Chemistry of the subalkalic silicic obsidians

Abstract

The data bank Description and geographical distribution of analyzed Analytical techniques Major-element analyses X-ray fluorescence analyses Instrumental neutron-activation analyses Other analytical methods Presentation of the data bank Completeness of the data bank Representativeness of samples Classification of subalkalic silicic obsidians Classification used in this paper Obsidians not accommodated by the classification scheme Comparison with the rhyolite groupings of Ewart (1979) -------Relations among SiO2, A12O3, CaO, and (Na^+K^O) in subalkalic obsidians The terms calcic, calc-alkalic, and alkali-calcic Relations among A12O3, CaO, and (NajO+K^O) and the significance of normative corundum Normative Q-Ab-Or-H2O and Or-Ab-An-H2O plots -Notes on the occurrence, geology, and petrography of the obsidian subgroups Group I: Obsidians from the early stages of arc Cobalt