Geochemistry and petrogenesis of metabasites from the Gol-e-Gohar Complex in southern Sanandaj-Sirjan metamorphic zone, South of Iran; Evidences for crustal extension and magmatism at early Palaeozoic.

In Gol-e-Gohar metamorphic Complex from south-eastern Sanandaj-Sirjan metamorphic zone (Kerman province, Iran), there are two types of metabasites, wich contain layered metamorphosed lava flows and younger meta-gabbros. The protoliths formed in the Paleozoic era and were metamorphosed during the early Cimmerian orogenic phase in the late Triassic, under temperatures of 640–680oC and pressures of ~7–10.5kbar (amphibolite facies). These rocks are garnet-bearing amphibolites, garnet-free amphibolites and metamorphosed gabbros. Many mineralogical and chemical aspects of these metabasites are similar, although the layered metabasites show tholeiitic and the metagabbros depict alkaline affinities. Evidences such as whole rock geochemical characteristics, Sr and Nd isotopic data, (143Nd/144Ndinitial=0.511913–0.512067; eNd550Ma=-0.31–2.68), relatively flat patterns of chondrite-normalized Rare Earth Elements and multi-elemental diagrams, the enrichment in TiO2 (average content ~2.16) and high Zr/Y ratios (3–8), indicate that all of Gol-e-Gohar metabasites were formed in an extensional intra-continental rift zone from tholeiitic to alkaline magmas. The data suggest that the parent magmas could derive from low degrees of partial melting of spinel-lherzolite sources in subcontinental lithospheric mantle. These evidences confirm the existence of extensional environments in the southern part of the Sanandaj-Sirjan metamorphic zone in the Paleozoic era, when large extensional depressions developed in the Sanandaj-Sirjan metamorphic zone with underlying asthenosphere ascent. Partial melting took place during this time. Gradually, thick sequences of continental detritic sediments and tholeiitic lava flows accumulated in these troughs. A subsequent magmatic event in the area was characterized by emplacement of alkaline gabbro intrusions. At the early Cimmerian orogeny, these sedimentary-igneous rock associations metamorphosed and the Gol-e-Gohar metabasites formed.