Zircon U-Pb Chronology,Geochemistry,and Their Tectonic Setting of Granitic Rocks from Northern Daocheng Batholith in West Sichuan
The genesis and tectonic setting of granitoids in the northern part of Daocheng batholith in West Sichuan are still debated.In this paper,a compilation of petrology,zircon U-Pb chronology,geochemistry and Hf isotopes was conducted on the granitoid to solve this uncertainty.LA-ICP-MS zircon U-Pb dating result shows that granitoids in the northern part of the batholith were formed at 213-212 Ma,slightly later than those in the southern part.Granitoids researched are mainly composed of granodiorite and monzogranite,the former of which contains many MME(mafic microgranular enclaves).Accessory minerals contain apatite,epidote,zircon and opaque minerals.Enrichment in sodium,and large ion lithophile elements,metaluminous to weak peraluminous are typical geochemical characteristics of the representative granitic samples.Their εHf(t)values are very scattered,ranging from-16.6 to 2.4(average-5.0),reflecting average crustal residence age(t2DM)of 2.04-1.25 Ga(average 1.4)of the granitic source.Combined with regional geological evidence,the granitoids are I-type garanites derived from partial melting of basement metabasalt from the Mesoproterozoic Kangding complex,part of metagreywacks maybe involved in the acid member.Upwelling of asthenosphere and partial melting of the middle and lower crusts triggered by slab detachment under post-orogenic extension environment are responsible for the formation of granitoids.
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