Factors controlling the development of prism faces in granite zircons: a microprobe study

Benisek, Artur; Finger, Friedrich

doi:10.1007/bf00321749

Cited by 129 publications

(55 citation statements)

References 15 publications

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“…We suggest that these features can be explained by the crystallization of the late zircon at relatively low temperature after the emplacement of the granitic magma. Hf contents tend to increase rimward in the late zircon from granitic rocks (Wang, 1989;Halden et al, 1993;Benisek and Finger, 1993;Caironi et al, 2000), which is consistent with decreasing temperature in the course of magma consolidation at the site of emplacement. In contrast, the rimward increase in Hf contents seems paradoxical, in light of the…”

Section: Fractionation Of Zr/hf In Granitic Zirconmentioning

confidence: 79%

“…The second type is characterized by brownish color, poor transparency and low birefringence due to metamictization, large and similar typological indices (I pr , I py and I el ), oscillatory zoning and high U and Th contents; this type commonly is included within the late forming-minerals such as K-feldspar and quartz (Speer, 1982;Broska et al, 1990;Vavra, 1994;Poitrasson et al, 1998;Pupin, 2000;Rubatto, 2002;Wang et al, 2007). Both types commonly occur together in granitic rocks in the form of single grains (Krasnobayev, 1980;Wang et al, 2007) or core-rim overgrowths (Krasnobayev, 1980;Speer, 1982;Hansmann et al, 1983;Broska et al, 1990;Paterson et al, 1992;Halden et al, 1993;Benisek and Finger, 1993;Vavra, 1994;Poitrasson et al, 1998;Nasdala et al, 1999;Charlier and Zellmer, 2000;Wang et al, 2007). The core-rim structure is clearly observed by backscattered electron or cathodoluminescence images (Fig.…”

Section: Fractionation Of Zr/hf In Granitic Zirconmentioning

confidence: 99%

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Hf contents and Zr/Hf ratios in granitic zircons

2010

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We present a statistical analysis of 2201 electron microprobe determinations of Hf contents and Zr/Hf ratios in zircon from 65 samples of granitic rocks. The modal Hf content and modal Zr/Hf ratio of zircon taken from the data are 1.43 wt% HfO 2 and 38.5 respectively. Estimated partition coefficients are 2520 for D Zr and 2420 for D Hf between zircon and granitic magma. The large and similar Zr and Hf partition coefficients indicate that the crystallization of zircon would deplete the melt in both Zr and Hf, but would not cause significant fractionation of Zr from Hf. On the basis of the geochemical behaviour of Hf, granitic zircons can be divided into three types (early, late and hydrothermal zircon). Compared to the early zircon in granitic rocks, late-crystallizing zircon and especially hydrothermal zircon are characterized by much higher Hf contents and lower Zr/Hf, which can be explained by a change in D Hf with decreasing crystallization temperature. The behavior of Hf in granitic zircon may be used as geochemical indicator to track the origins and crystallization environments of the host magma.

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Section: Fractionation Of Zr/hf In Granitic Zirconmentioning

confidence: 79%

Section: Fractionation Of Zr/hf In Granitic Zirconmentioning

confidence: 99%

Hf contents and Zr/Hf ratios in granitic zircons

2010

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“…Hence, the core-to-rim increase of Hf observed in most zircon grains ( Fig. 5; Electronic Appendix 2) may thus mirror magma differentiation (Linnen and Keppler 2002;Hoskin and Schaltegger 1993) during crystal fractionation (Benisek and Finger 1993). In turn, sharp indentations towards lower Hf values (e.g.…”

Section: Magma Mixing and Relationships With Other Accessory Phasesmentioning

confidence: 94%

“…The transition from high U-Th-Y zircon in patchyzoned cores to oscillatory zoning is characterised by a sharp drop in U, Th and Y. This steep chemical gradient suggests rapid zircon growth in response to magma influx (Benisek and Finger 1993). The drop is more accentuated for Th, which decreases by more than 95% compared to other elements such as U and Y, which decrease by 50-80% (e.g.…”

Section: Magma Mixing and Relationships With Other Accessory Phasesmentioning

confidence: 99%

Zircon texture and chemical composition as a guide to magmatic processes and mixing in a granitic environment and coeval volcanic system

Gagnevin

Daly

Kronz

2009

Contrib Mineral Petrol

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This study documents the chemical and textural responses of zircon in the Elba igneous complex, with particular reference to the 7-to 7.8-Ma-old Monte Capanne pluton in relation to its coeval volcanic counterpart (Capraia), using BSE imaging and quantitative electron microprobe analyses. The Monte Capanne pluton displays multiple field and geochemical evidence for magma mixing. The samples we have investigated (including monzogranitic, mafic enclave and dyke samples) display similar zircon textures and are associated with an extremely large range of trace and minor element (Hf, Y, HREE, Th, U) compositions, which contrast with relatively simple textures and zoning patterns in zircons from a Capraia dacite. We have used a relatively simple textural classification (patchy zoning, homogenous cores, oscillatory zoning and unzoned zircon) as the basis for discussing the chemical composition and chemical variation within zircons from the Monte Capanne pluton. Based on these data and other works in Lithos 78:101-118, 2004 , it is inferred that mixing between metaluminous and peraluminous melts occurred early in the evolution of the Monte Capanne magma chamber. In particular, mixing was responsible for the development of the patchy-zoning texture in the zircon cores, which was associated with reactions between other accessory phases (including monazite, apatite, allanite), which we infer to have significantly affected the Th distribution in zircon. Zircons from the MC pluton displaying ''homogeneous cores'' have chemical affinities with zircons in the coeval Capraia volcanic system, consistent with the participation of a Capraia-like mantle end-member during mixing. Further zircon growth in the MC pluton produced the oscillatory zoning texture, which records both long-term (crystal fractionation) and transient (recharge with both silicic and mafic magmas) events in a hybrid magma chamber. It is inferred that Hf and the Th/U ratio cannot be used alone to infer magmatic processes due to their dependency on temperature, nor are they a diagnostic feature of xenocrystic grains. This study shows that zircon chemistry coupled with detailed textural analysis can provide a powerful tool to elucidate the complex evolution of a magma system.

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“…%, the incorporation of U into the crystal lattice seems to be accompanied by increased contents of P 2 O 5 , ThO 2 and Y 2 O 3 . An increase in mean atomic number (and thus also the BSE intensity) due to elevated contents of U, Th, Hf and HREE was assumed by number of authors (e.g., Benisek and Finger 1993;Hanchar and Miller 1993;Corfu et al 2003;Nasdala et al 2003) but this does not need to be the case if vacancies or H 2 O are present in the crystal lattice (Kempe et al 2000;Nasdala et al 2003).…”

Section: Zirconmentioning

confidence: 99%

Hyperpotassic granulites from Blanský les (Moldanubian Zone, Bohemian Massif) revisited

Janoušek¹,

Krenn²,

Finger³

et al. 2012

J. Geosci.

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In the Blanský les granulite Massif (Moldanubian Unit, South Bohemia), built mainly by felsic calc-alkaline HP-HT garnet ± kyanite granulite, occur rare small bodies of hyperpotassic granulite with garnet (Plešovice type) or pyroxene (Lhotka type). The Plešovice type is dominated by slightly perthitic K-feldspar and almandine-pyrope rich garnet, the latter variously retrogressed to biotite ± plagioclase. The other conspicuous euhedral crystals are apatite and zircon. In the rock occur also Zr-Nb-rich rutile and much rarer primary monazite; originally LREE-rich apatites decompose into small Th-poor, MREE-rich monazite grains. The Lhotka type granulites contain pyroxene, often altered to actinolite, instead of garnet. The predominant perthitic K-feldspar encloses a small amount of unmixed celsian. Typical are large euhedral crystals of apatite with small unmixed monazite grains; primary monazite is rare. Noteworthy is the occurrence of secondary Ti phases with high REE, Y and Zr, formed at the expense of the primary pyroxene. The studied granulite types are highly potassic (K 2 O > 7 %, up to c. 14 %, K 2 O/Na 2 O = 3.1-9.2 wt. %), silica-poor (SiO 2 < 65 %), with low contents of most major-and minor-element oxides, apart from K and P. Characteristic are high concentrations of Cs, Rb, Ba and U at variable enrichments in Zr and Hf. Whole-rock contents some HFSE (Ti, Nb and Ta) are extremely low. The REE patterns show marked negative Eu anomalies and variable LREE enrichments increasing with rising silica due to a conspicuous drop in HREE. The Sr-Nd isotopic ratios document the derivation Sr/ 86 Sr 337 = 0.7109 for the Lhotka types). Apatite saturation temperatures are high (~1070 °C), close to the previously estimated conditions of (re)crystallization for both calc-alkaline and hyperpotassic granulites. The zircon saturation temperatures tend to be more variable, some exceeding 1000 °C but many unrealistically low, reflecting effects of disequilibrium melting, heterogeneous distribution of accumulated crystals in the magma and/or sampling bias. The hyperpotassic granulites are interpreted as Viséan igneous rocks. The parental magma could have originated by low degrees of HP-HT, non-eutectic partial melting. The low-scale melt was most likely expelled close to the HP-HT metamorphic peak or at early stages of decompression from common Moldanubian calc-alkaline granulites. This genetic link is documented by the presumed P-T conditions, similar age and complementary geochemical and Sr-Nd isotopic signatures. Subsequently the magma could have developed by garnet, apatite and zircon dominated fractional crystallization, with or without some crystal accumulation.

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Factors controlling the development of prism faces in granite zircons: a microprobe study

Cited by 129 publications

References 15 publications

Hf contents and Zr/Hf ratios in granitic zircons

Hf contents and Zr/Hf ratios in granitic zircons

Zircon texture and chemical composition as a guide to magmatic processes and mixing in a granitic environment and coeval volcanic system

Hyperpotassic granulites from Blanský les (Moldanubian Zone, Bohemian Massif) revisited

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