The interplay between melting, refertilization and carbonatite metasomatism in off-cratonic lithospheric mantle under Zealandia: An integrated major, trace and platinum group element study

dc.contributor.authorMcCoy-West, Alexander
dc.contributor.authorBennett, Victoria
dc.contributor.authorO'Neill, Hugh
dc.contributor.authorHermann, Joerg
dc.contributor.authorPuchtel, Igor
dc.date.accessioned2015-12-10T23:34:56Z
dc.date.issued2015
dc.date.updated2015-12-10T11:37:23Z
dc.description.abstractIt is widely accepted that stabilization of the continental crust requires the presence of sub-continental lithospheric mantle. However, the degree of melt depletion required to stabilize the lithosphere and whether widespread refertilization is a significant process remain unresolved. Here, major and trace element, including platinum group elements (PGE), characterization of 40 mantle xenoliths from 13 localities is used to constrain the melt depletion, refertilization and metasomatic history of lithospheric mantle underneath the micro-continent Zealandia. Our previously published Re-Os isotopic data for a subset of these xenoliths indicate Phanerozoic to Paleoproterozoic ages and, reinterpreted with the new major and trace element data presented here, demonstrate that a large volume (>2 million km3) of lithospheric mantle with an age of 1·99±0·21Ga is present below the much younger crust of Zealandia. A peritecticmelting model using moderately incompatible trace elements (e.g. Yb) in bulk-rocks demonstrates that these peridotites experienced a significant range of degrees of partial melting, between 3 and 28%. During subsolidus equilibration clinopyroxene gains significant rare earth elements (REE), which then leads to the underestimation of the degree of partial melting by ≤12% in fertile xenoliths. A new approach taking into account the effects of subsolidus reequilibration on clinopyroxene composition effectively removes discrepancies in the calculated degree of melting and provides consistent estimates of between 4 and 29%. The estimated amount of melting is independent of the Re-Os model ages of the samples. The PGE patterns record simple melt depletion histories and the retention of primary base metal sulfides in the majority of the xenoliths. A rapid decrease in Pt/IrN observed at c. 1·0wt % Al<inf>2</inf>O<inf>3</inf> is a direct result of the exhaustion of sulfide in the mantle residue at c. 20-25% partial melting and the inability of Pt to form a stable alloy phase. Major elements preserve evidence for refertilization by a basaltic component that resulted in the formation of secondary clinopyroxene and low-forsterite olivine. The majority of xenoliths show the effects of cryptic metasomatic overprinting, ranging from minor to strong light REE enrichments in bulk-rocks (La/Yb<inf>N</inf>=0·16-15·9). Metasomatism is heterogeneous, with samples varying from those with weak REE enrichment and notable positive Sr and U-Th anomalies and negative Nb-Ta anomalies in clinopyroxene to those that have extremely high concentrations of REE, Th-U and Nb. Chemical compositions are consistent with a carbonatitic component contributing to the metasomatism of the lithosphere under Zealandia. Notably, the intense metasomatism of the samples did not affect the PGE budget of the peridotites as this was controlled by residual sulfides.
dc.identifier.issn0022-3530
dc.identifier.urihttp://hdl.handle.net/1885/69639
dc.publisherOxford University Press
dc.sourceJournal of Petrology
dc.titleThe interplay between melting, refertilization and carbonatite metasomatism in off-cratonic lithospheric mantle under Zealandia: An integrated major, trace and platinum group element study
dc.typeJournal article
local.bibliographicCitation.issue3
local.bibliographicCitation.lastpage604
local.bibliographicCitation.startpage563
local.contributor.affiliationMcCoy-West, Alexander, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationBennett, Victoria, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationO'Neill, Hugh, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationHermann, Joerg, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationPuchtel, Igor, University of Maryland
local.contributor.authoremailu4789982@anu.edu.au
local.contributor.authoruidMcCoy-West, Alexander, u4789982
local.contributor.authoruidBennett, Victoria, u8904005
local.contributor.authoruidO'Neill, Hugh, u8101317
local.contributor.authoruidHermann, Joerg, u9907179
local.description.embargo2037-12-31
local.description.notesImported from ARIES
local.identifier.absfor040200 - GEOCHEMISTRY
local.identifier.ariespublicationa383154xPUB2080
local.identifier.citationvolume56
local.identifier.doi10.1093/petrology/egv011
local.identifier.scopusID2-s2.0-84929737616
local.identifier.uidSubmittedBya383154
local.type.statusPublished Version

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