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We present new zircon U–Pb–Hf and whole-rock geochemical data for volcanic rocks along the eastern margin of the Xing'an Massif of NE China in order to further our understanding of the history of subduction towards the SE and the spatial extent of the Mongol–Okhotsk tectonic regime. Zircon U–Pb dating indicates that the Triassic volcanism in the Xing'an Massif occurred in two stages during the Middle (ca. 242 Ma) and Late (ca. 223–228 Ma) Triassic. Middle Triassic basaltic andesites in the Heihe area have an affinity to arc-type volcanic rocks. The zircon ε Hf (t) values (+ 8.5 to + 12.7) suggest that the primary magma was generated by the partial melting of a relatively depleted mantle wedge that had been metasomatized by subduction-related fluids. The Late Triassic andesites in the Handaqi area exhibit geochemical affinities to high-Mg adakitic andesites. Their zircon ε Hf (t) values (+ 11.5 to + 14.5) and T DM2 ages (313–484 Ma) indicate that their primary magma was derived from the partial melting of a young subducted oceanic crust, followed by interaction with melts derived from mantle peridotite. The Late Triassic basaltic andesites, andesites, and dacites in the Zhalantun–Moguqi area have features similar to those of igneous rocks formed in subduction zones. Their zircon ε Hf (t) values (+ 8.4 to + 15.4) and T DM1 ages (260–542 Ma) indicate that their primary magma was derived from the partial melting of a depleted mantle wedge that had been metasomatized by subduction-related fluids. These data suggest that the Triassic volcanic rocks of the Xing'an Massif formed in an active continental margin setting associated with the southward subduction of the Mongol–Okhotsk oceanic plate towards the SE. We conclude that the Mongol–Okhotsk tectonic regime extended at least as far as the eastern margin of the Xing'an Massif, and that the tectonism spanned the period from the late Permian to early Early-Cretaceous. [ABSTRACT FROM AUTHOR]

We present the first evidence of an early Paleozoic terrane in the southern Yanbian region, NE China. We used LA-ICP-MS zircon U–Pb and Hf isotope techniques to analyze one plagioclase gneiss and two garnet-bearing two-mica quartz schists from the early Paleozoic Jiangyu Group, as well as two tonalites that intruded the Jiangyu Group. The tonalites yield weighted mean 206 Pb/ 238 U zircon crystallization ages of 423 and 422 Ma. Zircons from the Jiangyu Group gneiss and two schist samples yield maximum depositional ages of 439 ± 4, 443 ± 2, and 443 ± 5 Ma, respectively. These constraints, together with the age of the tonalite intrusion, indicate that the Jiangyu Group was deposited between 443 and 423 Ma (i.e., Silurian). In addition, detrital zircon age spectra of the three Jiangyu Group samples exhibit prominent age peaks at 442, 473, 513, 565, 600, 635, 671, 740, 1000, and 1162 Ma, as well as secondary peaks between 1344 and 3329 Ma. The occurrence of the prominent Meso- and Neoproterozoic detrital zircon age populations for the Jiangyu Group, combined with the corresponding zircon Hf isotopic data, reveals that the Jiangyu Terrane has a tectonic affinity with northeastern Gondwana. The early Paleozoic magmatism, as suggested by the medium-K calc-alkaline I-type tonalite intrusion and Jiangyu Group detrital zircon age spectra, corresponds to coeval subduction–accretion events along the southern margin of the eastern Central Asian Orogenic Belt (CAOB). Accordingly, we propose that the Jiangyu Group is part of an exotic terrane that rifted from northeastern Gondwana, drifted northward, and ultimately became involved in the early Paleozoic tectonic evolution of the southern margin of the eastern CAOB after the Early Cambrian. [ABSTRACT FROM AUTHOR]

Abstract: The Central Asian Orogenic Belt (CAOB) is a natural laboratory of the Phanerozoic accretionary orogen. The eastern section of the CAOB contains several microcontinental massifs, and it is unknown whether these massifs carry Precambrian basement. Here we present the results of U–Pb dating of detrital zircons from the Dongfengshan and Tadong groups in the eastern margin of the Songnen–Zhangguangcai Range Massif. The Dongfengshan and Tadong groups are subdivided, from bottom to top, into the Liangzihe, Huapigou, and Honglin formations, and the Lalagou and Zhudundian formations, respectively. Zircons from a two-mica quartz schist (sample HCM4-2) in the Liangzihe Formation yielded eight age populations, from 821 to 1802Ma, whereas zircons from a two-mica quartz schist (sample 12HCM3-2) in the Huapigou Formation yielded four age populations (752, 803, 821, and 851Ma). Zircons from a two-mica schist in the Lalagou Formation of the Tadong Group yielded two age populations (450 and 485Ma), and zircons from a biotite-bearing plagioclase gneiss in the lower part of the Zhudundian Formation yielded five main age populations, from 551 to 1815Ma. Samples 11NNA5-1 and 11HNA10-1 from the upper layer of the Zhudundian Formation yielded six main age groups, from 749 to 948Ma. These data, together with the ages of zircons within a tonalite that intrudes the Tadong Group and the overlying Chenming Formation, indicate the presence of a Precambrian terrane associated with sedimentation at various times during the Neoproterozoic, including at ~821–752, ~752–560, and ~750–516Ma, on the eastern margin of the Songnen–Zhangguangcai Range Massif. The Dongfengshan and Tadong groups were previously thought to be Proterozoic, but our study reveals that they constitute a Neoproterozoic–Late Paleozoic tectonic mélange. In addition, the widespread occurrence of detrital zircons with ages of 0.75–0.95, 1.5–1.6, 1.8, and 2.4–2.5Ga provides evidence of a Neoproterozoic magmatic event and the presence of remnant ancient basement material within the Songnen–Zhangguangcai Range Massif. [Copyright &y& Elsevier]

Abstract: The destruction (or reactivation) of the North China Craton (NCC) is one of the important issues related to the Phanerozoic evolution of eastern China, although the processes of destruction remain debated. Two main mechanisms – delamination and thermal/chemical erosion – have been proposed based on the geochemistry of Mesozoic–Cenozoic basalts and entrained deep–seated xenoliths. A key criterion in distinguishing between these mechanisms is the nature of the melt, derived from delaminated crust or the asthenosphere, that modified the lithospheric mantle. Here we investigate the mechanism of destruction of the NCC based on mineral compositions and oxygen isotopic data from olivines, and strontium isotopic data for clinopyroxenes within websterite xenoliths from the Early Cretaceous Feixian basalts in the eastern NCC. Olivines in websterite xenoliths have higher Mg# (86–86.4), Ni content (2187–2468ppm), and lower Ca (983–1134ppm), Ti (58.1–76.1ppm), and Mn (1478–1639ppm) contents than olivine phenocrysts (Mg#=71.0–77.3, Ni=233–1038ppm, Ca=1286–2857ppm, Ti=120–300ppm, and Mn=2092–4106ppm) from Late Cretaceous basalts. Additionally, olivines in websterite xenolith have δ18O values of 7.10±0.21‰ to 8.40±0.21‰, evidently higher than those of typical mantle-derived olivines. Similarly, orthopyroxenes (Opx) and clinopyroxenes (Cpx) in the websterite xenoliths have much higher Mg# (86.3–89.2 and 87.5–90.3, respectively), and Ni contents (1097–1491ppm and 581–809ppm, respectively) than orthopyroxene- and clinopyroxene-phenocrysts (Opx: Mg#=82.2–83.9, Ni=730–798ppm; Cpx: Mg#=74.2–84.6, Ni=117–277ppm) from Late Cretaceous basalts. The 87Sr/86Sr ratios of clinopyroxenes in the websterite xenoliths range from 0.70862 to 0.70979, and are much higher than those of clinopyroxene grains from peridotite xenoliths and basalts. These data indicate that olivines are the residue of ancient lithospheric mantle that was modified intensively by a melt derived from recycled continental crust, and that the silicic and calcic metasomatic melt might have been derived from the partial melting of the subducted Yangtze slab and delaminated lower crust of the NCC. The existence of recycled continental crust in the Mesozoic lithospheric mantle implies that delamination was an important mechanism of destruction of the NCC. [Copyright &y& Elsevier]