Zirconium abundance in granulite-facies minerals, with implications for zircon geochronology in high-grade rocks

Fraser, Geoff; Ellis, David J.; Eggins, Stephen

doi:10.1130/0091-7613(1997)025<0607:zaigfm>2.3.co;2

Cited by 294 publications

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“…Metamorphic precipitation of zircon could be a result of the breakdown of and/or exsolution from various Zr-bearing phases (Davidson and van Breemen, 1988) such as garnet, amphibole, (clino)pyroxene and ilmenite (e.g., Fraser et al, 1997;Degeling et al, 2001;Möller et al, 2003;Söderlund et al, 2004;Harley et al, 2007;Kelsey et al, 2008;Morisset and Scoates, 2008), hemo-ilmenite (Morisset et al, 2005), baddeleyite (Bingen et al, 2001;Söderlund et al, 2004), rutile (Harley et al, 2007;Tomkins et al, 2007;Morisset and Scoates, 2008;Kelsey and Powell, 2011;Ewing et al, 2013Ewing et al, , 2014Pape et al, 2016), epidote, titanite (Kohn et al, 2015), chlorite (Fraser et al, 2004), and biotite (Vavra et al, 1996). Zircon coronae have been reported around Martian baddeleyite as a result of shock metamorphism (Moser et al, 2013).…”

Section: Zr-bearing Phases Potentially Associated With Zircon Precipimentioning

confidence: 99%

“…Zircon growth and overgrowth formation during cooling stage and/or retrograde metamorphism may also result from metamorphic reactions and breakdown of other Zrbearing minerals (Fraser et al, 1997(Fraser et al, , 2004Degeling et al, 2001;Möller et al, 2002Möller et al, , 2003Tomkins et al, 2007). Fraser et al (1997) and Möller et al (2002) suggested that the source of newly precipitated zircon is Zrbearing rock-forming phases (e.g., garnet), which experience breakdown and release Zr.…”

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confidence: 99%

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Interpretation of zircon coronae textures from metapelitic granulites of the Ivrea–Verbano Zone, northern Italy: two-stage decomposition of Fe–Ti oxides

Kovaleva¹,

Austrheim²,

Klötzli³

2017

Solid Earth

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Abstract. In this study, we report the occurrence of zircon coronae textures in metapelitic granulites of the IvreaVerbano Zone. Unusual zircon textures are spatially associated with Fe-Ti oxides and occur as (1) vermicular-shaped aggregates 50-200 µm long and 5-20 µm thick and as (2) zircon coronae and fine-grained chains, hundreds of micrometers long and ≤ 1 µm thick, spatially associated with the larger zircon grains. Formation of such textures is a result of zircon precipitation during cooling after peak metamorphic conditions, which involved: (1) decomposition of Zr-rich ilmenite to Zr-bearing rutile, and formation of the vermicular-shaped zircon during retrograde metamorphism and hydration; and (2) recrystallization of Zr-bearing rutile to Zr-depleted rutile intergrown with quartz, and precipitation of the submicron-thick zircon coronae during further exhumation and cooling. We also observed hat-shaped grains that are composed of preexisting zircon overgrown by zircon coronae during stage (2). Formation of vermicular zircon (1) preceded ductile and brittle deformation of the host rock, as vermicular zircon is found both plastically and cataclastically deformed. Formation of thin zircon coronae (2) was coeval with, or immediately after, brittle deformation as coronae are found to fill fractures in the host rock. The latter is evidence of local, fluid-aided mobility of Zr. This study demonstrates that metamorphic zircon can nucleate and grow as a result of hydration reactions and mineral breakdown during cooling after granulite-facies metamorphism. Zircon coronae textures indicate metamorphic reactions in the host rock and establish the direction of the reaction front.

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Section: Zr-bearing Phases Potentially Associated With Zircon Precipimentioning

confidence: 99%

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confidence: 99%

Interpretation of zircon coronae textures from metapelitic granulites of the Ivrea–Verbano Zone, northern Italy: two-stage decomposition of Fe–Ti oxides

Kovaleva¹,

Austrheim²,

Klötzli³

2017

Solid Earth

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“…For new metamorphic zircon to form in hightemperature (HT) metamorphic rocks, either the presence of a hydrous fluid or melt phase is required (e.g. Watson and Harrison 1983;Fraser et al 1997;Tomaschek et al 2003;Tichomirowa et al 2005). In the absence of fluids, metamorphic zircon may form via solid-state (partial) recrystallisation (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…In the absence of fluids, metamorphic zircon may form via solid-state (partial) recrystallisation (e.g. Schaltegger et al 1999;Hoskin and Black 2000;Tomaschek et al 2003;Rubatto et al 2006) or by the breakdown of Zr-rich minerals (Fraser et al 1997;Degeling et al 2001;Bingen et al 2004;Ewing et al 2013;Pape et al 2016). …”

Section: Introductionmentioning

confidence: 99%

Zircon ages in granulite facies rocks: decoupling from geochemistry above 850 °C?

Kunz

Regis

Engi

2018

Contrib Mineral Petrol

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Granulite facies rocks frequently show a large spread in their zircon ages, the interpretation of which raises questions: Has the isotopic system been disturbed? By what process(es) and conditions did the alteration occur? Can the dates be regarded as real ages, reflecting several growth episodes? Furthermore, under some circumstances of (ultra-)high-temperature metamorphism, decoupling of zircon U-Pb dates from their trace element geochemistry has been reported. Understanding these processes is crucial to help interpret such dates in the context of the P-T history. Our study presents evidence for decoupling in zircon from the highest grade metapelites (> 850 °C) taken along a continuous high-temperature metamorphic field gradient in the Ivrea Zone (NW Italy). These rocks represent a well-characterised segment of Permian lower continental crust with a protracted high-temperature history. Cathodoluminescence images reveal that zircons in the mid-amphibolite facies preserve mainly detrital cores with narrow overgrowths. In the upper amphibolite and granulite facies, preserved detrital cores decrease and metamorphic zircon increases in quantity. Across all samples we document a sequence of four rim generations based on textures. U-Pb dates, Th/U ratios and Ti-in-zircon concentrations show an essentially continuous evolution with increasing metamorphic grade, except in the samples from the granulite facies, which display significant scatter in age and chemistry. We associate the observed decoupling of zircon systematics in high-grade non-metamict zircon with disturbance processes related to differences in behaviour of non-formula elements (i.e. Pb, Th, U, Ti) at high-temperature conditions, notably differences in compatibility within the crystal structure.

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“…Zircon is formed by various metamorphic processes, and can record the changed tectonic conditions as chemical and internal textural variations (e.g., Black et al, 1986;Williams et al, 1996;Fraser et al, 1997;Pan, 1997;Roberts and Finger, 1997;Scherer et al, 2007;Harley et al, 2007). During metamorphism, the preserved internal textures of detrital zircon, particularly igneous oscillatory zoning progressively change into convoluted, blurred, and thickened (broaden), and textures consisting of transgressive patches and lobes become dominant (e.g., Vavra et al, 1996;Ashwal et al, 1999;Hoskin and Black, 2000;Connelly, 2000;Schaltegger et al, 2002;Corfu et al, 2003;Scherer et al, 2007;Harley et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

Internal textures and U–Pb geochronology of zircons in metamorphic rocks from the Southwestern Highland Complex, Sri Lanka

Wanniarachchi

Akasaka

Hayasaka

et al. 2016

Journal of Mineralogical and Petrological Sciences

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Internal textures and U-Pb ages of zircons in garnet-biotite gneiss of the Southwestern Highland Complex (SWHC), Sri Lanka, were studied to clarify the repeated thermal events in the study area. The zircons from garnet-biotite gneiss consist of the detrital cores and overgrowths with two to five growth stages. The detrital zircon cores are rounded or euhedral to subhedral in shape, and show transgressive internal textures or oscillatory zoning.The rounded or subhedral to euhedral detrital core morphology suggests several major Archaean to Proterozoic sources of detritus zircons in the SWHC. Ages of the detrital cores are in a range of 3.3-1.7 Ga, and can be categorized into five ranges of 3380-3220, 2730-2660, 2550-2490, 2220-2170, and 1900-1700 Ma, implying the source rock ages. The detrital cores in the 3380-2170 Ma have Th/U-ratios of more than 0.3, suggesting igneous origin. The detrital cores in the range 1900-1700 Ma have Th/U of >0.3 or 0.3-0.1, suggesting an igneous or metamorphic origin. Some overgrowths with the ages in the ranges of 1900-1700 and 630-500 Ma have Th/U-ratios less than 0.1 implying that zircon growth corresponds to the thermal events. Zircons lacking detrital cores and having growth zones with characteristic metamorphic internal textures gave ages in a range of 630-500 Ma, implying the generation at the final granulite grade metamorphic event.

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Zirconium abundance in granulite-facies minerals, with implications for zircon geochronology in high-grade rocks

Cited by 294 publications

References 0 publications

Interpretation of zircon coronae textures from metapelitic granulites of the Ivrea–Verbano Zone, northern Italy: two-stage decomposition of Fe–Ti oxides

Interpretation of zircon coronae textures from metapelitic granulites of the Ivrea–Verbano Zone, northern Italy: two-stage decomposition of Fe–Ti oxides

Zircon ages in granulite facies rocks: decoupling from geochemistry above 850 °C?

Internal textures and U–Pb geochronology of zircons in metamorphic rocks from the Southwestern Highland Complex, Sri Lanka

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