Origin of basaltic magmas in the Mojave Desert area, California

✍ Scribed by William S. Wise

• Publisher: Springer
• Year: 1969
• Tongue: English
• Weight: 632 KB
• Volume: 23
• Category: Article
• ISSN: 0010-7999
• DOI: 10.1007/bf00371332

✦ Synopsis

The basaltic lavas erupted throughout the Mojave Desert are basanites (Si0~<46%, normative nepheline>5%, and K~0>1.5%), alkali-olivine bas~lts (Si0~46--48%; ne= 0--5% ; and K~O = 1.0--1.5%), and low-alumina, sub-alkaline basalts (SiO~ =48--51% ; ne ~ 0; K20< 1.0%). One volcano, Pisgah Crater, erupted five times, with lava from each successive phase containing more silica and less potash than the one preceeding it. This compositional trend is the reverse of that expected from differentiation of a single alkalic magma, and therefore, may represent a succession of magmas tapped from a zone of continuing partial melting in the mantle.

These lava compositions suggest that first melting was under high water pressure and was followed by relatively dry partial melting of garnet-orthopyroxene-clinopyroxene-olivine assemblages. The successive increase in silica and alkali decrease also requires that the partial melting zone move to shallower levels.

All lavas sampled in the Mojave Desert area have compositions that can best be explained by the extraction of magma from such a rising melting zone, analogous to the mantle diapits suggested by GREEN and RrsGWOOD.