GEOCHEMISTRY AND PETROLOGY OF GABBRO INTRUSIONS AND ULTRAMAFIC ROCKS FROM WESTERN MARGIN OF MAKRAN ACCRETIONARY WEDGE (COLOURED MELANGE) COMPLEX, SE IRAN

The Makran accretionary wedge is exposed in SE Iran and SW Pakistan. Makran active subduction zone has been recorded history of subduction of Mesozoic Neo Tethys Ocean and present day subduction of Oman sea beneath central Iran (Lut block). in this study we represent new geochemical,petrological approaches and field observations of Mesozoic Alpine orogeny related coloured melange complex of Cretaceous Makran Ophiolites which still remains enigmatic in cases.

The study area to be known as 'Chahar Dahane' consists of an assemblage of metric to decametric thick slices mainly represented by Mantle Peridotites and Gabbroic intrusions. Based on EPMA datas of Mantle Peridotites, we estimated pressure 5-7 kb and temperature 1150-1200 C for clinopyroxene crystallization by using two pyroxene method at hydrous magma conditions, The Mantle peridotites Chrome Spinels are ferrian Paleonaste in composition but the Enrichment of Al³⁺ ratio to Fe³⁺ in spinels from lherzolites suggests that Lherzolites spinels formed at lower Oxygen fugacity and higher pressure than those spinels in Dunites which shows Al³⁺ depletion. we also carry out Olivines are forsterite in composition with 88-91 Mg# and finally we determine supra-subduction tectonic environment for Mantle peridotites with 15-25% partial melting at hydrous conditions.

Gabbroic intrusions mostly cross cut the Mantle Harzburgites, field observations approve that late or post injection of Gabbros based on brittle facies and fine grain recrystallized contact margin between Gabbro bodies and their Peridotite host.

for investigation on tectonic setting and characteristics of magma for gabbro bodies we decided to use ICP-MS datas. we selected post magmatic stable elements such as: Nb,Ta,Y,Zr,Ti,Th,La,Sm to achieve the aim of study. the results from La/Sm, Ba/Th and Th/Ta Vs Zr ratios shows signatures of sediment melting components from down going Neo Tethyan slab were added to sub Arc Mantle wedge and soviniour Arc characteristics and signatures for gabbros which approved by Back-Arc tectonic setting at active continental margin for formation of this Gabbro bodies in extensional environment by melting of 5-10 % Spinel Peridotite at Makran Mesozoic magmatic Arc.

in brief we suggest that Mantle Peridotites section undergoes 15-20% partial melting at Supra-Subduction tectonomagmatic setting in Neo-Tethyan Back-Arc system.