Writers : Ghasemi.H , Sabzehei.M , and Juteau.T
Refference : Geosciences Scientific Quarterly Journal,No.:29-30,P.:32

Abstract :

Sikhoran Complex is a polygenetic, mafic- ulramalic complex composed of three main parts with different ages including a mafic.uftramafic part, a large isotropic gabbro intrusion and scattered diabasic dykes. Mafic- ulramafic part consists of an harzburgitic dunitic unit with mantle character and an ultramafic and a mafic- untramafic cumulate untis with magmatic sturtures. The harzburgitic dunitic- part consists of foliaated porphyroclastic harzburgites with orthopyoxene lineations in the lower part and porphyroclastic dunites and stratiform chromitites in the upper part.
Ultramafic cumulates are a thick sequence of cumulative dunites, chromitites, wehrlites, olivine websterites and olivine clinopyroxenites. Mat Ic- ultramafic cumulates contain a thick sequence of feldspathic peridotites and layered gabbros including melagabbros, picrtic troctolites, olivine gabbrox, allivalites, noritic gabbros and ferrgabbros intruded in the ultramafic and mafic cumulates and Paleozoic metamorphic rocks created an intense contact metamorphism. Scattered diabasic dykes cut all of them.
Paleozoic metamorphic rocks including amphibilites, marbles, gneiss, anatectic granites and greenschists with an angular unconformity and a basal conglomerate overlain by Lower Jurassic deposits. Absolute age determinations by K-Ar method show 337 ± 7.7 Ma (Middle. Upper Carboniferous) for gneiss and anatectic granite on the biotite and muscovite, 245 ± 7.4 Ma (Permian) for gabbro- pegmatoidic dykes cutting the mafic- ultramafic cumulates on the amphibole, 220 ± 8 Ma (Middle Triassic) on the hornblendes of the basic migmatites in the contact of isotropic gabbros and Paleozoic metamorphics (Age of gabbro emplacement) and 165 ± 12.35 Ma (Upper Jurassic) on the whole rock for diabasic dykes. Field observations, petrographic, mineralogic and geochemistry studies indicate that this complex is not similar to ophiolitic complexes and resulted form mantle upwelling in an extensional tectonic environment.

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