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Article: Petrology and geochemistry of garnet-bearing dioritic prophyry of east Kunlun: Implications for genesis of adakitic rocks

TitlePetrology and geochemistry of garnet-bearing dioritic prophyry of east Kunlun: Implications for genesis of adakitic rocks
Authors
KeywordsAdakitic Rocks
Apatite
Crust-Mantle Transition Zone
East Kunlun
Garnet
High-Pressure Fractionation
Issue Date2010
Citation
Scientia Geologica Sinica, 2010, v. 45 n. 1, p. 122-145 How to Cite?
AbstractThis paper reports a garnet-bearing dioritic porphyry, which was first recognized in east Kunlun, NW China. The rocks formed in the late Triassic and consisted mainly of Ca-rich(CaO >5 wt%), Mn-poor (MnO < 3 wt%) garnet, Al-rich hornblende (> 15.9 wt%), andesitic plagioclase, quartz phenocrysts and matrix. The rock possesses intermediate SiO 2 (61.1 ̃ 62.2 wt%), low MgO(<2.0 wt%), K 2O(<1.3 wt%) and relatively high Al 2O 3(>17 wt%), showing metaluminous to slightly peraluminous characteristics(ACNK = 0.89 ̃ 1.05). On the aspect of trace elements, the rock is enriched in large ion lithosphile elements and light rare element elements and depleted in Nb-Ta-Ti, displaying typical features of subduction-related magma. The extremely low HREE (Yb < 0.8 × 10 -6) and relatively high Sr/Y ratios (̃ 38) indicate garnet was a residual phase, while relatively high Al 2O 3, mostly positive Eu-anomalies suggest accumulation of plagioclase in late stage of magma due to depressed crystallization by high water content. Nd-Sr isotopic composition(ε Nd(t)= -2.33 ̃ 1.38 ; 87Sr/ 86Sr = 0.706 5 ̃ 0.706 7) and reversed zoning of plagioclase imply an important role of magma mixing during the genesis of the rock. Garnet phenocrysts and ilmenite inclusions enclosed in garnet contain relatively low MgO, and hornblende enclosing garnet formed under relatively high pressure(8 ̃ 10 kb), suggesting that these minerals most likely crystallized from a silicic magma probably around the crust-mantle transition zone. Although the rock is very similar to adakites on various aspects, such as Al-rich, HREE-poor and high Sr/Y ratios, its intermediate Sr contents(<260 × 10 -6) and La/Yb ratios(16 ̃ 21) are strikingly lower than those of typical adakites and Archean TTG. Considering high partitioning parameters of Sr and LREE of apatite and the common occurrence in garnet, we propose that crystallization of apatite may effectively scavenge Sr and LREE from melt. This suggests that, even under high water fugacity, substantial crystallization of apatite during early stage of magmatic evolution is able to prevent some arc magmatism from evolving into adakitic rocks.
Persistent Identifierhttp://hdl.handle.net/10722/151306
ISSN
2015 SCImago Journal Rankings: 0.206
References

 

DC FieldValueLanguage
dc.contributor.authorYuan, Cen_US
dc.contributor.authorSun, Men_US
dc.contributor.authorXiao, Wen_US
dc.contributor.authorLiu, Xen_US
dc.contributor.authorLi, Jen_US
dc.contributor.authorLong, Xen_US
dc.contributor.authorYe, Ken_US
dc.date.accessioned2012-06-26T06:20:22Z-
dc.date.available2012-06-26T06:20:22Z-
dc.date.issued2010en_US
dc.identifier.citationScientia Geologica Sinica, 2010, v. 45 n. 1, p. 122-145en_US
dc.identifier.issn0563-5020en_US
dc.identifier.urihttp://hdl.handle.net/10722/151306-
dc.description.abstractThis paper reports a garnet-bearing dioritic porphyry, which was first recognized in east Kunlun, NW China. The rocks formed in the late Triassic and consisted mainly of Ca-rich(CaO >5 wt%), Mn-poor (MnO < 3 wt%) garnet, Al-rich hornblende (> 15.9 wt%), andesitic plagioclase, quartz phenocrysts and matrix. The rock possesses intermediate SiO 2 (61.1 ̃ 62.2 wt%), low MgO(<2.0 wt%), K 2O(<1.3 wt%) and relatively high Al 2O 3(>17 wt%), showing metaluminous to slightly peraluminous characteristics(ACNK = 0.89 ̃ 1.05). On the aspect of trace elements, the rock is enriched in large ion lithosphile elements and light rare element elements and depleted in Nb-Ta-Ti, displaying typical features of subduction-related magma. The extremely low HREE (Yb < 0.8 × 10 -6) and relatively high Sr/Y ratios (̃ 38) indicate garnet was a residual phase, while relatively high Al 2O 3, mostly positive Eu-anomalies suggest accumulation of plagioclase in late stage of magma due to depressed crystallization by high water content. Nd-Sr isotopic composition(ε Nd(t)= -2.33 ̃ 1.38 ; 87Sr/ 86Sr = 0.706 5 ̃ 0.706 7) and reversed zoning of plagioclase imply an important role of magma mixing during the genesis of the rock. Garnet phenocrysts and ilmenite inclusions enclosed in garnet contain relatively low MgO, and hornblende enclosing garnet formed under relatively high pressure(8 ̃ 10 kb), suggesting that these minerals most likely crystallized from a silicic magma probably around the crust-mantle transition zone. Although the rock is very similar to adakites on various aspects, such as Al-rich, HREE-poor and high Sr/Y ratios, its intermediate Sr contents(<260 × 10 -6) and La/Yb ratios(16 ̃ 21) are strikingly lower than those of typical adakites and Archean TTG. Considering high partitioning parameters of Sr and LREE of apatite and the common occurrence in garnet, we propose that crystallization of apatite may effectively scavenge Sr and LREE from melt. This suggests that, even under high water fugacity, substantial crystallization of apatite during early stage of magmatic evolution is able to prevent some arc magmatism from evolving into adakitic rocks.en_US
dc.languageengen_US
dc.relation.ispartofScientia Geologica Sinicaen_US
dc.subjectAdakitic Rocksen_US
dc.subjectApatiteen_US
dc.subjectCrust-Mantle Transition Zoneen_US
dc.subjectEast Kunlunen_US
dc.subjectGarneten_US
dc.subjectHigh-Pressure Fractionationen_US
dc.titlePetrology and geochemistry of garnet-bearing dioritic prophyry of east Kunlun: Implications for genesis of adakitic rocksen_US
dc.typeArticleen_US
dc.identifier.emailSun, M:minsun@hku.hken_US
dc.identifier.authoritySun, M=rp00780en_US
dc.description.naturelink_to_subscribed_fulltexten_US
dc.identifier.scopuseid_2-s2.0-77953978553en_US
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-77953978553&selection=ref&src=s&origin=recordpageen_US
dc.identifier.volume45en_US
dc.identifier.issue1en_US
dc.identifier.spage122en_US
dc.identifier.epage145en_US
dc.publisher.placeChinaen_US
dc.identifier.scopusauthoridYuan, C=35241599200en_US
dc.identifier.scopusauthoridSun, M=25932315800en_US
dc.identifier.scopusauthoridXiao, W=7202456615en_US
dc.identifier.scopusauthoridLiu, X=8890184100en_US
dc.identifier.scopusauthoridLi, J=26643194200en_US
dc.identifier.scopusauthoridLong, X=14012199100en_US
dc.identifier.scopusauthoridYe, K=7102173832en_US

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