Metamorphic zircon formation by solid-state recrystallization of protolith igneous zircon
TL;DR: In this paper, the age of metamorphic zircon has been determined using trace element analysis and integrated cathodoluminescence, U-Pb isotope, trace element and electron backscatter diffraction pattern (EBSP) analyses.
Abstract: Protolith zircon in high-grade metagranitoids from Queensland, Australia, partially recrystallized during granulite-grade metamorphism. We describe the zircon in detail using integrated cathodoluminescence, U–Pb isotope, trace element and electron backscatter diffraction pattern (EBSP) analyses. Primary igneous oscillatory zoning is partially modified or obliterated in areas within single crystals, but is well preserved in other areas. A variety of secondary internal structures are observed, with large areas of transgressive recrystallized zircon usually dominant. Associated with these areas are recrystallization margins, interpreted to be recrystallization fronts, that have conformable boundaries with transgressive recrystallized areas, but contrasting cathodoluminescence and trace element chemistry. Trace element analyses of primary and secondary structures provide compelling evidence for closed-system solid-state recrystallization. By this process, trace elements in the protolith zircon are purged during recrystallization and partitioned between the enriched recrystallization front and depleted recrystallized areas. However, recrystallization is not always efficient, often leaving a ‘memory’ of the protolith trace element and isotopic composition. This results in the measurement of ‘mixed’ U–Pb isotope ages. Nonetheless, the age of metamorphism has been determined. A correlation between apparent age and Th/U ratio is indicative of incomplete re-setting by partial recrystallization. Recrystallization is shown to probably not significantly affect Lu–Hf ages. Recrystallization has been determined by textural and trace element analysis and EBSP data not to have proceeded by sub-grain rotation or local dissolution/re-precipitation, but probably by grain-boundary migration and defect diffusion. The formation of metamorphic zircon by solid-state recrystallization is probably common to high-grade terranes worldwide. The recognition of this process of formation is essential for correct interpretation of zircon-derived U–Pb ages and subsequent tectonic models.
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TL;DR: The importance of zircon in crustal evolution studies is underscored by its predominant use in U-Th-Pb geochronology and investigations of the temporal evolution of both the crust and lithospheric mantle as discussed by the authors.
Abstract: Zircon is the main mineral in the majority of igneous and metamorphic rocks with Zr as an essential structural constituent. It is a host for significant fractions of the whole-rock abundance of U, Th, Hf, and the REE (Sawka 1988, Bea 1996, O’Hara et al. 2001). These elements are important geochemically as process indicators or parent isotopes for age determination. The importance of zircon in crustal evolution studies is underscored by its predominant use in U-Th-Pb geochronology and investigations of the temporal evolution of both the crust and lithospheric mantle. In the past decade an increasing interest in the composition of zircon, trace-elements in particular, has been motivated by the effort to better constrain in situ microprobe-acquired isotopic ages. Electron-beam compositional imaging and isotope-ratio measurement by in situ beam techniques—and the micrometer-scale spatial resolution that is possible—has revealed in many cases that single zircon crystals contain a record of multiple geologic events. Such events can either be zircon-consuming, alteration, or zircon-forming and may be separated in time by millions or billions of years. In many cases, calculated zircon isotopic ages do not coincide with ages of geologic events determined from other minerals or from whole-rock analysis. To interpret the geologic validity and significance of multiple ages, and ages unsupported by independent analysis of other isotopic systems, has been the impetus for most past investigations of zircon composition. Some recent compositional investigations of zircon have not been directly related to geochronology, but to the ability of zircon to influence or record petrogenetic processes in igneous and metamorphic systems.
Sedimentary rocks may also contain a significant fraction of zircon. Although authigenic zircon has been reported (Saxena 1966, Baruah et al. 1995, Hower et al. 1999), it appears to be very rare and may in fact be related to …
3,777 citations
Cites background from "Metamorphic zircon formation by sol..."
...This was documented by Hoskin and Black (2000) for zircon from a meta-granitoid gneiss (Fig....
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...Analogous textures in zircon from high-grade metamorphic rocks were described from Mount Sones, Antarctica (Black et al. 1986), Northwest Territories, Canada (van Breemen et al. 1987), Seve Nappes, Scandinavia (Williams and Claesson 1987), Vosges Mountains, France (Schaltegger et al. 1999) and the Georgetown Region, Australia (Hoskin and Black 2000)....
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...…a wide range of temperatures and pressures during prograde (Liati and Gebauer 1999, Bingen et al. 2001), retrograde (Pan 1997, Roberts and Finger 1997, Degeling et al. 2001, Whitehouse and Platt 2003) and peak (Bea and Montero 1999, Hoskin and Black 2000, Möller et al. 2002) metamorphic conditions....
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...The mechanism or driving-force for recrystallization proposed by Hoskin and Black (2000) is thermoactivated grain-boundary and defect migration and the reduction of structural strain imposed by substituted trace elements....
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...2 of Hoskin and Black 2000)....
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TL;DR: In this paper, a selection of both the most typical, but also of the less common, features seen in zircon, categorized according to the different geological processes responsible for their formation are presented.
Abstract: The mineral zircon is extremely variable both in terms of external morphology and internal textures. These features reflect the geologic history of the mineral, especially the relevant episode(s) of magmatic or metamorphic crystallization (and recrystallization), strain imposed both by external forces and by internal volume expansion caused by metamictization, and chemical alteration. The paper presents a selection of both the most typical, but also of the less common, features seen in zircon, categorized according to the different geological processes responsible for their formation. The atlas is intended as a general guide for the interpretation of zircon characteristics, and of related isotopic data.
Zircon has become one of the most widely used minerals for the extraction of information on the prehistory and genesis of magmatic, metamorphic and sedimentary rocks. Much of the geological usefulness of zircon stems from its suitability as a geochronometer based on the decay of U (and Th) to Pb, but in addition it is also the major host of the radiogenic isotopic tracer Hf, and it is used to determine oxygen isotopic compositions and REE and other trace element abundances, all of which yield useful clues concerning the history of the host rock, and in some case, the parent rock in which the precursor zircon crystallized.
One of the major advantages of zircon is its ability to survive magmatic, metamorphic and erosional processes that destroy most other common minerals. Zircon-forming events tend to be preserved as distinct structural entities on a pre-existing zircon grain. Because of this ability, quite commonly zircon consists of distinct segments, each preserving a particular period of zircon-formation (or consumption). A long experience and modern instrumentation and techniques have provided the “zircon community” the means to image and interpret preserved textures, and hence to decipher the history and evolution of a rock. One …
3,069 citations
TL;DR: In this article, the trace element distribution coefficients between zircon and garnet were analyzed for trace elements using LA-ICP-MS and SHRIMP ion microprobe.
2,246 citations
Cites background from "Metamorphic zircon formation by sol..."
...Similar patterns have previously been observed in zircon rims from HT gneisses (Peucat et al., 1995; Hoskin and Black, 2000)....
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...07), as is commonly observed in magmatic zircon (Hinton and Upton, 1991; Paterson et al., 1992; Hoskin, 1998; Cornell et al., 1999; Hoskin and Black, 2000; Hoskin and Ireland, 2000)....
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..., 1992; Hoskin and Ireland, 2000) and HT metamorphic rocks (Schaltegger et al., 1999; Hoskin and Black, 2000; Rubatto et al., 2001)....
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...The application of zircon trace element geochemistry to metamorphic environments, however, is limited to a few studies dealing with hightemperature (HT) metamorphic rocks (Peucat et al., 1995; Schaltegger et al., 1999; Hoskin and Black, 2000)....
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...Several previous studies (Murali et al., 1983; Heaman et al., 1990; Hinton and Upton, 1991; Maas et al., 1992; Paterson et al., 1992; Barbey et al., 1995; Peucat et al., 1995; Schaltegger et al., 1999; Hoskin and Black, 2000; Hoskin and Ireland, 2000) have documented the preference of zircon for Hf, Y and the HREE over the LREE, and the presence in terrestrial zircon of a positive Ce anomaly and a negative Eu anomaly....
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TL;DR: Whitaker et al. as mentioned in this paper integrated U-Pb dating, Hf-isotope analysis and trace-element analysis to detrital zircon populations offers a rapid means of assessing the geochronology and crustal evolution history of different terranes within a composite craton.
1,008 citations
TL;DR: In this article, three methods have been proposed to link zircon U-Pb age to metamorphic conditions: (i) internal structure; (ii) trace element feature; (iii) mineral inclusion composition.
Abstract: Zircon U-Pb dating is the most commonly used method for isotopic geochronology. However, it has been a difficult issue when relating zircon U-Pb ages to metamorphic conditions in complex metamorphic rocks. Much progress has been made in the past decade with respect to the genesis of zircon and its constraints on interpretation of U-Pb age. Three methods have been proposed to link zircon U-Pb age to metamorphic conditions: (i) internal structure; (ii) trace element feature; (iii) mineral inclusion composition. Magmatic zircon shows typical oscillatory zoning and/or sector zoning, whereas metamorphic zircon has internal structures such as no zoned, weakly zoned, cloudy zoned, sector zoned, planar zoned, and patched zoned ones. Zircons formed in different geological environments generally have characteristic internal structures. Magmatic zircons from different rock types have variable trace element abundances, with a general trend of increasing trace element abundances in zircons from ultramafic through mafic to granitic rocks. Zircons formed under different metamorphic conditions have different trace element characteristics that can be used to relate their formation to metamorphic conditions. It is an effective way to relate zircon growth to certain P-T conditions by studying the trace element partitioning between coexisting metamorphic zircon and garnet in high-grade metamorphic rocks containing both zircon and garnet. Primary mineral inclusions in zircon can also provide unambiguous constraints on its formation conditions. Therefore, interpretation of zircon U-Pb ages can be constrained by its internal structure, trace element composition, mineral inclusion and so on.
900 citations
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TL;DR: In this article, the authors reported that the resulting densities in the lower mantle are in good agreement with shock-wave measurements on rocks having FeO contents in the range 10 ± 2% by weight.
Abstract: RECENTLY, Birch1 reported data on the density and composition of the mantle and core. He wrote: “The resulting densities in the lower mantle are found to be in good agreement with shock-wave measurements on rocks having FeO contents in the range 10 ± 2% by weight … except for iron oxide, the chemical composition of the mantle is indeterminate. The density of the outer core is lower than that of iron by about 10%”.
2,659 citations
TL;DR: In this article, new SHRIMP and TIMS zircon ages, 40Ar/39Ar ages, and eclogite locations contribute significantly to our understanding of the ultrahigh-pressure Dabie Shan.
894 citations
"Metamorphic zircon formation by sol..." refers background in this paper
...The large spread in LREE concentrations, Th/U ratio, the incomplete separation of trace element fieldsprecipitated zircon reveal it to have a ‘spongy’ texture (Wayne & Sinha, 1992; Hacker et al., 1998, Fig....
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TL;DR: In this paper, a metasedimentary and a meta-igneous quartz-feldspar granulite from the Val Sesia and Val Mastallone area of the Ivrea Zone (Southern Alps) are compared with respect to crystal morphology and U/Pb ages.
Abstract: Zircons from a metasedimentary and a meta-igneous quartz-feldspar granulite from the Val Sesia and Val Mastallone area of the Ivrea Zone (Southern Alps) differ in their response to granulite facies metamorphism with respect to crystal morphology and U/Pb ages. Detrital zircons in the metasediment developed an isometric overgrowth by the addition of Zr derived mainly from co-existing minerals, most probably biotite, decomposing during anatectic melting. The overgrowth started in the pelitic layer of the metasediment in the Late Carboniferous at approximately 296 Ma, significantly earlier than in the adjacent psammitic layer where it started only at 261 ± 4 Ma (95% confidence level). These ages are ascribed to the differential initiation of anatexis in the two layers. The delay of melting in the psammitic layer was probably due to the different position and less steep slope of its solidus in P-T-space, as compared to the solidus in the pelitic layer. Accordingly, the melting in the psammitic layer at 261 Ma was initiated by a thermal pulse and/or by a decompression event. Decompression melting is supported by a characteristic shell morphology of the zircon overgrowth in the psammitic layer, which might have grown under shear movements during high-temperature extensional faulting. The typically magmatic zircon population of the meta-igneous granulite crystallized at 355 ± 6 Ma (95% confidence level). The morphology of the zircons and the chemistry of the rock suggest that the magma was calcalkaline. A minor subpopulation of crystals is morphologically similar to the zircons in the pelitic layer of the metasediment. This points to the admixture of a minor sediment component and, thus, to a largely volcaniclastic origin of the protolith. In contrast to the detrital zircons in the metasediment, the magmatic zircons show rare and little overgrowth and, instead, have been strongly resorbed by anatectic melt. In addition, they became partially recrystallized and the rejuvenated ages from the most thoroughly recrystallized domains indicate that the rock was subject to prograde metamorphism after 279 Ma. This may correspond to the regional temperature increase prior to the climax of metamorphism or to a local thermal pulse due to nearby mafic intrusions. An Upper Triassic event at 226 ± 5 Ma is reflected by distinct peripheral zones in the overgrowths of some zircons in the metapelite. These are interpreted as a second metamorphic pulse, possibly induced by the infiltration of fluids.
703 citations
"Metamorphic zircon formation by sol..." refers background in this paper
...Zone, Southern European Alps (Vavra et al., 1996), the Cyclades, Greece (Keay, 1998), and south-west 2 Electron backscatter diffraction pattern analyses indicate that recrystallization proceeded without subMadagascar (Ashwal et al....
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...Geologically meaningful ages were determined by Vavra et al. (1996) for metamorphically recrystallized rims in zircon in granulites from western Europe....
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...Zone, Southern European Alps (Vavra et al., 1996), the Cyclades, Greece (Keay, 1998), and south-west 2 Electron backscatter diffraction pattern analyses indicate that recrystallization proceeded without sub-Madagascar (Ashwal et al., 1999)....
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TL;DR: In this article, the Seve Nappes can be followed for more than 700 km along the Scandinavian Caledonides, and zircon data from a migmatitic paragneiss leucosome give almost concordant Caledonian U-Pb ages, and define together with strongly discordant zircons from the paragneis a discordia line with the intercept ages 423±26 Ma and 1512±36 Ma.
Abstract: The Seve Nappes can be followed for more than 700 km along the Scandinavian Caledonides. Seve paragneisses are in part migmatitic, metamorphosed to granulite facies and eclogite-bearing. This probably reflects an ancient continent-continent collision. Zircon data presented here from a migmatitic paragneiss leucosome give almost concordant Caledonian U-Pb ages, and define together with strongly discordant zircons from the paragneiss a discordia line with the intercept ages 423±26 Ma and 1512±36 Ma. Strongly discordant zircon from another paragneiss, composed of cores overgrown with thick transparent mantles, also fits this chord. A stepwise dissolution experiment on these zircons demonstrates the existence of a component with Caledonian age in the crystals, and 3 of 5 dissolution steps plot along the discordia line defined by the conventional analyses of the same sample. The zircon data reflect high grade Caledonian metamorphism of sediments with Proterozoic protoliths. Sm-Nd model ages (TDM and TCHUR) for whole rock samples cluster around 1.9 and 1.55 Ga, respectively, demonstrating a Proterozoic average crustal provenance age for the detritus in these sediments. The zircon data support a correlation between the Seve Nappes and the Western Gneiss Region in Norway.
404 citations
"Metamorphic zircon formation by sol..." refers background in this paper
...Commonly, ‘ghost’ zoning isCanada (van Breemen et al., 1987), Seve Nappes, Scandinavia (Williams & Claesson, 1987), Lewisian observed in recrystallized areas, a remnant of the original igneous trace element distribution....
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...Isotopic evidence for thethe Thelon Tectonic Zone, Healey Lake and Artillery Lake map areas, NWT. Current Research Part A. Geological Survey Precambrian provenance and Caledonian metamorphism of high grade paragneisses from the Seve Nappes, Scandinavianof Canada Paper, 87-1A, 783–801....
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TL;DR: In this article, finite difference numerical simulations were used to characterise the rates of diffusion-controlled dissolution and growth of zircon in melts of granitic composition under geologically realistic conditions.
Abstract: Finite difference numerical simulations were used to characterise the rates of diffusion-controlled dissolution and growth of zircon in melts of granitic composition under geologically realistic conditions. The simulations incorporated known solubility and Zr diffusivity relationships for melts containing 3 wt% dissolved H2O and were carried out in both one and thre dimensions under conditions of constant temperature, linearly time-dependent temperature and for a variety of host system thermal histories. The rate of zircon dissolution at constant temperature depends systematically on time (t½−12;), temperature (exp T−1) and degree of undersaturation of the melt with respect to zircon (in ppm Zr). Linear dissolution and growth rates fall in the range 10−19 10−15 cm s−1 at temperatures of 650-850°C. Radial rates are strongly dependent on crystal size (varying in inverse proportion to the radius, r): for r>30 μm, dissolution and growth rates fall between 10−17 and 10−13 cm s−1. During crustal magmatism, the chances of survival for relict cores of protolith zircons depend on several factors, the most important of which are: the initial radius of the zircon; the intensity and duration of the magmatic event; and the volume of the local melt reservoir with which the zircon interacts. In general, only the largest protolith zircons (>120 μm radius) are likely to survive magmatic events exceeding 850°C. Conversely, only the smallest zircons (<50 μm radius) are likely to be completely consumed during low-temperature anatexis (i.e. not exceeding ≍700°C).The effects of stirring the zircon-melt system are unimportant to dissolution and growth behaviour; except under circumstances of extreme shearing (e.g. filter pressing?), zircon dissolution is controlled by diffusion of Zr in the melt.
387 citations