华南陆块岩石圈有效弹性厚度及其构造意义

华南陆块受多阶段超大陆聚合、裂解,碰撞、陆内造山,及伸展等作用影响,造成其深部结构和构造极其复杂。岩石圈有效弹性厚度(Te)是表征地质时间尺度上岩石圈力学强度的定量指标,可为深入认识岩石圈力学结构及演化提供有效约束。本文基于导纳和相关函数联合方法对地壳布格重力异常和地形数据进行计算,获得华南陆块Te的空间分布。Te高值(>20 km)区域主要分布于扬子地块的四川盆地周边区域,而Te低值(<20 km)区域集中于华夏地块和江南造山带区域。由于Te分布特征与地热场、地震关系密切。通过分析研究区Te与地热场(地表热流、居里面深度)、地震之间的关系,本文得到如下认识:(1)Te与地热场参数具有较好的相关性,但受浅部地壳被破坏,深部仍为克拉通地壳影响,导致龙门山断裂带和江南造山带区域的Te与地表热流或居里面深度之间的部分对应关系相反。(2)Te与地震关系复杂,Te较薄区域并不代表着地震频发区域,地震活动性与其所处的深部环境相关。龙门山断裂带强震频发的原因是受周边两块体中上地壳刚性地层长期相互作用,致使应力和能量积累较强;华夏地块区域地震较少是因为深部热物质上涌对华夏地块的壳幔进行强烈...

The Effective Elastic Thickness of Lithosphere and Its Tectonic Implications in the South China Block

The South China Block (SCB) has undergone multi-stage tectonic events (e.g., polymerization, fission, collision, orogeny, extension) that have led to its complex deep structure and construction. The effective elastic thickness (Te) of the lithosphere represents the response of the lithosphere to long-term flexural strength. It can reflect the deformation mechanism and thermodynamic state of the lithosphere. In this study, we applied a joint inversion of admittance and coherence for calculated the spatial variations of Te in the SCB based on topography and the crustal Bouguer gravity anomaly data. The Sichuan Basin within the Yangtze Block (YB) and its surroundings mostly corresponded to high Te (>20 km), whereas the Cathaysian Block (CB) and Jiangnan Orogenic Belt (JOB) tended to display low Te (<20 km). Moreover, the Te distribution characteristics were closely related to geothermal state and earthquakes. We analyzed the relationship of between Te and geothermal state (terrestrial heat flow and the Curie depth), earthquakes, and their tectonic implications. The results are as follows: (1) The Te had a good correlation with geothermal state parameters, but the Longmenshan fault and the JOB had a contrary correspondence between Te and terrestrial heat flow or the Curie depth. The above anomaly phenomenon may have been the disruption of the shallow crust disrupted, and the deep crust is still the craton. (2) The relationship between earthquake and Te is complicated. The Te thinner areas did not equat with the areas of high-frequency earthquake occurrences. The frequency of earthquake occurrences are related to the deep environment. The high frequency of earthquakes in the Longmenshan fault is due to the long-term interaction between the rigid strata of the upper-middle crust of the YB and Songpang-Ganzi Block. It resulting in a strong accumulation of stress and energy. The low frequency of earthquake occurrences in the CB because the crust-mantle was strongly reformation by the upwelling of deep thermal material, and has lateral distribution uneven weak strata in the crust to absorb the stress. The stronger lithospheric mechanics strength of the YB resulted in fewer earthquakes distribution.