Geodynamics of ophiolites and formation of hydrocarbon fields on the shelf of eastern Sakhalin

Abstract

A model is proposed showing the formation of hydrocarbon fields on the shelf of eastern Sakhalin as being caused by sustained (from the Late Cretaceous to the present) extension in the adjacent deepwater Deryugin Basin with exposure of the upper mantle rocks at the bottom of the sedimentary basin. The thrust faults and detachments formed through this process facilitated the penetration of seawater into ultramafic rocks, thus providing large-scale serpentinization accompanied by generation of hydrocarbons. Extension in the Deryugin Basin was compensated by horizontal shortening at its margins, and as a result, by the formation of ophiolitic allochthons as constituents of the accretionary prism of eastern Sakhalin. Hydrocarbons were injected and pumped in the root zones of the allochthons, giving rise to their westward migration and the formation of petroleum pools in fault-line and underthrust traps on the shelf of Sakhalin Island. The Deryugin Basin is a petroleum-collecting area for oil and gas fields localized in the upper part of its western margin. More broadly, the work considers interrelations between hydrocarbon generation and the geodynamics of tectonic couples of ophiolitic allochthons and adjacent deepwater basins of marginal seas, in particular, in the western Pacific.