Soudan2

Southern Yemen / Oman Offshore

On this idealized geological cross-section of the southern Yemen / Oman offshore from the Mid-Oceanic Ridge to the onshore we can recognize: (i) The oceanic crust, probably, represented by pillow lava coming out of submerged complex of sheeted dykes overlying the lower part of the crust composed by ultramafic rocks ; (ii) The SDRs, i.e., sub-aerial lava-flows emerging from outcropping sheeted dykes formed just after the breakup of the Gondwana lithosphere; (iii) Thinned and highly intruded Lower Continental Crust (when the mantle's intruded material becomes predominant there separation and creation of two continents) ; (iv) A Volcano, i.e., a fissure in the Earth's surface through which molten lava and gases erupted forming an outward complex of lava-flows ; (v) The lengthened Upper Continental Crust with the associated Rift-Type Basins, which are, generally, are filled by non-marine sediment, since they predate the breakup of the Gondwana lithosphere and (vi) The Breakup Unconformity, which emphasize the breakdown of the Gondwana, mainly, by the changing of a differential subsidence to a thermal subsidence, which is, mainly, responsible for the sediment accommodation's magnitude during the Atlantic-type divergent margin deposition (eustasy , i.e., the absolute sea level's changes are, primarily, responsible for the cyclicity of space available for the sediments (accommodation).

Taking into account the geological model depicted on the geological cross-section (previous plate) and assuming that "Theory precedes Observation" (K. Popper, 1934), this tentative geological interpretation of a Canvas autotrace of a seismic line shot in the northern part of the Gulf of Aden does not falsify the proposed model. In fact on this tentative interpretation, the breakup unconformity can be picked between the lengthened Gondwana continental crust in which rift-type basin were developed and the Atlantic-type margin sediments including the lava-flows (volcanic sector of the Atlantic-type margin) exhaled by the volcano. However, a Canvas autotrace of a nearby parallel seismic line allows a more refined alternative interpretation, as illustrated below.

On this autotrace, SDRs, i.e., seaward dipping reflectors, interpreted as lava-flows emitted by sub-aerial spreading centers, created by the breakdown of a thinned and highly intruded continental crust, are quite obvious, on the left middle border of the autotrace. In fact, and particularly, in volcanic Atlantic-type divergent margin, the breakup of the continental crust seems to be the result of a continue and progressively intrusion of of molten basaltic magma, via sheeted dykes, into the crust, i.e., since the basaltic material becomes predominant there is a partition of the crust (breakup). When the molten basaltic material reaches the Earth's surface it flows laterally (SDRs). When the basaltic material reaches the sea floor, it frozen (solidify) as pillow lava (oceanic crust). When basaltic material does not reach the surface or the sea floor, it solidified as sheeted dykes. On the other hand, on this autotrace, rift-type basins are recognized without major difficulty. They are induced by the lengthening of the Gondwana continental crust and so they predate the breakdown. A volcano, i.e., vent from which, magma and other substances erupted to the surface, formed, after the breakup, a typical conic land-form due a staking of solidified lava and lava-flows.