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Article: Differentiation, crustal contamination and emplacement of magmas in the formation of the Nantianwan mafic intrusion of the ~260 Ma Emeishan large igneous province, SW China

TitleDifferentiation, crustal contamination and emplacement of magmas in the formation of the Nantianwan mafic intrusion of the ~260 Ma Emeishan large igneous province, SW China
Authors
KeywordsEmeishan Large Igneous Province
Magma Chamber Process
Nantianwan Intrusion
Platinum-Group Elements
Sr-Nd And Re-Os Isotopes
Issue Date2012
PublisherSpringer Verlag. The Journal's web site is located at http://link.springer.de/link/service/journals/00410/index.htm
Citation
Contributions To Mineralogy And Petrology, 2012, p. 1-21 How to Cite?
AbstractThe Nantianwan mafic intrusion in the Panxi region, SW China, part of the ~260 Ma Emeishan large igneous province, consists of the olivine gabbro and gabbronorite units, separated by a transitional zone. Olivine gabbros contain olivine with Fo values ranging from 83 to 87, indicating crystallization from a moderately evolved magma. They have 0.2 to 0.9 wt % sulfide with highly variable PGE (17-151 ppb) and variable Cu/Pd ratios (1,500-32,500). Modeling results indicate that they were derived from picritic magmas with high initial PGE concentrations. Olivine gabbros have negative εNd(t) values (-1.3 to -0.1) and positive γOs(t) values (5-15), consistent with low degrees of crustal contamination. Gabbronorites include sulfide-bearing and sulfide-poor varieties, and both have olivine with Fo values ranging from 74 to 79, indicating crystallization from a more evolved magma than that for olivine gabbros. Sulfide-bearing gabbronorites contain 1.9-4.1 wt % sulfide and 37-160 ppb PGE and high Cu/Pd ratios (54,000-624,000). Sulfide-poor gabbronorites have 0.1-0.6 wt % sulfide and 0.2-15 ppb PGE and very high Cu/Pd ratios (16,900-2,370,000). Both sulfide-bearing and sulfide-poor gabbronorites have εNd(t) values (-0.9 to -2.1) similar to those for olivine gabbros, but their γOs(t) values (17-262) are much higher and more variable than those of the olivine gabbros. Selective assimilation of crustal sulfides from the country rocks is thus considered to have resulted in more radiogenic 187Os of the gabbronorites. Processes such as magma differentiation, crustal contamination and sulfide saturation at different stages in magma chambers may have intervened during formation of the intrusion. Parental magmas were derived from picritic magmas that had fractionated olivine under S-undersaturated conditions before entering a deep-seated staging magma chamber, where the parental magmas crystallized olivine, assimilated minor crustal rocks and reached sulfide saturation, forming an olivine- and sulfide-laden crystal mush in the lower part and evolved magmas in the upper part of the chamber. The evolved magmas were forced out of the staging chamber and became S-undersaturated due to a pressure drop during ascent to a shallow magma chamber. The magmas re-attained sulfide saturation by assimilating external S from S-rich country rocks. They may have entered the shallow magma chamber as several pulses so that several gabbronorite layers each with sulfide segregated to the base and a sulfide-poor upper part. The olivine gabbro unit formed from a new and more primitive magma that entrained olivine crystals and sulfide droplets from the lower part of the staging chamber. A transitional zone formed along the boundary with the gabbronorite unit due to chemical interaction between the two rock units. © 2012 Springer-Verlag.
Persistent Identifierhttp://hdl.handle.net/10722/151367
ISSN
2015 Impact Factor: 3.218
2015 SCImago Journal Rankings: 2.582
ISI Accession Number ID

 

DC FieldValueLanguage
dc.contributor.authorWang, CYen_US
dc.contributor.authorZhou, MFen_US
dc.contributor.authorSun, Yen_US
dc.contributor.authorArndt, NTen_US
dc.date.accessioned2012-06-26T06:21:13Z-
dc.date.available2012-06-26T06:21:13Z-
dc.date.issued2012en_US
dc.identifier.citationContributions To Mineralogy And Petrology, 2012, p. 1-21en_US
dc.identifier.issn0010-7999en_US
dc.identifier.urihttp://hdl.handle.net/10722/151367-
dc.description.abstractThe Nantianwan mafic intrusion in the Panxi region, SW China, part of the ~260 Ma Emeishan large igneous province, consists of the olivine gabbro and gabbronorite units, separated by a transitional zone. Olivine gabbros contain olivine with Fo values ranging from 83 to 87, indicating crystallization from a moderately evolved magma. They have 0.2 to 0.9 wt % sulfide with highly variable PGE (17-151 ppb) and variable Cu/Pd ratios (1,500-32,500). Modeling results indicate that they were derived from picritic magmas with high initial PGE concentrations. Olivine gabbros have negative εNd(t) values (-1.3 to -0.1) and positive γOs(t) values (5-15), consistent with low degrees of crustal contamination. Gabbronorites include sulfide-bearing and sulfide-poor varieties, and both have olivine with Fo values ranging from 74 to 79, indicating crystallization from a more evolved magma than that for olivine gabbros. Sulfide-bearing gabbronorites contain 1.9-4.1 wt % sulfide and 37-160 ppb PGE and high Cu/Pd ratios (54,000-624,000). Sulfide-poor gabbronorites have 0.1-0.6 wt % sulfide and 0.2-15 ppb PGE and very high Cu/Pd ratios (16,900-2,370,000). Both sulfide-bearing and sulfide-poor gabbronorites have εNd(t) values (-0.9 to -2.1) similar to those for olivine gabbros, but their γOs(t) values (17-262) are much higher and more variable than those of the olivine gabbros. Selective assimilation of crustal sulfides from the country rocks is thus considered to have resulted in more radiogenic 187Os of the gabbronorites. Processes such as magma differentiation, crustal contamination and sulfide saturation at different stages in magma chambers may have intervened during formation of the intrusion. Parental magmas were derived from picritic magmas that had fractionated olivine under S-undersaturated conditions before entering a deep-seated staging magma chamber, where the parental magmas crystallized olivine, assimilated minor crustal rocks and reached sulfide saturation, forming an olivine- and sulfide-laden crystal mush in the lower part and evolved magmas in the upper part of the chamber. The evolved magmas were forced out of the staging chamber and became S-undersaturated due to a pressure drop during ascent to a shallow magma chamber. The magmas re-attained sulfide saturation by assimilating external S from S-rich country rocks. They may have entered the shallow magma chamber as several pulses so that several gabbronorite layers each with sulfide segregated to the base and a sulfide-poor upper part. The olivine gabbro unit formed from a new and more primitive magma that entrained olivine crystals and sulfide droplets from the lower part of the staging chamber. A transitional zone formed along the boundary with the gabbronorite unit due to chemical interaction between the two rock units. © 2012 Springer-Verlag.en_US
dc.languageengen_US
dc.publisherSpringer Verlag. The Journal's web site is located at http://link.springer.de/link/service/journals/00410/index.htmen_US
dc.relation.ispartofContributions to Mineralogy and Petrologyen_US
dc.subjectEmeishan Large Igneous Provinceen_US
dc.subjectMagma Chamber Processen_US
dc.subjectNantianwan Intrusionen_US
dc.subjectPlatinum-Group Elementsen_US
dc.subjectSr-Nd And Re-Os Isotopesen_US
dc.titleDifferentiation, crustal contamination and emplacement of magmas in the formation of the Nantianwan mafic intrusion of the ~260 Ma Emeishan large igneous province, SW Chinaen_US
dc.typeArticleen_US
dc.identifier.emailZhou, MF:mfzhou@hkucc.hku.hken_US
dc.identifier.authorityZhou, MF=rp00844en_US
dc.description.naturelink_to_subscribed_fulltexten_US
dc.identifier.doi10.1007/s00410-012-0738-4en_US
dc.identifier.scopuseid_2-s2.0-84864357977en_US
dc.identifier.spage1en_US
dc.identifier.epage21en_US
dc.identifier.isiWOS:000306421600006-
dc.publisher.placeGermanyen_US
dc.identifier.scopusauthoridWang, CY=55148386700en_US
dc.identifier.scopusauthoridZhou, MF=7403506005en_US
dc.identifier.scopusauthoridSun, Y=55148645100en_US
dc.identifier.scopusauthoridArndt, NT=7004860212en_US
dc.identifier.citeulike10544479-

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