Gravity, heat flow, and seismic constraints on the processes of crustal extension : Northern margin of the South China Sea
Gravity, heat flow, and seismic constraints on the processes of crustal extension : Northern margin of the South China Sea
复制标题
DOI：
10.1029/95jb01868
复制
发表时间：
1995-11
影响因子：
--
通讯作者：
S. Nissen;D. Hayes;Yao Bochu;W. Zeng;Yong-shun Chen;Xiaupin Nu
中科院分区：
文献类型：
--
作者：
S. Nissen;D. Hayes;Yao Bochu;W. Zeng;Yong-shun Chen;Xiaupin Nu
多道地震数据和重力数据已被用于构建横跨南海北部裂谷边缘的三条（东部、中部、西部）剖面的地壳厚度剖面。然后通过对两种极端类型的伸展过程（纯剪切和简单剪切）的影响进行建模，来解释该边缘现今的地壳构造。通过将沉降和热流的模型预测与边缘的观测结果进行比较，评估了每种过程对华南边缘伸展的适用性。当使用标准输入参数的典型值时，这两种极端模型都不能令人满意地拟合华南边缘东部和中部剖面的观测数据；两种模型都显著低估了所得的热流。在纯剪切模型的情况下，要么假设初始稳态岩石圈厚度异常薄（约60公里），要么假设原始未伸展的大陆地壳内有异常大的地壳放射性热产生，才能使热流观测结果相符。一种也许更合理的替代方案是假设存在一个初始比“正常”稳态岩石圈略薄（厚度约为90 - 100公里）的岩石圈，同时原始地壳有大量的上地壳放射性热产生。华南边缘下方基底内存在白垩纪花岗岩体（假设的）可以容纳这种热产生。然而，在简单剪切模型的情况下，只有假设稳态岩石圈厚度异常薄（约60公里），才能使华南裂谷边缘观测到的高热流相符。因为在纯剪切情况下，使用更符合实际的输入参数可以使表征岩石圈伸展的观测地球物理数据相符，所以在解释华南边缘大规模裂谷作用时，纯剪切伸展比简单剪切伸展更受青睐，被认为是主要机制。然而，对于地壳内的伸展，考虑到已发表的关于华南边缘贯穿地壳断层的地震证据，两种过程的组合不仅是可能的，而且是很有可能的。
Multichannel seismic data and gravity data have been used to construct crustal thickness profiles for three transects (eastern, central, western) across the rifted northern margin of the South China Sea. The present-day crustal configuration of the margin is then interpreted by modeling the effects of two end-member classes of extension processes, pure shear and simple shear. The applicability of each of these processes to the extension of the south China margin has been evaluated by comparing model predictions of subsidence and heat flow with observations across the margin. Neither of these end-member models satisfactorily fits the observed data on the eastern and central transects across the south China margin when typical values for standard input parameters are used; the resulting heat flow is significantly underestimated by both models. In the case of a pure shear model, heat flow observations may be matched either by assuming an uncommonly thin initial steady state lithospheric thickness (∼60 km) or by assuming an unusually large crustal radiogenic heat production within the original, unextended continental crust. A perhaps more reasonable alternative scenario presumes the existence of an initially slightly thinner than “normal” steady state lithosphere (thicknesses of ∼90–100 km) in conjunction with a significant amount of upper crustal radiogenic heat production. Such heat production could be accommodated by the presence of Cretaceous granitic bodies (hypothesized) within the basement beneath the south China margin. In the case of a simple shear model, however, the observed high heat flow on the rifted south China margin may only be matched if the steady state lithospheric thickness is assumed to be uncommonly thin (∼60 km). Because the observed geophysical data characterizing lithospheric extension may be matched using more realistic input parameters in the pure shear case, pure shear extension is preferred over simple shear extension as the dominant mechanism for explaining the large-scale rifting of the south China margin. For extension within the crust, however, combinations of both processes are not only possible, but probable, given published seismic evidence for through-going crustal faults on the south China margin.