The presence of oxidation at the crystal rims, and the formation of a reaction halo of orthopyroxene
around the phenocrysts suggest that olivine might be a xenocryst that is not in equilibrium with the melt that carried it to the surface.
The Talavera sample shows large anhedral poikilitic orthopyroxene
crystals, leading to a hypidiomorphic subophitic to ophitic texture.
Thin sections of dyke contacts show microporphyritic crystals of plagioclase, augite, and orthopyroxene
scattered in a dark glassy matrix (Fig.
2006, Investigating the depth of komatiite melting using experimentally determined olivine and orthopyroxene
melt reaction coefficients: American Geophysical Union, Fall Meeting, 2006, abstract V24B-05.
Harzburgites have granular, amorph granular and Milonite textures and amorph Olivine 70-80%), amorph Orthopyroxene
(15-25%), Clinopiroxine (5%) and Chrome Spinel (less than 2%) and Menitite crystals are seen in their mineralogy composition.
Modal mineralogies are defined by plagioclase (~30-95 vol%), orthopyroxene
(<1-45 vol%) and clinopyroxene (<1-25 vol%), with accessory (<10 vol%) abundances of Feo-Ti oxide, olivine, hornblende, biotite, apatite, and secondary minerals (e.
The mineral assemblage is composed by plagioclase, orthopyroxene
and clinopyroxene (augite), opaque minerals and apatite.
Plagioclase is characterized by complex zoning patterns that reflect disequilibrium conditions (Shelley 1993; Stewart and Fowler 2001; Murphy 2006) For both tholeiitic and calcalkalic suites, clinopyroxene phenocrysts occur in mafic to intermediate lavas, olivine phenocrysts are typically restricted to the more mafic lavas and orthopyroxene
, amphibole and quartz phenocrysts are more common in intermediate to felsic lavas.
Objectives of this study include: 1) determining mineral composition of olivine, clinopyroxene, and orthopyroxene
in the xenoliths; 2) examining individual chemical zoning characteristics or orthopyroxene
, clinopyroxene, and olivine; 3) comparing mineral chemistry and zoning differences between xenoliths from different eruption styles; and 4) use xenolith compositions to determine lithospheric mantle pressure and temperature.
The occurrence of orthopyroxene
and hercynite, and specific chemical composition of high-grade phases, such as a high Ti content in biotite and a high Al content in orthopyroxene
, are in accordance with the other geothermobarometric estimates, which suggests the peak temperature of formation over 800[degrees]C and pressure of 5-6 kbar (Fig.
do occur but is far lesser in amount than orthopyroxene
while olivine is present as a minor phase in the sample.
They are darker than their host rock and display a porphyritic texture, with plagioclase, orthopyroxene
, amphibole, and quartz phenocrysts in a microlitic groundmass mainly composed of acicular plagioclase and accessory opaque minerals.