2017 年 123 巻 1 号 p. 23-29
The results of petrography and whole-rock major and trace element analyses of igneous rocks from Iheya North Knoll, middle Okinawa Trough, SIP Expedition CK14-04 (Exp. 907) are reported. During Expedition CK14-04, three holes were drilled for taking core samples: one at Site C9016 (Hole C9016B) and two at Site C9015 (Holes C9015B and C). Five pumice pebbles from Hole C9016B and three altered volcanic rocks from each of Holes C9015B and C9016B were analyzed. The pumices were essentially unaltered, and major and trace element compositions were similar to the literature values for middle Okinawa Trough rhyolites, except for Cu and Pb. The altered volcanic rocks appeared to be rhyolites based on microscopic core observations, and various degrees of silicification in terms of whole-rock geochemical composition were observed. Nevertheless, some of the altered rhyolites preserve igneous geochemical features that are similar to the overlying pumices and the middle Okinawa Trough rhyolites.
