The Central Asian Orogenic Belt was one of the most important sites for juvenile crustal growth during the Phanerozoic worldwide, and Eastern Tianshan, Northwest China, located in southern Central Asian Orogenic Belt, is one of the key areas for unravelling the accretionary processes and continental growth. Zircon U–Pb geochronological, Hf isotopic, and whole‐rock geochemical analyses are reported for the Upper Carboniferous Qishan Formation rhyolites from the Kalatage area in the middle of the Harlik–Dananhu arc, Eastern Tianshan, to investigate its petrogenesis and geodynamic setting. Zircon U–Pb ages obtained by laser‐ablation inductively coupled mass spectrometry (LA‐ICP‐MS) indicated that zircon crystallization age of the rhyolite was 299.1 ± 2.1 Ma. The rhyolites are classified as subalkaline and high‐K calc‐alkaline series with A/CNK values mainly lower than 1.10. The REE patterns exhibit right inclined curves with negative Eu anomalies, and the trace element spider diagrams show depletions in Nb, Ta, and Eu, which is consistent with the geochemical characteristics of the island arc calc‐alkaline magma suffered fractional crystallization. In situ zircons Hf isotopic analyses yielded positive initial εHf(t) values ranging from 8.0 to 11.9 and the two‐stage Hf isotope crustal model ages (T DM C ) of 554 to 807 Ma. It indicated that the rhyolite was derived from remelting of juvenile crust. The geochemical data for the rhyolites indicate that they were probably generated in a suprasubduction zone setting. It is proposed that the North Tianshan oceanic crust subducted northward beneath the Harlik–Dananhu arc during the Late Upper Carboniferous, and the rhyolites were derived from remelting of juvenile crust and generated in a suprasubduction zone setting.
The Precambrian banded iron formations (BIFs) not only relate to the evolution of life, ocean, and atmosphere but also provide important reserves of iron around the world. The Gongchangling iron ore deposit located in the Anshan‐Benxi area of Liaoning Province, China, is oxide facies Algoma‐type BIFs, and the Gongchangling No.2 mining area is famous for the production of high‐grade iron ore in China. Magnetite is the main ore mineral in the Gongchangling iron ore deposit, and the magnetite mainly exhibits three modes of occurrence: BIFs (without actinolite), actinolite‐bearing BIFs, and high‐grade iron ore. Trace elemental compositions of the magnetite with different occurrences of the Gongchangling iron ore deposit were obtained by laser ablation inductively coupled plasma mass spectrometry to constrain the genesis of the high‐grade iron ore. The magnetite from actinolite‐bearing BIFs shows relatively lower contents of Mg, Al, Mn, and Zn compared to the magnetite from BIFs (without actinolite), suggesting that coexisting minerals have played an important role in the trace element concentration in magnetite. The magnetite from high‐grade iron ore has lower contents of Ti and V and higher contents of Al and Mn than counterpart from BIFs (with/without actinolite), indicating that the high‐grade iron ore may be reformed by high temperature metamorphic hydrothermal fluid. The staurolite‐garnet‐biotite schist is the wall‐rock of high‐grade iron ore, and the garnet‐biotite geothermometry is used to evaluate the metamorphic temperature of 593 ± 17 °C. It is proposed that the metamorphic hydrothermal fluid produced during regional metamorphism reformed BIFs to generate high‐grade iron ore.
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