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Spatial and temporal controls on the development and evolution of the Tanzanian continental margin

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SiiHowThengP_0917_egisRA.pdf (237.1Mb)
SiiHowThengP_0917_egisRA1.pdf (3.542Mb)
Date
2017-02
Author
Sii How Theng, Pollux
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Abstract
The East African seaboard has historically been considered to be a passive continental margin formed following rifting and continental break-up in the Middle Jurassic. Whilst much of the margin conforms to the standard passive margin model of pre-, syn- and post-rift sequences and a rift-drift subsidence history, the occurrence of anticlines forming the core to the islands of Zanzibar and Pemba attest to a more complicated tectonic evolution. Regional interpretation of a grid of high fidelity 2D and 3D seismic data, including a subset of long-offset, deep lines provides new insights into the margin’s crustal structure and shows geometries not normally attributed to passive margin development. These comprise a gently folded seabed, bedrock subcrop, a series of angular unconformities in the shallow section and an underlying zone of intense deformation associated with contractional reactivation of a precursor normal fault. This is consistent with the margin having undergone a hitherto unrecognized phase of structural inversion in the Neogene. Likewise, inversion and transpression structures are recognised offshore along NNW-SSE striking lineaments such as the Davie-Walu Trough, documenting additional contractional phases during the Cretaceous. Inboard of the zone of structural inversion, the Pemba Channel represents a protected remnant of extension and is still influenced by an E-W extensional regime, something that is substantiated by surface GPS data and earthquake focal mechanisms. The short-lived compressional events are envisaged to be related to external horizontal forces and far-field stresses associated with regional tectonism, particularly within the East African Rift System. However the crustal structure and basement fabric also play a role in the localisation of these stresses. Crustal identification along the margin supports lineaments set up during the initial NNW-SSE extension and N-S dextral southwards motion of Madagascar which may have reactivated under appropriately directed stress.
URI
http://hdl.handle.net/10399/4487
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©Heriot-Watt University, Edinburgh, Scotland, UK EH14 4AS.

Maintained by the Library
Tel: +44 (0)131 451 3577
Library Email: libhelp@hw.ac.uk
ROS Email: open.access@hw.ac.uk

Scottish registered charity number: SC000278

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