Garnet U–Pb Age of Skarns from Dashkesan Deposit (Lesser Caucasus)

Stifeeva, M. V.; Сальникова, Е. Б.; Самсонов, А. В.; Kotov, A. B.; Gritsenko, Yu. D.

doi:10.1134/s1028334x19080178

Cited by 10 publications

(4 citation statements)

References 7 publications

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“…The secondary reference materials Afrikanda garnet (Salnikova et al (2019) TIMS age 378 ± 3 Ma; our ages, calculated from fractionation-corrected Tera-Wasserburg discordia lower intercept isotope ratios for session 1: 378 ± 7 Ma, MSWD = 2.6, n = 12; and session 2: 378 ± 4 Ma, MSWD = 1.7, n = 12), Dashkesan garnet (Stifeeva et al (2019) TIMS age 147 ± 2 Ma; our fractionationcorrected weighted mean 206 Pb/ 238 U ages for session 1: 144.3 ± 1.3 Ma, MSWD = 1.7, n = 11; and session 2: 146.1 ± 1.3 Ma, MSWD = 0.84, n = 7) and Chikskii garnet (Salnikova et al (2018) TIMS age 492 ± 2 Ma; our fractionation-corrected weighted mean 206 Pb/ 238 U ages for session 1: 492 ± 8 Ma, MSWD = 5.4, n = 10; and session 2: 478 ± 9 Ma, MSWD = 18, n = 10) were employed after U-Pb fractionation correction and treated in the same manner as the unknowns. Uncertainties are fully propagated and reported at the 2σ level here and throughout.…”

Section: Methodsmentioning

confidence: 99%

Uranium–lead geochronology applied to pyrope garnet with very low concentrations of uranium

O’Sullivan

Hoare²,

Mark

et al. 2023

Geol. Mag.

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We present U–Pb dates from peridotitic pyrope-rich garnet from four mantle xenoliths entrained in a kimberlite from Bultfontein, South Africa. Garnet dates magmatic emplacement due to the high mantle residence temperatures of the source material prior to eruption, which were most likely above the closure temperature for the pyrope U–Pb system. We determine a U–Pb date of 84.0 ± 8.1 Ma for the emplacement of the Bultfontein kimberlite from garnet in our four xenolith samples. The date reproduces previous dates obtained from other mineral-isotope systems (chiefly Rb–Sr in phlogopite). Garnet can be dated despite extremely low concentrations of U (median ∼0.05 μg/g), because concentrations of common Pb are often low or non-detectable. This means that sub-concordant garnets can be dated with moderate precision using very large laser-ablation spots (130 μm) measured by quadrupole inductively coupled plasma – mass spectrometry (LA-Q-ICP-MS). Our strategy demonstrates successful U–Pb dating of a U-poor mineral due to high initial ratios of U to common Pb in some grains, and the wide spread of isotopic compositions of grains on a concordia diagram. In addition, the analytical protocol is not complex and uses widely available analytical methods and strategies. This new methodology has some advantages and disadvantages for dating kimberlite emplacement versus established methods (U-based decay systems in perovskite and zircon, or Rb- or K-based systems in phlogopite). However, this method has unique promise for its potential application to detrital diamond prospecting and, more speculatively, to the dating of pyrope inclusions in diamond.

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Section: Methodsmentioning

confidence: 99%

Uranium–lead geochronology applied to pyrope garnet with very low concentrations of uranium

O’Sullivan

Hoare²,

Mark

et al. 2023

Geol. Mag.

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“…However, many analyses exhibited undesirably high age uncertainty. An uncertainty filter was therefore applied following the approach of Chew et al ( 2020), such that: Afrikanda, Dashkesan, and Chikskii garnets were used as secondary reference materials and treated as unknowns throughout the data reduction process (reference U-Pb TIMS ages 377 ± 3 Ma, 147 ± 2 Ma, and 492 ± 2 Ma, respectively; Salnikova et al, 2018Salnikova et al, , 2019Stifeeva et al, 2019). Afrikanda yielded a lower-intercept U-Pb age of 368.1 ± 2.6 Ma (MSWD = 1.2, n = 51), and Dashkesan 146.0 ± 1.3 Ma (MSWD = 0.92, n = 50); both are slightly discordant.…”

Section: Garnet U-pb and Trace-element Analysis By La-q-icpmsmentioning

confidence: 99%

Detrital Garnet Geochronology by In Situ U‐Pb and Lu‐Hf Analysis: A Case Study From the European Alps

Mark,

O’Sullivan,

Glorie

et al. 2023

JGR Earth Surface

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Detrital geochronology employing the widely‐used zircon U‐Pb proxy is biased towards igneous events and metamorphic anataxis; additionally, zircon is highly refractory and frequently polycyclic. Garnet, a rock‐forming and thus commonly‐occuring mineral, is predominantly metamorphic and much less refractory. Here, we report in‐situ U‐Pb and Lu‐Hf ages from detrital garnet hosted in ancient and modern sediments of the European Alps. Both geochronometers are biased towards the most recent garnet‐crystallising metamorphic event in the source area, with fewer inherited ages. This likely reflects efficient removal of inherited garnet during diagenesis and metamorphism, and is in contrast to detrital zircon, apatite, and rutile U‐Pb data which largely record pre‐Alpine ages. Neither the U‐Pb nor Lu‐Hf system in garnet exhibits a relationship between age recovery and composition. However, the Lu‐Hf system in garnet yields significantly better age recovery than the U‐Pb system. Estimated initial 238U/206Pbc values at the time of crystallization are near unity for the garnet analysed in this study, suggesting that garnet does not significantly partition U from Pb during crystallization, at least for the generally almandine‐rich garnets analysed in this study. Hence, Lu‐Hf geochronology of detrital garnet offers an effective method to detect and date the most recent phase of mid‐grade metamorphism in sub‐anatectic source areas, in which detrital zircon U‐Pb analysis may be of less utility.

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“…Regional studies of aillikites have highlighted a close temporal and spatial association with carbonatite magmatism, particularly during the early stages of intra‐continental rifting, including supercontinent break‐up (I. Ashchepkov et al., 2020; Srivastava et al., 2009; Tappe et al., 2006, 2009; Zozulya et al., 2020). Periods of aillikite magmatism occurred during the Paleogene (Zandkopsdrift Complex; Ogungbuyi et al., 2022), Cretaceous (Damodar Valley Alkaline Field; Srivastava et al., 2009; Alto Paranaíba Igneous Province; Velásquez Ruiz et al., 2023), Jurassic (Tikiusaaq Field; Tappe et al., 2009), Triassic (Chadobets Aillikite; Nosova et al., 2018), Devonian (Glen Gollaidh Aillikite Dyke; Hutchison et al., 2018; Ilbokich Aillikite; Nosova et al., 2018; Kola Alkali Province; Stifeeva et al., 2023), Cambrian (Ungava Bay; Digonnet et al., 2000), Neoproterozoic (Aillik Bay; Tappe et al., 2006; Arbarastakh Alkaline‐Carbonatite Complex; Doroshkevich et al., 2022; Beloziminsky Alkaline Ultrabasic‐Carbonatite Massif; I. Ashchepkov et al., 2020; Vinoren Aillikite; Zozulya et al., 2020), and Mesoproterozoic (Ilímaussaq Complex; Upton et al., 2006). The petrogenesis of aillikites is thought to involve the volatile‐rich melting of veined‐phlogopite and carbonate‐bearing garnet peridotite at depths beyond 150 km (Foley et al., 2009, 2019; Veter et al., 2017).…”

Section: Introductionmentioning

confidence: 99%

Petrology, Age, and Rift Origin of Ultramafic Lamprophyres (Aillikites) at Mount Webb, a New Alkaline Province in Central Australia

Sudholz,

Reddicliffe,

Jaques

et al. 2023

Geochem Geophys Geosyst

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Diamond exploration over the past decade has led to the discovery of a new province of kimberlitic pipes (the Webb Province) in the Gibson Desert of central Australia. The Webb pipes comprise sparse macrocrystic olivine set in a groundmass of olivine, phlogopite, perovskite, spinel, clinopyroxene, titanian‐andradite and carbonate. The pipes resemble ultramafic lamprophyres (notably aillikites) in their mineralogy, major and minor oxide chemistry, and initial 87Sr/86Sr and εNd‐εHf isotopic compositions. Ion probe U‐Pb geochronology on perovskite (806 ± 22 Ma) indicates the eruption of the pipes was co‐eval with plume‐related magmatism within central Australia (Willouran‐Gairdner Volcanic Event) associated with the opening of the Centralian Superbasin and Rodinia supercontinent break‐up. The equilibration pressure and temperature of mantle‐derived garnet and chromian (Cr) diopside xenocrysts range between 17 and 40 kbar and 750–1320°C and define a paleo‐lithospheric thickness of 140 ± 10 km. Chemical variations of xenocrysts define litho‐chemical horizons within the shallow, middle, and deep sub‐continental lithospheric mantle (SCLM). The shallow SCLM (50–70 km), which includes garnet‐spinel and spinel lherzolite, contains Cr diopside with weakly refertilized rare earth element compositions and unenriched compositions. The mid‐lithosphere (70–85 km) has lower modal abundances of Cr diopside. This layer corresponds to a seismic mid‐lithosphere discontinuity interpreted as pargasite‐bearing lherzolite. The deep SCLM (>90 km) comprises refertilized garnet lherzolite that was metasomatized by a silicate‐carbonatite melt.

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Garnet U–Pb Age of Skarns from Dashkesan Deposit (Lesser Caucasus)

Cited by 10 publications

References 7 publications

Uranium–lead geochronology applied to pyrope garnet with very low concentrations of uranium

Uranium–lead geochronology applied to pyrope garnet with very low concentrations of uranium

Detrital Garnet Geochronology by In Situ U‐Pb and Lu‐Hf Analysis: A Case Study From the European Alps

Petrology, Age, and Rift Origin of Ultramafic Lamprophyres (Aillikites) at Mount Webb, a New Alkaline Province in Central Australia

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