tertiary andesitic basalts of the sirjan area, urmieh-dokhtar magmatic arc, iran, contain plagioclase phenocrysts enclosed in a matrix of amphibole, clinopyroxene and rare olivine crystals. textural and compositional evidence suggests two significantly different types of plagioclase phenocrysts occur in the andesitic basalts. the most common type of plagioclase phenocrysts have zoning patterns ...

Introduction: Ureilitic meteorites are ultramafic rocks with highly depleted REE abundance, while showing primitive signatures, such as abundant noble gases and oxygen isotopic heterogeneities. A lack of basaltic components among ureilitic meteorites is the major cause of our poor understanding of their evolution. Especially, chronological studies of ureilites are limited because of depletion o...

Electrostatic calculations estimated the energy of hypothetical ion clustering in intermediate plagioclase feldspars. The calculated energy appears too great to allow segregation of Ca and Na atoms into domains upon annealing without a corresponding movement of A1 and Si from an original disordered structure. The calculated energy may be sufficiently small that Ca and Na atoms can disorder part...

Higgins (1999) proposed that microcline megacrysts in the Cathedral Peak granodiorite resulted from Ostwald ripening in which textural coarsening of earlier formed small K-feldspar crystals were sacrificed to feed the growth of a select few larger crystals. Textural evidence shows that Ostwald ripening did not occur, but, instead, the megacrysts resulted from K-replacement of broken plagioclase...

Precambrian quartzo-feldspathic gneiss was encountered at an elevation of —3616 feet in the Herman 1A well drilled in southeastern Erie County, Ohio, by the Amerada Petroleum Corporation. The five samples of this gneiss that were studied exhibit varying degrees of gneissose foliation. In order of decreasing abundance, microcline, plagioclase, quartz, and biotite together account for an average ...

Precambrian quartzo-feldspathic gneiss was encountered at an elevation of —3616 feet in the Herman 1A well drilled in southeastern Erie County, Ohio, by the Amerada Petroleum Corporation. The five samples of this gneiss that were studied exhibit varying degrees of gneissose foliation. In order of decreasing abundance, microcline, plagioclase, quartz, and biotite together account for an average ...

Precambrian quartzo-feldspathic gneiss was encountered at an elevation of —3616 feet in the Herman 1A well drilled in southeastern Erie County, Ohio, by the Amerada Petroleum Corporation. The five samples of this gneiss that were studied exhibit varying degrees of gneissose foliation. In order of decreasing abundance, microcline, plagioclase, quartz, and biotite together account for an average ...