LA-ICP-MS Zircon U-Pb Dating,Sr-Nd-Hf Isotopic Analysis Of The Early Paleozoic Intermediate-acidic Intrusions In The Wenquan Area,Xinjiang

The Tianshan orogenic belt is located in the southern margin of the Central Asian orogenic belt,There are abundant mineral resources and a large number of magmatic rocks,and they are closely related.Wenquan area is located at the northern edge of the Yili-Siberia plate,where developed a belt of early Palaeozoic intrusive rocks and that is also a key area to study of the northern Yili Block tectonic setting and evolution of the old Junggar Ocean.On the basis of field geological survey and petrographic observation,in this paper,we present new whole-rock data,U-Pb ages and Sr-Nd-Hf isotopic datas for the early Palaeozoic diorite which from the Wenquan in norhern edges of Yili Block.Zircon U-Pb dating demonstrates that the weighted mean²⁰⁶Pb/²³⁸U age for the zircons from quartz diorite is 457.1±3.9Ma,455.4±5.0Ma and467.7±5.4Ma,i.e.,it indicated these diorite bodies crystallization time is from early Ordovician to middle Ordovician.The petrology and chemical composition show that these diorite samples are characterized by low Si O₂?50.19%⁶1.91%,average content:56.57%?and TiO₂?0.84%¹.13%,average content:1.01%?conents,a slightly higher MgO?2.36%⁸.17%,average content:4.60%??Ca O?3.94%⁹.45%,average content:6.50%?and total alkali?Na₂O+K₂O=3.74⁷.06%,average content:5.41%?conents,moreover,high Na₂O/K₂O rate?2.50⁴.61,average content:3.69?,but low A/CNK rate?0.70⁰.95,average content:0.84?.Geochemical datas suggest that these diorite bodies are calcium alkaline-high potassium calcium alkaline series rocks.Besides,the diorite samples are enriched large ion lithophile elements?Rb,K?,but high field strength elements?Nb,Ta,Ti?show a loss,the“V”REE pattern which is left high and right low and with minor negative Eu anomalies??Eu=0.67¹.12,average content:0.90?.Thus geochemically resembling the diorite bodies are formed in the continental margin arc.Various binary diagrams reveal fractional crystallization of olivine,clinopyroxene and hornblende.The presence of stratum relicts and the La/Sm value?2.99⁸.59,average value:5.95?suggest the limited crustal contamination during the rise of the magma.The isotopes of these diorites are characterized by high(⁸⁷Sr/⁸⁶Sr)_i?from 0.707604 to 0.708662?,low(¹⁴³Nd/¹⁴⁴Nd)_i?from 0.512270 to0.512377?,low?_Nd?t??from-1.73 to-0.70?.Zircon Hf isotopic compositions of the quartz diorite are mainly characterized by?Hf?t?values of 3.9⁷.0,two-stage model ages of 991Ma to 1191Ma?average value:1083Ma?which is older than U-Pb age.Petrology,geochemical datas and zircon Hf isotopic compositions implying the primary magma derived from a depleted mantle,and may have been added metasomatic enriched lithospheric mantle components,and also contaminated by crustal material.Based on the regional magmatism and previous studies,the authors inferred that the old Junggar Ocean crust subducted southward beneath the northern edges of Yili Block during 467.7Ma⁴55.4Ma.