Potrillo Volcanic Field - Pyroxenites

Pyroxenites

A pyroxenite is defined as an ultra mafic rock that is composed of by and large of minerals of the pyroxene group for example enstatite, bronzite or diopside and are sorted into clinopyroxenite, orthopyroxenite and the websterites. Pyroxenites have been located as layers inside large masses of peridotite. These pyroxenite layers have come to be inferred as a yield of the reaction between rising magmas and peridotite of the upper mantle. The Southern Rio Grande Rift, including the Portrillo volcanic field, is an area where pyroxenites are most prevalent. Pyroxenites are generally coupled with zones of extension implying that there is a correlation between asthenospheric outpouring and invasive growth of mantle pyroxenites. The methods by which pyroxenites are formed is somewhat undefined. Pyroxenites may possibly represent preserved remnants of Farallon (oceanic) plate that subducted under the North American plate and mixed with mantle melts and created the xenoliths that have surfaced in Kilbourne Hole and Potrillo Maar. However others suggest that they could be cumulates derived from alkali basaltic pyroxenite samples continue to preserve a more widespread reaction which is specifically helpful in examining the thermal and chemical alteration of the Rio Grande rifting. More evidence showing this rock contact and with melt deep in the mantle is that primary mantle carbonates are present in many of the pyroxenites found in the Rio Grande Rift magmas or primary melt compositions that crystallized in the upper mantle.