Geosystems and Geoenvironment (Aug 2023)
Geochemistry of volcanic rocks and dykes from the Remeshk-Mokhtarabad and Fannuj-Maskutan Ophiolites (Makran Accretionary Prism, SE Iran): New constraints for magma generation in the Middle East neo-Tethys
Abstract
The Remeshk-Mokhtarabad and Fannuj-Maskutan ophiolites represent two major ophiolitic units in the North Makran Domain (Makran Accretionary Prism). Volcanic rocks and dykes of these ophiolites mainly consist of basalts and rare basaltic andesites, andesites and dacites. No chemical distinction can be seen in basalts from these two ophiolitic units, or between volcanic rocks and dykes. Basaltic rocks show a broad MORB-type nature but variable chemical composition (e.g., SiO2= 42.64–52.63 wt%; TiO2= 0.98–2.43 wt%; Mg# = 71–50). They show both N-MORB (Type 1) and E-MORB (Type 2) compositions (MORB: mid-ocean ridge basalt; N: normal; E: enriched). Type 1 rocks are very rare in both ophiolitic units, whereas Type 2 rocks are predominant. Type 1 rocks show low Th (0.10–0.16 ppm), Nb (1.86–2.82 ppm), Ta (0.09–0.17 ppm) abundance and low (La/Yb)N (0.50–0.75), (La/Sm)N (0.48–0.72) ratios. Compared to N-MORBs, Type 2 basalts show slight enrichment in Th (0.42–1.60 ppm), Nb (6.09–14.6 ppm), and Ta (0.227–0.792 ppm), as well as (La/Yb)N and (La/Sm)N ratios >1 like those observed in typical E-MORB. Trace element petrogenetic models indicate that primitive basalts derived from partial melting of a heterogeneous sub-oceanic mantle variably metasomatized by plume-type (OIB-) components. Type 1 basalts derived from partial melting of mantle regions with no enrichment in OIB-type components, whereas Type 2 basalts derived from partial melting of DMM sources variably enriched by OIB-components. These rocks formed in an oceanic basin that was strongly affected by mantle plume activity and different extents of plume-ridge interaction.
