Correlation of Volcanic Ash Deposits by Activation Analysis of Glass Separates

Abstract

Volcanic ash deposits whose source is the Cascade Mountains area were correlated on the basis of 19 elemental abundances obtained by instrumental neutron activation analysis (INAA). After activation of glassy separates in a TRIGA reactor, gammaray spectra were obtained and analyzed with computer programs. The elements Na, Sm, Sc, Fe, Ce, Hf, and Th were determined with relative standard deviations less than 5%; the precision for La, Co, Eu, Yb, Cs, Ba, and Lu was less than 17%; larger errors were obtained for Rb, Ta, Nd, Tb, and Cr. A statistical method was developed for correlation on the basis of relative elemental compositions unique to the ash deposits. Elemental abundances of Mazama glassy separates were independent of distance from the source. The site to site chemical variability of crystal rich Glacier Peak and St. Helens ash layers was greater than for Mazama and Newberry ashes. The Rb, Yb, Lu, Th, and Ta contents in Newberry glass were more than twice those in Mazama glass. The concentrations of trace elements in Glacier Peak and St. Helens ashes generally were less than one-half those in Mazama glass. The presence of Mazama ash has been confirmed at sites in Oregon, Washington, Alberta, and in sediments of the Pacific Ocean.

Correlation, dispersal, and preservation of the Kawakawa Tephra and other late Quaternary tephra layers in the Southwest Pacific Ocean

“…Low standard deviations for element concentrations indicate all samples comprise homogeneous and unmixed populations of glass shards, consistent with derivation from a particular eruptive event. Comparisons of analyses to type material (Table 3) produce similarity coefficients (SC) close to 100 (Borchardt et al 1971), thereby confirming our identifications.…”

Geomorphological Processes on Terrestrial Planetary Surfaces

“…Layers of tephra incorporated within other Quaternary materials have long been used as a basis for correlation and relative www.annualreviews.org/aronline Annual Reviews dating (Swinford 1949, Wilcox 1965, D. G. W. Smith & Westgate 1969, Izett et al 1970, H. W. Smith et al 1977a, b, Porter 1978. Modern chemical and petrological analyses provide means of fingerprinting tephra layers from different sources more effectively (Borchardt et al 1971), and improvements in precision of 4°K/4°A analyses of younger materials have made absolute age assignments increasingly reliable.…”

Late Neogene unconformity‐bounded tuffaceous sequences: Northwestern Chatham Rise, New Zealand

“…We compare glass compositions for correlation purposes using similarity coefficients (SC) (Borchardt et al 1971), based on all oxides except Cl, which is often invariant. High values of SC (>0.92) are obtained for correlative samples.…”