Isomorphous cation substitution in dioctahedral phyllosilicates by means of ab initio quantum mechanical calculations on clusters
Abstract
A critical question in radiometric dating of metamorphic rocks is whether minerals used to define internal isochrons have achieved isotopic equilibrium during a given metamorphic event, followed by preservation of the equilibrium afterward. A garnet peridotite at Zhimafang in the Sulu terrane of eastern China shows incongruent U-Pb, Rb-Sr, and Sm-Nd ages. Zircon SHRIMP U-Pb dating yielded an isochron age of 224 ± 8 Ma, pointing to zircon growth during Triassic UHP metamorphism. Two mineral assemblages gave consistent Rb-Sr internal isochron ages of 201 ± 4 and 205 ± 4 Ma, but much older Sm-Nd internal isochron ages of 376 ± 16 and 378 ± 24 Ma. Apparently, the Sm-Nd radiometric system fails to reequilibrate among the dated minerals during the Triassic UHP metamorphic event for the garnet peridotite. This result is confirmed by the state of oxygen isotope equilibrium (or disequilibrium) among the constituent minerals in the garnet peridotite. In particular, garnet is not in oxygen isotope equilibrium with any other of the analyzed minerals. The degree of oxygen isotope disequilibria among the other minerals varies from pair to pair. Oxygen isotope equilibrium is observed only between orthopyroxene and olivine for both samples and between phlogopite and clinopyroxene for one sample. It appears that the U-Pb, Rb-Sr, Sm-Nd, and O isotope systems in minerals of the garnet peridotite are in partial equilibrium during UHP metamorphism, i.e., equilibrium with respect to some isotopes and minerals, but not all. Based on available experimental diffusion data, our study of the combined U-Pb, Rb-Sr, Sm-Nd, and O isotope systems in the garnet peridotite demonstrates that the time scale for the UHP metamorphism and subsequent HP eclogite-facies recrystallization is possibly in the range of about 12 to 26 Ma, which was not long enough for the reequilibration of the Sm-Nd and O isotope systems, but just long enough for the reequilibration of the Rb-Sr isotope systems. Therefore, the rate of Sr diffusion in phlogopite (thus Sr isotope reequilibration between the mafic minerals) is constrained to be faster than rates of Nd and O diffusion in garnet (thus Sm-Nd and O isotope reequilibration between the same minerals) under conditions of subduction zone metamorphism.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Partial equilibrium of radiogenic and stable isotope systems in garnet peridotite during ultrahigh-pressure metamorphism
- Experimental determination of Au solubility in rhyolite melt and magnetite: Constraints on magmatic Au budgets
- Surface oxidation of chalcocite (Cu2S) under aqueous (pH = 2–11) and ambient atmospheric conditions: Mineralogy from Cu L- and O K-edge X-ray absorption spectroscopy
- Determination of molar absorptivity of IR fundamental OH-stretching vibration in rhyolitic glasses
- The effect of radiation damage on local structure in the crystalline fraction of ZrSiO4: Investigating the 29Si NMR response to pressure in zircon and reidite
- The structural behavior of Al3+ in peralkaline melts and glasses in the system Na2O-Al2O3-SiO2
- Hydromaghemite, an intermediate in the hydrothermal transformation of 2-line ferrihydrite into hematite
- Carbon isotope “stratigraphy” in a single graphite crystal: Implications for the crystal growth mechanism of fluid-deposited graphite
- Woodruffite: A new Mn oxide structure with 3 × 4 tunnels
- Calderonite, a new lead-iron-vanadate of the brackebuschite group
- Low-temperature microdiamond aggregates in the Maksyutov Metamorphic Complex, South Ural Mountains, Russia
- Crystal structure of protoanthophyllite: A new mineral from the Takase ultramafic complex, Japan
- Crystallization of AlPO4-SiO2 solid solutions from granitic melt and implications for P-rich melt inclusions in pegmatitic quartz
- On the formation of peridotite-derived Os-rich PGE alloys
- Viscosity of hydrous rhyolitic melts inferred from kinetic experiments, and a new viscosity model
- Geothermobarometry and U-Pb Geochronology of metapelitic granulites and pelitic migmatites from the Lokoho region, Northern Madagascar
- The aperiodic states of zircon: an ab initio molecular dynamics study
- Cathodoluminescence investigations on the Popigai, Ries, and Lappajärvi impact diamonds
- Isomorphous cation substitution in dioctahedral phyllosilicates by means of ab initio quantum mechanical calculations on clusters
- Alacranite, As8S9: structural study of the holotype and re-assignment of the original chemical formula
- Influence of layer charge on the hydroxyl stretching of trioctahedral clay minerals: A vibrational study of synthetic Na- and K-saponites
- Stacking faults and twin boundaries in sphalerite crystals from the Trepcˇa mines in Kosovo
- Letters. Rock-forming moissanite (natural α-silicon carbide)
- Water solubility in carbonatite melts
- Trace element partitioning between mantle wedge peridotite and hydrous MgO-rich melt
- Rubidium- and cesium-dominant micas in granitic pegmatites
- Nanoscale mineralogy of arsenic in a region of New Hampshire with elevated As-concentrations in the groundwater
- Micro- and nanochemistry of fly ash from a coal-fired power plant
- Thermal behavior of dental enamel and geologic apatite: An infrared spectroscopic study
- Black carbon pollution of speleothems by fine urban aerosols in tourist caves
- Decay-induced biomineralization of the saguaro cactus (Carnegiea gigantea)
- The distribution of zeolites and their effects on the performance of a nuclear waste repository at Yucca Mountain, Nevada, U.S.A.
- Transformation of 2-line ferrihydrite to 6-line ferrihydrite under oxic and anoxic conditions
- Iron-rich precipitates in a mine drainage environment: Influence of pH on mineralogy
- Efflorescent iron sulfate minerals: Paragenesis, relative stability, and environmental impact
- Secondary mineralogy and microtextures of weathered sulfides and manganoan carbonates in mine waste-rock dumps, with implications for heavy-metal fixation
- Acquisition and evaluation of thermodynamic data for morenosite-retgersite equilibria at 0.1 MPa
- On the thermochemistry of the solid solution between jarosite and its chromate analog
- The Composition and Morphology of Amphiboles from the Rainy Creek Complex, Near Libby, Montana
- Composition, Fe3+/ΣFe, and crystal structure of non-asbestiform and asbestiform amphiboles from Libby, Montana, U.S.A.
- A rapid and accurate procedure for the determination of refractive indices of regulated asbestos minerals
- Ferrous saponite from the Deccan Trap, India, and its application in adsorption and reduction of hexavalent chromium
- Nanomorphology of montmorillonite particles: Estimation of the clay edge sorption site density by low-pressure gas adsorption and AFM observations
- Medieval stained glass in a Mediterranean climate: Typology, weathering and glass decay, and associated biomineralization processes and products
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- The reactivity of seven Mn-oxides with Cr3+aq: A comparative analysis of a complex, environmentally important redox reaction
- Sorption mechanisms of Sr and Pb on zeolitized tuffs from the Nevada test site as a function of pH and ionic strength
- Letters. Tailoring calcite: Nanoscale AFM of coccolith biocrystals