Petrogenesis of the Darvazeh mafic-intermediate intrusive bodies, Qorveh, Sanandaj-Sirjanzone, Iran
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ORIGINAL PAPER
Petrogenesis of the Darvazeh mafic-intermediate intrusive bodies, Qorveh, Sanandaj-Sirjanzone, Iran Tahereh Molaei Yeganeh 1 & Ashraf Torkian 1 & Eric H. Christiansen 2 & Ali A. Sepahi 1 Received: 1 November 2016 / Accepted: 16 April 2018 # Saudi Society for Geosciences 2018
Abstract The Darvazeh intrusion in the northern Sanandaj-Sirjan zone in the Alpine-Himalayan orogenic belt is composed of olivine gabbro, gabbroic diorite and granitoid units that intruded Jurassic metamorphic rocks. Field relations, textures, and whole rock geochemistry indicate that most of the mafic to intermediate composition rocks are not cumulates and instead represent liquid compositions. The tholeiitic (or ferroan) gabbros and magnesian gabbroic diorites evolved along liquid lines of descent and have different parental magmas. This conclusion is based on separate trends, often with overlapping MgO contents, for Si, Fe, Ti, Ni, Cr, Zn, Cu and Sr. The mineralogy (late versus early magnetite and contrasting proportions of magmatic amphibole) of the two suites are also slightly different as is the trace element patterns (for example Th, U, Ti and Sr). The Mg# of mafic-intermediate rocks ranges from 46 to 73, implying that the ultimate source for the most mafic rocks was in the mantle, not the crust. Flat HREE patterns, Sm/Yb ratios ( 0.70 along with Ni > 400 ppm and Cr > 1000 ppm; Wilson 1989). Only the most MgO-enriched gabbro approaches these values, but none of the gabbroic diorites do. The gabbroic diorites are consistently more chemically evolved than the gabbros (Fig. 7). Thus, the most mafic gabbro may have crystallized from a near primary magma, but significant differentiation has occurred between the mantle source regions and the level of emplacement for most of the other rocks. In addition to the field and textural evidence, the Darvazeh rocks are chemically distinct from cumulates like those in the nearby Malayer-Boroujerd complex (Deevsalar et al. 2014) or to those erupted as xenoliths from arc volcanoes (e.g., Costa et al. 2002). Compared to the amphibole-bearing cumulate xenoliths of San Pedro volcano, the Darvazeh gabbros have higher contents of
SiO2 and Na2O and lower concentrations of MgO and TiO2. Unlike the cumulate Malayer-Bououjerd gabbros, most of the Darvazeh gabbros lack positive Eu anomalies (Fig. 8) and have low Sr/Y ratios and high incompatible trace element concentrations inconsistent with a cumulate nature (Fig. 8). Moreover, mineral compositions in the Darvazeh pluton are approximately in equilibrium with melts of the same composition as the whole rocks. Thus, we conclude that most of the samples are representative of liquids. When plotted on MgO variation diagrams, the compositions of the gabbros and gabbroic diorites form more or less continuous trends for some elements (Fig. 6). Al2O3, CaO, Cr, and Ni contents decrease with decreasing MgO, with the gabbroic diorites being depleted in these apparently compatible elements. On the other hand, SiO2, Na2O, K2O, P2O5, Zr and
Arab J Geosci (2018
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