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  • 1
    Online Resource
    Online Resource
    A New Appraisal of Sri Lankan BB Zircon as a Reference Material for LA‐ICP‐MS U‐Pb Geochronology and Lu‐Hf Isotope Tracing
    Wiley ; 2017
    In:  Geostandards and Geoanalytical Research Vol. 41, No. 3 ( 2017-09), p. 335-358
    Details
    In: Geostandards and Geoanalytical Research, Wiley, Vol. 41, No. 3 ( 2017-09), p. 335-358
    Abstract: A potential zircon reference material ( BB zircon) for laser ablation‐inductively coupled plasma‐mass spectrometry ( LA ‐ ICP ‐ MS ) U‐Pb geochronology and Hf isotope geochemistry is described. A batch of twenty zircon megacrysts (0.5–1.5 cm 3 ) from Sri Lanka was studied. Within‐grain rare earth element ( REE ) compositions are largely homogeneous, albeit with some variation seen between fractured and homogeneous domains. Excluding fractured cathodoluminescence bright domains, the variation in U content for all analysed crystals ranged from 227 to 368 μg g −1 and the average Th/U ratios were between 0.20 and 0.47. The Hf isotope composition (0.56–0.84 g/100 g Hf) is homogeneous within and between the grains – mean 176 Hf/ 177 Hf of 0.281674 ± 0.000018 (2 s ). The calculated alpha dose of 0.59 × 10 18  g −1 for a number of BB grains falls within the trend of previously studied, untreated zircon samples from Sri Lanka. Aliquots of the same crystal (analysed by ID‐TIMS in four different laboratories) gave consistent U‐Pb ages with excellent measurement reproducibility (0.1–0.4% RSD ). Interlaboratory assessment (by LA ‐ ICP ‐ MS ) from individual crystals returned results that are within uncertainty equivalent to the TIMS ages. Finally, we report on within‐ and between‐grain homogeneity of the oxygen isotope systematic of four BB crystals (13.16‰ VSMOW ).
    Type of Medium: Online Resource
    ISSN: 1639-4488 , 1751-908X
    URL: Issue
    URL: Article
    DOI: 10.1111/ggr.2017.41.issue-3
    DOI: 10.1111/ggr.12167
    Language: English
    Publisher: Wiley
    Publication Date: 2017
    detail.hit.zdb_id: 2276474-4
    detail.hit.zdb_id: 2595219-5
    detail.hit.zdb_id: 2134777-3
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  • 2
    Online Resource
    Online Resource
    The Diamantina Monazite: A New Low‐Th Reference Material for Microanalysis
    Wiley ; 2018
    In:  Geostandards and Geoanalytical Research Vol. 42, No. 1 ( 2018-03), p. 25-47
    Details
    In: Geostandards and Geoanalytical Research, Wiley, Vol. 42, No. 1 ( 2018-03), p. 25-47
    Abstract: Most monazite reference materials ( RM s) for in situ U‐Pb geochronology are rich in Th; however, many hydrothermal ore deposits contain monazite that is low in trace element contents, including Th, U and Pb. Because of potential problems with matrix effects and the lack of appropriate matrix‐matched RM s, such variations can bias dating of hydrothermal deposits. In this paper, we describe a polycrystalline low‐U and low‐Th Diamantina monazite from the Espinhaço Range, SE Brazil. It has a U‐Pb ID ‐ TIMS weighted mean 207 Pb * / 235 U ratio of 0.62913 ± 0.00079, 206 Pb * / 238 U of 0.079861 ± 0.000088 and 207 Pb * / 206 Pb * of 0.057130 ± 0.000031, yielding a weighted mean 206 Pb * / 238 U date of 495.26 ± 0.54 Ma (95% c.l.). In situ dates acquired with different methods ( LA ‐(Q, SF , MC )‐ ICP ‐ MS and SIMS ) are within uncertainty of the ID ‐ TIMS data. U‐Pb LA ‐(Q, MC )‐ ICP ‐ MS runs, using Diamantina as a primary RM , reproduced the ages of other established RM s within 〈 1% deviation. The LA ‐ MC ‐ ICP ‐ MS analyses yielded homogeneous Sm‐Nd isotopic compositions ( 143 Nd/ 144 Nd = 0.511427 ± 23, 2 s ; 147 Sm/ 144 Nd = 0.1177 ± 13, 2 s ) and εNd (495 Ma) of −18.7 ± 0.5 (2 s ). SIMS oxygen isotope determinations showed measurement reproducibility better than ± 0.3‰ (2 s ), confirming Diamantina's relative homogeneity at test portion masses below 1 ng.
    Type of Medium: Online Resource
    ISSN: 1639-4488 , 1751-908X
    URL: Issue
    URL: Article
    DOI: 10.1111/ggr.2018.42.issue-1
    DOI: 10.1111/ggr.12192
    Language: English
    Publisher: Wiley
    Publication Date: 2018
    detail.hit.zdb_id: 2276474-4
    detail.hit.zdb_id: 2595219-5
    detail.hit.zdb_id: 2134777-3
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  • 3
    Online Resource
    Online Resource
    Reconstructing the metamorphic evolution of the Araçuaí orogen (SE Brazil) using in situ U–Pb garnet dating and P – T modelling
    Wiley ; 2021
    In:  Journal of Metamorphic Geology Vol. 39, No. 9 ( 2021-12), p. 1145-1171
    Details
    In: Journal of Metamorphic Geology, Wiley, Vol. 39, No. 9 ( 2021-12), p. 1145-1171
    Abstract: The Araçuaí orogen of SE Brazil consists of a suite of deformed, metamorphosed, and partly migmatitic sedimentary rocks and granitoid batholiths that predominantly formed during collision of the São Francisco and Congo cratons during West Gondwana assembly in the late Neoproterozoic. While widespread anatexis and a prolonged magmatic record are well‐established, insufficient information exists about the extensive exposure of metamorphic rocks along the Araçuaí orogen. Combining information from a wide range of these metamorphic rocks is essential to reconstruct mountain‐building processes and heat sources that operate in convergent tectonic settings. New petrographic observations, mineral chemistry, and phase equilibria modelling were used to constrain peak metamorphic conditions of amphibolite facies metasedimentary rocks from the central domain of the orogen at 580–620°C and 7–9 kbar. We applied in situ low‐U ( 〈 1 µg/g) garnet U–Pb geochronology, which yielded ages in the range of 590–565 Ma, interpreted as the timing of bulk garnet growth during prograde metamorphism, and consistent with previously established monazite ages for the peak metamorphic event. Metamorphic zircon ages of c . 630 Ma are related to a cryptic terrane accretion event prior to the orogeny, whereas garnet U–Pb ages record the main orogenic event as revealed by disequilibrium rare earth element partitioning between the two minerals. A compilation of our results with previously reported metamorphic conditions defines a clockwise P–T evolution for the Araçuaí orogeny, characterized by slow burial to depths of 26–30 km, followed by nearly isothermal decompression from ~10 to 6 kbar. Substantial differences of peak temperatures in various domains of the orogen are consistent with the presence of different protoliths in the crustal sections. The higher concentration of heat‐producing elements (HPEs) in lithologies from the anatectic domains may have triggered partial melting of metasedimentary rocks. This suggests that HPEs were a significant heat source for crustal reworking during West Gondwana convergent tectonics.
    Type of Medium: Online Resource
    ISSN: 0263-4929 , 1525-1314
    URL: Issue
    URL: Article
    DOI: 10.1111/jmg.v39.9
    DOI: 10.1111/jmg.12605
    RVK:
    RA 1000
    RVK:
    TE 1000
    Language: English
    Publisher: Wiley
    Publication Date: 2021
    detail.hit.zdb_id: 2020499-1
    SSG: 13
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