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 …

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The Composition of Zircon and Igneous and Metamorphic Petrogenesis

Plesovice zircon : A new natural reference material for U-Pb and Hf isotopic microanalysis

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 …

Atlas of Zircon Textures

Assembly, configuration, and break-up history of Rodinia: A synthesis

We present the first finding of continental crust-derived Precambrian zircons in garnet/spinel pyroxenite veins within mantle xenoliths carried by the Neogene Hannuoba basalt in the central zone of the North China Craton (NCC). Petrological and geochemical features indicate that these mantle-derived composite xenoliths were formed by silicic melt^lherzolite interaction. The Precambrian zircon ages can be classified into three age groups of 2·4^2·5 Ga, 1·6^2·2 Ga and 0·6^1·2 Ga, coinciding with major geological events in the NCC. These Precambrian zircons fall in the field of continental granitoid rocks in plots of U/Yb vs Hf and Y. Their igneous-type REE patterns and metamorphic zircon type CL images indicate that they were not crystallized during melt^peridotite interaction and subsequent high-pressure metamorphism.The 2·5 Ga zircons have positive eHf(t) values (2·9^10·6), whereas the younger Precambrian zircons are dominated by negative eHf(t) values, indicating an ancient continental crustal origin.These observations suggest that the Precambrian zircons were xenocrysts that survived melting of recycled continental crustal rocks and were then injected with silicate melt into the host peridotite. In addition to the Precambrian zircons, igneous zircons of 315 3 Ma (2 ), 80^170 Ma and 48^64 Ma were separated from the garnet/spinel pyroxenite veins; these provide evidence for lower continental crust and oceanic crust recycling-induced multi-episodic melt^peridotite interactions in the central zone of the NCC. The combination of the positive eHf(t) values (2·91^24·6) of the 315 Ma zircons with the rare occurrence of 302^324 Ma subduction-related diorite^granite plutons in the northern margin of the NCC implies that the 315 Ma igneous zircons might record melt^peridotite interactions in the lithospheric mantle induced by Palaeo-Asian oceanic crust subduction. Igneous zircons of age 80^170 Ma generally coexist with the Precambrian metamorphic zircons and have lower Ce/Yb and Th/U ratios, higher U/Yb ratios and greater negative Eu anomalies.The eHf(t) values of these zircons vary greatly from ^47·6 to 24·6.The 170^110 Ma zircons are generally characterized by negative eHf(t) values, whereas the 110^100 Ma zircons have positive eHf(t) values.These observations suggest that melt^peridotite interactions at 80^170 Ma were induced by partial melting of recycled continental crust. The 48^64 Ma igneous zircons are characterized by negligible Ce anomalies, unusually high REE, U and Th contents, and positive eHf(t) values.These features imply that the melt^peridotite interactions at 48^64 Ma could be associated with a depleted mantle-derived carbonate melt or fluid.

Continental and Oceanic Crust Recycling-induced Melt^Peridotite Interactions in the Trans-North China Orogen: U^Pb Dating, Hf Isotopes and Trace Elements in Zircons from Mantle Xenoliths

The source of halogens in geothermal fluids from the Taupo Volcanic Zone, North Island, New Zealand

Chemistry of hydrothermal zircon; investigating timing and nature of water-rock interaction

Sapphire crystallization, age and origin, Ban Huai Sai, Laos: age based on zircon inclusions

Silicic volcanism and back-arc extension related to migration of the Late Cainozoic Australian-Pacific plate boundary

The fluorine concentration in NIST SRM 610 was determined by SIMS to be 295 16 μg g−1 (5.40% relative standard deviation). Accuracy of the measurement was determined from a calibration involving the synthesis of glass calibration samples doped with varying concentrations of fluorine and characterized by electron microprobe analysis and SIMS. The calibration was accurate to about 5%. Multiple analyses of the calibration samples and SRM 610 in three different analytical sessions combine to produce a low relative standard deviation of the mean (0.23% RSD) in the mean fluorine value for SRM 610. Analytical uncertainty in the fluorine value was 5.40% (RSD), originating from a combination of calibration and ion counting uncertainties as determined from multiple analyses. Evaluation of the SIMS technique using the new fluorine value in SRM 610 shows that this element can be determined with a precision and accuracy superior to that of EPMA. Measurements of fluorine in igneous and hydrothermal zircon suggest that F-ligands may have been responsible for Zr transportation in hydrothermal fluids also responsible for W-Au mineralisation. Other applications for low-level fluorine determinations may include melt inclusions and nominally anhydrous mineral phases, particularly mantle phases.



La concentration en fluor du materiau de reference NIST SRM 610 a ete mesuree a 295 16 μg g−1 (5.40% de deviation relative standard). La precision de cette mesure a ete determinee a partir de verres de synthese etalonnes, dopes avec differentes concentrations en fluor et caracterises par microsonde electronique et SIMS. L'etalonnage etait precis a 5%. Les analyses repetees des echantillons etalonnes et de SRM 610 lors de trois differentes sessions d'analyse donnent une deviation standard relative (0.23 %ecart-type relatif) sur la valeur moyenne en fluor dans SRM 610. L'incertitude analytique sur la concentration en fluor etait de 5.40% (ecart-type relatif) et resultait des effets combines des incertitudes de la calibration elle-meme et du comptage d'ions, comme demontre par les analyses repetees. L'evaluation de la technique SIMS en utilisant la nouvelle teneur en fluor de SRM 610 montre que cet element peut etre determine avec une precision et une justesse superieures a celles obtenues par EPMA. La mesure du fluor dans des zircons ignes ou hydrothermaux suggere que des ligands du fluor peuvent etre responsables du transport du Zr dans les solutions hydrothermales, eux-memes responsables des mineralisations a W et Au. D'autres applications pour le dosage des faibles concentrations en fluor concernent les inclusions vitreuses et typiquement toutes les phases minerales anhydres, en particulier celles du manteau.

Paul W.O. Hoskin

Papers

The source of halogens in geothermal fluids from the Taupo Volcanic Zone, North Island, New Zealand

Chemistry of hydrothermal zircon; investigating timing and nature of water-rock interaction

Sapphire crystallization, age and origin, Ban Huai Sai, Laos: age based on zircon inclusions

Silicic volcanism and back-arc extension related to migration of the Late Cainozoic Australian-Pacific plate boundary

SIMS Determination of μg g−1-Level Fluorine in Geological Samples and its Concentration in NIST SRM 610