Letter. In situ 238U-230Th disequilibrium dating of pyrochlore at sub-millennial precision
-
Florian Wetzel
,
Axel K. Schmitt
Abstract
We report the application of high-resolution in situ 238U-230Th disequilibrium dating to pyrochlore [(Ca,Na,REE,Th,U)2(Nb,Ti,Ta,Zr)2O6(OH,F)]. Compositionally zoned pyrochlore is an accessory phase in intrusive carbonatitic syenites, which were ejected as cognate clasts during the eruption of the phonolitic Laacher See volcano, East Eifel, Germany, 12.9 ka ago. Separated individual pyrochlore crystals were analyzed for U-Th isotopes and elemental abundances at high spatial resolution (~25 μm) using secondary ion mass spectrometry (SIMS) with an internal precision for the 238U-230Th isochron of ~700 a (2σ). U and Th were also analyzed by electron microprobe in SIMS spots. Instrumental mass fractionation for Th/U was corrected using an EMP vs. SIMS calibration curve, and the resulting pyrochlore isochron age of 26.1 ± 1.4 ka (including external calibration uncertainty) is concordant with the 23 +7/-6 ka U-Th zircon ages for the same sample. By contrast, AM206 pyrochlore from a Cretaceous alkali granite shows significant disequilibrium with (230Th)/(238U) = 0.90 ± 0.04. The tightly defined isochron implies that U-Th in Laacher See pyrochlore remained a closed decay system during protracted residence in the magma chamber carapace, and was unaffected by hydrothermal alteration or post-eruptive weathering over time scales of tens of thousands of years. By contrast, disequilibrium in AM206 pyrochlore indicates U-Th mobilization during protracted near-surface residence.
© 2015 by Walter de Gruyter Berlin/Boston
Articles in the same Issue
- Resonant X-ray emission study of the lower-mantle ferropericlase at high pressures
- Uranyl phosphate sheet reconstruction during dehydration of metatorbernite [Cu(UO2)2(PO4)2·8H2O]
- Detection of structurally bound hydroxyl in fluorapatite from Apollo Mare basalt 15058,128 using TOF-SIMS
- Quantum-mechanical evaluation of Np-incorporation into studtite
- Electronic structure and local environment of substitutional V3+ in grossular garnet Ca3Al2(SiO4)3: K-edge X-ray absorption spectroscopy and first-principles modeling
- Elbrusite-(Zr)—A new uranian garnet from the Upper Chegem caldera, Kabardino-Balkaria, Northern Caucasus, Russia
- What drives the distribution in nature of 3T vs. 2M1 polytype in muscovites and phengites? A general assessment based on new data from metamorphic and igneous granitoid rocks
- Radiation damage and uranium concentration in zircon as assessed by Raman spectroscopy and neutron irradiation
- The Cr X-ray absorption K-edge structure of poorly crystalline Fe(III)-Cr(III)-oxyhydroxides
- Protracted oceanic subduction prior to continental subduction: New Lu-Hf and Sm-Nd geochronology of oceanic-type high-pressure eclogite in the western Dabie orogen
- Time-resolved in situ studies of apatite formation in aqueous solutions
- X-ray Rietveld and 57Fe Mössbauer studies of epidote and piemontite on the join Ca2Al2Fe3+Si3O12(OH)–Ca2Al2Mn3+Si3O12(OH) formed by hydrothermal synthesis
- Elastic behavior of zeolite boggsite in silicon oil and aqueous medium: A case of high-pressure-induced over-hydration
- Low-temperature infrared spectroscopic study of OH-stretching modes in kaolinite and dickite
- Stability field of the high-temperature orthorhombic phase in the enstatite-diopside system
- Unique crystal chemistry of two polymorphs of topaz-OH: A multi-nuclear NMR and Raman study
- Crystal chemistry of chromian pumpellyite from Osayama, Okayama Prefecture, Japan
- Toturite Ca3Sn2Fe2SiO12—A new mineral species of the garnet group
- The structure of schwertmannite, a nanocrystalline iron oxyhydroxysulfate
- Crystal chemistry of Cr-spinels from the lherzolite mantle peridotite of Ronda (Spain)
- Lead-tellurium oxysalts from Otto Mountain near Baker, California: I. Ottoite, Pb2TeO5, a new mineral with chains of tellurate octahedra
- Lead-tellurium oxysalts from Otto Mountain near Baker, California: II. Housleyite, Pb6CuTe4O18(OH)2, a new mineral with Cu-Te octahedral sheets
- The behavior of the Hf isotope system in radiation-damaged zircon during experimental hydrothermal alteration
- Letter. Crystal structure of a new high-pressure polymorph of topaz-OH
- Letter. In situ 238U-230Th disequilibrium dating of pyrochlore at sub-millennial precision
Articles in the same Issue
- Resonant X-ray emission study of the lower-mantle ferropericlase at high pressures
- Uranyl phosphate sheet reconstruction during dehydration of metatorbernite [Cu(UO2)2(PO4)2·8H2O]
- Detection of structurally bound hydroxyl in fluorapatite from Apollo Mare basalt 15058,128 using TOF-SIMS
- Quantum-mechanical evaluation of Np-incorporation into studtite
- Electronic structure and local environment of substitutional V3+ in grossular garnet Ca3Al2(SiO4)3: K-edge X-ray absorption spectroscopy and first-principles modeling
- Elbrusite-(Zr)—A new uranian garnet from the Upper Chegem caldera, Kabardino-Balkaria, Northern Caucasus, Russia
- What drives the distribution in nature of 3T vs. 2M1 polytype in muscovites and phengites? A general assessment based on new data from metamorphic and igneous granitoid rocks
- Radiation damage and uranium concentration in zircon as assessed by Raman spectroscopy and neutron irradiation
- The Cr X-ray absorption K-edge structure of poorly crystalline Fe(III)-Cr(III)-oxyhydroxides
- Protracted oceanic subduction prior to continental subduction: New Lu-Hf and Sm-Nd geochronology of oceanic-type high-pressure eclogite in the western Dabie orogen
- Time-resolved in situ studies of apatite formation in aqueous solutions
- X-ray Rietveld and 57Fe Mössbauer studies of epidote and piemontite on the join Ca2Al2Fe3+Si3O12(OH)–Ca2Al2Mn3+Si3O12(OH) formed by hydrothermal synthesis
- Elastic behavior of zeolite boggsite in silicon oil and aqueous medium: A case of high-pressure-induced over-hydration
- Low-temperature infrared spectroscopic study of OH-stretching modes in kaolinite and dickite
- Stability field of the high-temperature orthorhombic phase in the enstatite-diopside system
- Unique crystal chemistry of two polymorphs of topaz-OH: A multi-nuclear NMR and Raman study
- Crystal chemistry of chromian pumpellyite from Osayama, Okayama Prefecture, Japan
- Toturite Ca3Sn2Fe2SiO12—A new mineral species of the garnet group
- The structure of schwertmannite, a nanocrystalline iron oxyhydroxysulfate
- Crystal chemistry of Cr-spinels from the lherzolite mantle peridotite of Ronda (Spain)
- Lead-tellurium oxysalts from Otto Mountain near Baker, California: I. Ottoite, Pb2TeO5, a new mineral with chains of tellurate octahedra
- Lead-tellurium oxysalts from Otto Mountain near Baker, California: II. Housleyite, Pb6CuTe4O18(OH)2, a new mineral with Cu-Te octahedral sheets
- The behavior of the Hf isotope system in radiation-damaged zircon during experimental hydrothermal alteration
- Letter. Crystal structure of a new high-pressure polymorph of topaz-OH
- Letter. In situ 238U-230Th disequilibrium dating of pyrochlore at sub-millennial precision
