Genesis and evolution of low-Al orthopyroxene in spinel peridotite xenoliths, Grand Canyon field, Arizona, USA

Article Abstract:

Orthopyroxene porphyroblasts banded to irregularly low interiors of Al and Cr and with several olivine inclusions are found in some spinel peridotite xenoliths from the Colorado Plateau. It is proposed that Al-poor formations stabilized in chlorite peridotite ahead of porphyroblast evolution during heating and resultant responses that excluded talc, chlorite and tremolite. Data indicated that models of extension and crustal magmatism could have been affected by discrete orthopyroxene textures which were formed due to olivine-talc reactions during heating.

Arizona, Spinel

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Chlorite-rich ultramafic reaction zones in Colorado Plateau xenoliths: recorders of sub-Moho hydration

Article Abstract:

A study on chlorite-rich ultramafic reaction zones in Colorado Plateau xenoliths shows the existence of water storage and transport in the mantle within the stability field of garnet peridotite. It occurs at the depths of 75 km and results in metasomatism in the mantle. The pressures could be greater than 2.2 GPa. A xenolith contains a combination of chlorite, enstatite, diopside, ilmenite and titanian chondrodite, separated by a combination of diopside, talc, diopside, ilmenite and pyrite.

Observations, Hydration, Rehydration solutions, Colorado Plateau

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Compositional zonation in garnets in peridotite xenoliths

Article Abstract:

An analysis of garnet compositional zonation in peridotite xenoliths is presented. The analysis tests garnets from 42 samples taken from southern Africa. The samples were examined by using electron probe to determine possible correlations between compositional zonation and rock history. It is shown that xenoliths maybe classified into six groups. The groups are based on element enrichment and zonation levels.

Analysis, Garnet

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