Late Devonian to early Carboniferous magmatism in the western Songliao–Xilinhot block, Northeast China: Implications for eastward subduction of the Nenjiang oceanic lithosphere

Abstract

The timing and direction of narrowing and closure of the Nenjiang Ocean (NJO) by plate subduction remain poorly constrained. This paper presents geochemical, isotopic, and geochronological results for Late Devonian to early Carboniferous intrusive rocks in the western Songliao–Xilinhot block to constrain the evolution of subduction in the NJO region. The Late Devonian syenogranites and monzogranites formed at 366–360 Ma and are classified as A‐type granites. The wide range of εHf(t) values (−17.62 to +8.13) and TDM2 ages (789–2,208 Ma) of the syenogranites indicate that the primary magma was derived from partial melting of multiple sources, including both young accreted continental crust and old lower crust rocks. The early Carboniferous granitic mylonites formed at 342 Ma and are I‐type granites. Their high SiO2 and K2O contents, εHf(t) values of +6.61 to +9.86, and young TDM2 ages of 675 to 857 Ma suggest a preexisting juvenile crustal material source region. The early Carboniferous hornblende gabbros formed at 334 Ma and are part of an appinite suite. The gabbros have low silica and high MgO contents, E‐MORB‐like trace element features, εHf(t) values of +1.34 to +8.97, and young TDM1 ages of 595 to 902 Ma, which together suggest a primitive magmatic source including juvenile MORB and/or enriched lithospheric mantle. Magmatism in the western Songliao–Xilinhot block formed a late Palaeozoic magmatic arc stretching along the eastern Hegenshan–Heihe suture. A new model of the evolution of subduction in the NJO region and associated coeval magmatic events is proposed that includes westward subduction of NJO oceanic crust during the Late Devonian at 366–360 Ma, bidirectional subduction during the early Carboniferous at ~342 Ma, and break‐off/delamination of the eastward subducting slab at ~334 Ma.

Micro‐Blocks in NE Asia Amalgamated Into the Unified Amuria Block by ∼300 Ma: First Paleomagnetic Evidence From the Songliao Block, NE China

“…In more recent studies, several lines of evidence from the NHS region support closure of the Nenjiang Ocean by the Late Carboniferous. These include (a) sedimentary facies transition from marine strata in the Early Carboniferous to continental facies in the Late Carboniferous (Liu et al., 2017); (b) the 320 Ma syn‐tectonic S‐type granites in the Moguqi area (Ma et al., 2020) which imply a syn‐collision tectonic setting; (c) evidence for extension throughout the studied region during the Early Permian and extensive coeval post‐orogenic A‐type granites (Feng et al., 2015; Liu et al., 2017; Shi et al., 2015; Wu et al., 2002) and rift‐related bimodal volcanic rocks (Zeng et al., 2011).…”

“…The western margin of the Songliao‐Jiamusi block developed on Precambrian basement whereas the interior Songliao basin is floored by Mesozoic and late Paleozoic basement (Qian et al., 2018; Wu et al., 2018). Silurian to Carboniferous arc‐related igneous rocks that recorded bilateral subduction of the Nenjiang Ocean are preserved on both sides of the NHS (Feng et al., 2015; Liu et al., 2019; Ma et al., 2020). A suite of Upper Carboniferous to Upper Permian volcanic‐sedimentary sequences outcrop in the Ulanhot area (Figures 1b and 2; IMBGMR, 1991).…”

“…Previous late Paleozoic reconstructions typically adopted a paleogeographic configuration showing the unified Amuria block situated along the northern margin of the Paleo‐Asian Ocean (PAO) (e.g., Domeier & Torsvik, 2014; Kent & Muttoni, 2020; Kravchinsky, Sorokin, & Courtillot, 2002; Wilhem et al., 2012; Zhao et al., 1996). This configuration was challenged by studies on the closure of the Nenjiang Ocean, which separated the Songliao‐Jiamusi block from the Mongolia block during the late Paleozoic (Figure 1a; Liu et al., 2017, 2019; Ma et al., 2020; Miao et al., 2004; Song et al., 2015; Zhao et al., 2010; Zhou et al., 2015). The existence of the Nenjiang Ocean precludes the existence of Amuria prior to the amalgamation of the Songliao‐Jiamusi and Mongolia blocks.…”

“…Previous studies posit that the final closure of the Nenjiang Ocean occurred sometime between the Early Devonian to Early Triassic (e.g., Han et al, 2012;Liu et al, 2017Liu et al, , 2019Ma et al, 2020;Miao et al, 2004;Zhao et al, 2010Zhao et al, , 2014Zhang, 2013;Xu et al, 2015). Those studies exclusively relied on the geological evidence for closure such as stratigraphy and the geochemistry of affiliated ophiolites and igneous rocks; however, only limited paleomagnetic data are available to quantify the age of final closure.…”

Accretionary tectonics, deep structures and metallogeny of southern Altaids

“…The timing and direction of narrowing and closure of the Nenjiang Ocean (NJO) by plate subduction remain poorly constrained. Ma et al (, this issue) report geochemical, isotopic, and geochronological data for Late Devonian to early Carboniferous intrusive rocks in the western Songliao–Xilinhot block. A new model are proposed in this study, in which westward subduction of NJO oceanic crust during the Late Devonian at 366–360 Ma was followed by bidirectional subduction during the early Carboniferous at ~342 Ma, and ended up with break‐off/delamination of the eastward subducting slab at ~334 Ma.…”