Paleogeography of Late Jurassic large-igneous-province activity in the Paleo-Pacific Ocean: Constraints from the Mikabu greenstones and Chichibu accretionary complex, Kanto Mountains, Central Japan

The Mikabu Unit (Mikabu greenstones) was an oceanic plateau that was in the Mesozoic Paleo-Pacific Ocean. Large-igneous-province (LIP) activity has been proposed as the origin of the oceanic plateau of the Mikabu Unit. This study aims to reveal LIP activity in the Paleo-Pacific Ocean. We present geochemical and geochronological data for the Mikabu Unit and the Middle Jurassic to Early Cretaceous Chichibu accretionary complex (i.e., the Kashiwagi and Kamiyoshida units), both of which underwent the same high-pressure low-temperature metamorphism as theMikabu Unit, in the Kanto Mountains, central Japan. The Mikabu Unit contains oceanic plateau basalts characterized by incompatible element depletion and high chondrite normalized Gd/Yb ratios. These basalts are interpreted to have erupted in the age of 157.0 +/- 0.9 Ma (Late Jurassic), based on zircon U-Pb dating of anorthosite. The basalt geochemistry indicates that oceanic plateau basalts occur in the Kashiwagi Unit. Although basalts in the Mikabu Unit were thought to have formed at the Pacific-Izanagi-Farallon triple junction in the previous studies, we propose they formed on older oceanic crust of the Izanagi Plate during the Late Jurassic, which was located several thousand kilometers from the triple junction. The Kashiwagi and Mikabu units were accreted to Asia during the Early Cretaceous. (C) 2020 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Automated summary

This study investigates LIP activity in the Mesozoic Paleo-Pacific Ocean and presents geochemical and geochronological data for the Mikabu Unit, indicating the presence of oceanic plateau basalts formed during the Late Jurassic. The analysis also suggests these basalts were formed on older oceanic crust of the Izanagi Plate, located thousands of kilometers away from the triple junction, and were later accreted to Asia during the Early Cretaceous.