Search

The magma source, petrogenesis, tectonic setting and geochronology of the late Paleozoic A‐type granites widely exposed in the Zhaheba area, East Junggar, have thus far not been well‐constrained. A better understanding of these issues will help to reveal the magmatic processes and continental growth of Central Asia. The A‐type granites in Zhaheba include the Ashutasi alkaline granites and the Yuyitasi syenogranites, which were emplaced at 321.5 ± 4.8 Ma and 321.7 ± 0.6 Ma, respectively. The major rock‐forming minerals are orthoclase, perthite, arfvedsonite and quartz, which exhibit the following principal geochemical characteristics of A2‐type granites. (1) Their REE distribution curves each exhibit a 'V'‐shaped pattern and a marked depletion in Eu. They are rich in large‐ion lithophile elements Rb, Th and U as well as high‐field‐strength elements Nb, Ta, Zr and Hf, but significantly depleted in Ba, Sr, P and Ti. (2) Their (87Sr/86Sr)i values (0.7021–0.7041), εNd(t) values (4.57–5.16) and REE distribution patterns are in basic agreement with those of the Kalamaili A‐type granite belt in East Junggar. The TDM2 values of the alkaline granites and syenogranites range from 661 to 709 Ma. The A‐type granites may be the products of upwelling asthenosphere‐triggered partial melting of immature lower crust. The alkaline granites were late‐stage products of crystallization and differentiation. Compared to the syenogranites, the alkaline granites are significantly lower in K2O, Na2O, Al2O3, FeO, MgO and CaO, but significantly higher in incompatible elements (e.g., SiO2, Rb, and Sr). The magmatic crystallization temperatures of the syenogranites and alkaline granites are 874°C and 819°C, respectively. As their age gradually decreases (peak ages: 322 Ma and 307 Ma, respectively), there is a gradual decrease in the TDM2 of the A‐type granites and a gradual increase in the εNd(t) value from the Ulungur belt to the Kalamaili belt in East Junggar. The study of A‐type granites is therefore one of the keys to understanding the laws and mechanisms of crustal accretion during the Phanerozoic period, as well as also being of great significance for understanding the Paleozoic accretion. [ABSTRACT FROM AUTHOR]

The article discusses a study which aimed to determine the formation ages, petrogenesis and tectonic settings of the A-type granitoids in the Ulungur granite belt in East Junggar in China. Topics covered include the temporal relationships of the granitoids with the southern Kalamaili A-type granite belts, insights into the tectonic setting in East Junggar during the end of the Early Carboniferous, and the laws and mechanisms of crustal accretion during the Phanerozoic period.

[Display omitted] • The ore-bearing diorite and gabbro-diorite of the Yundunkala deposit formed at ∼ 401 Ma. • The ore-bearing magmas are hybrid. • The Yundunkala deposit formed at an island arc environment. Ongoing exploration in East Junggar, Northwest China, has led to the discovery of the intrusion-related Yundukala Au–Cu–Co deposit. The alteration and mineralization in the Yundukala deposit are closely related to diorite and gabbro-diorite, whereas the geochemical features of these ore-related plutons are still unclear. In this study, in order to unlock the nature of the ore-forming magmas, zircon U–Pb dating, whole-rock major and trace elemental and Sr–Nd isotope analysis, as well as zircon O–Hf isotope analysis, were conducted. Our results show that diorite and gabbro-diorite were both generated in the Early Devonian, with ages being 401.3 ± 3.8 Ma and 401.6 ± 4.5 Ma, respectively. Geochemically, they are all characterized by LREE-enriched patterns in chondrite-normalized REE diagrams, and evident enrichment of Rb, U and K and depletion of Nb and Ta contents in primitive mantle-normalized patterns, although the degrees of enrichment and depletion are variable. Isotopically, the diorite and gabbro-diorite display relatively high initial 87Sr/86Sr (0.704966–0.707395) and positive ε Nd (t) (1.29–3.84) of whole-rock, as well as positive zircon δ18O (5.3–8.9 ‰) and ε Hf (t) (2.4–18.8). These lines of evidence collectively indicate that these magmatic rocks were generated by mixing between mantle- and crustal-derived melts, and were emplacement in an island arc environment. The magma mixing during the formation of ore-bearing diorite and gabbro-diorite might bring abundant sulfur and metals, thus favoring the formation of Au–Cu–Co mineralization. This work emphasizes that further mineral exploration in East Junggar needs to pay attention to the Early Devonian granitoids. [ABSTRACT FROM AUTHOR]