Patchy zoning plagioclase series

Paleoproterozoic highpressure metamorphic history of the. Reverse zoning can occur for a number of reasons such as an increase in magma temperature, or increases in. Plagioclase zoning includes oscillatory and patchy zonation and sieve textures. Zoning in crystal is the difference between the inner core of the crystal and its outer rim. The porphyry consists of euhedral plagioclase crystals imbedded in felt of plagioclase, hornblende, biotite, and quartz. In sections cut parallel to 010 the included plagioclase typically forms irregular. Crystals affected by disequilibrium textures at the core i. Amphibole zoning, a record of progressive oxidation during. Narich plagioclase and alkalifeldspar occur together in patchy intergrowths. 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. 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. Plagioclase zoning includes oscillatory and patchy.

Formation of patchy zoning by some such form of diffusive reaction. 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. Magmatic processes in developing oceanic crust revealed in a. 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 in hand samples is often identified by its polysynthetic crystal twinning or recordgroove effect. Normal, reversed and patchy zoning are typical for all studied crystals fig. Igneous petrology eosc 321 university of british columbia. Hornblendes are commonly unzoned, but some show simple, multiple or patchy zoning. Patchy zoning of corrosion, is commonly rather uniform in the plagioclase of a given magmatic body. Backscattered electron bsederived zoning patterns of plagioclase phenocrysts are used to identify magma processes at bezymianny volcano, kamchatka, based on the 20002007 sequence of. Citeseerx magma evolution and opensystem processes at. The textures and kinetics of reaction between plagioclase and melts have been investigated experimentally, and origin of dusty plagioclase in andesites has been discussed. Crystals exhibiting reverse zoning are said to be reverse zoned. Plagioclase xenocrysts and mafic magmatic enclaves in some.

Finally, mixing with a further mafic magma appears to have locally occurred also in the bag. Plagioclase exhibits both internal and external resorption ir and er, respectively in b and c. Ansrnlcr faceted, reversely zoned plagioclase inclusions surrounded by ca depletion halos and. Magma storage constrains by compositional zoning of plagioclase. The feldspars are divided into two groups, the alkali feldspars and the plagioclase feldspars. Zoning results from the minerals inability to maintain chemical equilibrium with a magma during rapid cooling. Inclusions of lightbrown and grey glass are very common and give the plagioclase a sieved texture. Plagioclase commonly shows patchy or reverse zoning with core and rim compositions of ab 96. We compare plagioclase zoning relationships in the 1974 vulcanian and 1999 strombolian. The names of members of the series designate relative proportions of the endmembers. 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.

Polysynthetic twinning is diagnostic of plagioclase. See hand sample 1844 as a good example of what to look for. The plagioclase feldspars are a complete solid solution series between ab and an, and. 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. Insights into magmatic evolution and recharge history in. Feldspars, exsolution, zoning, and twinning the feldspar minerals are the most common minerals in the earths crust. The plagioclase from the monzogranites and leucogranites is zoned from an 2520 to an 105.

Patchy compositional zoning is occasionally observed in both plagioclase and clinopyroxene oikocrysts. Dark coloured rock containing 1mm grains of plagioclase and biotite as the most abundant phases. Although plagioclase grains in some rocks are essentially homogeneous, those in many rocks are zonedi. 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. In crosspolarized light fine oscillatory zoning is visible, in which the composition varies back and forth between more and less anorthiterich compositions. Calcium depletion halos and femnmg zoning around faceted. Plagioclase mineral data, information about plagioclase, its properties and worldwide locations. Variable parent magmas and recharge regimes of the parinacota. This page provides mineralogical data about plagioclase. Crystal residence times from trace element zoning in. Sometimes the zoning is quite pronounced and can be seen using a polarized light microscope. Crystal residence times from trace element zoning in plagioclase reveal changes in magma transfer dynamics at mt. Plagioclase exhibits complex zoning such as oscillatory oz and patchy zoning pz in b and c. Moonstone is an orthoclase feldspar and amazonite is microcline.

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. For example, a plagioclase can be zoned from a carich core to an narich rim. The chemical compositions of the matrix monazites showing patchy grains v and vi in fig. Linking in situ crystallization and magma replenishment. Citeseerx document details isaac councill, lee giles, pradeep teregowda. Zoning forms in minerals that form a solid solution series in which mineral composition changes with temperature and pressure. Many zircons with oscillatory zoning also show a patchwork replacement of zoned by unzoned zircon. Inclusions of this sodic plagioclase within the corroded cores give the feldspar a mottled appearance and suggest the term patchy. Reverse zoning can occur for a number of reasons such as an increase in magma temperature, or increases in pressure. Four main types are present in plagioclase phyric oceanic basalts. Ansrnlcr little information on prograde pz paths in granulites is generally preserved because.

Core data from the deep sea drilling project dsdp, noaa. Normal concentric, reverse, oscillatory, patchy, and sector zoning are all apparent, even in individual thin sections. Also remember to distinguish between orthoclase, orthoklase, which is an individual species and oligoclase, ohligohklase, which is in the plagioclase series. Multilevel magma plumbing at agung and batur volcanoes. The olivine foliation observed at the outcrop scale is also apparent in thin section, controlled by elongate and branching olivine crystals. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Sr isotope zoning in plagioclase from parinacota volcano. The volume proportion of intercumulus material can vary significantly between. The plagioclase in some igneous bodies characteristically shows two or more distinct stages of corrosion and patchy zoning see figs. 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. Zoning appears concentric in transmitted light, however cl imaging reveals irregular patches. The diversity of plagioclase zoning suggests that several batches of rhyolitic magmas with distinct histories might be involved. Markussen department of earth and environmental science, rensselaer polytechnic institute, troy, ny 12180, usa detailed petrologic analysis of ten metaanorthosites and related introduction.

Deep roots for midoceanridge volcanoes revealed by. Plagioclase phenocrysts in the plagioclase phyric basalt from hole u1433b of iodp expedition 349 in the south china sea show complex zoning patterns e. Archive of core and sitehole data and photographs from the deep sea drilling project dsdp. The boundary between the core and rim may be euhedral or somewhat irregular and embayed. Plagioclase lapilli and phenocrysts in the lavas of the 2012. The unzoned zircon occurs as rounded, transgressive patches distributed throughout the zoned zircon. Magma interaction recorded in plagioclase zoning in granitoid. Phenocryst zoning patterns are used to identify opensystem magmatic processes in the products of the 2001 eruption of shiveluch volcano, kamchatka.

Plagioclase group solid solution between albite anorthite. 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. 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. The highest ca contents are confined to the boundary separating the patchy and concentriczoned parts figure 1 a, b. Deformationdriven differentiation of granitic magma. Jul 12, 2018 plagioclase is normally euhedral to subhedral. They are aluminosilicates of potassium, calcium, and sodium. Plagioclase textures and zoning patterns in the miocene. Anovrrz department of geosciences, university of arizona, tucson, arizona 85721, u. Oscillatory zoning this sometimes occurs in plagioclase. The plagioclase series is essentially continuous at both high and low temperatures. Plagioclase microstructures and compositions as tracers of. On the other hand, the observed patchy zoning suggests decompression starting under waterundersaturated conditions and ending under watersaturated conditions.

The birefringence is sligltly higher than normal resulting in a yellow tint to come crystals. Insights into magmatic evolution and recharge history in capraia volcano italy from chemical and isotopic zoning in plagioc lase phenocrysts. Citeseerx citation query volcanic rock series in island. In situ uthpbtotal dating of polychronous monazite in the. Additionally, the exercise is to give the student an. 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. Pdf the origin and petrogenesis of mount hasan small mt. Zircons are subhedral and vary in length from 150300 m. Plagioclase displays patchy optical zoning, particularly near crspinel seams, and clinopyroxene can also be optically zoned, although this is rare.

Wnrrnny department of geological sciences, aj20, university of washington, seattle, washington 98195, u. Oct 06, 2010 quartz forms anhedral crystals in the framework of the rock. 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. A few contain inclusions of brighter phases, but these were excluded from the caidtims. In crosspolarized light fine oscillatory zoning is visible, in which the composition varies back and. Pdf plagioclase zoning as an indicator of magma processes. The plagioclase from the granodiorites display concentric diffuse oscillatory zoning, from an 43 to an 21. The plagioclases possess complex patchy and concentrically zoned patterns 1112 figure1. Fluid inclusions fi are found only in the vi plagioclases only in areas with a high ca contents. Plagioclase feldspar grows in igneous environments and crystals which grow early in a cooling magma contain more calcium than those formed at the end of crystallization, which are enriched in sodium.

Feb 23, 2009 zoning in crystal is the difference between the inner core of the crystal and its outer rim. Such an origin, however, is incompatible with certain textural features of the patchy zoning. The importance of accurate knowledge concerning the causes of composition zoning in plagioclases lies in the possibility that such zoning may throw light on the magmatic history of the rock of which the zoned felspar is a component. Albite and carlsbad twinning are visible in the xpl view, and also concentric growth zoning is seen in crystals near extinction. Probable relations between plagioclase zoning and magma dynamics, fuego volcano, guatemala arpre,o t. Probable relations between plagioclase zoning and magma. 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. So if we take a microprobe to a plagioclase crystal we should see a core with high calcium and a rim with high sodium. Joseph vance 1965 has made another valuable contribution to. Plagioclase zone formation, especially those in the volcanic rocks is reflected in the fact that from. The petrology and geochemistry of a xenolith, a fragment of a melt. The unzoned zircon occurs as rounded, transgressive patches distributed throughout the zoned zircon and as. The plagioclase feldspars can range in color from colorless to white to greenish yellow and even flesh red. 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.

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. Magma evolution and opensystem processes at shiveluch. For the most part, 15 mm plagioclase oikocrysts are dominant, although subordinate clinopyroxene oikocrysts of a similar size to the plagioclase also occur. Pdf plagioclase zoning as an indicator of magma processes at.

Zoning results from the minerals inability to maintain chemical. As noted above, the included plagioclase is in optical continuity with and has the same composi. All plagioclase crystals are interpreted as inherited. Mineral zoning, ptxm phase relations, and metamorphic evolution of some adirondack granulites, new york frank s. Origin and age of the eisenkappel gabbro to granite suite. The plagioclase in this rock is more calcic than normal in a gabbro, and is classified as bytownite. The patchy zone includes large glass inclusions and, in some crystals, several internal discontinuities, interpreted as dissolution surfaces. Linking in situ crystallization and magma replenishment via. 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. Department of the geophysical sciences the university of chicago, chicago, illinois 60637 abstract millimetersized plagioclase phenocrysts were explosively erupted in highalumina. Twentytwo crystals from 1974 and thirtyseven crystals from 1999 ash were weighed, oriented, sectioned and optically characterized to delineate zoning differences. 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. Formation of patchy zoning by some such form of diffusive reaction has been advocated by fuster 1954 and by fuster and ibarrola 1956. 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. The plagioclase series is the most important group of silicate minerals, both volumetrically and chemically, in the earth and lunar crusts. Plagioclase phenocrysts in site 648 basalts range in size from zoning patterns even within individual thin sections. When both patterns are presented in the same crystal the patchy one composes the core and the concentrically zoned form a periphery. New insights into the processes controlling compositional. Crystal lapilli are characterized by the oscillatory zoning with an fluctuations around an5763 fig. The mme generally have sharp fine chilled margins and show no in situ mixing between the mme and the host granite.

The lavas and pumices studied are hornblende plagioclase andesites with average preeruptive temperatures of 840c and fo2 of 1. 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. Complex phenocryst textures and zoning patterns in andesites and. Plagioclase zoning as an indicator of magma processes at. This grain appears quite homogeneous in plane light, without concentric zones of inclusions that are commonly seen elsewhere. Magma interaction recorded in plagioclase zoning in. These textures provide us with information concerning conditions of magmatic evolution and histories of magmatic systems. 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. Some grains also exhibit a discontinuous outer albiterich rim ab 97. In a paper on patchy zoning in igneous plagioclase which has published in this. This optical zoning is a reflection of chemical zoning in the mineral. Patchy zoning abstract many igneous plagioclases exhibit irregular zoning consisting of corroded cores embayed and surrounded in crystallographic continuity by more sodic plagioclase. Calcium depletion halos and femnmg zoning around faceted plagioclase inclusions in garnet from a highgrade pelitic gneiss donna l. Several grains have rounded cores with irregular zoning patterns.