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Article: High-pressure granulites (Retrograded Eclogites) from the Hengshan Complex, North China Craton: Petrology and tectonic implications

TitleHigh-pressure granulites (Retrograded Eclogites) from the Hengshan Complex, North China Craton: Petrology and tectonic implications
Authors
Issue Date2001
PublisherOxford University Press. The Journal's web site is located at http://petrology.oxfordjournals.org/
Citation
Journal Of Petrology, 2001, v. 42 n. 6, p. 1141-1170 How to Cite?
AbstractBoth high- and medium-pressure granulites have been found as enclaves and boudins in tonalitic-trondhjemitic-granodioritic gneisses in the Hengshan Complex. Petrological evidence from these rocks indicates four distinct metamorphic assemblages. The early prograde assemblage (M 1) is preserved only in the high-pressure granulites and represented by quartz and rutile inclusions within the cores of garnet porphyroblasts, and omphacite pseudomorphs that are indicated by clinopyroxene + sodic plagioclase symplectic intergrowths. The peak assemblage (M 2) consists of clinopyroxene + garnet + sodic plagioclase + quartz ± hornblende in the high-pressure granulites and orthopyroxene + clinopyroxene + garnel + plagioclase + quartz in the medium-pressure granulites. Peak metamorphism was followed by near-isothermal decompression (M 3), which resulted in the development of orthopyroxene + clinopyroxene + plagioclase symplectites and coronas surrounding embayed garnet grains, and decompression-cooling (M 4), represented by hornblende + plagioclase symplectiles on garnet. The THERMOCALC program yielded peak (M 2) P-T conditions of 13.4-15.5 kbar and 770-840°C for the high-pressure granulites and 9-11 kbar and 820-870°C for the medium-pressure granulites, based on the core compositions of garnet, matrix pyroxene and plagioclase. The P-T conditions of pyroxene + plagioclase symplectite and corona (M 3) were estimated at ~6-5-8.0 kbar and 750-830°C, and hornblende + plagioclase symplectile (M 4) at ~4.5-6.0 kbar and 680-790°C. The P-T conditions of the early prograde assemblage (M 1) cannot be quantitatively estimated because of the absence of modal minerals. The combination of petrographic textures, mineral compositions, metamorphic reaction history, petrogenetic grids and thermobarometric data defines a near-isothermal decompressional clockwise P-T path for the Hengshan granulites, suggesting that the Hengshan Complex underwent initial crustal thickening, subsequent exhumation, and cooling and retrogression. This tectonothermal path is considered to record a major phase of collison between two continental blocks, which resulted in the final assembly of the North China Craton at ~ 1.8 Ga.
Persistent Identifierhttp://hdl.handle.net/10722/151056
ISSN
2015 Impact Factor: 3.768
2015 SCImago Journal Rankings: 2.992

 

DC FieldValueLanguage
dc.contributor.authorZhao, Gen_US
dc.contributor.authorCawood, PAen_US
dc.contributor.authorWilde, SAen_US
dc.contributor.authorLu, Len_US
dc.date.accessioned2012-06-26T06:16:36Z-
dc.date.available2012-06-26T06:16:36Z-
dc.date.issued2001en_US
dc.identifier.citationJournal Of Petrology, 2001, v. 42 n. 6, p. 1141-1170en_US
dc.identifier.issn0022-3530en_US
dc.identifier.urihttp://hdl.handle.net/10722/151056-
dc.description.abstractBoth high- and medium-pressure granulites have been found as enclaves and boudins in tonalitic-trondhjemitic-granodioritic gneisses in the Hengshan Complex. Petrological evidence from these rocks indicates four distinct metamorphic assemblages. The early prograde assemblage (M 1) is preserved only in the high-pressure granulites and represented by quartz and rutile inclusions within the cores of garnet porphyroblasts, and omphacite pseudomorphs that are indicated by clinopyroxene + sodic plagioclase symplectic intergrowths. The peak assemblage (M 2) consists of clinopyroxene + garnet + sodic plagioclase + quartz ± hornblende in the high-pressure granulites and orthopyroxene + clinopyroxene + garnel + plagioclase + quartz in the medium-pressure granulites. Peak metamorphism was followed by near-isothermal decompression (M 3), which resulted in the development of orthopyroxene + clinopyroxene + plagioclase symplectites and coronas surrounding embayed garnet grains, and decompression-cooling (M 4), represented by hornblende + plagioclase symplectiles on garnet. The THERMOCALC program yielded peak (M 2) P-T conditions of 13.4-15.5 kbar and 770-840°C for the high-pressure granulites and 9-11 kbar and 820-870°C for the medium-pressure granulites, based on the core compositions of garnet, matrix pyroxene and plagioclase. The P-T conditions of pyroxene + plagioclase symplectite and corona (M 3) were estimated at ~6-5-8.0 kbar and 750-830°C, and hornblende + plagioclase symplectile (M 4) at ~4.5-6.0 kbar and 680-790°C. The P-T conditions of the early prograde assemblage (M 1) cannot be quantitatively estimated because of the absence of modal minerals. The combination of petrographic textures, mineral compositions, metamorphic reaction history, petrogenetic grids and thermobarometric data defines a near-isothermal decompressional clockwise P-T path for the Hengshan granulites, suggesting that the Hengshan Complex underwent initial crustal thickening, subsequent exhumation, and cooling and retrogression. This tectonothermal path is considered to record a major phase of collison between two continental blocks, which resulted in the final assembly of the North China Craton at ~ 1.8 Ga.en_US
dc.languageengen_US
dc.publisherOxford University Press. The Journal's web site is located at http://petrology.oxfordjournals.org/en_US
dc.relation.ispartofJournal of Petrologyen_US
dc.rightsJournal of Petrology. Copyright © Oxford University Press.-
dc.titleHigh-pressure granulites (Retrograded Eclogites) from the Hengshan Complex, North China Craton: Petrology and tectonic implicationsen_US
dc.typeArticleen_US
dc.identifier.emailZhao, G: gzhao@hkucc.hku.hken_US
dc.identifier.authorityZhao, G=rp00842en_US
dc.description.naturelink_to_subscribed_fulltexten_US
dc.identifier.scopuseid_2-s2.0-0034970475en_US
dc.identifier.hkuros57266-
dc.identifier.volume42en_US
dc.identifier.issue6en_US
dc.identifier.spage1141en_US
dc.identifier.epage1170en_US
dc.publisher.placeUnited Kingdomen_US

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