Amphibole in quaternary basalts of the Yucca Mountain region: Significance to volcanism models

The purpose of this investigation is to gain an understanding of the origin of amphibole in Quaternary basalt in the Yucca Mountain region for use in constraining volcanism models. Heavy minerals were concentrated from relatively fresh scoriae at cones in the Yucca Mountain region. Electron microprobe analyses indicates that the amphiboles crystallized from basaltic magma with greater than 2 wt % but less than 5 wt % H2O. Models of mafic volcanic processes for Yucca Mountain should consider that magmatic water contents slightly above 2 wt % may be characteristic of the Quaternary basaltic system. Petrogenetic models also must consider the effects of variable magmatic water contents on the stability of plagioclase and amphibole in differentiating systems