Phase relations and melting of nominally ‘dry’ residual eclogites with variable CaO/Na₂O from 3 to 5 GPa and 1250 to 1500 °C; implications for refertilisation of upwelling heterogeneous mantle

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dc.contributor.authorRosenthal, A.
dc.contributor.authorYaxley, G.M.
dc.contributor.authorCrichton, W.A.
dc.contributor.authorKovács, I.J.
dc.contributor.authorSpandler, C.
dc.contributor.authorHermann, J.
dc.contributor.authorSándorné, J.K.
dc.contributor.authorRose-Koga, E.
dc.contributor.authorPelleter, A.A.
dc.date.issued2018
dc.description.abstractThis study investigates the phase and melting relations of nominally ‘dry’ residual eclogites (Res2 and Res3), with varying bulk CaO/Na2O ratios (4 and 12, respectively), from ~160 (5 GPa) to ~90 km (3 GPa) depth. Garnet, clinopyroxene and minor quartz/coesite are subsolidus phases in both compositions. In contrast to Res2, in Res3, the proportions of garnet always exceeding those of clinopyroxene. This also leads to higher modal quartz/coesite in Res3 relative to Res2. In modelling melting along a near-adiabatic upwelling path with a mantle potential temperature of ~1360 °C, at 5 GPa, near-solidus andesitic Res3 partial melts are much less siliceous and sodic, and are more calcic and magnesian than the incipient dacitic melts of Res2. Continuously self-fluxed melting increases considerably from 4 to 3 GPa due to the increased breakdown of Ca-Eskolaite solid solution component in clinopyroxene along the adiabat. This causes a steepening of the solidus, but more-so for Res2 than for Res3. At 3 GPa, the near exhaustion of residual clinopyroxene causes higher melt productivity for Res3 (~60%) than for Res2 (~30%), despite both melts being of basaltic-andesite composition. Resulting Res3 melts are therefore significantly more calcic and magnesian, and less sodic than those of Res2 melts. As Res3 undergoes a higher degree of melting relative to Res2 during adiabatic ascent, Res3 eclogitic residues become significantly more refractory; with relatively higher Mg# and grossular in garnet, higher Mg# and Ca-tschermaks, and lower jadeite components of clinopyroxene, and higher garnet/clinopyroxene ratios than eclogitic Res2 residuals. In upwelling heterogenous mantle domains, the siliceous eclogitic melts formed within a body of eclogite will react with encapsulating mantle peridotite, effectively refertilising it and producing hybrid pyroxene- and garnet-rich rocks. Subsequent melting of these sources may lead to compositionaly diverse primitive mantle-derived magmas, with high Ca/Al and low Na/Ca signatures indicators of preferential melting of a heterogeneous mantle, previously refertilised by recycled Ca-rich oceanic crustal material, and primitive magmas with low Ca/Al and high Na/Ca derived from melting of mantle with a ‘normal recycled crustal material signature’. Thus, compositional magma diversity may directly reflect precursor compositions of the mantle source region.
dc.description.statementofresponsibilityAnja Rosenthal, Gregory M. Yaxley, Wilson A. Crichton, István J. Kovács, Carl Spandler, Joerg Hermann, Judit K. Sándorné, Estelle Rose-Koga, Anne-Aziliz Pelleter
dc.identifier.citationLithos, 2018; 314-315:506-519
dc.identifier.doi10.1016/j.lithos.2018.05.025
dc.identifier.issn0024-4937
dc.identifier.issn1872-6143
dc.identifier.orcidSpandler, C. [0000-0003-2310-0517]
dc.identifier.urihttp://hdl.handle.net/2440/126105
dc.language.isoen
dc.publisherElsevier
dc.relation.granthttp://purl.org/au-research/grants/arc/DP0558189
dc.rights© 2018 Elsevier B.V. All rights reserved.
dc.source.urihttps://doi.org/10.1016/j.lithos.2018.05.025
dc.subjectExperimental petrology; residual eclogites; phase relations; heterogeneous mantle melting; petrogenesis of primitive mantle-derived magmas
dc.titlePhase relations and melting of nominally ‘dry’ residual eclogites with variable CaO/Na₂O from 3 to 5 GPa and 1250 to 1500 °C; implications for refertilisation of upwelling heterogeneous mantle
dc.title.alternativePhase relations and melting of nominally ‘dry’ residual eclogites with variable CaO/Na(2)O from 3 to 5 GPa and 1250 to 1500 °C; implications for refertilisation of upwelling heterogeneous mantle
dc.typeJournal article
pubs.publication-statusPublished

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