Whole-rock Geochemistry and Zircon U-Pb Ages of Cretaceous Volcanic Rocks in the Incheon-Gimpo Area

Cretaceous volcanic and volcaniclastic rocks are sporadically distributed around the Ganghwa Strait in the Incheon-Gimpo area in the western Korean Peninsula. While their existence was documented by several public geological maps, these rock units have remained largely neglected in scientific research. To foster further research, the zircon U-Pb age and whole-rock geochemical analysis results on these Cretaceous volcanic rocks acquired during the recent geological mapping have been made publicly available through an open-access database. The Cretaceous rocks in the Incheon-Gimpo area, mostly found as isolated bodies forming small islands, exhibit diverse lithologies including tuff, dacite, andesite, and tuffaceous conglomerate-mudstone. Geochemical analyses reveal a predominance of calc-alkaline, dacitic compositions, with subordinate andesitic or rhyolitic rock bodies occurring locally in the marginal parts. Zircon U-Pb ages of tuff and dacite samples range from 112 to 108 Ma, corresponding to the Albian stage of the Cretaceous. In contrast, age dating results of a tuffaceous sandstone sample suggest post-108 Ma deposition, indicating that the several-hundred-meter-thick volcaniclastic successions in the middle part of the study area may represent late-stage basin-fill deposits, rather than syn-volcanic as previously interpreted. The tectonostratigraphic evolution of this area is presumed to be closely linked to the Cretaceous basins with contemporaneous volcanic activities, developed along the western Gyeonggi Massif, namely the Cheorwon, Tando-Namyang, and Cheonsuman Basins.