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High-precision high field strength element partitioning between garnet, amphibole and alkaline melt from Kakanui, New Zealand

Fulmer, Eric; Nebel, Oliver; van Westrenen, Wim

Description

The high field strength elements (HFSE: Zr, Hf, Nb, Ta, and W) are an important group of chemical tracers that are increasingly used to investigate magmatic differentiation processes. Successful modeling of these processes requires the availability of accurate mineral-melt partition coefficients (D). To date, these have largely been determined by ion microprobe or laser ablation-ICP-MS analyses of the run products of high-pressure, high-temperature experiments. Since HFSE are (highly)...[Show more]

dc.contributor.authorFulmer, Eric
dc.contributor.authorNebel, Oliver
dc.contributor.authorvan Westrenen, Wim
dc.date.accessioned2015-12-10T22:35:46Z
dc.identifier.issn1872-9533
dc.identifier.urihttp://hdl.handle.net/1885/56409
dc.description.abstractThe high field strength elements (HFSE: Zr, Hf, Nb, Ta, and W) are an important group of chemical tracers that are increasingly used to investigate magmatic differentiation processes. Successful modeling of these processes requires the availability of accurate mineral-melt partition coefficients (D). To date, these have largely been determined by ion microprobe or laser ablation-ICP-MS analyses of the run products of high-pressure, high-temperature experiments. Since HFSE are (highly) incompatible, relatively immobile, high-charge, and difficult to ionize, these experiments and their analysis are challenging. Here we explore whether high-precision analyses of natural mineral-melt systems can provide additional constraints on HFSE partitioning.The HFSE concentrations in natural garnet and amphibole and their alkaline host melt from Kakanui, New Zealand are determined with high precision isotope dilution on a multi-collector-ICP-MS. Major and trace element compositions combined with Lu-Hf isotopic systematics and detailed petrographic sample analysis are used to assess mineral-melt equilibrium and to provide context for the HFSE D measurements. The whole-rock nephelinite, ∼1mm sized amphiboles in the nephelinite, and garnet megacrysts have similar initial Hf isotope ratios with a mean initial 176Hf/177Hf(34 Ma)=0.282900±0.000026 (2σ). In contrast, the amphibole megacrysts are isotopically distinct (176Hf/177Hf(34 Ma)=0.282830±0.000011). Rare earth element D values for garnet megacryst-nephelinite melt and ∼1mm amphibole-nephelinite melt plotted as a function of ionic radii show classic near-parabolic trends that are in excellent agreement with crystal lattice-strain models. These observations are consistent with equilibrium between the whole-rock nephelinite, the ∼1mm amphibole grains within the nephelinite and the garnet megacrysts.High-precision isotope dilution results for Zr and Hf in garnet (DZr=0.220±0.007 and DHf=0.216±0.005 [2σ]), and for all HFSE in amphibole are consistent with previous experimental findings. However, our measurements for Nb and Ta in garnet (DNb=0.0007±0.0001 and DTa=0.0011±0.0006 [2σ]) show that conventional methods may overestimate Nb and Ta concentrations, thereby overestimating both Nb and Ta absolute D values for garnet by up to 3 orders of magnitude and underestimating DNb/DTa by greater than a factor of 100. As a consequence, the role of residual garnet in imposing Nb/Ta fractionation may be less important than previously thought. Moreover, garnet DHf/DW=17 and DNb/DZr=0.003 imply fractionation of Hf from W and Nb from Zr upon garnet crystallization, which may have influenced short-lived 182Hf-182W and 92Nb-92Zr isotopic systems in Hadean time.
dc.publisherPergamon-Elsevier Ltd
dc.sourceGeochimica et Cosmochimica Acta
dc.subjectKeywords: amphibole; crystallization; experimental mineralogy; garnet; high pressure; high temperature; ion microprobe; isotopic composition; isotopic ratio; lattice dynamics; partition coefficient; partitioning; rare earth element; trace element; Kakanui; New Zeal
dc.titleHigh-precision high field strength element partitioning between garnet, amphibole and alkaline melt from Kakanui, New Zealand
dc.typeJournal article
local.description.notesImported from ARIES
local.identifier.citationvolume74
dc.date.issued2010
local.identifier.absfor040203 - Isotope Geochemistry
local.identifier.absfor040304 - Igneous and Metamorphic Petrology
local.identifier.ariespublicationu9503261xPUB361
local.type.statusPublished Version
local.contributor.affiliationFulmer, Eric, VU University Amsterdam
local.contributor.affiliationNebel, Oliver, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationvan Westrenen, Wim, VU University Amsterdam
local.description.embargo2037-12-31
local.bibliographicCitation.startpage2741
local.bibliographicCitation.lastpage2759
local.identifier.doi10.1016/j.gca.2010.02.020
local.identifier.absseo970104 - Expanding Knowledge in the Earth Sciences
dc.date.updated2016-02-24T12:02:20Z
local.identifier.scopusID2-s2.0-77950516625
CollectionsANU Research Publications

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