霍面比地震莫霍面浅得多，可能反映了岩石圈过程中以NW-SE向挤压变形为主的均衡状态。密度模拟结果进一步预测了鄂尔多斯地块北方边缘下地壳可能存在一个高密度体，该高密度体可能是一个向西倾斜的中上地壳残留物，滞留在西部地块下地壳中。中高压变质作用的麻粒岩相或榴辉岩相，造成后续的大陆增厚在大陆碰撞可能是负责修改剩余的俯冲残余。
The crustal structure between different subregions of the North China craton (NCC) plays an important role in improving our understanding on the craton evolution. Here we present a flexural Moho map and isostatic residual gravity field of the NCC derived from the GO_CONS_GCF_2_TIM_R3 model.We first investigate the influence of additional sources on the forward flexure calculation, especially the distinct thinning of the lithospheric thickness from west to east. After removing the gravity effects of the LAB undulations, the flexural Moho and isostatic residual gravity field of the NCC are calculated using the Vening-Meinesz regional isostasy models. There are high to medium positive residual anomalies beneath the Eastern block and Trans-North China Orogen, while negative residual anomalies delineate the Yinshan block, Ordos plateau and Khondalite belt. This obvious disparity is consistent well with the decreasing depth of the flexural Moho from west to the east. A profile across the Eastern block, Trans-North China orogen and the Western block was employed to construct a density structure of the crust and uppermost mantle. By comparing the surface topography, Bouguer gravity, isostatic Moho and seismological Moho undulations, we find that the flexural Moho is much shallower than the seismic Moho beneath the northern margin of the Ordos block, possibly indicating the over-compensated isostatic state caused by the dominant NW–SE oriented compressional deformation in the lithospheric processes. Density modeling results further predicted that a high density body may exist in the lower crust beneath the northern margin of the Ordos block, which could be a westward-dipping upper-middle crust remnant stagnating in the lower crust beneath the Western block. Medium to high pressure metamorphism of granulite facies or eclogite facies, resulting from subsequent continental thickening during the continental collision may be responsible for modifying the remaining subduction remnant.