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Article: Measured and calculated seismic velocities and densities for granulites from xenolith occurrences and adjacent exposed lower crustal sections: A comparative study from the North China craton

TitleMeasured and calculated seismic velocities and densities for granulites from xenolith occurrences and adjacent exposed lower crustal sections: A comparative study from the North China craton
Authors
KeywordsLower crust
Seismic velocity
Xenolith
Issue Date2000
PublisherAmerican Geophysical Union.
Citation
Journal Of Geophysical Research B: Solid Earth, 2000, v. 105 B8, p. 18965-18976 How to Cite?
AbstractGranulites from the Neogene xenolith-bearing Hannuoba alkaline basalt and from the Manjinggou-Wayaokou exposed lower crustal section in the Archean Huai'an terrain, which occurs within and surrounds the Hannuoba basalt, provide a unique opportunity for a comparative study on petrophysical properties and composition of the lower crust represented by these two types of samples. P and S wave velocities and densities of 12 Hannuoba lower crustal xenoliths and one associated spinel lherzolite xenolith as well as nine granulites and granulite-facies metasedimentary rocks from the Archean Huai'an terrain were measured in laboratory at pressures up to 600 MPa and temperatures up to 600°C. Calculations of P and S wave velocities were also made for the same suite of samples based on modal mineralogy and single-crystal velocities whose variations with composition are considered by using microprobe analyses and velocities of end members. The measured and calculated Vp at room temperature and 600 MPa, where the microcrack effect is considered to be almost eliminated, agree within 4% for rocks from the Manjinggou-Wayaokou section and the adjacent Wutai-Jining upper crustal to upper lower crustal section. In contrast, the xenoliths show systematically lower measured Vp by up to 15% relative to calculated velocities, even if decompression-induced products of kelyphite and glass are taken into account. The lower measured velocities for xenoliths are attributed to grain boundary alteration and residual porosity. This implies that although granulite xenoliths provide direct information about lower crustal constitution and chemical composition, they are not faithful samples for studying in situ seismic properties of the lower crust in terms of measured velocities due to alterations during their entrainment to the surface, which changes their physical properties significantly. In this respect, granulites from high-grade terrains are better samples because they are not subjected to significant changes during their slow transport to the surface and because physical properties depend primarily on mineralogy in addition to pressure and temperature. On the other hand, calculated velocities for granulite xenoliths are consistent with velocities for granulites from terrains, suggesting that they can be also used to infer lower crust composition by correlating with results from seismic refraction studies. Copyright 2000 by the American Geophysical Union.
Persistent Identifierhttp://hdl.handle.net/10722/72627
ISSN
2015 Impact Factor: 3.318
2015 SCImago Journal Rankings: 2.310
ISI Accession Number ID
References

 

DC FieldValueLanguage
dc.contributor.authorGao, Sen_HK
dc.contributor.authorKern, Hen_HK
dc.contributor.authorLiu, YSen_HK
dc.contributor.authorJin, SYen_HK
dc.contributor.authorPopp, Ten_HK
dc.contributor.authorJin, ZMen_HK
dc.contributor.authorFeng, JLen_HK
dc.contributor.authorSun, Men_HK
dc.contributor.authorZhao, ZBen_HK
dc.date.accessioned2010-09-06T06:43:36Z-
dc.date.available2010-09-06T06:43:36Z-
dc.date.issued2000en_HK
dc.identifier.citationJournal Of Geophysical Research B: Solid Earth, 2000, v. 105 B8, p. 18965-18976en_HK
dc.identifier.issn0148-0227en_HK
dc.identifier.urihttp://hdl.handle.net/10722/72627-
dc.description.abstractGranulites from the Neogene xenolith-bearing Hannuoba alkaline basalt and from the Manjinggou-Wayaokou exposed lower crustal section in the Archean Huai'an terrain, which occurs within and surrounds the Hannuoba basalt, provide a unique opportunity for a comparative study on petrophysical properties and composition of the lower crust represented by these two types of samples. P and S wave velocities and densities of 12 Hannuoba lower crustal xenoliths and one associated spinel lherzolite xenolith as well as nine granulites and granulite-facies metasedimentary rocks from the Archean Huai'an terrain were measured in laboratory at pressures up to 600 MPa and temperatures up to 600°C. Calculations of P and S wave velocities were also made for the same suite of samples based on modal mineralogy and single-crystal velocities whose variations with composition are considered by using microprobe analyses and velocities of end members. The measured and calculated Vp at room temperature and 600 MPa, where the microcrack effect is considered to be almost eliminated, agree within 4% for rocks from the Manjinggou-Wayaokou section and the adjacent Wutai-Jining upper crustal to upper lower crustal section. In contrast, the xenoliths show systematically lower measured Vp by up to 15% relative to calculated velocities, even if decompression-induced products of kelyphite and glass are taken into account. The lower measured velocities for xenoliths are attributed to grain boundary alteration and residual porosity. This implies that although granulite xenoliths provide direct information about lower crustal constitution and chemical composition, they are not faithful samples for studying in situ seismic properties of the lower crust in terms of measured velocities due to alterations during their entrainment to the surface, which changes their physical properties significantly. In this respect, granulites from high-grade terrains are better samples because they are not subjected to significant changes during their slow transport to the surface and because physical properties depend primarily on mineralogy in addition to pressure and temperature. On the other hand, calculated velocities for granulite xenoliths are consistent with velocities for granulites from terrains, suggesting that they can be also used to infer lower crust composition by correlating with results from seismic refraction studies. Copyright 2000 by the American Geophysical Union.en_HK
dc.languageengen_HK
dc.publisherAmerican Geophysical Union.en_HK
dc.relation.ispartofJournal of Geophysical Research B: Solid Earthen_HK
dc.rightsCreative Commons: Attribution 3.0 Hong Kong Licenseen_HK
dc.subjectLower crust-
dc.subjectSeismic velocity-
dc.subjectXenolith-
dc.titleMeasured and calculated seismic velocities and densities for granulites from xenolith occurrences and adjacent exposed lower crustal sections: A comparative study from the North China cratonen_HK
dc.typeArticleen_HK
dc.identifier.openurlhttp://library.hku.hk:4550/resserv?sid=HKU:IR&issn=0148-0227&volume=105 NoB8&spage=18965&epage=18976&date=2000&atitle=Measured+and+calculated+seismic+velocities+and+densities+for+granulites+from+xenolith+occurrences+and+adjacent+exposed+lower+crustal+sections:a+comparative+study+from+the+North+China+Craton.en_HK
dc.identifier.emailSun, M:minsun@hku.hken_HK
dc.identifier.authoritySun, M=rp00780en_HK
dc.description.naturepublished_or_final_version-
dc.identifier.doi10.1029/2000JB900100-
dc.identifier.scopuseid_2-s2.0-0034632573en_HK
dc.identifier.hkuros57990en_HK
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-0034632573&selection=ref&src=s&origin=recordpageen_HK
dc.identifier.volume105en_HK
dc.identifier.issueB8en_HK
dc.identifier.spage18965en_HK
dc.identifier.epage18976en_HK
dc.identifier.isiWOS:000088794600004-
dc.publisher.placeUnited Statesen_HK
dc.identifier.scopusauthoridGao, S=36078559200en_HK
dc.identifier.scopusauthoridKern, H=7102832445en_HK
dc.identifier.scopusauthoridLiu, YS=26643294600en_HK
dc.identifier.scopusauthoridJin, SY=7401822347en_HK
dc.identifier.scopusauthoridPopp, T=7003804418en_HK
dc.identifier.scopusauthoridJin, ZM=7403625930en_HK
dc.identifier.scopusauthoridFeng, JL=7403884197en_HK
dc.identifier.scopusauthoridSun, M=25932315800en_HK
dc.identifier.scopusauthoridZhao, ZB=8398165900en_HK

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