Geochronological and geochemical insights into the tectonic evolution of the Paleoproterozoic Jiao-Liao-Ji Belt, Sino-Korean Craton

Abstract

The Sino-Korean Craton, which is part of the Columbia supercontinent, was originally formed and stabilized by the amalgamation of several distinctly different tectonic units during the Paleoproterozoic period. Although the early tectonic framework of the Sino-Korean Craton remains controversial, the Paleoproterozoic Jiao-Liao-Ji Belt is accepted to divide the eastern unit of this craton into Archean Nangrim-Liaonan and Longgang blocks. This orogenic belt is thus the key to revealing the geodynamic processes that occurred during the assemblage and breakup of the Paleoproterozoic supercontinent Columbia. Due to late polyphase tectonothermal events (e.g., subduction of the paleo-Pacific Plate), considerable and continuing controversy has surrounded how this Paleoproterozoic orogenic belt formed, with models including (1) opening and closing of an intracontinental rift, (2) collision of a continent–arc–continent system, (3) a rifting–initial ocean formation–oceanic subduction–collision cycle, and (4) opening and closure of a back-arc basin or retro-arc foreland basin.Here, we synthesize the geochronological, geochemical, and isotopic data on the Paleoproterozoic igneous rocks in the JLJB. The available data suggest that the Paleoproterozoic magmatism in the JLJB lasted from ca. 2200 Ma to ca. 1800 Ma, with five magmatic flare-ups at ca. 2190–2160 Ma, ca. 2160–2110 Ma, ca. 2110–2080 Ma, ca. 2010–1895 Ma and ca. 1875–1850 Ma. These data, in combination with previous studies on voluminous meta-sedimentary rocks, Archean basement relict slices and granitic leucosomes within the JLJB, allow us to reconstruct the tectonic evolution of the JLJB based on rock petrogenesis as described below. (1) During the early stage of northwestward subduction of Paleoproterozoic oceanic plate between the Longgang-Liaonan-Nangrim Block (i.e., the Eastern Block) and the West Australian Craton (WAC) and/or North Australian Craton (NAC), strong slab rollback resulted in trench retreat and extension of the overriding plate (i.e., the Longgang-Liaonan-Nangrim Block) and induced upwelling and decompression melting of asthenospheric mantle to produce basaltic magma. The overriding Archean continental crust was heated by the underlying basaltic magma and melted to produce ~2190–2160 Ma aluminous A2-type granites, and minor basaltic magma mixed with this crustal melt to form ~2180–2160 Ma calc-alkaline, andesitic-rhyolitic tuffs. (2) With ongoing extension, the overriding plate thinned, and a back-arc basin opened and widened. The asthenospheric mantle that was metasomatized by limited subduction-related fluids and/or melts began to melt in the spinel-garnet stability field, and produced ~2160–2110 Ma tholeiitic mafic rocks with the geochemical features of both mid-oceanic ridge basalt (MORB) and volcanic arcs. (3) Decreased back-arc mafic magmatism suggests that subduction ceased due to collision between the WAC and/or NAC and the active subduction zone during ~2110–2080 Ma. After the collision, the subduction polarity reversed, from northwestward to southeastward, forming new subduction initiation in the southeastern margin of the back-arc basin, and this new subduction further resulted in forearc extension. Decompression melting of the subarc mantle produced basaltic magma, which was metasomatized by subducted slab- and ancient sediment-derived melts to form ~2110–2080 Ma mafic rocks with both calc-alkaline and tholeiitic features. Simultaneously, the overriding continental crust was heated by the basaltic magma and melted to form ~2110–2080 Ma aluminous A2-type granites. These processes, including opening and closure of back-arc basin, were accompanied by the deposition of voluminous sedimentary rocks in this back-arc basin, and the deposition lasted for at least 180 Myr. (4) After the collision between the WAC and/or NAC, the arc terrane (Nangrim-Liaonan Block + Gyeonggi massif?) and the Longgang Block, the orogeny that involved Archean basement rocks, Paleoproterozoic sedimentary rocks and associated mafic and granitic intrusions began. This process was accompanied by prograde or peak metamorphism and minor magmatism, which produced the ~2000–1895 Ma adakitic granites derived from partial melting of thickened lower crust. (5) During the late Paleoproterozoic, termination of the collisional orogenic event occurred, as evidenced by strong postcollisional extension, which generated widespread ~1875–1850 Ma igneous rocks in the JLJB and was accompanied by a regional partial melting event related to the exhumation of the JLJB. In summary, the five stages of magmatism, and associated sedimentation and metamorphism in the JLJB record a complete tectonic cycle, including oceanic plate subduction, back-arc extension, closure of the back-arc basin, collisional orogeny and postcollisional extension. These processes further support the conclusion that plate tectonic processes in the Paleoproterozoic period resulted in the amalgamation of microcontinents and arcs to form the Sino-Korean Craton and the Columbia supercontinent.