Geochemistry and zircon U–Pb geochronology of mafic rocks in the Kaiyuan tectonic mélange of northern Liaoning Province, NE China: Constraints on the tectonic evolution of the Paleo‐Asian Ocean

Abstract

The Kaiyuan tectonic mélange makes up the western part of the Kaiyuan–Yanji Accretionary Complex Belt, NE China, and there has been a long‐standing controversy about its age and tectonic setting. In this paper, we present new zircon U–Pb ages and geochemical data for the mafic rocks of the Lujiapuzi Formation in the Kaiyuan tectonic mélange, and these data provide insights into the tectonic setting during the late Paleozoic and the evolutionary history of the Paleo‐Asian Ocean in the eastern segment of the Central Asian Orogenic Belt (CAOB). SHRIMP U–Pb dating of zircons from samples of albite–actinolite schist and amphibolite yielded a crystallization age of 258 ± 5.5 Ma for the protoliths, suggesting that the protoliths formed during the late Permian. The albite–actinolite schists and amphibolites have similar geochemical characteristics, and they represent metamorphosed basaltic volcanic rocks. Major, rare earth and trace element data show that the mafic rocks have a close affinity with mid‐ocean ridge basalt. REE petrogenetic modelling indicates that the primary magma was generated through the partial melting of a mixed garnet‐ and spinel‐bearing mantle source, and assimilated crustal material and underwent crystal fractionation during ascent. The geochemical features and inherited/xenocrystic zircons in the mafic samples indicate that they formed in a tectonic setting similar to the back‐arc basin. These new findings, together with other previously published data, indicate that the Paleo‐Asian Ocean still existed in the eastern segment of the CAOB during the late Permian to Early Triassic. The Kaiyuan tectonic mélange formed during the Middle Triassic, and its formation may represent the timing of final closure of the Paleo‐Asian Ocean.

Preface: Tectonics of China

“…Guan et al () reports a tectonic mélange, that is, Kaiyuan tectonic mélange in Kaiyuan, easternmost NE China, in which the protolith of albite‐actinolite schist and amphibolite was formed at 258 ± 5.5 Ma in a back‐arc tectonic setting. They suggest that the Kaiyuan tectonic mélange formed during the Middle Triassic, and its formation may represent the time of the final closure of the Palaeo‐Asian Ocean.…”

Macro‐and Microstructural, Textural Fabrics and Deformation Mechanism of Calcite Mylonites from Xar Moron‐Changchun Dextral Shear Zone, Northeast China

“…The timing of the final closure of the Paleo-Asian Ocean along the Solonker-Xar Moron-Changchun-Yanji suture has been a controversial issue and the various proposals including Middle Devonian to Late Carboniferous or earlier (Tang, 1990;Zhao et al, 2013;Xu et al, 2013Xu et al, , 2015Chen et al, 2016Chen et al, , 2017, late Early Permian (Feng et al, 2010), or Middle Mesozoic (Nozaka and Liu, 2002). However, abundant new geological, paleobiogeography, lithofacies paleogeography, geochronological, geochemical and paleomagnetic data that have been obtained over the past decades have provided convincing evidence that the final closure of the Paleo-Asian Ocean occurred during the Late Permian-Early or Middle Triassic in a scissor-like style eastwards (Sengör et al, 1993;Xiao et al, 2003Xiao et al, , 2015Sun et al, 2004;Li, 2006;Wu et al, 2007Wu et al, , 2011Cao et al, 2012Cao et al, , 2013Eizenhöfer et al, 2014;Han et al, 2016Han et al, , 2017Wang et al, 2015;Du et al, 2017;Li et al, 2014Wang et al, 2017;Zhou et al, 2018;Liu et al, 2017;Guan et al, 2019;JBGMR, 1988JBGMR, , 1997Jian et al, 2008). If the Changchun-Yanji suture is the eastern extension of the Solonker-Xar Moron-Changchun suture, preserved relics of the suture should exist in the Changchun area.…”

Permian Tectonic Evolution in the Middle Part of Central Asian Orogenic Belt: Evidence from Newly Identified Volcanic Rocks in the Bilutu Area, Inner Mongolia

“…Some researchers proposed that the final closure of PAO was during the middle-Late Devonian to Early Carboniferous, when there was a limit intra-continental ocean basin or rift since early Permian which closed in early Mesozoic Xu et al, 2013;Zhao et al, 2013;Chu et al, 2014;Zhang J R et al, 2018). Whereas others suggested that the PAO existed during the whole Paleozoic and closed in late Permian-early Triassic (Xiao et al, 2010(Xiao et al, , 2015Li et al, 2013;Chen et al, 2014;Chen et al, 2016;Eizenhöfer and Zhao, 2018;Guan et al, 2018;). One key to the question is to figure out the tectonic setting in Permian, that is, is it an extension or a compression setting.…”