Modern Analogue for Interlayered Evaporites and Seaward Dipping Volcanic Reflectors: Danakil Depression, Northern Afar, East Africa

Teunis Heyn¹, Elizabeth Baker², Mark Thompson³, and Kevin P. Boyd^3
1BP America, Houston, TX
²Royal Holloway University, London, United Kingdom
³BP Exploration, Sunbury, United Kingdom

Seaward Dipping Reflectors (SDR’s) are observed on seismic data of passive margins, but their relationship to salt is difficult to observe. In Northern Afar a series of shield volcanoes have formed from extension between the Danakil Horst (microplate) and the Ethiopian Plateau (20 mm/yr). This region, known as the Danakil depression, lies below sea level and is characterized by Quaternary shield volcanoes fed by magma from deep chambers and dykes. Volcanic crests along the centre of the Depression rise above sea level leaving the surrounding low lying valleys to accumulate evaporites; 1.6 km of halite was deposited near Dallol along the north flank of the northern shield volcano located closest to the Red Sea. Thin gypsum deposits are observed on Landsat images further south along the depression. Basaltic flows from the shield volcanoes will develop into SDR’s if continued extension and subsidence of the surrounding valleys occurs. Old lava flows will rotate beneath the loads of progressively younger eruptions. Accommodation space for the rotated flanks of the volcanoes must be provided by plastic deformation in the asthenosphere. The depression is expected to widen as the crust is progressively thinned by episodes of dike injection and faulting and will continue to be infilled with evaporites and lava flows. Eventually, extension and subsidence will outpace salt deposition when the Danakil microplate breaks away. Marine incursion will occur and submarine pillow basalts will begin to form instead. In this process, the mantle must rise below the subsiding Danakil Depression as continental crust is progressively attenuated. The Danakil Depression is experiencing the transition from rift to drift and represents a modern analogue for understanding evaporites and SDR’s.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas