Cambro-Ordovician potassic (alkaline) magmatism in Central Oman: Petrological and geochemical constraints on petrogenesis

Cambro-Ordovician alkaline magmatism is exposed in four small laccolithic intrusions in the Huqf area of Central Oman. 40Ar/39Ar dating suggests the presence of two pulses of magmatism at approximately 513–526 Ma and 452–461 Ma. The emplacement of ultramafic foidites characterized the earlier stage of magmatism, while later stage resulted in the intrusion of a sequence of mildly potassic minettes and tephrites. The source of the magmas has many similarities to that of EM1 oceanic island basalts. Trace element evidence however, suggests enrichment of the protolith by supra-subduction zone fluids. The petrogenesis of the suite is therefore explained by mixing of melts derived by small degree partial melting of previously enriched garnet- and spinel–peridotite-facies mantle sources, caused by a perturbed geotherm during minor lithospheric extension.