Abstract

Six small basanite intrusions were emplaced into the allochthonous Batain Nappes of NE Oman along approximately north–south to NNW–SSE lineaments. They contain olivine, clinopyroxene, plagioclase, analcite, ulvöspinel and apatite ± biotite ± calcite. The basanites are primitive, with Mg numbers (100Mg/(Mg + Fe2+)) from 63.18 to 69.37, and are nepheline normative. Compositional variation suggests fractionation of olivine and clinopyroxene. Thermobarometric studies on rare spinel lherzolite xenoliths suggests re-equilibration at shallow depth. 143Nd/144Nd and 87Sr/86Sr isotopic data and REE modelling indicate that the magmas were formed by 1–2% melting of an ocean-island basalt (OIB)-like source containing about 3–4% garnet. Deviations from OIB are explained by mobilization of incompatible elements from potassic layers in the lithosphere during ascent. Sedimentological studies and three new whole-rock Ar/Ar ages (39.77 ± 0.26, 37.63 ± 0.46 and 36.51 ± 0.21 Ma, Lutetian to Priabonian time) suggest intrusion during maximum deepening of the Abat Trough. Movements were related to dextral strike-slip movement along major tectonic structures during the initial stages of the opening of the Gulf of Aden. The basanites were formed by decompressional melting of an asthenospheric mantle source facilitated by thinned lithosphere and depression of the solidus by H2O- and CO2-rich fluids.

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