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Article: Podiform chromitites in the Luobusa ophiolite (Southern Tibet): Implications for melt-rock interaction and chromite segregation in the upper mantle

TitlePodiform chromitites in the Luobusa ophiolite (Southern Tibet): Implications for melt-rock interaction and chromite segregation in the upper mantle
Authors
KeywordsBoninitic magmas
Dunite envelopes
Melt-rock interaction
Morb peridotites
Podiform chromitites
Issue Date1996
PublisherOxford University Press. The Journal's web site is located at http://petrology.oxfordjournals.org/
Citation
Journal Of Petrology, 1996, v. 37 n. 1, p. 3-21 How to Cite?
AbstractThe Luobusa ophiolite in the Indus-Yarlung Zangbo suture of southern Tibet hosts the largest known chromite deposit in China. The podiform chromitites occur in a well-preserved mantle sequence consisting of harzburgite with abundant lenses of dunite. The harzburgites have relatively uniform bulk-rock compositions with mg-numbers [100Mg/(Mg + Fe)] ranging from 89 to 91 and show flat, unfractionated, chonarite-normalised platinum group element (PGE) patterns. Their accessory chromite varies widely in cr-number [100Cr/(Cr +Al)] (18-66). These rocks are essentially residua left after extraction of mid-ocean ridge basalt (MORB)-type magmas. The podiform chromitites display nodular, massive, disseminated and banded textures and typically have dunite envelopes that grade into the surrounding harzburgite and diopsidic harzburgite with increasing pyroxene contents. They consist of relatively uniform chromite with high cr-numbers (74-82), have strongly fractionated, chondrite-normalized PGE patterns with enrichment in Os, Ir and Ru relative to Rh, Pt and Pt, and are believed to have formed from a boninitic magma produced by a second stage of melting. Dunites contain accessory chromite intermediate in composition between those of harzburgite and chromitite and are believed to be the products of reaction between new boninitic magmas and old MORB-type peridotites. The melt-rock reaction removed pyroxene from the peridotites and precipitated olimne, forming dunite envelopes around the chromitite pods. The melts thus became more boninitic in composition and chromite saturated, leading to precipitation of chromite alone. The interplay of melt-rock interaction, chromite fractionation and magma mixing should lead to many fluctuations in melt composition, producing both massive and disseminated chromitites and phase layering within individual podiform bodies observed in the Luobusa ophiolite.
Persistent Identifierhttp://hdl.handle.net/10722/150983
ISSN
2015 Impact Factor: 3.768
2015 SCImago Journal Rankings: 2.992
References

 

DC FieldValueLanguage
dc.contributor.authorZhou, MFen_HK
dc.contributor.authorRobinson, PTen_HK
dc.contributor.authorMalpas, Jen_HK
dc.contributor.authorLi, Zen_HK
dc.date.accessioned2012-06-26T06:15:28Z-
dc.date.available2012-06-26T06:15:28Z-
dc.date.issued1996en_HK
dc.identifier.citationJournal Of Petrology, 1996, v. 37 n. 1, p. 3-21en_HK
dc.identifier.issn0022-3530en_HK
dc.identifier.urihttp://hdl.handle.net/10722/150983-
dc.description.abstractThe Luobusa ophiolite in the Indus-Yarlung Zangbo suture of southern Tibet hosts the largest known chromite deposit in China. The podiform chromitites occur in a well-preserved mantle sequence consisting of harzburgite with abundant lenses of dunite. The harzburgites have relatively uniform bulk-rock compositions with mg-numbers [100Mg/(Mg + Fe)] ranging from 89 to 91 and show flat, unfractionated, chonarite-normalised platinum group element (PGE) patterns. Their accessory chromite varies widely in cr-number [100Cr/(Cr +Al)] (18-66). These rocks are essentially residua left after extraction of mid-ocean ridge basalt (MORB)-type magmas. The podiform chromitites display nodular, massive, disseminated and banded textures and typically have dunite envelopes that grade into the surrounding harzburgite and diopsidic harzburgite with increasing pyroxene contents. They consist of relatively uniform chromite with high cr-numbers (74-82), have strongly fractionated, chondrite-normalized PGE patterns with enrichment in Os, Ir and Ru relative to Rh, Pt and Pt, and are believed to have formed from a boninitic magma produced by a second stage of melting. Dunites contain accessory chromite intermediate in composition between those of harzburgite and chromitite and are believed to be the products of reaction between new boninitic magmas and old MORB-type peridotites. The melt-rock reaction removed pyroxene from the peridotites and precipitated olimne, forming dunite envelopes around the chromitite pods. The melts thus became more boninitic in composition and chromite saturated, leading to precipitation of chromite alone. The interplay of melt-rock interaction, chromite fractionation and magma mixing should lead to many fluctuations in melt composition, producing both massive and disseminated chromitites and phase layering within individual podiform bodies observed in the Luobusa ophiolite.en_HK
dc.languageengen_US
dc.publisherOxford University Press. The Journal's web site is located at http://petrology.oxfordjournals.org/en_HK
dc.relation.ispartofJournal of Petrologyen_HK
dc.rightsJournal of Petrology. Copyright © Oxford University Press.-
dc.subjectBoninitic magmasen_HK
dc.subjectDunite envelopesen_HK
dc.subjectMelt-rock interactionen_HK
dc.subjectMorb peridotitesen_HK
dc.subjectPodiform chromititesen_HK
dc.titlePodiform chromitites in the Luobusa ophiolite (Southern Tibet): Implications for melt-rock interaction and chromite segregation in the upper mantleen_HK
dc.typeArticleen_HK
dc.identifier.emailZhou, MF: mfzhou@hkucc.hku.hken_HK
dc.identifier.emailMalpas, J: jgmalpas@hku.hken_HK
dc.identifier.authorityZhou, MF=rp00844en_HK
dc.identifier.authorityMalpas, J=rp00059en_HK
dc.description.naturelink_to_subscribed_fulltexten_US
dc.identifier.scopuseid_2-s2.0-0029769254en_HK
dc.identifier.hkuros23040-
dc.identifier.hkuros13206-
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-0029769254&selection=ref&src=s&origin=recordpageen_HK
dc.identifier.volume37en_HK
dc.identifier.issue1en_HK
dc.identifier.spage3en_HK
dc.identifier.epage21en_HK
dc.publisher.placeUnited Kingdomen_HK
dc.identifier.scopusauthoridZhou, MF=7403506005en_HK
dc.identifier.scopusauthoridRobinson, PT=7403720506en_HK
dc.identifier.scopusauthoridMalpas, J=7006136845en_HK
dc.identifier.scopusauthoridLi, Z=7409080919en_HK
dc.customcontrol.immutablesml 130308-

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