Rift that will Host Important Deposits of Hydrocarbons: A Review of the Petrologic Constraints Recorded by the Mantle Peridotites from Ophiolite Massifs

Abstract

Rift formation has long been the focus of attention for researchers, and numerous studies have been carried out in order to understand causes and modes of whole lithospheric extension. The process of lithospheric rifting is classically considered to be a product of “active rifting” or “passive rifting”, depending upon which forces are involved at the inception of rifting. Continental rifting is conventionally described as a thinning process of the whole lithosphere, ultimately leading to rupture of the continent, onset of sea-floor spreading and the consequent formation of a mid-oceanic ridge. Rifting is the initial and fundamental process by which the separation of a continent into two tectonic plates takes place. Active rifting or mantle-activated rifting has been classically ascribed to the ascent of a mantle plume impinging upon the base of the lithosphere, with consequent heating and thinning of the lithosphere. Passive rifting has been classically considered the result of horizontal stretching of the continental lithosphere, in which far-field tectonic stresses, generated at the boundaries of the lithospheric plates, result in lithosphere extension. Continental rifts are the sites of significant oil and gas accumulations, such as the Viking Graben and the Gulf of Suez Rift. Thirty percent of giant oil and gas fields are found within such a setting. In 1999 it was estimated that there were 200 billion barrels of recoverable oil reserves hosted in rifts.