Middle Miocene forearc alkaline magmatism in Amami-Oshima Island, central Ryukyu Arc: implications for paleoreconstruction of Shikoku Basin

A significant discovery of middle Miocene forearc alkaline magmatism on Amami-Oshima Island, central Ryukyu Arc, challenges previous assumptions about the southwestern margin of such magmatic activity. The study identifies basaltic dikes with ocean island basalt (OIB)-like chemical signatures, indicating low-degree partial melting from a deep mantle source. 40Ar/39Ar dating and paleomagnetic analyses reveal that these dikes intruded simultaneously around 16.5–16.4 Ma during reversed polarity chron C5Cn.2r. This finding suggests the northern end of the Kyushu-Palau Ridge was south of Amami-Oshima Island at this time, later moving eastward to its current location. The research employs a combination of chemical analysis, radiometric dating, and paleomagnetic studies to reconstruct the paleogeography of the Shikoku Basin.

Motohashi, G., Ishizuka, O., Oda, H., Sano, T., Sekimoto, S., & Ujiie, K. (2023). Middle Miocene forearc alkaline magmatism in Amami-Oshima Island, central Ryukyu Arc: implications for paleoreconstruction of Shikoku Basin. Earth, Planets and Space, 75(1). https://doi.org/10.1186/s40623-022-01760-w