High-Mg andesites from the Gila Bend Mountains, southwestern Arizona; evidence for hydrous melting of lithosphere during Miocene extension

Abstract

Miocene andesites and basaltic andesites from the eastern Gila Bend Mountains have high Mg# values (most 66-72), high concentrations of Ni and Cr, and olivine phenocrysts as Mg rich as Fo (sub 90). Cores of euhedral olivine phenocrysts in some andesites are in equilibrium with the whole-rock Mg# values, and the compositions of chromian spinel inclusions in olivine phenocrysts are similar to those from boninites and other primitive magnesian silicic volcanic rocks. The Gila Bend lavas are interpreted to have evolved from a variety of primary mantle-derived melts, some as silicic as approximately 56% SiO (sub 2) . All the lavas have strong lithospheric geochemical characteristics

28 samples from this reference