Diffusion versus recrystallization processes in Rb–Sr geochronology: Isotopic relics in eclogite facies rocks, Western Gneiss Region, Norway

Glodny, Johannes; Kühn, Alexander; Austrheim, Håkon

doi:10.1016/j.gca.2007.10.021

Cited by 107 publications

(78 citation statements)

References 81 publications

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“…Even rocks that are considered 'dry', such as eclogites, owe their recrystallization at the metamorphic peak to the availability of water (Bjørnerud et al 2002;Schneider et al 2007). The isotope systematics of eclogites are accordingly controlled by precisely those rare fluid circulation events (Glodny et al 2008). The paradox first pointed out by Thöni & Jagoutz (1992), that especially eclogites (but also many other metamorphic rocks) very rarely give satisfactory internal isochrons, can be understood by examining the presence or absence of complete petrological equilibrium.…”

Section: Discussionmentioning

confidence: 99%

Disequilibrium textures versus equilibrium modelling: geochronology at the crossroads

Villa

2010

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Submicroscopic microchemical disequilibrium in minerals is extremely widespread. Disequilibrium recrystallization is promoted by water in metamorphic terranes and near granites, contact aureoles, and faults. Recrystallization is energetically less costly at almost any temperature than diffusive re-equilibration.Radiogenic isotopes (except 4 He) never diffusively re-equilibrate faster than major elements forming the mineral structure. Isotopic inheritance tied to relicts was demonstrated for zircon, monazite, amphibole, K-feldspar, biotite and muscovite.The mechanism for resetting the isotope record in nature depends more on the availability of recrystallization-enhancing water than on reaching a preset temperature. Laboratory diffusion experiments on hydrous minerals were plagued, to a variable but always large extent, by dissolution-reprecipitation. Mineral geochronometers should be viewed as 'geohygrometers' that essentially date the fluid circulation episodes.Thanks to submicroscopic petrology, isotopic disequilibria can be put into context with petrogenetic disequilibria. Analytical advances allow the successful dating of each mineral generation. This has opened up a much richer wealth of data on the P-T-A-X-d history of rocks, which in the long run will also improve our ability to develop credible numeric models.

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Section: Discussionmentioning

confidence: 99%

Disequilibrium textures versus equilibrium modelling: geochronology at the crossroads

Villa

2010

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“…Fluids in highpressure (HP) metamorphic rocks also play a key role in promoting equilibration of isotopic systems used as geochronometers (Glodny et al, 2003). Multimineral isochrons record fluidinduced recrystallization events rather than stages of cooling because full isotopic homogenization is not achieved in rocks that remain devoid of fluids (Glodny et al, 2003(Glodny et al, , 2008. Without fluids, isotopic resetting is kinetically locked or restricted to sluggish intermineral diffusion.…”

Section: Introductionmentioning

confidence: 99%

A stable (Li, O) and radiogenic (Sr, Nd) isotope perspective on metasomatic processes in a subducting slab

et al. 2011

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Two distinct types of eclogites from the Raspas Complex (Ecuador), which can be distinguished based on petrography and trace element geochemistry, were analyzed for their stable (Li, O) and radiogenic (Sr, Nd) isotope signature to constrain metasomatic changes due to fluid-overprinting in metabasaltic rocks at high-pressure conditions and to identify fluid sources. MORB-type eclogites are characterized by a relative LREE depletion similar to MORB. High-pressure (HP) minerals from this type of eclogite have highly variable oxygen isotope compositions (garnet: +4.1 to +9.

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“…Synthetic clinopyroxene can contain a significant amount of Sr in M2 site (e.g., Najorka et al, 1999), and hence omphacite may have stored some amount of Sr under the eclogite -facies conditions. Natural omphacite in eclogitic rocks from various orogenic belts contains some 10 -to 200 -ppm Sr (e.g., Thöni and Jagoutz, 1992;Messiga et al, 1995; ;Schärer and Labrousse, 2003;Glodny et al, 2008). The data compiled here, however, indicated that most of omphacite grains show Sr contents less than 100 ppm (Fig.…”

Section: Discussionmentioning

confidence: 57%

“…Apatite is also an important container of Sr and contains up to ∼ 7000 -ppm Sr (Fig. 7) (Glodny et al, 2002(Glodny et al, , 2003Schärer and Labrousse, 2003;Meffan -Main et al, 2004;Glodny et al, 2008). Apatite is rare, but present in the sample studied here.…”

Section: Discussionmentioning

confidence: 86%

“…This study underscores the need for careful petrographic analysis prior to use of geochemical data in interpretation of subduction -zone cycling. Compiled data for Sr and Rb contents of omphacite and apatite in eclogitic rocks (Thöni and Jagoutz, 1992;Glodny et al, 2002Glodny et al, , 2003Schärer and Labrousse, 2003;Meffan -Main et al, 2004;Glodny et al, 2008).…”

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Sr-sulphate and associated minerals found from kyanite-bearing eclogite in the Moldanubian Zone of the Bohemian Massif, Czech Republic

Nakamura

Kobayashi

Shimobayashi

et al. 2010

Journal of Mineralogical and Petrological Sciences

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Sr -sulphate, celestine, was newly found in a kyanite -bearing eclogite associated with the Nové Dvory peridotite mass in the Moldanubian Zone of the Bohemian Massif, Czech Republic. Celestine is closely associated with anhydrite, pyrite, pyrrhotite and chalcopyrite, and those minerals occur in the matrix, where fine -grained omphacite aggregate and kelyphites after garnet develop. A common Sr reservoir in eclogite is known to be epidote, but the maximum pressure -temperature (P -T) conditions of the studied eclogite was estimated as about 1050 -1150 °C, 4.5 -4.9 GPa. In such extremely high P -T conditions, epidote should be unstable. In fact, epidote is absent from most of eclogites in the Moldanubian Zone of Czech Republic. These facts suggest that a Sr -reservoir after the epidote -breakdown in subducting eclogite might be celestine, or its high -P polymorph, although the formation stage of celestine in the study sample and maximum stability limits of celestine are not known. Another idea is that celestine in the study sample was formed at relatively shallow levels after the ascent of the eclogite. In this case, omphacite and apatite would have contained significant amount of Sr under the eclogitefacies conditions. Otherwise, metasomatic infiltration of Sr -rich fluids into the eclogite is necessary for the formation of celestine in order to provide sufficient amount of Sr. A Ba -rich alumino -silicate, probably celsian, was also found as a retrograde product around pyrrhotite in kelyphite and in symplectites mainly composed of augite and plagioclase after omphacite. Several grains of biotite are also present along the margin of garnet and in the symplectites after omphacite. In addition, small amounts of muscovite and amphibole are present in the symplectites after omphacite. These findings suggest that metasomatism with Sr -and Ba -rich fluids may have occurred during decompression of the eclogite and may not be indicative of the UHP history of these rocks.

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Diffusion versus recrystallization processes in Rb–Sr geochronology: Isotopic relics in eclogite facies rocks, Western Gneiss Region, Norway

Cited by 107 publications

References 81 publications

Disequilibrium textures versus equilibrium modelling: geochronology at the crossroads

Disequilibrium textures versus equilibrium modelling: geochronology at the crossroads

A stable (Li, O) and radiogenic (Sr, Nd) isotope perspective on metasomatic processes in a subducting slab

Sr-sulphate and associated minerals found from kyanite-bearing eclogite in the Moldanubian Zone of the Bohemian Massif, Czech Republic

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