The volcanic stratigraphy and petrogenesis of the Oman ophiolite complex

Abstract

The volcanic stratigraphy and trace element geochemistry of the Oman ophiolite complex indicate a multistage magmatic origin comprising: (1) magmatism due to sea-floor spreading in a marginal basin; (2) magmatism associated with discrete submarine volcanic centres or seamounts; (3) magmatism associated with crustal uplift and rifting; and (4) magmatism associated with continent-arc collision. Trace element petrogenetic modelling is used to investigate the nature of the mantle source region and the partial melting and fractional crystallization history for each magmatic event. The petrogenetic pathway for the 'sea-floor spreading' lavas requires a high degree of melting of a mantle that was depleted in incompatible elements prior to subduction but subsequently selectively enriched in certain elements (mostly LIL elements and H2O) from an underlying subduction zone; it also requires magma mixing in an 'open system' magma chamber prior to eruption. The 'seamount' lavas were probably derived by a similar degree of partial melting of a similar source, but fractional crystallization was restricted to smaller high-level magma chambers. The 'rifting' lavas were derived from a mantle source that was more depleted than the 'seamount' lavas prior to subduction but which was later modified by a larger subduction zone component. The 'syn-collision' lavas were however derived from an enriched mantle source, which probably underlay the passive continental margin rather than the marginal basin complex. Results such as these may provide considerable insight into the petrogenetic changes accompanying the transitions from spreading to arc volcanism in a supra-subduction zone setting. © 1982 Springer-Verlag.