Fu-Ping Pei

Geochronology and provenance of detrital zircons from late Palaeozoic strata of central Jilin Province, Northeast China: implications for the tectonic evolution of the eastern Central Asian Orogenic Belt

Here we present new U–Pb and Hf isotopic data for detrital zircons obtained from six samples of late Palaeozoic units from central Jilin Province, Northeast China, and use these data and sedimentary formations to constrain the late Palaeozoic tectonic evolution of the eastern segment of the southern margin of the Central Asian Orogenic Belt. The majority of the detrital zircons from the six samples are euhedral–subhedral and exhibit oscillatory zoning, indicating a magmatic origin. Zircons from sandstones in the Devonian Wangjiajie and Xiaosuihe formations yield seven main age populations (399, 440, 921, 1648, 1864, 1911, and 2066 Ma) and two minor age populations (384 and 432 Ma), respectively. Zircons from a quartz sandstone in the Carboniferous Luquantun Formation yield four age populations (~332, 363, 402, and 428 Ma), and zircons from quartz sandstones of the Permian Shoushangou, Fanjiatun, and Yangjiagou formations yield age populations of 265, 369, 463, 503, and 963 Ma; 264, 310, 337, 486, and 529 Ma; and 262, 282, 312, 338, 380, 465, and 492 Ma, respectively. These data, together with the ages of magmatic zircons from interbedded volcanics and biostratigraphic evidence, as well as analysis of formations, give rise to the following conclusions. (1) The Wangjiajie and Xiaosuihe formations were deposited in an extensional environment during Middle and Middle–Late Devonian time, respectively. The former was sourced mainly from ancient continental material of the North China Craton with minor contributions from newly accreted crust, while the latter was sourced mainly from newly accreted crust. (2) The Luquantun Formation formed in an extensional environment during early–late Carboniferous time from material sourced mainly from newly accreted crust. (3) The Shoushangou, Fanjiatun, and Yangjiagou formations formed during a period of rapid uplift in the late Permian, from material sourced mainly from newly accreted crust.

Geochronology and geochemistry of early Paleozoic igneous rocks from the Zhangguangcai Range, northeastern China: Constraints on tectonic evolution of the eastern Central Asian Orogenic Belt

This study presents new geochronological and geochemical data for early Paleozoic igneous rocks of the Zhangguangcai Range, northeastern China, and uses these data to further define the early Paleozoic tectonic evolution of the Songnen–Zhangguangcai Range block (SZB) and the Jiamusi block, and provide insights into crustal growth and reworking processes in these blocks of the eastern Central Asian Orogenic Belt. New zircon U-Pb data indicate widespread early Paleozoic magmatism (ca. 516, 496–482, 475–461, and 426 Ma) in the southeastern SZB. The ca. 516 Ma magmatism formed Na-rich tonalites that contain low concentrations of rare earth elements, are enriched in Eu and Sr, have high CaO/Al2O3 and Ba/La ratios, low Rb/Sr and Rb/Ba ratios, and negative Ce anomalies and zircon εHf(t) values. These features suggest an origin from magmas generated by partial melting of ancient accumulated gabbroic rocks with the addition of subducted-sediment–derived fluids. The ca. 496–482 Ma magmatism formed calc-alkaline I-type biotite granodiorites and monzogranites, whereas the ca. 475–461 Ma igneous rocks include biotite monzogranites with K-rich adakitic signatures and alkali-feldspar granites. These ca. 496–461 Ma granitoids have zircon εHf(t) values from –0.82 to +5.44 and two-stage depleted-mantle model (TDM2) ages of 1490–1103 Ma, suggesting they formed from magmas generated by partial melting of heterogeneous Mesoproterozoic lower crustal material. The ca. 426 Ma Na-rich tonalites are geochemically similar to the ca. 516 Ma tonalites and also originated by partial melting of ancient gabbroic or amphibolitic rocks with the involvement of subducted-sediment–derived fluids. The geochemistry of these early Paleozoic igneous rock assemblages is indicative of formation in an active continental margin setting associated with northwestward subduction beneath the southeastern SZB. The zircon Hf isotopic compositions of these early Paleozoic igneous rocks indicate that Paleoproterozoic–Mesoproterozoic crustal material was reworked during the early Paleozoic subductionand collision-related tectonism. LITHOSPHERE; v. 9; no. 5; p. 803–827 | Published online 9 August 2017 https://doi.org/10.1130/L639.1

Modification of the lithospheric mantle by melt derived from recycled continental crust evidenced by wehrlite xenoliths in Early Cretaceous high-Mg diorites from western Shandong, China

This paper reports petrographic, mineral chemical, olivine oxygen isotopic, and whole-rock geochemical data for wehrlite xenoliths from the Early Cretaceous Tietonggou high-Mg diorites in western Shandong Province, in the eastern part of the North China Craton (NCC), and describes the origin of these wehrlites and the processes that affected the deep lithospheric mantle in this area. Wehrlite xenoliths are rounded and vary in size between 3 cm × 4 cm × 5 cm and 3 cm × 2 cm × 1 cm. Olivine within these xenoliths occurs as an isolated residual phase within clinopyroxene, has Fo contents between 89 and 91, and contains between 1414 and 3629 ppm Ni, similar to the values of olivine from peridotite xenoliths in the Cenozoic basalts of eastern China, but lower than the values of olivine from harzburgite xenoliths in the Early Cretaceous high-Mg diorites in western Shandong. In situ oxygen isotope analysis yielded δ18O values of olivine from (6.03±0.33)‰ to (6.82±0.35)‰, averaging (6.5±0.4)‰; this is higher than typical mantle-derived olivine ((5.2±0.3)‰). Compared with clinopyroxenes from peridotite xenoliths in the Late Cretaceous and Cenozoic basalts, clinopyroxenes in the wehrlites contain relatively low concentrations of Na2O, TiO2, and Al2O3, high concentrations of CaO, and higher Mg# (91.2–94.1) and Ti/Eu ratios (2082–2845), being similar in composition to clinopyroxenes within harzburgite xenoliths in the Early Cretaceous high-Mg diorites. Clinopyroxenes from wehrlite xenoliths are characterized by low total REE abundance, enrichment in light REEs, and depletion in high field strength elements such as Nb, Ta, Zr, and Hf. Moreover, the 87Sr/86Sr, 143Nd/144Nd, and 187Os/188Os (125 Ma) ratios of these wehrlites vary from 0.70596 to 0.70737, 0.512181 to 0.512416, and 0.12661 to 0.57650, respectively. These data suggest that these wehrlite xenoliths were formed by modification of the lithospheric mantle by melts derived from recycled continental crust.