Comment on "Zircon Thermometer Reveals Minimum Melting Conditions on Earliest Earth" I

Glikson, Andrew Y.

doi:10.1126/science.1120073

Cited by 16 publications

(5 citation statements)

References 12 publications

(2 reference statements)

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“…For example, it is known that detrital zircon preservation is inversely proportional to U and Th contents, as radiation-damaged grains will tend not to survive erosion and sedimentary transport (Fedo et al, 2003). Thus we take issue with the view that tonalite-trondhjemite-granodiorites are zircon-poor and thus underrepresented in detrital zircon populations (Glikson, 2006) for two reasons. The fi rst is that tonalites are Zr-rich (150-210 ppm; http://earthref.org/GERM/) rela tive to anatectic granitoids (~50 ppm; Vidal et al, 1982) and thus have the potential to crystallize abundant zircon.…”

Section: Discussionmentioning

confidence: 99%

“…It was subsequently argued that the lowtemperature Hadean peak ( Fig. 1) could be derived from zircons originating in mafi c magmas (Valley et al, 2006;Coogan and Hinton, 2006) or refl ect zircon saturation at low temperatures in rocks of the tonalite-trondhjemitegranodiorite suite (Nutman, 2006;Glikson, 2006). Glikson (2006) proposed that Hadean zircons could have originated in tonalitetrondhjemite -granodiorites that formed at high temperatures but did not crystallize zircon until near-eutectic temperatures were reached, and thus "zircon-poor tonalite-trondhjemitegranodiorites would be underrepresented in the detrital zircon population."…”

Section: Zircon Crystallization Temperaturementioning

confidence: 99%

“…1) could be derived from zircons originating in mafi c magmas (Valley et al, 2006;Coogan and Hinton, 2006) or refl ect zircon saturation at low temperatures in rocks of the tonalite-trondhjemitegranodiorite suite (Nutman, 2006;Glikson, 2006). Glikson (2006) proposed that Hadean zircons could have originated in tonalitetrondhjemite -granodiorites that formed at high temperatures but did not crystallize zircon until near-eutectic temperatures were reached, and thus "zircon-poor tonalite-trondhjemitegranodiorites would be underrepresented in the detrital zircon population." Similarly, Nutman (2006) argued on the basis of calculated T sat zir for granitoids of intermediate composition that hightemperature melts do not crystallize zircon until they cool to temperatures near that of minimum melting (i.e., zircons from both wet tonalite and minimum melts yield similarly low T Ti zir ).…”

Section: Zircon Crystallization Temperaturementioning

confidence: 99%

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Temperature spectra of zircon crystallization in plutonic rocks

Harrison

Watson

Aikman

2007

Geol

277

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The Ti-in-zircon thermometer is a potentially powerful new petrological tool, but conclusions drawn from such data are meaningful only to the extent that the underlying interpretational framework is sound. In the case of interpretation of detrital zircon crystallization temperature spectra, it has been assumed that comparisons can be made with potential host rocks based on calculated bulk zircon saturation thermometry. We show by calculation that most igneous rocks formed at high temperature (>750 °C) will yield Ti-in-zircon temperatures (T Ti zir) well above the wet granite solidus. This prediction is borne out by results from the Dala igneous complex, southeastern Tibet, which show a 300 °C range in T Ti zir beginning >100 °C above the calculated bulk zircon saturation temperature. Thus the dominant T Ti zir peak of >4 Ga zircons at ~680 °C implies a wet, anatectic magma source rather than an origin in intermediate and mafi c magmas. Given that preservation and analytical effects select against, or obscure recognition of, zircons formed at low temperature, the best explanation for the low Hadean T Ti zir peak is that it refl ects derivation from rocks that experienced prograde melting conditions under near-water-saturated conditions.

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Section: Discussionmentioning

confidence: 99%

Section: Zircon Crystallization Temperaturementioning

confidence: 99%

Section: Zircon Crystallization Temperaturementioning

confidence: 99%

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Temperature spectra of zircon crystallization in plutonic rocks

Harrison

Watson

Aikman

2007

Geol

277

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“…Alternative views have been presented which argue that the Ti thermometer cannot be used to constrain zircon provenance [ Fu et al , 2005; Kamber et al , 2005; Nutman , 2006; Glikson , 2006; Valley et al , 2006; Coogan and Hinton , 2006]. A criticism common to these reports is the concern over uncertainties in Zr and Ti activities in Hadean zircon source melts.…”

Section: Discussionmentioning

confidence: 99%

Constraints on Hadean zircon protoliths from oxygen isotopes, Ti‐thermometry, and rare earth elements

Trail¹,

Mojzsis

Harrison³

et al. 2007

Geochem Geophys Geosyst

174

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[1] We report zircon oxygen isotope ratios and reconnaissance Ti-in-zircon concentrations, guided by cathodoluminescence image studies, for detrital zircons up to 4.34 Ga from the Narryer Gneiss Complex of Western Australia. Zircon oxygen isotope results bolster the view that some Hadean (>3.85 Ga) zircon source melts were enriched in heavy oxygen, a sensitive proxy for melt contamination by sediments altered in liquid water. Zircon crystallization temperatures calculated from Ti concentration in pre-3.8 Ga zircons yield values around 680°C in all cases except for one lower value in a 4.0 Ga grain. Elevated zircon d 18O values reported here and elsewhere, combined with low minimum-melt crystallization temperatures, and analysis of zircon/melt partitioning of rare earth elements (REEs) provide mutually consistent lines of evidence that the Hadean Earth supported an evolved rock cycle which included formation of granitic water-saturated melts, extensive continental crust, hydrosphere-lithosphere interactions, and sediment recycling within the first 150 million years of planet formation.

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“…Several critiques of the Watson-Harrison hypothesis have appeared but essentially reflect two specific arguments: Hadean zircons (a) are potentially sourced from late-stage differentiates of mafic magmas (Coogan & Hinton 2006, Rollinson 2008 or (b) reflect lowtemperature zircon saturation in tonalitic magmas (Glikson 2006, Nutman 2006. addressed these concerns, pointing out, in the former case, that crystallization temperatures and trace element characteristics (also see Grimes et al 2007, Hellebrand et al 2007) of Hadean and mafic zircon populations are distinctively different, and that, in the latter case, assumptions made regarding the applicability of zircon saturation thermometry are flawed (i.e., unaltered tonalites are unlikely to be characterized by an average T zir Ti of <700 • C).…”

Section: Figurementioning

confidence: 99%

The Hadean Crust: Evidence from >4 Ga Zircons

Harrison

2009

Annu. Rev. Earth Planet. Sci.

368

231

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A review of continental growth models leaves open the possibilities that Earth during the Hadean Eon (∼4.5-4.0 Ga) was characterized by massive early crust or essentially none at all. Without support from the rock record, our understanding of pre-Archean continental crust must largely come from investigating Hadean detrital zircons. We know that these ancient zircons yield relatively low crystallization temperatures and some are enriched in heavy oxygen, contain inclusions similar to modern crustal processes, and show evidence of silicate differentiation at ∼4.5 Ga. These observations are interpreted to reflect an early terrestrial hydrosphere, early felsic crust in which granitoids were produced and later weathered under high water activity conditions, and even the possible existence of plate boundary interactions-in strong contrast to the traditional view of an uninhabitable, hellish world. Possible scenarios are explored with a view to reconciling this growing but fragmentary record with our knowledge of conditions then extant in the inner solar system. 479 Annu. Rev. Earth Planet. Sci. 2009.37:479-505. Downloaded from arjournals.annualreviews.org by Memorial University of Newfoundland on 08/28/09. For personal use only.

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Comment on "Zircon Thermometer Reveals Minimum Melting Conditions on Earliest Earth" I

Cited by 16 publications

References 12 publications

Temperature spectra of zircon crystallization in plutonic rocks

Temperature spectra of zircon crystallization in plutonic rocks

Constraints on Hadean zircon protoliths from oxygen isotopes, Ti‐thermometry, and rare earth elements

The Hadean Crust: Evidence from >4 Ga Zircons

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