Geochemistry, geodynamic setting and probable origin of orthogneiss in Belqeis Mountain (NW of Iran)

As a part of Takab Metamorphic Complex (TMC), Belqeis Mountain has a variety of ýmetamorphic rocks including orthogneiss, pelitic schists, meta-ýultramafics and mafic rocks and dolomitic marbles. This complex was metamorphosed, faulted and folded ýduring Late Neoproterozoic-Early Cambrian Pan-African orogeny and invaded by ýgranitoid pertinent to the subduction of the Neo-Tethys oceanic crust beneath the ýIranian crust during Tertiary. Geochemically, the protolith of orthogneiss of ýBelqeis Mountain is ýhigh K and has calc-alkaline affinity and both fractional crystallization and magma mixing have been incorporated significantly to produce the protolith of them. The pattern of trace elements normalized to chondrite and primitive mantle points to enrichment in LILE and LREE, depletion of HFSE and HREE and shows negative anomalies in Eu, Ba, ýNb, Sr, Ti and P. Depletion in HFSE was accompanied with enrichment of LILEs and ýLREEs indicating the generation of protolith in subduction setting related to active ýcontinental margins. Tectonic discrimination diagrams suggest a combination of volcanic ýarc and continental collision settings for the studied samples. There are many evidence including La/Nb>1 and relatively high values of several ratios such as Zr/Nb (14.7), Th/Nb (1.5), Ba/Nb (58), La/Nb (3), Ti/Zr (14.9), Nb/Ce (0.24) and (La/Sm)n (3.76),close to crust values, confirming that mantle was not incorporated solely but both crust and mantle sources were contributed in origin of these rocks. All aforementioned ýpoints in addition to occurrence of paleo-suture zone and ophiolitic ýrocks (i.e. serpentinites, meta-mafic and meta-ultramafic rocks) around these medium to ýhigh grade metamorphic rocks confirm that subduction of an oceanic lithosphere followed ýby collision in the study area. ý