Ion microprobe identification of 4,100–4,200 Myr-old terrestrial zircons

Froude, D. O.; Ireland, Trevor; Kinny, Peter D.; Williams, Ian S.; Compston, W.; Williams, Ian; Myers, John S.

doi:10.1038/304616a0

Cited by 441 publications

(110 citation statements)

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“…Data obtained from SIMS analysis has been used extensively for in situ U-Pb geochronology of zircon [6][7][8][9][10][11]. However, its application to metamorphic studies has been restricted to the analysis of zircon overgrowths inferred to have grown during metamorphism [e.g., 12].…”

Section: Introductionmentioning

confidence: 99%

A metamorphic history from micron-scale 207Pb/206Pb chronometry of Archean monazite

DeWolf

Belshaw

O’Nions

1993

Earth and Planetary Science Letters

163

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Ion microprobe measurements of Pb isotope ratios in monazites have been obtained, in situ, from thin sections using the Cambridge ISOLAB 120. Molecular interferences are sufficiently resolved at an RP of 6500 to allow 2°7pb/Z°6pb dating of monazite with precisions as low as 4-5 Ma (2~r). The results presented here provide important information on the chronological history of the Late Archean metamorphism of the Wind River Range, Wyoming (USA).Matrix monazites and monazite inclusions in garnets from a metapelite from the northern Wind River Range have been analysed by SIMS. In a previous study peak metamorphic conditions (T = 800°C; P = 8 + 1 kb *) were estimated using inclusion assemblages in garnets from this same sample. Isolated monazite inclusions in garnet yield 2°7pb/Z°6pb age estimates of 2781 + 6 to 2809 + 10 Ma. Those along fractures yield lower ages (2603-2687 Ma) which are similar to TIMS and SIMS ages of matrix monazites. A single large (500 /xm) monazite grain locally preserves growth zoning, but has a recrystallised core and a resorbed (recrystallised?) rim. Age estimates for these three regions are 2788 _+ 9 Ma, 2663 _+ 4 and 2523 + 6 Ma, respectively. Thus the inclusion assemblages of Sharp and Essene * may record peak metamorphic conditions at ca. 2.8 Ga, and indicate a phase of metamorphism that predates by over 100 Ma the emplacement of the Bridget Batholith, the major lithologic component of the northern Wind River Range.The analysed monazite grains appear to preserve ca. 300 Ma history, even within a single grain. Monazite inclusions in garnet that are fully armoured may provide estimates for the time of garnet growth, even in high grade terranes where most chronometers are reset. The age pattern preserved by the large monazite grain cannot be simply related to diffusion controlled closure. Instead, a chronology is preserved which can be related to the petrographic setting of individual grains through in situ analysis.

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Section: Introductionmentioning

confidence: 99%

A metamorphic history from micron-scale 207Pb/206Pb chronometry of Archean monazite

DeWolf

Belshaw

O’Nions

1993

Earth and Planetary Science Letters

163

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“…12 The first isotope ratios for Pb from galena samples were measured in 1980, and the first analytical results were published in the international literature in 1983. 134 The success of SHRIMP in dating zircons and other accessory minerals containing U and/or Th led to an enormous demand for instrument time from a variety of researchers both in Australia and overseas. It was therefore decided to design and build a second generation SHRIMP II, backed by substantial financial assistance from the Bureau of Mineral Resources.…”

Section: Another Shrimp On the Drawing Boardmentioning

confidence: 99%

A history of mass spectrometry in Australia

Downard

Laeter

2005

J. Mass Spectrom.

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This article traces the history of mass spectrometry in its many guises and applications in the island continent of Australia. An article such as this can never be complete. It instead focuses on contributions of scientists who played a major role in the early establishment of mass spectrometry in Australia. In general, those who are presently active in the field, and whose histories are incomplete, have been mentioned at best only briefly despite their important contributions to the field.

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“…Hadean zircons have been identified from multiple regions around the globe including northern Canada (29), West Greenland (30), and Western Australia (31). However, the most extensively studied are those from the Narryer Gneiss Complex (NGC), located on the northern margin of the Yilgarn Craton, Western Australia (32)(33)(34)(35).…”

Section: Methodsmentioning

confidence: 99%

“…First recognized at outcrops near the Mt. Narryer homestead (31), even more ancient Hadean zircons were documented in the Jack Hills region (36).…”

Section: Methodsmentioning

confidence: 99%

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A search for thermal excursions from ancient extraterrestrial impacts using Hadean zircon Ti-U-Th-Pb depth profiles

Abbott

Harrison

Schmitt

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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Few terrestrial localities preserve more than a trace lithic record prior to ca. 3.8 Ga greatly limiting our understanding of the first 700 Ma of Earth history, a period inferred to have included a spike in the bolide flux to the inner solar system at ca. 3.85-3.95 Ga (the Late Heavy Bombardment, LHB). An accessible record of this era may be found in Hadean detrital zircons from the Jack Hills, Western Australia, in the form of μm-scale epitaxial overgrowths. By comparing crystallization temperatures of pre-3.8 Ga zircon overgrowths to the archive of zircon temperature spectra, it should, in principle, be possible to identify a distinctive impact signature. We have developed Ti-U-Th-Pb ion microprobe depth profiling to obtain age and temperature information within these zircon overgrowths and undertaken a feasibility study of its possible use in identifying impact events. Of eight grains profiled in this fashion, four have overgrowths of LHB-era age. Age vs. temperature profiles reveal a period between ca. 3.85-3.95 Ga (i.e., LHB era) characterized by significantly higher temperatures (approximately 840-875°C) than do older or younger zircons or zircon domains (approximately 630-750°C). However, temperatures approaching 900°C can result in Pb isotopic exchange rendering interpretation of these profiles nonunique. Coupled age-temperature depth profiling shows promise in this role, and the preliminary data we report could represent the first terrestrial evidence for impactrelated heating during the LHB.early Earth | impact crater | lunar cataclysm | secondary ion mass spectrometry T he LHB is the period from ca. 3.85-3.95 Ga during which an intense flux of asteroidal and/or cometary bodies is hypothesized to have impacted the Moon (1). A variety of theories have been proposed to explain the LHB (2-5) culminating with the "Nice model" (5-7). This model posits that a fundamental shift in orbital resonance among the Jovian planets at ca. 3.9 Ga destabilized the disk of planetesimals in the outer solar system resulting in the scattering of numerous bodies into the inner solar system. Tera et al. (1) introduced the concept of a late lunar cataclysm to explain isotopic fractionations in rocks returned from the heavily cratered lunar highlands. Specifically, U-Pb, and Rb-Sr isochrons yielded recrystallization ages between 3.85-3.95 Ga. The parent/daughter behavior in these two geochronologic systems are quite different but result in similar system disturbances (i.e., U and Sr are highly refractory whereas Pb and Rb are variably volatile). Thus, a profound thermal event, such as from an impact at the appropriate scale of a "cataclysm," could have caused resetting of both chronometers, albeit for different reasons. Much of the evidence in support of the LHB hypothesis comes from 40 Ar∕ 39 Ar age spectra of lunar highland crust samples (3,8,9), interpreted to yield apparent "plateau" ages between 3.8-4.0 Ga due to the resetting of the K-Ar system via collisional heating (see review in 10).

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Ion microprobe identification of 4,100–4,200 Myr-old terrestrial zircons

Cited by 441 publications

References 1 publication

A metamorphic history from micron-scale 207Pb/206Pb chronometry of Archean monazite

A metamorphic history from micron-scale 207Pb/206Pb chronometry of Archean monazite

A history of mass spectrometry in Australia

A search for thermal excursions from ancient extraterrestrial impacts using Hadean zircon Ti-U-Th-Pb depth profiles

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