11:45 AM - 12:00 PM
[SIT09-11] From Birth to Death: Fate of The Extremely High-T Subduction Zone of The Oman Ophiolite
Keywords:Oman Ophiolite, boninite, high-T subduction zone, metamorphic sole, subduction initiation, obduction
Melt inclusions in Cr spinel derived from boninite comprise homogeneous glass of mostly low-Si boninitic [3,4] and slightly differentiated composition, with SiO2 ranging in 52-62 wt% and MgO up to 16 wt%. The primary boninite magma assumed as the most magnesian melt inclusion can coexist with mantle olivine and orthopyroxene  at 0.4-0.6 GPa and 1350°C. This T-P conditions indicate a segregation depth of ~17 km from the mantle with a potential T of 1400°C. Meanwhile, the peak metamorphic conditions for the subducted slab that liberated high-T fluids to form boninite and arc tholeiite magmas are 770–900°C and 1.1-1.3 GPa [1,6,7].
The keys of the Oman subduction zone are 1) the preservation of diapiric structures in the mantle , 2) short time interval of the V1 and V2 magmatism <2 m.y., 3) T-P conditions for a primary low-Si boninite (Umino et al., 2014); and 4) extremely high T & low-P metamorphic conditions for the sole that liberated the fluids generating the V2 magmas [1,5]. These lines of evidence are most readily explained by intraoceanic thrusting initiated near the ridge axis that developed into a shallow and hot subduction zone [1,2,8,10].
Forced subduction of such an extremely high-T, buoyant slab suppressed convection in the mantle wedge, resulted in the progressive depletion of the source mantle through the V2 arc magmatism. Numerical modeling suggests that melting of the slab and mantle wedge occurrs only in the early stage and ceases as the mantle wedge cools because of the absence of convection . Consequently, the Oman arc volcanism terminated in only a few million years. After several million years, parts of the subducted slab delaminated and induced upwelling and adiabatic melting of DMM asthenosphere, resulted in the generation of alkalic magmas of V3 extruded onto thick pelagic sediments before colliding onto the Arabian Peninsula.
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