Lithospheric thinning and ignition of a Cordilleran magmatic flare-up: Geochemical and O-Hf isotopic constraints from Cretaceous plutons in southern Korea

• Published in: Di xue qian yuan. 2023-01, Vol.14 (1), p.101492, Article 101492
• Main Authors: Cheong, Albert Chang-sik, Jung, Min-Ji, Jo, Hui Je, Kim, Jeongmin, Lee, Shinae, Jeong, Youn-Joong
• Format: Article
• Language: English
• Subjects: Anomalies; Asthenosphere; Basements; Belts; Chondrites; Cordilleran arc; Cretaceous flare-up; Crustal rejuvenation; Delamination; Evolution; Geochemistry; Geochronology; Granite; Igneous rocks; Isotopes; Korean Peninsula; Lava; Lithospheric thinning; Magma; Massifs; National parks; Rare earth elements; Rocks; Shear zone; Thinning; Ytterbium; Yttrium; Zircon
• ISSN: 1674-9871; 2588-9192
• DOI: 10.1016/j.gsf.2022.101492

[Display omitted] •The Cretaceous flare-up along central Korea commenced in the Albian.•The flare-up was ignited by delamination of an overthickened arc lithosphere.•Late Cretaceous granites were derived from rejuvenated crustal basement.•Zircon O-Hf isotopes reflect a selective input from mantle and crustal reservoirs.•Core-to-rim variation in zircon O-Hf isotopes reflects a sequence of magma process. Northeast Asian continental margins contain the products of magma emplacement driven by prolonged subduction of the (paleo-)Pacific plate. As observed in many Cordilleran arcs, magmatic evolution in this area was punctuated by high-volume pulses amid background periods. The present study investigates the early evolution of the Cretaceous magmatic flare-up using new and published geochronological, geochemical, and O-Hf isotope data from plutonic rocks in the southern Korean Peninsula. After a long (∼50 m.y.) magmatic hiatus and the development of the Honam Shear Zone through flat-slab subduction, the Cretaceous flare-up began with the intrusion of monzonites, granodiorites, and granites in the inboard Gyeonggi Massif and the intervening Okcheon Belt. Compared to Jurassic granitoids formed during the former flare-up, Albian (∼111 Ma) monzonites found in the Eopyeong area of the Okcheon Belt have distinctly higher zircon εHf(t) (−7.5 ± 1.3) and δ18O (7.78‰ ± 0.25‰) values and lower whole-rock La/Yb and Sr/Y ratios. The voluminous coeval granodiorite and granite plutons in the Gyeonggi Massif are further reduced in Sr/Y and to a lesser extent, in La/Yb, and have higher zircon εHf(t) values (−13 to −19) than the Precambrian basement (ca. −30). These chemical and isotopic features indicate that Early Cretaceous lithospheric thinning, most likely resulting from delamination of tectonically and magmatically overthickened lithospheric keel that was metasomatized during prior subduction episodes, and consequent asthenospheric upwelling played vital roles in igniting the magmatic flare-up. The O-Hf isotopic ranges of synmagmatic zircons from the Albian plutons and their Paleoproterozoic and Jurassic inheritance attest to the involvement of lithospheric mantle and crustal basement in magma generation during this decratonization event. Arc magmatism then migrated trenchward and culminated in the Late Cretaceous, yielding widespread granitoid rocks emplaced at shallow crustal levels. The early Late Cretaceous (94–85 Ma) granites now prevalent in Seoraksan-Woraksan-Sokrisa