Timing of crystallization of the lunar magma ocean constrained by the oldest zircon

Nemchin, A. A.; Timms, Nicholas E.; Pidgeon, R. T.; Geisler, Thorsten; Reddy, Steven M.; Meyer, C.

doi:10.1038/ngeo417

Cited by 198 publications

(157 citation statements)

References 24 publications

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“…We also use electron-backscatter diffraction patterns (EBSP) to qualitatively examine the degree of radiation damage present in individual chips (Nemchin et al 2009). In addition, we have used EBSD to assess whether there is a crystallographic orientation effect on secondary ion sputtering that is similar to that observed in baddeleyite (Wingate & Compston 2000).…”

Section: Results From Electron-backscatter Diffraction (Ebsd)mentioning

confidence: 99%

GRENVILLE SKARN TITANITE: POTENTIAL REFERENCE MATERIAL FOR SIMS U-Th-Pb ANALYSIS

Kennedy¹,

Kamo²,

Nasdala³

et al. 2010

The Canadian Mineralogist

129

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We have investigated the homogeneity, chemical composition, structure, degree of radiation damage, and post-formation evolution of titanite crystals from skarns of the Grenville Province of the Canadian Shield using SHRIMP, TIMS, Raman and PL spectroscopy, EBSD, and EPMA-WDS. These results are used to assess the potential of the titanite as Reference Material (RM) for micro-analytical U-Th-Pb age dating. The SHRIMP data show that these megacrysts (5-31g) have concordant U-Pb isotope systematics, 60 to 500 ppm U, 120 to 1200 ppm Th , 206 Pb/ 204 Pb between 500 and 2500, ages of ~1 Ga, and excellent homogeneity at the scale of the analytical volume of the ion probe. The ID-TIMS titanite data for OLT1, OLT2 and TCB show that these crystals are essentially concordant. Data for OLT1 and OLT2 show slight scatter (i.e., in excess of that expected from the uncertainty in an individual analysis). For OLT1, one of seven analyses shows Pb loss or, possibly, a younger period of growth. Crystals OLT1 and OLT2 have respective TIMS concordia ages of 1014.8 ± 2.0 Ma (2s, n = 6, MSWD = 1.8) and 998.0 ± 4.5 Ma (2s, n = 3, MSWD = 3.3) for domains that have not lost Pb. The TIMS analyses of TCB are tightly clustered and give a concordia age of 1018.1 ± 1.7 Ma (2s, n = 4, MSWD = 0.92). Raman and PL spectra show a low to moderate degree of accumulated radiation-induced damage in the Grenville Skarn Titanite crystals and uniform internal distributions of this damage. The EDSB contrast images indicate little or no crystallographic misorientation. The EMPA-WDS data show that the outer 50-100 mm of the OLT1 and TCB crystals are enriched in Al and F, and depleted in Fe and Nb, when compared with the interior. In spite of the variation in composition and degree of radiation damage amongst samples, there are no identifiable matrix effects in our SHRIMP data. Some Grenville skarn titanite (GST) crystals have potential as RM for micro-analytical U-Th-Pb age dating. Crystal TCB has excellent homogeneity of U-Th-Pb isotopic composition. Crystals OLT1 and OLT2 have minor TIMS age heterogeneity. However, this heterogeneity is smaller than that of the Khan titanite, our current in-house titanite standard. Careful selection of analysis areas during SIMS, and of chips for TIMS analysis, allows high-quality isotopic data to be obtained from these large crystals of titanite.

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Section: Results From Electron-backscatter Diffraction (Ebsd)mentioning

confidence: 99%

GRENVILLE SKARN TITANITE: POTENTIAL REFERENCE MATERIAL FOR SIMS U-Th-Pb ANALYSIS

Kennedy¹,

Kamo²,

Nasdala³

et al. 2010

The Canadian Mineralogist

129

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“…Magma oceans are widely considered to have existed on planetary bodies in the early Solar System, given the monominerallic nature of much of the lunar crust (Wood et al, 1970) and extremely ancient ages obtained for lunar, martian and asteroidal igneous rock (e.g., Debaille et al, 2007;Nemchin et al, 2009;Schiller et al 2011). These may have been produced by planetary scale melting induced by heating of short-lived 26 Al in the case of early-formed protoplanets such as…”

Section: Introductionmentioning

confidence: 99%

Tracking the formation of magma oceans in the Solar System using stable magnesium isotopes

Schiller¹,

Dallas²,

Creech³

et al. 2017

Geochem. Persp. Let.

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Vesta (Greenwood et al., 2005), or giant impacts such as the Moon-forming event in the case of the Earth and Moon (Tonks and Melosh, 1993). As such, finding robust geochemical fingerprints of these ancient magma oceans is important for understanding the earliest stages of planetary evolution.A range of newly developed stable isotope systems are yielding novel insights into planetary accretion, differentiation and evolution (e.g., Greenwood et al., 2005;Georg et al., 2007). However, many of these systems are multiply affected by a range of processes, potentially including core formation and crystallisation of accessory minerals, which makes interpretation of such data challenging. The lithophile, major element magnesium (Mg) is almost unique in this regard, as stable isotope fractionation in magmatic systems will be almost entirely controlled by crystallisation of high-Mg, mafic minerals, assuming isotopic fractionations exist between such minerals and magma.The large degree of planetary melting required to generate a magma ocean would produce highly magnesian magmas, which would then subsequently crystallise large amounts of mafic, Mg-rich minerals such as olivine. Small Mg stable isotope fractionations exist between co-existing terrestrial mantle olivine, orthopyroxene and clinopyroxene, with olivine being the isotopically lightest phase (Handler et al., 2009;Young et al., 2009;Pogge von Strandmann et al., 2011;Xiao et al., 2013). Consequently, it should also be possible to detect progressive Mg isotope changes in the products of a crystallising magma ocean.Vesta is the second largest asteroid in the Solar System and comprises a metal core, silicate mantle and crust (Russell et al., 2012). Based on spectral observations and the Dawn Mission, the howardite-eucrite-diogenite (HED) meteorite suite is inferred to come from Vesta (McCord et al., 1970;Binzel and Xu, 1993; Russell et al., 2012). Most HED meteorites also share common nucleosynthetic isotope signatures for some elements that demonstrate their genetic affinity (Greenwood et al., 2005). These lithologically diverse meteorites provide a unique archive of the timing and processes of protoplanet formation and differentiation. Diogenites are mostly orthopyroxenites, and are conventionally viewed as cumulate igneous rocks formed in a magma ocean or bodies on Vesta, whereas eucrites are basaltic and gabbroic rocks predominantly composed of pigeonite and plagioclase (Mittlefehldt, 2014).Despite many decades of petrological, geochemical and chronological study, the petrogenesis of eucrites and diogenites and the relationship between them remain enigmatic. End-member models include limited partial melting or extensive (i.e. magma ocean) melting of Vesta (Stolper, 1977; Mandler and ElkinsTanton, 2013;Mittlefehldt, 2014). Nearly all models are difficult to reconcile with the large range of incompatible trace element concentrations in diogenites and eucrites. However, a recent study by Mandler and Elkins-Tanton (2013) has used both chemical and physical arguments to ...

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“…For example, radiometric ages of lunar pristine sample rocks are varied and can be influenced by later impact heat and shock (e.g., Nemchin et al, 2009). …”

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confidence: 99%

The relative timing of Lunar Magma Ocean solidification and the Late Heavy Bombardment inferred from highly degraded impact basin structures

Kamata

Sugita

Abe

et al. 2015

Icarus

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The solidification of the Lunar Magma Ocean (LMO) and formation of impact basins are important events that took place on the early Moon. The relative timing of these events, however, is poorly constrained. The aim of this study is ing substantial viscous lateral flow in the crust. Recent geodetic measurements reveal that the lunar crust is thinner than previously estimated, indicating that an extremely high crustal temperature is required for lateral flow to occur. In this study, we calculate lunar thermal evolution and viscoelastic deformation of basins and investigate the thermal state at the time of basin formation using recent crustal thickness models. We find that a Moho temperature >1300-1400K at the time of basin formation is required for substantial viscous relaxation of topography to occur; the implied elastic thickness at the time of loading is <30 km. Such a high temperature can be maintained only for a short time (i.e., <50Myr for most conditions) after solidification of the LMO or after mantle overturn if it took place; relaxed impact basins forming ≥150 Myr later than LMO solidification are unlikely. This result is in conflict with an intensive Late Heavy Bombardment (LHB) model, which assumes that most impact basins were formed at ∼3.9 Ga, since it requires LMO solidification time extremely later than previous theoretical estimates. Either the LHB was moderate, or the majority of proposed early PN basins were not in fact formed by impacts.

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Timing of crystallization of the lunar magma ocean constrained by the oldest zircon

Cited by 198 publications

References 24 publications

GRENVILLE SKARN TITANITE: POTENTIAL REFERENCE MATERIAL FOR SIMS U-Th-Pb ANALYSIS

GRENVILLE SKARN TITANITE: POTENTIAL REFERENCE MATERIAL FOR SIMS U-Th-Pb ANALYSIS

Tracking the formation of magma oceans in the Solar System using stable magnesium isotopes

The relative timing of Lunar Magma Ocean solidification and the Late Heavy Bombardment inferred from highly degraded impact basin structures

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