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Zircon U-Pb-Hf isotopes, integrated with bulk-rock major, trace element, and isotopic compositions of amphibolites from the Makran ophiolitic mélange complex (OMC), carry implications on the evolution of the Neo-Tethys Ocean. Field and petrographical-geochemical data confirm these amphibolites as products of the metamorphism of a mafic protolith. Zircons from the amphibolites have U-Pb ages of Late Early Permian (273 Ma) to Late Triassic (210 Ma), and their εHf(t) values vary from +6.32 to +15.4. The Makran amphibolites are geochemically similar to transitional- or enriched-MORBs. The 143Nd/144Nd(t) ratios for amphibolites range from 0.51260 to 0.512551, and 87Sr/86Sr(t) from 0.704433 to 0.706244. The Pb-isotope composition of these rocks is radiogenic, ranging from 15.61-15.64 for 207Pb/204Pb(t), 18.98-19.21 for 206Pb/204Pb(t) and 38.88-39.36 for 208Pb/204Pb(t). The isotopic and geochemical signatures of these rocks suggest that they were most likely formed during continental rifting and originated from a relatively enriched mantle source. This is also attested by their high zircon Ce/Ce* ratios. We interpret these amphibolites related to the Permian-Triassic plumes that triggered Gondwana rifting to open the Neo-Tethyan Ocean before metamorphosed, fragmented, and accreted into the Makran accretionary complex probably during Early to Late Cretaceous time. [ABSTRACT FROM AUTHOR]

The Makran complex in southeast Iran provides a spectacular subduction-related accretionary complex to understand the mechanism of oceanic accretion and the evolution of subduction zones. In this paper, we present new major and trace element data as well as isotopic compositions of mafic volcanic blocks from the Makran ophiolitic mélange complex (OMC). Our aim is to assess the genesis of these rocks and discuss their implications on the evolution of Neotethys Ocean. These volcanic blocks are composed mainly of basalts with minor trachytes. The Makran lavas are occasionally interlayered with tuff layers. Zircons from these tuffs give U-Pb ages of 95 Ma, which is well in accordance with the reposted microfossil data for the interlayered pelagic limestones with pillow lavas. Makran basalts can be geochemically subdivided into four groups; normal to transitional MORB, enriched-MORB, Plume-type MORB and alkaline (-OIB-like) basalts. The OIB-like pillow lavas are represented by high values of Th/Tb (6.3–7.4) which are higher than other basalts (group 1 = 0.3–0.8; groups 2 = 0.7–1.6; group 3 = 1.58–1.36).143Nd/144Nd(t) ratios for basalts ranges from 0.51247 to 0.51292, whereas 87Sr/86Sr(t) isotopic composition of the OMC lavas varies from 0.704433 to 0.709466. The Pb isotopic composition of the lavas are quite high, ranging from 15.49–15.66 for 207Pb/204Pb(t), 18.09–19.12 for 206Pb/204Pb(t) and 37.80–39.23 for 208Pb/204Pb(t). The chemistry of these rocks suggests that they were formed most likely in an oceanic setting with clear plume-ridge interaction. These rocks can form from partial melting of a highly heterogeneous mantle source, which is extensively metasomatized with deep mantle OIB-type components. We suggest these rocks have been generated in an oceanic ridge with plume-ridge interaction, similar to the Iceland-Reykjanes Ridge, before being fragmented and accreted into the Makran accretionary complex. [ABSTRACT FROM AUTHOR]