Geochemistry and magmatic petrology of meta-ophiolites from the Bajgan Complex (Makran Accretionary Prism, SE Iran): new insights on the nature of the Early Cretaceous Middle East Neotethys

Abstract

The Bajgan Complex in the North Makran Domain (Makran Accretionary Prism) comprises disrupted meta-ophiolitic sequences originating from oceanic crust protoliths. They include ultramafic and mafic cumulates, isotropic gabbros, plagiogranites, and basalts. Ultramafic-mafic cumulates and plagiogranites exhibit compositions akin to rocks formed in mid-ocean ridge settings. Isotropic gabbro and basalt protoliths can be subdivided in three distinct geochemical types. Type-1 rocks is sub-alkaline (Nb/Y < 0.1) with low Th, Nb, and Ta contents and La N /Yb N ratios <1, resembling those of normal-type (N-) mid-ocean ridge basalts (MORB). Type-2 rocks display slight enrichment in Th, Ta, Nb (Nb/Y = 0.36 – 0.45), and La N /Yb N = 2.12 – 3.20, resembling the chemistry of enriched-type (E-) MORB. Type-3 basalts show an alkaline nature (Nb/Y=0.88-1.82), significant Th, Ta, Nb enrichment, and high La N /Yb N ratios (7.01 – 20.08), resembling the chemistry of alkaline basalts (OIB). Petrogenetic modeling indicates that N-MORB protoliths originated from a depleted MORB mantle source, while E-MORB and OIB protoliths were generated from partial melting of sub-oceanic depleted sources that underwent varying degrees of OIB-type enrichment. The Bajgan meta-ophiolitic protoliths were formed within a Late Jurassic to Cretaceous oceanic basin influenced by mantle plume activity and plume-ridge interaction. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists Supplementary material: https://doi.org/10.6084/m9.figshare.c.7193937