Evidence for a Picritic, Volatile-rich Magma beneath Mt. Shasta, California

Author:
  • AAAlfred T. Anderson
    Alfred T. Anderson
Publisher website
Google Scholar
Abstract
Large, magnesium-rich olivines are plentiful in several Holocene cinder cones within 20 km of Mt. Shasta Summit. Glasses (formerly silicate melts) included in the olivines are high alumina basalts (tholeiites and olivine tholeiites). In the most magnesian olivines the glass inclusions have large vapor bubbles. Surrounding some of the glass inclusions are broad Fe-rich zones and ghost outlines. These facts indicate crystallization of major proportions of olivine from the initial trapped melts. The initial melts contained an inferred 24 per cent of MgO and were rich in volatiles. The inferred entrapment temperature of the initial melt is 1410 °C. The initial liquid is a possible mantle derived parent of Mt. Shasta basalts and andesites and of some hidden alpine peridotite.