Abstract
Thick Miocene basaltic pile has been confirmed in the MITI “Kanazawa-Oki” well which was drilled in the Hokuriku Basin upon the eastern part of Southwest Japan backarc shelf. Utilizing refractive index of plagioclase and lithology, the upper part (500m thick) of the volcanics is correlated with the Kurokabe Pyroclastic Rocks near Kanazawa City. Seismic data estimates the volume of the Miocene basalts aroand the well to be ca. 100km3. Major constituent of the basaltic body is inferred to be porous hyaloclastite on the basis of two dimensional gravity modeling which shows a subtle positive Bouguer anomaly on the moand. Magneto- and biostratigraphy elucidates that the basalts rapidly erupted at aroand 16Ma, when Southwest Japan was rotating clockwise associated with formation of the Sea of Japan back-arc basin. The specific volcanism is attributed to tensional thinning of lithosphere considering paleoenvironment of the Hokuriku Province und geochemical data of volcanic rocks. Higher temperatures in the rift stage and subsequent gradual cooling is inferred from maturation level at the bottom of the well.
