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Article: Probing the basement of southern Tibet: Evidence from crustal xenoliths entrained in a Miocene ultrapotassic dyke

TitleProbing the basement of southern Tibet: Evidence from crustal xenoliths entrained in a Miocene ultrapotassic dyke
Authors
Issue Date2009
PublisherGeological Society Publishing House. The Journal's web site is located at http://www.geolsoc.org.uk/gsl/publications/journals/jgs
Citation
Journal Of The Geological Society, 2009, v. 166 n. 1, p. 45-52 How to Cite?
AbstractA variety of felsic and mafic granulites and ultramafic rocks occur as xenoliths within a 12.7 Ma ultrapotassic dyke intruding Xigaze flysch immediately to the north of the Yarlung-Tsangpo suture zone in southern Tibet. Garnet-clinopyroxene-plagioclase-quartz thermobarometry on mafic granulite xenoliths gives temperatures of 1130-1330 °C and pressures between 22 and 26 kbar indicating equilibration in the high-pressure and ultrahigh-temperature granulite field and defining a geotherm of c. 16 °C km -1. Ultramafic xenoliths consist mainly of hornblende and biotite, probably of restitic crustal rather than mantle origin, and attained peak metamorphic conditions of 920-1130 °C and 17-24 kbar, whereas felsic granulites equilibrated at 870-900 °C at an inferred pressure of 17 kbar. In situ U-(Th)-Pb laser ablation inductively coupled plasma mass spectrometry dating of zircons shows that protoliths may include Proterozoic basement rocks, Late Cretaceous calc-alkaline tonalites of the Gangdese batholith root and/or remnants of a Neo-Tethyan oceanic arc. Certain zircons from a felsic granulite and an ultramafic xenolith have mean 206Pb/ 238U ages of 16.8 ± 0.9 Ma and 15.6 ± 0.6 Ma, respectively, and monazites from a micaceous xenolith yielded a mean 208Pb/ 232Th age of 14.4 ± 0.4 Ma. These results show that the southern Tibet basement reached a thickness of c. 80 km by 17-14 Ma at the latest and has remained unchanged until the present day. © 2009 Geological Society of London.
Persistent Identifierhttp://hdl.handle.net/10722/58661
ISSN
2015 Impact Factor: 2.473
2015 SCImago Journal Rankings: 1.449
ISI Accession Number ID
Funding AgencyGrant Number
Croucher Foundation Scholarship
HKU CRCG
Research Grants Council of the Hong Kong Special Administrative Region, ChinaFIKU 7001/04P
NERC20427
Funding Information:

We thank V Pashley, N. Charnley and P. Jackson for sample preparation and analysis. G.H.-N.C. has been funded by a Croucher Foundation Scholarship. This work was supported by HKU CRCG and the Research Grants Council of the Hong Kong Special Administrative Region, China (FIKU 7001/04P) to J. Aitchison. Isotope work at NIGL was Funded by NERC (NIGFSC project 20427). The earliest version of the manuscript benefited from the comments of S. Harley, B. Hacker and L. Ratschbacher. T. Argles and an anonymous reviewer are thanked for their insightful comments.

References

 

DC FieldValueLanguage
dc.contributor.authorChan, GHNen_HK
dc.contributor.authorWaters, DJen_HK
dc.contributor.authorSearle, MPen_HK
dc.contributor.authorAitchison, JCen_HK
dc.contributor.authorHorstwood, MSAen_HK
dc.contributor.authorCrowley, Qen_HK
dc.contributor.authorLo, CHen_HK
dc.contributor.authorChan, JSLen_HK
dc.date.accessioned2010-05-31T03:34:35Z-
dc.date.available2010-05-31T03:34:35Z-
dc.date.issued2009en_HK
dc.identifier.citationJournal Of The Geological Society, 2009, v. 166 n. 1, p. 45-52en_HK
dc.identifier.issn0016-7649en_HK
dc.identifier.urihttp://hdl.handle.net/10722/58661-
dc.description.abstractA variety of felsic and mafic granulites and ultramafic rocks occur as xenoliths within a 12.7 Ma ultrapotassic dyke intruding Xigaze flysch immediately to the north of the Yarlung-Tsangpo suture zone in southern Tibet. Garnet-clinopyroxene-plagioclase-quartz thermobarometry on mafic granulite xenoliths gives temperatures of 1130-1330 °C and pressures between 22 and 26 kbar indicating equilibration in the high-pressure and ultrahigh-temperature granulite field and defining a geotherm of c. 16 °C km -1. Ultramafic xenoliths consist mainly of hornblende and biotite, probably of restitic crustal rather than mantle origin, and attained peak metamorphic conditions of 920-1130 °C and 17-24 kbar, whereas felsic granulites equilibrated at 870-900 °C at an inferred pressure of 17 kbar. In situ U-(Th)-Pb laser ablation inductively coupled plasma mass spectrometry dating of zircons shows that protoliths may include Proterozoic basement rocks, Late Cretaceous calc-alkaline tonalites of the Gangdese batholith root and/or remnants of a Neo-Tethyan oceanic arc. Certain zircons from a felsic granulite and an ultramafic xenolith have mean 206Pb/ 238U ages of 16.8 ± 0.9 Ma and 15.6 ± 0.6 Ma, respectively, and monazites from a micaceous xenolith yielded a mean 208Pb/ 232Th age of 14.4 ± 0.4 Ma. These results show that the southern Tibet basement reached a thickness of c. 80 km by 17-14 Ma at the latest and has remained unchanged until the present day. © 2009 Geological Society of London.en_HK
dc.languageengen_HK
dc.publisherGeological Society Publishing House. The Journal's web site is located at http://www.geolsoc.org.uk/gsl/publications/journals/jgsen_HK
dc.relation.ispartofJournal of the Geological Societyen_HK
dc.titleProbing the basement of southern Tibet: Evidence from crustal xenoliths entrained in a Miocene ultrapotassic dykeen_HK
dc.typeArticleen_HK
dc.identifier.emailAitchison, JC: jona@hku.hken_HK
dc.identifier.authorityAitchison, JC=rp00658en_HK
dc.description.naturelink_to_subscribed_fulltext-
dc.identifier.doi10.1144/0016-76492007-145en_HK
dc.identifier.scopuseid_2-s2.0-69249185378en_HK
dc.identifier.hkuros162131en_HK
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-69249185378&selection=ref&src=s&origin=recordpageen_HK
dc.identifier.volume166en_HK
dc.identifier.issue1en_HK
dc.identifier.spage45en_HK
dc.identifier.epage52en_HK
dc.identifier.isiWOS:000262572600006-
dc.publisher.placeUnited Kingdomen_HK
dc.identifier.scopusauthoridChan, GHN=20733736600en_HK
dc.identifier.scopusauthoridWaters, DJ=7201385334en_HK
dc.identifier.scopusauthoridSearle, MP=7101792510en_HK
dc.identifier.scopusauthoridAitchison, JC=7102533858en_HK
dc.identifier.scopusauthoridHorstwood, MSA=35801083300en_HK
dc.identifier.scopusauthoridCrowley, Q=6507350759en_HK
dc.identifier.scopusauthoridLo, CH=35078881900en_HK
dc.identifier.scopusauthoridChan, JSL=47361050600en_HK

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