Experimental evidence of decompression melting during exhumation of subducted continental crust

Auzanneau, Estelle; Vielzeuf, Daniel; Schmidt, Max W.

doi:10.1007/s00410-006-0104-5

Cited by 244 publications

(185 citation statements)

References 62 publications

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“…Their bulk compositions differ mainly in Al 2 O 3 , FeO and Na 2 O concentrations ( Table 1). The starting materials have already been used in previous studies for other purposes (Vielzeuf and Holloway 1988;Vielzeuf and Montel 1994;Montel and Vielzeuf 1997;Schmidt et al 2004;Auzanneau et al 2006) and they have been described in detail by Vielzeuf and Montel (1994) and Vielzeuf and Holloway (1988), respectively.…”

Section: Starting Materialsmentioning

confidence: 99%

Titanium in phengite: a geobarometer for high temperature eclogites

Auzanneau

Schmidt

Vielzeuf

et al. 2009

Contrib Mineral Petrol

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184

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Phengite chemistry has been investigated in experiments on a natural SiO 2 -TiO 2 -saturated greywacke and a natural SiO 2 -TiO 2 -Al 2 SiO 5 -saturated pelite, at 1.5-8.0 GPa and 800-1,050°C. High Ti-contents (0.3-3.7 wt %), Ti-enrichment with temperature, and a strong inverse correlation of Ti-content with pressure are the important features of both experimental series. The changes in composition with pressure result from the Tschermak substitution (Si ? R 2? = Al IV ? Al VI ) coupled with the substitution:The latter exchange is best described using the end-member Ti-phengite (KMgTi[Si 3 Al]O 10 (OH) 2 , TiP). In the rutile-quartz/coesite saturated experiments, the aluminoceladonite component increases with pressure while the muscovite, paragonite and Ti-phengite components decrease. A thermodynamic model combining data obtained in this and previous experimental studies are derived to use the equilibrium MgCel ? Rt = TiP ? Cs/Qz as a thermobarometer in felsic and basic rocks. Phengite, rutile and quartz/coesite are common phases in HT-(U)HP metamorphic rocks, and are often preserved from regression by entrapment in zircon or garnet, thus providing an opportunity to determine the T-P conditions of crystallization of these rocks. Two applications on natural examples (Sulu belt and Kokchetav massif) are presented and discussed. This study demonstrates that Ti is a significant constituent of phengites that could have significant effects on phase relationships and melting rates with decreasing P or increasing T in the continental crust.

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Section: Starting Materialsmentioning

confidence: 99%

Titanium in phengite: a geobarometer for high temperature eclogites

Auzanneau

Schmidt

Vielzeuf

et al. 2009

Contrib Mineral Petrol

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184

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“…K-feldspar within inclusion has a feature of melt crystallization (Figure 3(e)), indicating that it may have crystallized from melt in inclusion. Since garnet is generally the reaction product of dehydration melting of phengite [1,22] (Figure 1(c) and (e)), therefore, the third type of inclusion suggests that the initial melting reaction of phengite should occur in the UHP gneiss by Ph+Grt-I→Grt-II+Kfs (Melt).…”

Section: The Low-degree Partial Melting Of Uhp Eclogite: Evidence Fromentioning

confidence: 99%

“…The breakdown curves of phengite are after [30] (hydrous basalt), [31] (KCMASH), [1] (metagreywacke) and [22] (phengite-bearing eclogite), respectively. mineral assemblage is consistent with the experimental results [1], demonstrating hydration melting event induced by phengite breakdown occurred at higher temperature in the UHP gneissic rock. Based on the composition of garnets and mineral assemblage in the matrix (Figure 3(e)), we inferred that such a melting reaction may be expressed as Ph+ Qz±Ep→Grt+Bt+Melt (Kfs+Qz).…”

Section: The Low-degree Partial Melting Of Uhp Eclogite: Evidence Fromentioning

confidence: 99%

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Dehydration melting of UHP eclogite and paragneiss in the Dabie orogen: Evidence from laboratory experiment to natural observation

Liu

2013

Chin. Sci. Bull.

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Dehydration melting of subducted continental crust is significant during exhumation, and its study from both experimental and petrological observations is of great importance to our understanding of continental geodynamics. Dehydration melting experiments were carried out on ultrahigh-pressure (UHP) eclogite from Bixiling in the Dabie orogen using a piston cylinder at 1.5-3.0 GPa and 800-950°C to investigate partial melting of eclogite induced by phengite breakdown. The phengite-bearing eclogite started to melt at T800-850°C and P=1.5-2.0 GPa and produced about 3% granitic melt. The products of dehydration melting vary with temperature and pressure. Such results provide valuable constraints on the micro-texture related to partial melting of UHP rocks in the Dabie-Sulu orogenic belt. Three types of polyphase inclusions were identified in garnet from the Shuanghe UHP eclogite. K-feldspar and quartz inclusions are interpreted to represent the products of segregation and crystallization of minor amounts of melt that formed during dehydration melting of phengite by the inferred reaction Phengite+Omphacite±Quartz→ Amphibole±Garnet+Melt (K-feldspar+Quartz±Plagioclase). Polyphase inclusions of phengite and K-feldspar+Quartz inclusions were also found in zoisite/clinozoisite and garnet from the Shuanghe garnet-bearing paragneiss. These polyphase inclusions provide evidence for a continuous process from sub-solidus dehydration to partial melting within the UHP gneissic rocks. The compositional variation of garnets demonstrates that breakdown of epidote-group minerals may have played a crucial role during dehydration melting reaction of phengite. The Ti-in-zircon thermometry and Si content of phengite in zircon suggest that partial melting would occur at 783-839°C and 2.0-2.5 GPa. Therefore, both experimental results and petrological observations indicate that dehydration melting and fluid activity within the Dabie UHP rocks at micro-scale are controlled by the breakdown of phengite. dehydration melting, phengite, experimental petrology, polyphase inclusions, ultrahigh-pressure metamorphism, Dabie orogen Citation:Liu Q, Wu Y. Dehydration melting of UHP eclogite and paragneiss in the Dabie orogen: Evidence from laboratory experiment to natural observation. Chin Sci Bull, 2013Bull, , 58: 43904396, doi: 10.1007 Recent studies from experimental petrology [1-3], geochemical analyses [4][5][6] and geochronological data [7][8][9] have indicated that deeply subducted continental crust experienced partial melting during exhumation. Such anatexis can change mechanical and chemical behaviours of ultrahigh-pressure (UHP) metamorphic rocks. It has significant effects on facilitating the deformation mechanisms (or strain localization) of UHP rocks [10,11], increasing the buoyancy of melted rocks and promoting the segregation of partial melts. Thus, partial melting of subducted continental crust is of great significance for understanding the melting event and fluid activity at great depths as well as the rheological property of UHP ro...

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“…Fertile components within the rocks that had been subjected to ultrahigh-pressure (UHP) metamorphism could experience partial melting [6][7][8][9][10][11][12][13][14][15] and produce granitic melts and even supercritical fluids [16] during the deep subduction or the early stage of rapid exhumation of continental slab. Under pressures high enough to surpass the second critical termination point, fluids and hydrous melts could mix completely and form homogenous supercritical fluids [17,18].…”

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confidence: 99%

Metamorphic solid salt (KCl-NaCl) in quartzo-feldspathic polyphase inclusions in the Sulu ultrahigh-pressure eclogite

Zeng

Chen

2012

Chin. Sci. Bull.

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Unusual polyphase inclusions of K-feldspar + quartz + titanite + solid salt and K-feldspar + albite + quartz + epidote with textures similar to the other K-feldspar + quartz inclusions were found in omphacite grains from the Sulu ultrahigh pressure (UHP) eclogites. One of these inclusions contain square to round solid salt inclusions of KCl-NaCl composition. Such a mineral assemblage within K-feldspar-bearing inclusions hosted by UHP metamorphic phases suggests that (1) potassium granitic melts enriched in Cl components were presented during UHP metamorphism or at the early stage of rapid exhumation of deeply subducted continental slab; (2) they were resulted from reactions between the incoming granitic melts and quartz (or coesite); and (3) solid salt inclusions of NaCl-KCl were derived from dehydration and desiccation of Cl-bearing melts. Our new observations further demonstrate that during the tectonic evolution of UHP rocks, fertile components within deeply subducted continental materials could undergo partial melting, leading to the formation of Cl-bearing potassium granitic melts and substantial migration of fluid-conservative elements (e.g. Ti, Hf) within the UHP slab. [17,18]. Such fluids, geochemically similar to granitic melts, could dissolve not only a large quantity of large lithophile elements (LILE) and rare earth elements (REE), but also normally fluid-immobile elements such as high field strength elements (HFSE), and become an excellent medium to transport these elements. During the tectonic evolution of continental subduction zones, formation and migration of granitic melts or supercritical fluids not only affect the geochemical properties of the subducted continental slab itself, but also exert strong influences on the physical and chemical properties of the overlying slab. Therefore, identification whether the deeply subducted continental material experienced partial melting and whether supercritical fluids presented is one of the frontiers of recent UHP studies [16].Resolving these issues will promote our understanding and appreciation of the pronounced physical and chemical effects of deep subduction and associated UHP metamorphic reactions of continental materials. The geochemical nature of fluids associated with UHP metamorphism is commonly inferred from fluid inclusions in UHP phases. High salinity fluid inclusions have been

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Experimental evidence of decompression melting during exhumation of subducted continental crust

Cited by 244 publications

References 62 publications

Titanium in phengite: a geobarometer for high temperature eclogites

Titanium in phengite: a geobarometer for high temperature eclogites

Dehydration melting of UHP eclogite and paragneiss in the Dabie orogen: Evidence from laboratory experiment to natural observation

Metamorphic solid salt (KCl-NaCl) in quartzo-feldspathic polyphase inclusions in the Sulu ultrahigh-pressure eclogite

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