Electron Microprobe Petrochronology

Williams, Michael L.; Jercinovic, Michael J.; Mahan, K. H.; Dumond, Gregory

doi:10.2138/rmg.2017.83.5

Cited by 60 publications

(43 citation statements)

References 126 publications

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“…So, we suggest partial replacement rather than "re-equilibration". To ascertain whether this (or some alternative) process was responsible for monazite growth, geochemical tracers for monazite should be analyzed, and readily interpretable ones are available: Th and Y contents and their zoning (Kohn et al 2005;Williams et al 2017, this volume) are most helpful.…”

Section: Timing Of Porphyroblast Growthmentioning

confidence: 99%

“…However, the solubility of monazite as well as the melt volume increase with temperature (Montel 1993;Stepanov et al 2012), one would expect resorption not growth (Kelsey et al 2008). Chemical characterization of monazite-ideally based on compositional maps (Mahan et al 2006;Williams et al 2007Williams et al , 2017, this volume)-is best done prior to chronological microanalysis (Kohn et al 2005). Other studies have reported that monazite rims may also form during cooling from crystallizing melt (Pyle and Spear 2003;Kohn et al 2004;Johnson et al 2015).…”

Section: And Accessory Mineralsmentioning

confidence: 99%

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Local Bulk Composition Effects on Metamorphic Mineral Assemblages

Lanari

Engi

2017

Reviews in Mineralogy and Geochemistry

152

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Section: Timing Of Porphyroblast Growthmentioning

confidence: 99%

Section: And Accessory Mineralsmentioning

confidence: 99%

Local Bulk Composition Effects on Metamorphic Mineral Assemblages

Lanari

Engi

2017

Reviews in Mineralogy and Geochemistry

152

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“…Monazite electron microprobe Th-U-total Pb dating can achieve a lateral spot size of 3 µm (or less) to simultaneously gather geochronological and trace element data from monazite domains (e.g. Kohn et al 2005;Krenn et al 2008;Majka et al 2012;Petrík and Konečný 2009;Pyle et al 2005;Spear et al 2009;Suzuki and Adachi 1991;Williams et al 2007Williams et al , 2017. Zircon depth-profiling, using either Laser Ablation Inductively Coupled Mass Spectrometry (LA-ICP-MS) or Secondary Ion Mass Spectrometry (SIMS), has proven to be a powerful technique to extract radiogenic isotopes and trace elements from micrometerscale rims (e.g.…”

Section: Introductionmentioning

confidence: 99%

High-spatial resolution dating of monazite and zircon reveals the timing of subduction–exhumation of the Vaimok Lens in the Seve Nappe Complex (Scandinavian Caledonides)

Barnes

Majka

Schneider

et al. 2018

Contrib Mineral Petrol

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In-situ monazite Th-U-total Pb dating and zircon LA-ICP-MS depth-profiling was applied to metasedimentary rocks from the Vaimok Lens in the Seve Nappe Complex (SNC), Scandinavian Caledonides. Results of monazite Th-U-total Pb dating, coupled with major and trace element mapping of monazite, revealed 603 ± 16 Ma Neoproterozoic cores surrounded by rims that formed at 498 ± 10 Ma. Monazite rim formation was facilitated via dissolution-reprecipitation of Neoproterozoic monazite. The monazite rims record garnet growth as they are depleted in Y 2 O 3 with respect to the Neoproterozoic cores. Rims are also characterized by relatively high SrO with respect to the cores. Results of the zircon depth-profiling revealed igneous zircon cores with crystallization ages typical for SNC metasediments. Multiple zircon grains also exhibit rims formed by dissolution-reprecipitation that are defined by enrichment of light rare earth elements, U, Th, P, ± Y, and ± Sr. Rims also have subdued Eu anomalies (Eu/Eu* ≈ 0.6-1.2) with respect to the cores. The age of zircon rim formation was calculated from three metasedimentary rocks: 480 ± 22 Ma; 475 ± 26 Ma; and 479 ± 38 Ma. These results show that both monazite and zircon experienced dissolution-reprecipitation under high-pressure conditions. Caledonian monazite formed coeval with garnet growth during subduction of the Vaimok Lens, whereas zircon rim formation coincided with monazite breakdown to apatite, allanite and clinozoisite during initial exhumation.

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“…Polished thin sections were commercially prepared from cut samples and then coated with 20 nm of aluminum followed by 8 nm of carbon (Jercinovic et al 2008). We identified monazite and conducted basic textural and compositional mapping of thin sections using a CAMECA SX-50 microprobe for wavelength-dispersive spectroscopy mapping of full thin sections for major elements (Mg and Ca) and trace elements associated with monazite and other actinide-rich minerals (Ce or La, Y, and Zr) (Williams et al 2017). After identifying grains of monazite suitable for dating, we used the SX-50 to obtain higher-resolution compositional maps of the individual grains, focusing on elements likely to distinguish compositional domains within monazite grains (Y, Th, U, Ca, and Nd or Si).…”

Section: Methodsmentioning

confidence: 99%

“…After identifying grains of monazite suitable for dating, we used the SX-50 to obtain higher-resolution compositional maps of the individual grains, focusing on elements likely to distinguish compositional domains within monazite grains (Y, Th, U, Ca, and Nd or Si). Most of the samples we discuss here contain additional grains of monazite that we did not map or attempt to date because our approach favors detailed analysis of selected grains with well characterized textural and compositional context (Williams et al 2007(Williams et al , 2017).…”

Section: Methodsmentioning

confidence: 99%

Monazite U–Th–Pb geochronology of the Central Metasedimentary Belt Boundary Zone (CMBbz), Grenville Province, Ontario Canada

et al. 2018

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The Central Metasedimentary Belt boundary zone (CMBbz) is a crustal-scale shear zone that juxtaposes the Central Gneiss Belt and the Central Metasedimentary Belt of the Grenville Province. Geochronological work on the timing of deformation and metamorphism in the CMBbz is ambiguous, and the questions that motivate our study are: how many episodes of shear zone activity did the CMBbz experience, and what is the tectonic significance of each episode? We present electron microprobe data from monazite (the U–Th–Pb chemical method) to directly date deformation and metamorphism recorded in five garnet–biotite gneiss samples collected from three localities of the CMBbz of Ontario (West Guilford, Fishtail Lake, and Killaloe). All three localities yield youngest monazite dates ca. 1045 Ma; most of the monazite domains that yield these dates are high-Y rims. In comparison with this common late Ottawan history, the earlier history of the three CMBbz localities is less clearly shared. The West Guilford samples have monazite grain cores that show older high-Y domains and younger low-Y domains; these cores yield a prograde early Ottawan (1100–1075 Ma) history. The Killaloe samples yield a well-defined prograde, pre- to early Shawinigan history (i.e., 1220–1160 Ma) in addition to some evidence for a second early Ottawan event. In other words, the answers to our research questions are: three events; a Shawinigan event possibly associated with crustal thickening, an Ottawan event possibly associated with another round of crustal thickening, and a late Ottawan event that resists simple interpretation in terms of metamorphic history but that coincides chronologically with crustal thinning at the base of an orogenic lid.

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Electron Microprobe Petrochronology

Cited by 60 publications

References 126 publications

Local Bulk Composition Effects on Metamorphic Mineral Assemblages

Local Bulk Composition Effects on Metamorphic Mineral Assemblages

High-spatial resolution dating of monazite and zircon reveals the timing of subduction–exhumation of the Vaimok Lens in the Seve Nappe Complex (Scandinavian Caledonides)

Monazite U–Th–Pb geochronology of the Central Metasedimentary Belt Boundary Zone (CMBbz), Grenville Province, Ontario Canada

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