Patchy zoning plagioclase series

The names of members of the series designate relative proportions of the endmembers. Zircons are subhedral and vary in length from 150300 m. The lavas and pumices studied are hornblende plagioclase andesites with average preeruptive temperatures of 840c and fo2 of 1. The plagioclases possess complex patchy and concentrically zoned patterns 1112 figure1. Such an origin, however, is incompatible with certain textural features of the patchy zoning. Plagioclase phenocrysts in site 648 basalts range in size from zoning patterns even within individual thin sections. Zoning appears concentric in transmitted light, however cl imaging reveals irregular patches. The petrology and geochemistry of a xenolith, a fragment of a melt. As noted above, the included plagioclase is in optical continuity with and has the same composi. These textures provide us with information concerning conditions of magmatic evolution and histories of magmatic systems. Patchy zoning of corrosion, is commonly rather uniform in the plagioclase of a given magmatic body. Insights into magmatic evolution and recharge history in. Cumulus plagioclase is relatively homogeneous in norites and gabbronorites while plagioclase in anorthosites and troctolites shows more extensive zoning with normal, reversed and patchy zoning patterns, often within the same grain. Sometimes the zoning is quite pronounced and can be seen using a polarized light microscope.

Plagioclase lapilli and phenocrysts in the lavas of the 2012. Hornblendes are commonly unzoned, but some show simple, multiple or patchy zoning. Plagioclase in hand samples is often identified by its polysynthetic crystal twinning or recordgroove effect. Probable relations between plagioclase zoning and magma dynamics, fuego volcano, guatemala arpre,o t. Oct 06, 2010 quartz forms anhedral crystals in the framework of the rock. In situ uthpbtotal dating of polychronous monazite in the. Wnrrnny department of geological sciences, aj20, university of washington, seattle, washington 98195, u. Ansrnlcr little information on prograde pz paths in granulites is generally preserved because. Plagioclase microstructures and compositions as tracers of. The olivine foliation observed at the outcrop scale is also apparent in thin section, controlled by elongate and branching olivine crystals. Complex phenocryst textures and zoning patterns in andesites and.

Plagioclase zoning types the chemical variation in the composition of a solid solution mineral series from core to rim, as the result of separation of the mineral phases during its growth by loss of equilibrium in a continuous reaction series is called zoning. Zoning in crystal is the difference between the inner core of the crystal and its outer rim. Formation of patchy zoning by some such form of diffusive reaction. Plagioclase from bmg proximal to bag commonly displays disequilibrium features indicative of reaction with a more mafic magma, such as resorption surfaces, patchy zoning and especially reverse zoning with compositions approaching those of typical bag. Pdf the origin and petrogenesis of mount hasan small mt. Linking in situ crystallization and magma replenishment via. Plagioclase group solid solution between albite anorthite. Patchy zoning shows a range in composition from 45% an in dark patches to 55% an in light patches and 510% change in feo content. Reverse zoning can occur for a number of reasons such as an increase in magma temperature, or increases in pressure. Plagioclase commonly shows patchy or reverse zoning with core and rim compositions of ab 96. When both patterns are presented in the same crystal the patchy one composes the core and the concentrically zoned form a periphery.

Citeseerx document details isaac councill, lee giles, pradeep teregowda. Four main types are present in plagioclase phyric oceanic basalts. Patchy compositional zoning is occasionally observed in both plagioclase and clinopyroxene oikocrysts. In crosspolarized light fine oscillatory zoning is visible, in which the composition varies back and. Pdf plagioclase zoning as an indicator of magma processes. On the other hand, the observed patchy zoning suggests decompression starting under waterundersaturated conditions and ending under watersaturated conditions.

In crosspolarized light fine oscillatory zoning is visible, in which the composition varies back and forth between more and less anorthiterich compositions. Additionally, the exercise is to give the student an. Plagioclase phenocrysts from mafic magmatic enclaves and plagioclase crystals from host granitoids of some plutons of the central part of the sierra nevada batholith are complexly zoned and commonly divided into three neatly distinct parts. Magma storage constrains by compositional zoning of plagioclase. Narich plagioclase and alkalifeldspar occur together in patchy intergrowths. Some grains also exhibit a discontinuous outer albiterich rim ab 97. Paleoproterozoic highpressure metamorphic history of the. The plagioclase series is essentially continuous at both high and low temperatures.

The diversity of plagioclase zoning suggests that several batches of rhyolitic magmas with distinct histories might be involved. Igneous petrology eosc 321 university of british columbia. Oscillatory zoning in plagioclase phenocrysts, which may reflect rhythmic changes in temperature andor ph2o during crystal growth, shows both half high amplitudelow frequency and lahf low amplitudehigh. Plagioclase zoning as an indicator of magma processes at. Citeseerx magma evolution and opensystem processes at. Plagioclase crystals in magmatic rocks possess various textural types and zoning such as spongy, boxy and sieve texture, and oscillatory, patchy and normal zoning. Plagioclase exhibits complex zoning such as oscillatory oz and patchy zoning pz in b and c. New insights into the processes controlling compositional. For example, a plagioclase can be zoned from a carich core to an narich rim. Crystals affected by disequilibrium textures at the core i. The porphyry consists of euhedral plagioclase crystals imbedded in felt of plagioclase, hornblende, biotite, and quartz.

This page provides mineralogical data about plagioclase. Plagioclase zoning includes oscillatory and patchy zonation and sieve textures. The plagioclase in this rock is more calcic than normal in a gabbro, and is classified as bytownite. Calcium depletion halos and femnmg zoning around faceted plagioclase inclusions in garnet from a highgrade pelitic gneiss donna l.

The plagioclase from the granodiorites display concentric diffuse oscillatory zoning, from an 43 to an 21. In sections cut parallel to 010 the included plagioclase typically forms irregular. Anovrrz department of geosciences, university of arizona, tucson, arizona 85721, u. In a paper on patchy zoning in igneous plagioclase which has published in this. 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. The plagioclase series is the most important group of silicate minerals, both volumetrically and chemically, in the earth and lunar crusts. Oscillatory zoning this sometimes occurs in plagioclase. Textural evidence indicates that patchy zoning is the result of a twostage replacement process involving partial resorption of early plagioclase crystals followed by crystallization of a more sodic plagioclase. A sequence of oscillatory cores and thin, normally zoned, more sodic rims is characteristic of many igneous plagioclases, especially those of quartz diorites and granodiorites. Feldspars, exsolution, zoning, and twinning the feldspar minerals are the most common minerals in the earths crust. Amphibole zoning, a record of progressive oxidation during. Archive of core and sitehole data and photographs from the deep sea drilling project dsdp. In the experiments plagioclase of different compositions an96, an61, an54, an23, and an22 surrounded by glasses of six different compositions in the system diopsidealbiteanorthite was heated at. Reverse and oscillatory zoning in plagioclase felspars.

All plagioclase crystals are interpreted as inherited. Ansrnlcr faceted, reversely zoned plagioclase inclusions surrounded by ca depletion halos and. The patchy zone includes large glass inclusions and, in some crystals, several internal discontinuities, interpreted as dissolution surfaces. Oscillatory zoning is a common feature in zircons from acid igneous rocks and is believed to form during crystallisation of zircons from a magma by a mechanism which is not yet understood.

For the most part, 15 mm plagioclase oikocrysts are dominant, although subordinate clinopyroxene oikocrysts of a similar size to the plagioclase also occur. Backscattered electron bsederived zoning patterns of plagioclase phenocrysts are used to identify magma processes at bezymianny volcano, kamchatka, based on the 20002007 sequence of. Plagioclase displays patchy optical zoning, particularly near crspinel seams, and clinopyroxene can also be optically zoned, although this is rare. The lavas and pumices studied are hornblendeplagioclase andesites with average preeruptive temperatures of 840c and fo2 of 1. Inclusions of lightbrown and grey glass are very common and give the plagioclase a sieved texture.

Amphibole, an early phase together with sulfides and plagioclase, began to crystallize just after the mafic magma intruded into the chamber bottom 10 km in depth and then continued to crystallize as the mme floated. The plagioclase feldspars are a complete solid solution series between ab and an, and. Fluid inclusions fi are found only in the vi plagioclases only in areas with a high ca contents. Pdf backscattered electron bsederived zoning patterns of plagioclase phenocrysts are used to identify. Also remember to distinguish between orthoclase, orthoklase, which is an individual species and oligoclase, ohligohklase, which is in the plagioclase series. Sep 14, 2017 because eclogite is a typical highpressure rock formed within subduction zones, unraveling the metamorphic evolution of precambrian eclogites with preneoproterozoic ages is important in order to study the evolution of the early style of subduction occurring prior to the neoproterozoic.

The plagioclase in some igneous bodies characteristically shows two or more distinct stages of corrosion and patchy zoning see figs. Zoning results from the minerals inability to maintain chemical equilibrium with a magma during rapid cooling. Joseph vance 1965 has made another valuable contribution to. This grain appears quite homogeneous in plane light, without concentric zones of inclusions that are commonly seen elsewhere. Zoning forms in minerals that form a solid solution series in which mineral composition changes with temperature and pressure. Mineral zoning, ptxm phase relations, and metamorphic evolution of some adirondack granulites, new york frank s. Patchy zoning abstract many igneous plagioclases exhibit irregular zoning consisting of corroded cores embayed and surrounded in crystallographic continuity by more sodic plagioclase.

Probable relations between plagioclase zoning and magma. Magmatic processes in developing oceanic crust revealed in a. Mineral zoning, p t x m phase relations, and metamorphic. Bowens reaction series page 2 the minerals on the right arm of the y are the plagioclase feldspars, which form a continuous series from 100% ca plagioclase anorthite with the highest melting point, to 100% na plagioclase albite with the lowest melting point. The plagioclase from the monzogranites and leucogranites is zoned from an 2520 to an 105. Pdf plagioclase zoning as an indicator of magma processes at. Linking in situ crystallization and magma replenishment.

Magma evolution and opensystem processes at shiveluch. Although plagioclase grains in some rocks are essentially homogeneous, those in many rocks are zonedi. The feldspars are divided into two groups, the alkali feldspars and the plagioclase feldspars. Zoning results from the minerals inability to maintain chemical. See hand sample 1844 as a good example of what to look for. Crystal lapilli are characterized by the oscillatory zoning with an fluctuations around an5763 fig. Its usually caused by a change in the composition of the crystal, showing a difference in the composition of the fluid the crystal crystallized from, i. Inclusions of this sodic plagioclase within the corroded cores give the feldspar a mottled appearance and suggest the term patchy. Jul 12, 2018 plagioclase is normally euhedral to subhedral. Calcium depletion halos and femnmg zoning around faceted. Deformationdriven differentiation of granitic magma. Sr isotope zoning in plagioclase from parinacota volcano. They are aluminosilicates of potassium, calcium, and sodium. A few contain inclusions of brighter phases, but these were excluded from the caidtims.

Backscattered electron bsederived zoning patterns of plagioclase phenocrysts are used to identify magma processes at bezymianny volcano, kamchatka, based on the 20002007 sequence of eruptive products. Reverse zoning can occur for a number of reasons such as an increase in magma temperature, or increases in. Plagioclase zoning includes calcic cores with high sr concentration, and an extensive resorption zone with lower sr, patchy zoning and glass inclusions, surrounded by a narrow 10 m, highly calcic outer rim an 60 with low sr and very high fe contents, similar to the groundmass crystals. The birefringence is sligltly higher than normal resulting in a yellow tint to come crystals. Plagioclase mineral data, information about plagioclase, its properties and worldwide locations. In the studied rocks, plagioclase crystals display a variety of textures such as finescale oscillatory zoning, resorption surfaces, sieved and patchy zones, and a wide variability of anorthite an and trace element te content. Multilevel magma plumbing at agung and batur volcanoes. The volume proportion of intercumulus material can vary significantly between. Quartz is the next most common felsic mineral, whereas alkali feldspar is not common in calcalkaline volcanic rocks and is restricted only to the alkaline series. Plagioclase exhibits both internal and external resorption ir and er, respectively in b and c. Phenocryst zoning patterns are used to identify opensystem magmatic processes in the products of the 2001 eruption of shiveluch volcano, kamchatka. Plagioclase zoning includes oscillatory and patchy. Insights into magmatic evolution and recharge history in capraia volcano italy from chemical and isotopic zoning in plagioc lase phenocrysts.

Formation of patchy zoning by some such form of diffusive reaction has been advocated by fuster 1954 and by fuster and ibarrola 1956. The chemical compositions of the matrix monazites showing patchy grains v and vi in fig. Variable parent magmas and recharge regimes of the parinacota. Core data from the deep sea drilling project dsdp, noaa. Moonstone is an orthoclase feldspar and amazonite is microcline. Deep roots for midoceanridge volcanoes revealed by. So if we take a microprobe to a plagioclase crystal we should see a core with high calcium and a rim with high sodium. Crystal residence times from trace element zoning in. Magma interaction recorded in plagioclase zoning in granitoid.

The textures and kinetics of reaction between plagioclase and melts have been investigated experimentally, and origin of dusty plagioclase in andesites has been discussed. Citeseerx citation query volcanic rock series in island. Plagioclase xenocrysts and mafic magmatic enclaves in some. Polysynthetic twinning is diagnostic of plagioclase. The unzoned zircon occurs as rounded, transgressive patches distributed throughout the zoned zircon. The plagioclase feldspars can range in color from colorless to white to greenish yellow and even flesh red. The boundary between the core and rim may be euhedral or somewhat irregular and embayed. Plagioclase textures and zoning patterns in the miocene. 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. Learn vocabulary, terms, and more with flashcards, games, and other study tools. The phenocrysts exhibit a very intense oscillatory zoning and have lines of inclusions consisting of flakes of biotite, hornblende and magnetite dust parallel to the euhedral borders. Plagioclase phenocrysts in the plagioclase phyric basalt from hole u1433b of iodp expedition 349 in the south china sea show complex zoning patterns e.

Magma interaction recorded in plagioclase zoning in. Normal, reversed and patchy zoning are typical for all studied crystals fig. Several grains have rounded cores with irregular zoning patterns. Feb 23, 2009 zoning in crystal is the difference between the inner core of the crystal and its outer rim. Many zircons with oscillatory zoning also show a patchwork replacement of zoned by unzoned zircon. Finally, mixing with a further mafic magma appears to have locally occurred also in the bag. The highest ca contents are confined to the boundary separating the patchy and concentriczoned parts figure 1 a, b. Petrograpical fetures of each volcano are similar and they display disequilibrium textures indicative of mixingmingling processes, such as patchy zones and oscillatory zoning in plagioclase. Crystal residence times from trace element zoning in plagioclase reveal changes in magma transfer dynamics at mt. Normal concentric, reverse, oscillatory, patchy, and sector zoning are all apparent, even in individual thin sections. Origin and age of the eisenkappel gabbro to granite suite. Crystals exhibiting reverse zoning are said to be reverse zoned. The unzoned zircon occurs as rounded, transgressive patches distributed throughout the zoned zircon and as. Department of the geophysical sciences the university of chicago, chicago, illinois 60637 abstract millimetersized plagioclase phenocrysts were explosively erupted in highalumina.