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Geochemistry of ultrahigh-pressure anatexis: fractionation of elements in the Kokchetav gneisses during melting at diamond-facies conditions

Stepanov, Aleksandr; Hermann, Joerg; Korsakov, Andrey V; Rubatto, Daniela

Description

The Kokchetav complex in Kazakhstan contains garnet-bearing gneisses that formed by partial melting of metasedimentary rocks at ultrahigh-pressure (UHP) conditions. Partial melting and melt extraction from these rocks is documented by a decrease in K2O and an increase in FeO + MgO in the restites. The most characteristic trace element feature of the Kokchetav UHP restites is a strong depletion in light rare earth elements (LREE), Th and U. This is attributed to complete dissolution of...[Show more]

dc.contributor.authorStepanov, Aleksandr
dc.contributor.authorHermann, Joerg
dc.contributor.authorKorsakov, Andrey V
dc.contributor.authorRubatto, Daniela
dc.date.accessioned2015-12-13T22:16:25Z
dc.identifier.issn0010-7999
dc.identifier.urihttp://hdl.handle.net/1885/70850
dc.description.abstractThe Kokchetav complex in Kazakhstan contains garnet-bearing gneisses that formed by partial melting of metasedimentary rocks at ultrahigh-pressure (UHP) conditions. Partial melting and melt extraction from these rocks is documented by a decrease in K2O and an increase in FeO + MgO in the restites. The most characteristic trace element feature of the Kokchetav UHP restites is a strong depletion in light rare earth elements (LREE), Th and U. This is attributed to complete dissolution of monazite/allanite in the melt and variable degree of melt extraction. In contrast, Zr concentrations remain approximately constant in all gneisses. Using experimentally determined solubilities of LREE and Zr in high-pressure melts, these data constrain the temperature of melting to ~1,000 °C. Large ion lithophile elements (LILE) are only moderately depleted in the samples that have the lowest U, Th and LREE contents, indicating that phengite retains some LILE in the residue. Some restites display an increase in Nb/Ta with respect to the protolith. This further suggests the presence of phengite, which, in contrast to rutile, preferentially incorporates Nb over Ta. The trace element fractionation observed during UHP anatexis in the Kokchetav gneisses is significantly different from depletions reported in low-pressure restites, where generally no LREE and Th depletion occurs. Melting at UHP conditions resulted in an increase in the Sm/Nd ratio and a decoupling of the Sm-Nd and Lu-Hf systems in the restite. Further subduction of such restites and mixing with mantle rocks might thus lead to a distinct isotopic reservoir different from the bulk continental crust.
dc.publisherSpringer
dc.sourceContributions to Mineralogy and Petrology
dc.titleGeochemistry of ultrahigh-pressure anatexis: fractionation of elements in the Kokchetav gneisses during melting at diamond-facies conditions
dc.typeJournal article
local.description.notesImported from ARIES
local.identifier.citationvolume167
dc.date.issued2014
local.identifier.absfor040304 - Igneous and Metamorphic Petrology
local.identifier.ariespublicationU3488905xPUB2442
local.type.statusPublished Version
local.contributor.affiliationStepanov, Aleksandr, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationHermann, Joerg, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationKorsakov, Andrey V, Russian Academy of Sciences
local.contributor.affiliationRubatto, Daniela, College of Physical and Mathematical Sciences, ANU
local.description.embargo2037-12-31
local.bibliographicCitation.issue5
local.bibliographicCitation.startpage1
local.bibliographicCitation.lastpage25
local.identifier.doi10.1007/s00410-014-1002-x
local.identifier.absseo970104 - Expanding Knowledge in the Earth Sciences
dc.date.updated2015-12-11T07:26:01Z
local.identifier.scopusID2-s2.0-84901596312
local.identifier.thomsonID000336600400002
CollectionsANU Research Publications

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