Petrography and Geochemistry of Volcanic Glass: Leg 57, Deep Sea Drilling Project

Abstract

About 200 volcanic ash layers were recovered during DSDP Leg 57. The volcanic glass in some of these layers was investigated petrographically and chemically in this study. Volcanic glass is mainly rhyolitic and/or rhyodacitic in chemical composition, and its refractive index ranges from 1.496 to 1.529. Some volcanic ash layers consist of multiple grains of different chemical compositions. All the volcanic glass belongs to the tholeiitic and the calc-alkalic volcanic rock series, in SiO->-<Nap + K 2 O) diagram and FeO*/MgO-SiO 2 diagram. We correlated successfully three volcanic ash layers from the standpoint of chemical composition and biostratigraphy. Hydration of volcanic glass from Leg 57 is less intense than in other DSDP cores.

Middle America Neogene Explosive Volcanism and Ash Layers: Evidence from the Middle America Trench Transect, Deep Sea Drilling Project Leg 67

“…Considering that there is no noticeable alteration, we attribute this deficit to hydration, in accordance with the observations of Scheidegger et al (1978) and Fujioka et al (1980). Table 3 presents a large selection of different geochemical type analyses, whereas the average of acid compositions is shown in Table 4.…”

Nature and record of igneous activity in the Tonga arc, SW Pacific, deduced from the phase chemistry of derived detrital grains

“…pumice, glass shards). Alteration, however, is probably limited to simple hydration, which although diluting absolute elemental abundances, does not appear to have affected primary igneous trends or element ratios (Fujioka et al 1980;Cawood 1985). Miyashiro (1974).…”

Tephra from Deep Sea Drilling Project Leg 66: Middle America Trench Transect (Southern Mexico)

“…This systematic deficit, without visible alteration, can be attributed to hydration, according to Scheidegger et al (1978) and Fujioka et al (1980). This phenomenon, independent of the age and location of samples, seems to occur rapidly during pyroclastic deposition.…”