Geochemistry,geochronology and zircon Hf isotopes of the Dimunalike granite in South Altyn Tagn and its geological significance

The Dimunalike moyite intruded the Dimunalike shallow marine sedimentary strata in the South Altyn Tagh.Geochemical data shows that,this granite is high in SiO2,K2O and Al2O3,enriched in Rb,Th,K,La,Zr,depleted in Ba,Ta,Nb,Sr,P,Ti,and belongs to weakly peraluminous high-K calc-alkaline series.The Dimunalike moyite has characteristics of S-type granite.The magma of this granite might be derived from melting of greywacke under the temperature of 800℃ and pressure ~10kbar.Variations of eHf(t) are-3.52~0.95.Zircon LA-ICP-MS U-Pb dating yields a weighted average age of 452.8±3.1Ma.The crystallization age of the Dimunalike granite was consistent with the retrograde metamorphic age of the UHP rocks and significantly younger than the peak metamorphic age of the HP-UHP rocks.The Dimunalike granite occurred associated with the Changshagou-Qingshuiquan rifting-related banded mafic-ultramafic intrusion.A possibly reason for this is that,after break-off of the Altyn deep subducted continantal slab,the upwelling material and heat from the deep mantle triggered partial melting of the greywacke unit in the crust.The genesis of the Dimunalike granite displays characteristics of syn-exhumation magmatism.Combined with previous studies,tectonic setting evolution process of the Early Paleozoic granite plutons of the South Altyn continental subduction-collision complex can be subdivided into three stages:I) ~500Ma,this period was dominated by continent-continent collision and crustal thickening,and the age constraint is consistent with the peak age of the HP-UHP metamorphism;II) 462~451Ma,the study area was within an extensional tectonic setting caused by break-off of deep subducted continental slab as indicated by the retrograde metamorphic age of the UHP rocks;III) 426~406Ma,the tectonic setting of this stage is dominated by post-collisional extension and crustal thinning.