Seismic reflections from the lower crust around Britain
Seismic reflections from the lower crust around Britain
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DOI：
10.1144/gsl.sp.1986.024.01.03
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发表时间：
1986
期刊：
影响因子：
--
通讯作者：
D. Matthews
中科院分区：
文献类型：
--
作者：
D. Matthews
摘要 一幅卡通画展示了英国北部、西部和南部大陆架 BIRPS 剖面前 3000 公里的典型时间段。它显示了低角度正断层带上盘的中生代沉积盆地。倾斜断层反射与下地壳中的层状结构合并，在大约 6 秒的双向传播时间和大约 10 秒的地壳底部之间表现为几个强但短（约 4 公里）的水平反射。最上地幔没有反射，除非倾斜事件以 15 秒的双向时间从层状下地壳延伸到剖面底部。该漫画通过参考个人资料中的示例来证明其合理性。讨论状态提出了正在测试的假设。下地壳中的分层是真实的，这是由于宽约 4 公里、厚度数十米的平躺叶理透镜体造成的，其中地震速度因流体的存在而降低。有人建议用盐水来解释下地壳的电导率，而二氧化碳可能与麻粒岩有关。几何学表明，下地壳在断层发生时具有延展性，并且在西欧中生代拉伸期间，叶理变得水平。
Summary A cartoon is presented which represents a time-section typical of the first 3000 km of BIRPS profiling over the continental shelf north, west and south of Britain. It shows a Mesozoic sedimentary basin in the hanging wall of a low-angle normal fault zone. The dipping fault reflection merges with layering in the lower crust which appears as several strong but short (c. 4 km) horizontal reflections between about 6 s two-way travel time and the base of the crust at about 10 s. The uppermost mantle is devoid of reflections except where dipping events extend from the layered lower crust towards the base of the section at 15 s two-way time. The cartoon is justified by reference to examples from profiles. Discussion states present hypotheses that are being tested. The layering in the lower crust is real and due to lenses of flat-lying foliation about 4 km across and tens of metres in thickness in which the seismic velocity has been reduced by the presence of fluids. Brine has been suggested to account for the electrical conductivity of the lower crust, and carbon dioxide may be associated with granulites. The geometry implies that the lower crust was ductile at the time of faulting, and that the foliation became horizontal during Mesozoic stretching of West Europe.