摘要
华北克拉通是典型的克拉通破坏的区域,研究该区域的岩石圈有效弹性厚度(Te)及其各向异性特征有助于了解华北克拉通的强度构造及破坏机制.我们根据空间分辨率为30″×30″的地形数据和由自由空气异常解算得到的完全布格重力异常数据,利用Fan小波分析方法计算了两者之间的相关性,并基于Forsyth理论和正交各向异性薄板模型计算了华北克拉通地区的岩石圈Te和其各向异性分布情况.结果表明:(1)从各向同性Te分布来看,华北克拉通岩石圈在东部、中部和西部存在着明显的差异.鄂尔多斯地块、河淮盆地的Te值均较高;中华北克拉通、南北重力梯度带及鲁西隆起Te值较低,约10～25km;郯庐断裂带两侧Te有非常大的差异,西侧的Te明显小于东侧,推测郯庐断裂带在华北克拉通破坏过程中起着非常重要的作用.(2)从Te的各向异性来看,不同块体Te各向异性的大小或方向存在差异,并且研究区内地震大多分布在Te各向异性大小或方向转变的区域.(3)从地震波SKS各向异性和Te各向异性的比较来看,在华北克拉通西部阿拉善块体岩石圈变形趋于垂直连贯变形模式;鄂尔多斯地区各向异性源自历史构造事件的"化石"各向异性;山西裂谷带地区Te的弱轴方向和SKS的快波方向平行,而在山西裂谷带南部的秦岭—大别区域,SKS快波方向和Te弱轴方向相垂直,这可能与地幔热物质上涌等作用有关.此外,Te各向异性与现今构造应力场间的相关性不明显,体现出华北克拉通复杂的构造应力特征.
The North China Craton （NNC） is a typical rejuvenated craton in the world. For this reason, the lithospheric effective elastic thickness （Te） and its anisotropy are important to understand the deformation mechanism of the NNC as well as its tectonic structures. In this work, we apply the Fan wavelet method to compute the coherence between the topography data with spatial resolution of 30＂）〈 30＂ and the Bouguer gravity anomalies derived by free air gravity anomalies, and further calculate the effective lithospheric thickness and its anisotropy based on Forsyth＇s theory and a orthogonal 2D thin plate model. The results show that.. （1） Big isotropie T, variations can be observed between the eastern, central and western parts of the NNC. high Te regions mainly concentrate in the Ordos Block and Huanghe-Huaihe Basin; in central NNC, the North-South Gravity Lineament and west part of Shandong province, Te is relatively low, with typical value of 10~25 km~ across the Tanlu fault, To varies dramatically, the To value in the west side of Tanlu fault is much smaller than that in the east side. Based on this phenomenon, we speculate that the Tanlu fault may play an important role during the deformation process of the North China Craton. （2） The pattern of T, anisotropy distribute unevenly between different regions inside of the NNC, and the earthquakes mainly occurred in the areas where the directions and the magnitudes of T~ change dramatically. （3） Based on the comparison between the SKS seismic anisotropy and the Te anisotropy, we argue that the deformation of the Alashan block in the western NNC is coupled from the deeper depth to the surface, and the Te anisotropy in the Ordos block is belong to the fossil anisotropy which is originated from the historic tectonic movements. In the Shanxi rift, the directions of the weak To axis is parallel to the fast axes of SKS splitting data, and in the south end of the Shanxi rift zone and the Qinling-Dabie orogen, the two kinds of axes are perpendicular, based on the tectonic environment of these regions, we think this kind of coherency and discrepancy may due to the upwelling of the hot materials under the Shanxi rift zone. Generally speaking, the pattern of To anisotropy is not in good consistent with the tectonic stress field at present, which is an strong evidence that the tectonics in the NNC is very complex.
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2012年第11期3576-3590,共15页
Chinese Journal of Geophysics
基金
国家自然科学面上基金(41074052
41174086
40974034)
国家自然科学重点基金(90814009)资助
关键词
有效弹性厚度
各向同性
各向异性
华北克拉通
Effective elastic thickness, Isotropy, Anisotropy, North China Craton
