The effect of thermal weakening and buoyancy forces on rift localization: Field evidences from the Gulf of Aden oblique rifting

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• 作者：N. Bellahsen ; L. Husson ; J. Autin ; S. Leroy ; E. d'Acremont
• 关键词：Rifting ; Gulf of Aden ; Buoyancy forces ; Analog models
• 刊名：Tectonophysics
• 出版年：11 November, 2013
• 年：2013
• 卷：607
• 期：Complete
• 页码：80-97
• 全文大小：3785 K

文摘

On the basis of field and geophysical data, analog and numerical models, we here discuss the role of buoyancy forces arising from thickness variations in the lithosphere during rifting. In the Gulf of Aden, an oceanized Tertiary oblique rift, several successive directions of extension and associated normal faults suggest that transient stress rotations occurred during rifting. Especially, rift-parallel faults (070掳E) overprinted the early divergence-perpendicular normal faults (110掳E). Moreover, some first-order differences are noticeable between the western part of the Gulf, which deformed under the Afar hot spot influence, and the eastern part. In the western Gulf of Aden, the ocean-continent transition (OCT) and the oceanic ridge have cut obliquely through the inherited and reactivated Mesozoic basins (100掳E to 140掳E). The OCT trend is parallel to the overall Gulf trend (070掳E). In the eastern part, the oceanization occurred within few syn-rift 110掳E-trending basins and the OCT trends mostly perpendicular to the divergence direction. Here, we propose that this contrast is strongly controlled by the Afar hot spot: during rifting times, the hot spot likely induced a hot thermal anomaly in the western asthenosphere. This may have triggered both thermal buoyancy forces and thermal weakening of the lithosphere that helped localizing the rift obliquely. In such localized rift, rift-perpendicular trending crustal buoyancy forces (i.e. around 160掳E) have enhanced rift-parallel normal faults (070掳E) during final rift localization into a narrow zone strongly oblique to the early syn-rift basins. As a consequence of the Afar hot spot, in the west, the ridge is long and straight; in the east, the ridge segments are rather long too (although less than in the west) as the ridge initiated parallel to the OCT; in between, the ridge is more segmented as both the hot spot influence gradually decreases eastward and the ridge initiated obliquely to the OCT.