Geochronology and geochemistry of Triassic plutons in Korea Magmatic response to the interplay of collisional and accretionary orogenies in the Korean Peninsula: Geochronological, geochemical, and O-Hf isotopic perspectives from Triassic plutons Albert Chang-sik Cheong1,†, Hui Je Jo1,§, Youn-Joong Jeong1,§, and Xian-Hua Li2,§ 1Division of Earth and Environmental Sciences, Korea Basic Science Institute, Chungcheongbukdo 28119, Republic of Korea 2Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100027, China ABSTRACT geochemically arc-like Andong ultramafic Ernst, 2005, 2010; Cawood et al., 2009; Collins complex (222 Ma). Zircon O-Hf isotopic et al., 2011). Because orogenesis basically re- Phanerozoic internal and peripheral oro- compositions of the older plutons reflect the flects the resistance of a buoyant lithosphere to gens in Northeast Asia converge toward the mixing of metasomatized lithospheric man- plate underflow, the driving mechanism is more Korean Peninsula situated between cratonic tle, young (probably Paleozoic) arc crust, obvious in the case of continental subduction. Asia and the outboard magmatic arc. Wide- and Precambrian basement crust, whereas Continental collisional [also referred to as spread Mesozoic plutons in the peninsula those of the younger plutons reflect input of “Alpine” or Bally’s (1981) “type-A”] orogens, provide first-hand information about the the asthenospheric/lithospheric mantle and represented by wrinkled mountain belts in the magmatic response to the continental and mafic lower crust. Meanwhile, the Late Tri- internal part of the assembled (super)continent, oceanic plate subduction. The present study assic (233–224 Ma) potassic plutons in and mark the termination of a Wilson cycle of ocean addresses this issue using comprehensive (n around the Gyeonggi Massif represent post- opening and closing. The collisional boundaries >1100) whole-rock geochemical, zircon U-Pb collisional magmatism most likely induced are characterized by distinct geologic features, geochronological, and O-Hf isotopic data by slab breakoff, which may also have been such as oceanward verging thrust sheets neigh- obtained from Triassic gabbro-pyroxenite- responsible for the shoshonitic magmatism bored by elongated foreland basins, regional mangerite-monzonite-syenite-granodiorite- in the Yeongnam Massif. Spatial differences Barrovian metamorphism linked to crustal granite plutons in the central and southern in the age pattern and O-Hf isotopic signa- thickening, and exhumation of (ultra)high- parts of the peninsula. The intrusion of ture of inherited and synmagmatic zircons pressure rocks containing diamond or coesite ca. 265–250 Ma calc-alkaline granitoids, from the potassic plutons indicate a selective (e.g., Ernst et al., 1997; Rumble et al., 2003; including the high-silica adakite, along the contribution from an ancient metasoma- Song et al., 2014). On the other hand, accretion- outboard (in present coordinates) Yeongnam tized lithospheric mantle beneath the North ary [also termed as “Pacific” or Bally’s (1981) Massif is coeval with or slightly younger than China-like craton and an allochthonous “type-B”] plate convergence at sites of oceanic the Barrovian metamorphism recognized South China-like lithosphere. The formation subduction has produced subparallel belts con- in fold-and-thrust belts surrounding the of the Triassic plutons could be explained sisting of an outboard trench complex, a medial inboard (northward, present coordinates) by a series of tectonomagmatic events con- forearc basin, and an inboard arc, each of which Gyeonggi Massif, suggesting a close link sisting sequentially of the ridge subduction, has undergone contrasting pressure-temperature between the collisional orogenesis and sub- low-angle subduction, slab breakoff beneath conditions (Miyashiro, 1961). The negative duction initiation as commonly documented the collisional orogen, tectonic switch to an buoyancy of the sufficiently aged and cooled in Phanerozoic supercontinents. Subse- extension-dominated arc system, and delami- oceanic lithosphere provides most of the force quent Late Triassic plutons emplaced in the nation of an overthickened arc lithosphere. required for its sinking and rollback in sub- Yeongnam Massif are subdivided into the duction zones and consequent mantle convec- older (232–224 Ma) magnesian and alkali- INTRODUCTION tion (Stern, 2004, and references therein). This calcic to calc-alkalic group and the younger “Western Pacific” type [or “Mariana” (Uyeda (220–217 Ma) ferroan and alkalic to alkali- Orogenic belts have formed in response to and Kanamori, 1979) type] of subduction leads calcic group temporally intervened by the interior collisional and peripheral accretionary to the development of a retreating arc system, plate convergence since the onset of plate tec- where upper plate extension promotes the for- tonics on Earth. These two end-member types mation of arc-flanking basins. Conversely, the of subduction, with a broad continuum between advancing or “Andean” [or “Chilean” (Uyeda †Corresponding author: [email protected]. §Hui Je Jo—[email protected], Youn-Joong them, have left their own characteristic geologi- and Kanamori, 1979) type] arc system induced Jeong—[email protected], Xian-Hua Li—lixh@ cal and geochemical features among the oro- by the subduction of buoyant oceanic litho- gig.ac.cn. gens and associated igneous rocks (Bally, 1981; sphere, terrane accretion, or plate reorganization GSA Bulletin; March/April 2019; v. 131; no. 3/4; p. 609–634; https://doi.org/10.1130/B32021.1; 12 figures; 2 tables; Data Repository item 2018374; published online 29 November 2018. Geological Society of America Bulletin, v. 131, no. 3/4 609 © 2018 The Authors. Gold Open Access: This paper is published under the terms of the CC-BY license. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/131/3-4/609/4651432/609.pdf by guest on 01 October 2021 Chang-sik Cheong et al. results in the development of retroarc fold-and- The Paleozoic–Mesozoic history of the Europe to the Cenozoic Himalayan orogen be- thrust belts (Cawood et al., 2009). The accre- northwestern edge of the circum-Pacific is char- tween India and Asia. The Qinling-Dabie-Sulu tionary orogenic system may have switched acterized by the interplay of continental and orogen in central-eastern China is in the middle between phases of advance and retreat, possibly oceanic plate convergence (Engebretson et al., of such a spatiotemporal sequence. Triassic caused by transient flat subduction (Collins, 1985; Ernst et al., 2007). Phanerozoic internal (ca. 240–220 Ma) high-pressure and ultrahigh- 2002; Beltrando et al., 2007; Li and Li, 2007). and peripheral orogens in Northeast Asia con- pressure mineral parageneses have been re- Magmatic responses to collisional and ac- verge toward the Korean Peninsula, situated in ported from the leading edge of the Yangtze cretionary orogenies differ in terms of their a tectonic link between cratonic Asia and an Block in South China (Hacker et al., 2000, driving mechanism and general geochemical outboard magmatic arc. Widespread Mesozoic 2004). Before the Triassic continental colli- characteristics. Collisional orogeny is typi- plutons exposed in the peninsula provide first- sion, the Qinling-Tongbai-Hong’an areas to the cally associated with peraluminous, S-type hand information about the individual or super- west of the Dabie-Sulu Mountains had experi- leucogranites generated by partial melting of imposed roles of collisional and accretionary enced a series of oceanic subduction and arc- the overthickened crust virtually without man- orogenies in making the magma. The present continent collision from the latest Cambrian to tle input (Sylvester, 1998; Barbarin, 1999). It study addresses this issue using new and pub- the Carboniferous (Wu and Zheng, 2013, and has also been recognized that alkaline igne- lished whole-rock geochemical, in situ zircon references therein). The tectonic evolution of ous rocks and carbonatites are concentrated in U-Pb geochronological, and O-Hf isotopic data the curvilinear orogen extending eastward from some suture zones in Africa, the Kola Penin- obtained from gabbro-pyroxenite-mangerite- the Qinling-Dabie-Sulu belt is complicated by sula in Russia, the Himalayan Mountains, and monzonite-syenite-granodiorite-granite plutons severe tectonic and magmatic overprinting and in India (Burke et al., 2003; Burke and Khan, in the central and southern parts of the peninsula transverse fault activities (Ernst et al., 2007), 2006; Hou et al., 2006; Leelanandam et al., that intruded approximately coevally during making it difficult to trace the continuation of 2006). The generation of these rocks is consid- the Triassic, a period marking the culmination this belt into the Korean Peninsula. ered to have been facilitated by density- and of the collisional and accretionary orogenies. Widespread Phanerozoic plutons in North- thermally-driven vertical processes such as This comprehensive data set (n >1100) bears east Asia are believed to have been chiefly pro- delamination and slab breakoff. However, col- important implications for deciphering key is- duced in association with the (paleo-)Pacific lisional convergence does not generally gener- sues concerning the magmatic response to the plate subduction and, to a lesser extent, with ate a large volume of magma, probably due to continental and oceanic plate subduction, such continental collision between the North and the limited