Partial melting of ultrahigh-pressure metamorphic rocks at convergent continental margins: Evidences, melt compositions and physical effects
Ultrahigh-pressure (UHP) metamorphic rocks are distinctive products of crustal deep subduction, and are mainly exposed in continental subduction-collision terranes. UHP slices of continental crust are usually involved in multistage exhumation and partial melting, which has obvious influence on the r...
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Elsevier
2018-07-01
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| Series: | Geoscience Frontiers |
| Online Access: | http://www.sciencedirect.com/science/article/pii/S1674987117301354 |
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| author | Liang-Peng Deng Yi-Can Liu Xiao-Feng Gu Chiara Groppo Franco Rolfo |
| author_facet | Liang-Peng Deng Yi-Can Liu Xiao-Feng Gu Chiara Groppo Franco Rolfo |
| author_sort | Liang-Peng Deng |
| collection | DOAJ |
| description | Ultrahigh-pressure (UHP) metamorphic rocks are distinctive products of crustal deep subduction, and are mainly exposed in continental subduction-collision terranes. UHP slices of continental crust are usually involved in multistage exhumation and partial melting, which has obvious influence on the rheological features of the rocks, and thus significantly affect the dynamic behavior of subducted slices. Moreover, partial melting of UHP rocks have significant influence on element mobility and related isotope behavior within continental subduction zones, which is in turn crucial to chemical differentiation of the continental crust and to crust-mantle interaction.Partial melting can occur before, during or after the peak metamorphism of UHP rocks. Post-peak decompression melting has been better constrained by remelting experiments; however, because of multiple stages of decompression, retrogression and deformation, evidence of former melts in UHP rocks is often erased. Field evidence is among the most reliable criteria to infer partial melting. Glass and nanogranitoid inclusions are generally considered conclusive petrographic evidence. The residual assemblages after melt extraction are also significant to indicate partial melting in some cases. Besides field and petrographic evidence, bulk-rock and zircon trace-element geochemical features are also effective tools for recognizing partial melting of UHP rocks. Phase equilibrium modeling is an important petrological tool that is becoming more and more popular in P-T estimation of the evolution of metamorphic rocks; by taking into account the activity model of silicate melt, it can predict when partial melting occurred if the P-T path of a given rock is provided.UHP silicate melt is commonly leucogranitic and peraluminous in composition with high SiO2, low MgO, FeO, MnO, TiO2 and CaO, and variable K2O and Na2O contents. Mineralogy of nanogranites found in UHP rocks mainly consists of plagioclase + K-feldspar + quartz, plagioclase being commonly albite-rich. Trace element pattern of the melt is characterized by significant enrichment of large ion lithophile elements (LILE), depletion of heavy rare earth elements (HREE) and high field strength elements (HFSE), indicating garnet and rutile stability in the residual assemblage. In eclogites, significant Mg-isotope fractionation occurs between garnet and phengite; therefore, Mg isotopes may become an effective indicator for partial melting of eclogites. Keywords: Partial melting, Continental subduction-collision, Ultrahigh-pressure metamorphism, Leucosome, Phase equilibrium modeling |
| first_indexed | 2024-03-12T20:23:12Z |
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| id | doaj.art-3890bd17197348f29738f66016929da6 |
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| issn | 1674-9871 |
| language | English |
| last_indexed | 2024-03-12T20:23:12Z |
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| spelling | doaj.art-3890bd17197348f29738f66016929da62023-08-02T00:44:49ZengElsevierGeoscience Frontiers1674-98712018-07-019412291242Partial melting of ultrahigh-pressure metamorphic rocks at convergent continental margins: Evidences, melt compositions and physical effectsLiang-Peng Deng0Yi-Can Liu1Xiao-Feng Gu2Chiara Groppo3Franco Rolfo4CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, ChinaCAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China; Corresponding author. Fax: +86 551 63600367.CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, ChinaDepartment of Earth Sciences, University of Torino, Via Valperga Caluso 35, 1-10125 Torino, Italy; C.N.R. – I.G.G., Section of Torino, Via Valperga Caluso 35, 1-10125 Torino, ItalyDepartment of Earth Sciences, University of Torino, Via Valperga Caluso 35, 1-10125 Torino, Italy; C.N.R. – I.G.G., Section of Torino, Via Valperga Caluso 35, 1-10125 Torino, ItalyUltrahigh-pressure (UHP) metamorphic rocks are distinctive products of crustal deep subduction, and are mainly exposed in continental subduction-collision terranes. UHP slices of continental crust are usually involved in multistage exhumation and partial melting, which has obvious influence on the rheological features of the rocks, and thus significantly affect the dynamic behavior of subducted slices. Moreover, partial melting of UHP rocks have significant influence on element mobility and related isotope behavior within continental subduction zones, which is in turn crucial to chemical differentiation of the continental crust and to crust-mantle interaction.Partial melting can occur before, during or after the peak metamorphism of UHP rocks. Post-peak decompression melting has been better constrained by remelting experiments; however, because of multiple stages of decompression, retrogression and deformation, evidence of former melts in UHP rocks is often erased. Field evidence is among the most reliable criteria to infer partial melting. Glass and nanogranitoid inclusions are generally considered conclusive petrographic evidence. The residual assemblages after melt extraction are also significant to indicate partial melting in some cases. Besides field and petrographic evidence, bulk-rock and zircon trace-element geochemical features are also effective tools for recognizing partial melting of UHP rocks. Phase equilibrium modeling is an important petrological tool that is becoming more and more popular in P-T estimation of the evolution of metamorphic rocks; by taking into account the activity model of silicate melt, it can predict when partial melting occurred if the P-T path of a given rock is provided.UHP silicate melt is commonly leucogranitic and peraluminous in composition with high SiO2, low MgO, FeO, MnO, TiO2 and CaO, and variable K2O and Na2O contents. Mineralogy of nanogranites found in UHP rocks mainly consists of plagioclase + K-feldspar + quartz, plagioclase being commonly albite-rich. Trace element pattern of the melt is characterized by significant enrichment of large ion lithophile elements (LILE), depletion of heavy rare earth elements (HREE) and high field strength elements (HFSE), indicating garnet and rutile stability in the residual assemblage. In eclogites, significant Mg-isotope fractionation occurs between garnet and phengite; therefore, Mg isotopes may become an effective indicator for partial melting of eclogites. Keywords: Partial melting, Continental subduction-collision, Ultrahigh-pressure metamorphism, Leucosome, Phase equilibrium modelinghttp://www.sciencedirect.com/science/article/pii/S1674987117301354 |
| spellingShingle | Liang-Peng Deng Yi-Can Liu Xiao-Feng Gu Chiara Groppo Franco Rolfo Partial melting of ultrahigh-pressure metamorphic rocks at convergent continental margins: Evidences, melt compositions and physical effects Geoscience Frontiers |
| title | Partial melting of ultrahigh-pressure metamorphic rocks at convergent continental margins: Evidences, melt compositions and physical effects |
| title_full | Partial melting of ultrahigh-pressure metamorphic rocks at convergent continental margins: Evidences, melt compositions and physical effects |
| title_fullStr | Partial melting of ultrahigh-pressure metamorphic rocks at convergent continental margins: Evidences, melt compositions and physical effects |
| title_full_unstemmed | Partial melting of ultrahigh-pressure metamorphic rocks at convergent continental margins: Evidences, melt compositions and physical effects |
| title_short | Partial melting of ultrahigh-pressure metamorphic rocks at convergent continental margins: Evidences, melt compositions and physical effects |
| title_sort | partial melting of ultrahigh pressure metamorphic rocks at convergent continental margins evidences melt compositions and physical effects |
| url | http://www.sciencedirect.com/science/article/pii/S1674987117301354 |
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