Thermal events documented in Hadean zircons by ion microprobe depth profiles

Trail, Dustin; Mojzsis, Stephen J.; Harrison, T. Mark

doi:10.1016/j.gca.2007.06.003

Cited by 61 publications

(42 citation statements)

References 88 publications

(133 reference statements)

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“…From these zeroth-order estimates, we can reasonably infer that approximately one quarter to half of the crust would have potentially experienced conditions conducive to zircon reprocessing/ growth. Thus our observation that 12 of the 26 Hadean zircons thus far investigated via depth profiling (including 18 U-Th-Pb depth profiles) (16,59) experienced epitaxial growth between 3.85-3.95 Ga is consistent with this estimate. However, our empirical observations do not include the possibility that overgrowths grown during the LHB-era on Hadean cores may have been abraded prior to deposition in the host quartzite at ca.…”

Section: Discussionsupporting

confidence: 85%

“…While the rare terrestrial lithic record prior to >4 Ga limits the search for evidence of the LHB on Earth, Hadean detrital zircons may provide a source of such evidence (16). Zircon chemistry may be used to derive temperatures that provide insight into environmental source conditions during crystal growth.…”

Section: Discussionmentioning

confidence: 99%

“…Assessing the temperature-age relationships among LHB-era zircons requires an extensive sampling of the overgrowths within the detrital population. For additional details regarding LHB-era zircon overgrowths identified via U-Th-Pb depth profiles, refer to Trail et al (16) and Abbott (59). A PDF and CDF are graphically represented for 207 Pb∕ 206 Pb age (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…15). A potential source of such evidence is from Hadean (i.e., >4 Ga) detrital zircons (16). Because zircon is essentially restricted to the Earth's crust and Archean continental crust is thought to have been relatively thin due to high heat flow (e.g., 17), the vast majority of Hadean zircons of continental character likely resided within ca.…”

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confidence: 99%

“…We obtained time-temperature profiles with depth in zircons by combining empirical Ti-in-zircon thermometry (25,26) with ultrahigh resolution (nm scale) U-Th-Pb depth profiling (16,27). The ultimate goal is to obtain sufficient data to reconstruct a T-t path for each zircon's growth and compare results with LHB thermal models (28).…”

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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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Section: Discussionsupporting

confidence: 85%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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confidence: 99%

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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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Zircon growth in (U)HP quartzo-feldspathic host gneisses exhumed in the Woodlark Rift of Papua New Guinea

Zirakparvar

Baldwin

Schmitt

2014

Geochem. Geophys. Geosyst.

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Dating terrestrial impact structures: U‐Pb depth profiles and (U‐Th)/He ages of zircon

Wielicki

Harrison

Stöckli

2014

Geophysical Research Letters

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We investigate the presence of epitaxial overgrowth rims and "reset" zircon, complete loss of radiogenic lead (Pb*), from terrestrial impactites to constrain the occurrence of such phenomenon in impact environments and their possible use in dating impact events. We also explore (U-Th)/He dating of zircon to evaluate this geochronometer in accurately identifying impact ages, particularly when no dateable melt sheet exists. Our results show that (U-Th)/He ages of zircon from the brecciated, and presumably shocked target, can accurately date an impact event and provides another tool to determine impact ages when no melt sheet exists, an alternative to problematic interpretations of commonly used apparent 40 Ar/ 39 Ar plateau ages. No evidence of epitaxial overgrowth rims and/or reset zircon was observed, suggesting that zircons within shocked impactites have remarkably slow Pb diffusion and possibly explaining the relatively few reset grains reported in terrestrial impactites. IntroductionMeteorite impacts are thought to have lead to the formation of the Moon [Canup and Asphaug, 2001], substantially resurfaced the terrestrial planets at~3.9 Ga ([Tera et al., 1974] i.e., the "Late Heavy Bombardment" (LHB)) and profoundly influenced the habitability of the early Earth [Grieve et al., 2006;Abramov and Mojzsis, 2009]. However, the timing and magnitude of such events remain difficult to constrain. Due to planetary resurfacing and the inherent difficulties in dating complex, impact-derived samples, fewer than 10% of all-known craters, can be regarded as accurately and precisely dated [Jourdan et al., 2012]. Impact-derived samples range from large differentiated melt sheets to shocked impact breccias with little to no impact melt present. The presence of impact melt sheets provides opportunities to date neoformed zircons using the U-Pb method. When no melt sheet exists, 40 Ar/ 39 Ar step-heating analysis of impact melt-bearing breccias is commonly used to infer impact ages and can be problematic due to the presence of relic clasts, incomplete 40 Ar out gassing or excess 40 Ar, and recoil and shock effects [Harrison and Lovera, 2013].Recent studies have focused on zircon within impactites as recorders of impact events. Zircon (ZrSiO 4 ) occurs as a common accessory mineral in a variety of rock types and geologic environments, including terrestrial impactites. It is widely used for geochemical and isotopic studies because of its capacity to retain trace elements, including actinides, lanthanides, and radiogenic daughter products under extreme conditions. The preferential incorporation of U and Th into zircon coupled with its highly refractory nature, often surviving multiple geologic cycles, has made zircon the premier terrestrial geochronometer [Finch and Hanchar, 2003]. U-Pb depth profiles have been used to date epitaxial overgrowths, presumably grown or "reset" [Abramov et al., 2013] during impact heating of inherited zircon cores, potentially providing the first terrestrial evidence of the hypothesized LHB [...

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Thermal events documented in Hadean zircons by ion microprobe depth profiles

Cited by 61 publications

References 88 publications

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

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

Zircon growth in (U)HP quartzo-feldspathic host gneisses exhumed in the Woodlark Rift of Papua New Guinea

Dating terrestrial impact structures: U‐Pb depth profiles and (U‐Th)/He ages of zircon

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