Geochronology and geochemistry of late Paleozoic–early Mesozoic igneous rocks of the Erguna Massif, NE China: Implications for the early evolution of the Mongol–Okhotsk tectonic regime. (15th August 2017)

• Record Type: Journal Article
• Authors: Li, Yu; Xu, Wen-Liang; Wang, Feng; Tang, Jie; Zhao, Shuo; Guo, Peng
• Is Part Of: Journal of Asian earth sciences. Volume 144(2017)
• Page Start: 205
• Page End: 224
• Publication Date: 2017-08-15
• Subjects: Erguna Massif -- Late Paleozoic–early Mesozoic -- Geochronology -- Geochemistry -- Central Asian Orogenic Belt; Earth sciences -- Asia -- Periodicals; Sciences de la terre -- Asie -- Périodiques; Earth sciences; Asia; Periodicals; 555.05
• DOI: 10.1016/j.jseaes.2016.12.005
• Languages: English
• ISSNs: 1367-9120

Abstract

Highlights: Late Paleozoic–Early Mesozoic igneous rocks within the Erguna Massif are studied. Late Devonian rhyolites formed under an extensional environment. Late Carboniferous granitoids were derived from partial melting of thickened crust. Late Permian–Middle Triassic magmatisms formed by subduction of Mongol–Okhotsk plate. Abstract: We undertook geochemical and geochronological studies on late Paleozoic–early Mesozoic igneous rocks from the Erguna Massif with the aim of constraining the early evolution of the Mongol–Okhotsk tectonic regime. Zircon crystals from nine representative samples are euhedral–subhedral, display oscillatory growth zoning, and have Th/U values of 0.14–6.48, indicating a magmatic origin. U–Pb dating of zircon using SIMS and LA–ICP–MS indicates that these igneous rocks formed during the Late Devonian (∼365 Ma), late Carboniferous (∼303 Ma), late Permian (∼256 Ma), and Early–Middle Triassic (246–238 Ma). The Late Devonian rhyolites, together with coeval A-type granites, formed in an extensional environment related to the northwestwards subduction of the Heihe–Nenjiang oceanic plate. Their positive εHf ( t ) values (+8.4 to +14.4) and Hf two-stage model ages (TDM2 = 444–827 Ma) indicate they were derived from a newly accreted continental crustal source. The late Carboniferous granodiorites are geochemically similar to adakites, and their εHf ( t ) values (+10.4 to +12.3) and Hf two-stage model ages (TDM2 = 500–607 Ma) suggest they were sourced from thickened juvenile lower crustal material, this thickening may be related to the amalgamation of the Erguna–Xing'an and Songnen–Zhangguangcai Range massifs. Rocks of the late Permian to Middle Triassic suite comprise high-K calc-alkaline monzonites, quartz monzonites, granodiorites, and monzogranites. These rocks are relatively enriched in light rare earth elements and large ion lithophile elements, and depleted in heavy rare earth elements and high field strength elements. They were emplaced, together with coeval porphyry-type ore deposits, along an active continental margin where the Mongol–Okhotsk oceanic plate was subducting beneath the Erguna Massif.