Mechanisms and recognition of hyper-extension at magma-poor rifted margins

[摘要] Magma-poor rifted margins (MPRMs) are characterised by extreme crustal attenuation that increases ocean ward, serpentinised mantle, detachment fault systems and low volumes of syn-rift magmatism. An apparent “extension discrepancy” exists at MPRMs, whereby the amount of stretching accommodated by seismically observable faults is far less than that required to thin the entire crust to the extent observed on wide-angle seismic and gravity models. Unrecognised polyphase faulting can accommodate the required extension. High degrees of stretching require polyphase faulting (PPF), so that the extension discrepancy may simply be a failure to recognise multiple generations of faulting at MPRMs. The polyphase faulting hypothesis is tested through the consideration of the structural geometries likely to result, generation of synthetic seismic images from those geometries and comparison of synthetic images with reflection seismic data from the hyper-extended Porcupine Basin. From this comparison, I have identified at least two cross-cutting fault generations on the margins of the Porcupine Basin. The models demonstrate PPF can accommodate extremely high strain but is practically un-interpretable when β ≥ c.2.5, remaining hidden on hyper-extended crust. Crustal embrittlement is achievable over two fault generations (minimum) leading to hyper-extension and mantle serpentinisation, with the remaining extension likely accommodated by serpentinite detachment systems.

[发布机构] University:University of Birmingham;Department:School of Geography, Earth and Environmental Sciences

[关键词] G Geography. Anthropology. Recreation;GB Physical geography