Patchy zoning plagioclase rock

Peninsula, i have observed many examples of patchy zoning in plagioclase and, al though this zoning is generally. Inclusions of this sodic plagioclase within the cor roded cores give the feldspar a mottled appearance and suggest the term patchy zoning for these textures. This type of zoning may also be produced by physical inclusions of rock or other minerals. Patchy zoning this sometimes occurs in plagioclase crystals where irregularly shaped patches of the crystal show different compositions as evidenced by going extinct at angles different from other zones in the crystal. Fluids enter the cores of the plagioclase via microcracks andor twin planes. Magma storage constrains by compositional zoning of plagioclase. Concentric zoning may be more subtle as with garnet and feldspar, for example. The plagioclases possess complex patchy and concentrically zoned. Many igneous plagioclases exhibit irregular zoning consisting of corroded cores embayed and surrounded in crystallographic continuity by more sodic plagioclase. Pdf backscattered electron bsederived zoning patterns of plagioclase phenocrysts are used to identify magma processes at.

Plagioclase phenocrysts in the plagioclase phyric basalt from hole u1433b of iodp expedition 349 in the south china sea show complex zoning patterns e. Plagioclase zoning comprises a unique record of past changes in magmatic environment which can provide critical evidence on several fundamental problems of magmatic evolution. An example of this would be clay, hematite, or chlorite inclusions coating the surface of an inner layer of crystal growth. Pdf plagioclase zoning as an indicator of magma processes at. Can be confused with quartz if there is no twinning, however the optic axis figure will resolve this. Patchy zoning abstract many igneous plagioclases exhibit irregular zoning consisting of corroded cores embayed and surrounded in crystallographic continuity by more sodic plagioclase. This type of zoning is interpreted as a result of a decrease in confining p on waterdeficient magma during its rise in the crust vance, 1965. Inclusions of this sodic plagioclase within the corroded cores give the feldspar a mottled appearance and suggest the term patchy zoning for these textures. Magmatic fabrics are defined to have less than 20% recrystallized plagioclase and they typically contain. Mineral textures and zoning as evidence for open system. Plagioclase zoning in midpleistocene lavas from the. Often a grey color in comparison to other feldspars.

Chemical zoning is common the calcic core has a larger extinction angle than the sodic rim. Origin of patchy zoning in plagioclase from gabbroic rocks of. Patchy zoning is exceedingly widespread in magmatic plagioclase, especially in the common plagioclaserich volcanic and plu tonic rocks of calcalkaline. The presense of parallel striae on cleavage surfaces distinguishes plagioclase from kfeldspar. In the geological literature on the lepontine alps, there are several reports on irregularly zoned patchy plagioclase with wide variations in composition. Wholerock major element compositions and point counts. Whole rock maiorelement compositions, modal abundances, and rheological properties of turf point formation. Plagioclase zone formation, especially those in the volcanic rocks is reflected in. Patchy zoning is exceedingly widespread in magmatic plagioclase, especially in the common plagioclaserich volcanic and plu tonic rocks of calc alkaline. Distribution of plagioclase in carbonate rocks from the tertiary. Patchy zoning in plagioclase has been observed in gabbroic rocks in southwestern oregon.