Synexhumation anatexis of ultrahigh-pressure metamorphic rocks: Petrological evidence from granitic gneiss in the Sulu orogen

Chen, Yixiang; Zheng, Yong‐Fei; Hu, Zhaochu

doi:10.1016/j.lithos.2012.10.008

Cited by 96 publications

(100 citation statements)

References 121 publications

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“…This has been observed in many UHP metamorphic rocks where anatexis takes place at relatively high temperatures due to breakdown of hydrous UHP minerals such as phengite during decompression (Gao et al 2012(Gao et al , 2013Chen et al 2013;Liu et al 2013). In a series of experiments on the rheology of eclogite at 1,300 to 1,500 K and 3.0 GPa, on the other hand, Zhang et al (2004) observed partial melting of an eclogite that contained no hydrous minerals but only H 2 O of up to 300 ppm in garnet, 1,000 to 1,300 ppm in omphacite and 3,000 to 4,000 ppm in rutile.…”

Section: Water In Subduction-zone Rocksmentioning

confidence: 87%

“…The liberated water may result in the formation of retrograde hydrous minerals in UHP rocks . If exhumation occurs at elevated temperatures, the hydrous UHP minerals such as phengite may break down during decompression, resulting in local anatexis of the UHP rocks (Gao et al 2012(Gao et al , 2013Chen et al 2013;Liu et al 2013).…”

Section: Water In Subduction-zone Rocksmentioning

confidence: 99%

“…This also results in local dehydration melting, which is recorded by anatectic leucosomes, restites, and MSI in UHP metamorphic rocks (Zheng et al 2011a;Gao et al 2012Gao et al , 2013Chen et al 2012bChen et al , 2013Yu et al 2012;Liu et al 2013;Song et al 2014;Stepanov et al 2014). Fluids released from deeply subducting crustal rocks provide metasomatic agents for mass transfer at the slab-mantle interface in subduction channels (Figure 8a).…”

Section: Crust-mantle Interaction In Subduction Channelmentioning

confidence: 99%

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Geochemistry of continental subduction-zone fluids

Zheng

Hermann

2014

Earth, Planets and Space

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The composition of continental subduction-zone fluids varies dramatically from dilute aqueous solutions at subsolidus conditions to hydrous silicate melts at supersolidus conditions, with variable concentrations of fluid-mobile incompatible trace elements. At ultrahigh-pressure (UHP) metamorphic conditions, supercritical fluids may occur with variable compositions. The water component of these fluids primarily derives from structural hydroxyl and molecular water in hydrous and nominally anhydrous minerals at UHP conditions. While the breakdown of hydrous minerals is the predominant water source for fluid activity in the subduction factory, water released from nominally anhydrous minerals provides an additional water source. These different sources of water may accumulate to induce partial melting of UHP metamorphic rocks on and above their wet solidii. Silica is the dominant solute in the deep fluids, followed by aluminum and alkalis. Trace element abundances are low in metamorphic fluids at subsolidus conditions, but become significantly elevated in anatectic melts at supersolidus conditions. The compositions of dissolved and residual minerals are a function of pressure-temperature and whole-rock composition, which exert a strong control on the trace element signature of liberated fluids. The trace element patterns of migmatic leucosomes in UHP rocks and multiphase solid inclusions in UHP minerals exhibit strong enrichment of large ion lithophile elements (LILE) and moderate enrichment of light rare earth elements (LREE) but depletion of high field strength elements (HFSE) and heavy rare earth elements (HREE), demonstrating their crystallization from anatectic melts of crustal protoliths. Interaction of the anatectic melts with the mantle wedge peridotite leads to modal metasomatism with the generation of new mineral phases as well as cryptic metasomatism that is only manifested by the enrichment of fluid-mobile incompatible trace elements in orogenic peridotites. Partial melting of the metasomatic mantle domains gives rise to a variety of mafic igneous rocks in collisional orogens and their adjacent active continental margins. The study of such metasomatic processes and products is of great importance to understanding of the mass transfer at the slab-mantle interface in subduction channels. Therefore, the property and behavior of subduction-zone fluids are a key for understanding of the crust-mantle interaction at convergent plate margins.

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Section: Water In Subduction-zone Rocksmentioning

confidence: 87%

Section: Water In Subduction-zone Rocksmentioning

confidence: 99%

Section: Crust-mantle Interaction In Subduction Channelmentioning

confidence: 99%

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Geochemistry of continental subduction-zone fluids

Zheng

Hermann

2014

Earth, Planets and Space

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211

113

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“…The aqueous fluid and hydrous melt are generated from UHP metamorphic rocks during their exhumation from mantle depths to crustal levels [16][17][18][19]. As such, there are not only physical mixing but also chemical reaction at the slab-mantle interface ( Figure 2).…”

Section: Subduction Channel Processesmentioning

confidence: 99%

Continental subduction channel processes: Plate interface interaction during continental collision

2013

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The study of subduction-zone processes is a key to development of the plate tectonic theory. Plate interface interaction is a basic mechanism for the mass and energy exchange between Earth's surface and interior. By developing the subduction channel model into continental collision orogens, insights are provided into tectonic processes during continental subduction and its products. The continental crust, composed of felsic to mafic rocks, is detached at different depths from subducting continental lithosphere and then migrates into continental subduction channel. Part of the subcontinental lithospheric mantle wedge, composed of peridotite, is offscrapped from its bottom. The crustal and mantle fragments of different sizes are transported downwards and upwards inside subduction channels by the corner flow, resulting in varying extents of metamorphism, with heterogeneous deformation and local anatexis. All these metamorphic rocks can be viewed as tectonic melanges due to mechanical mixing of crust-and mantle-derived rocks in the subduction channels, resulting in different types of metamorphic rocks now exposed in the same orogens. The crust-mantle interaction in the continental subduction channel is realized by reaction of the overlying ancient subcontinental lithospheric mantle wedge peridotite with aqueous fluid and hydrous melt derived from partial melting of subducted continental basement granite and cover sediment. The nature of premetamorphic protoliths dictates the type of collisional orogens, the size of ultrahigh-pressure metamorphic terranes and the duration of ultrahigh-pressure metamorphism. In continental collision orogens, exposed ultrahigh-pressure (UHP) metamorphic terranes contain the lithotectonic records of Alpine-type subduction [1]. These records highlight metamorphic P-T conditions and mass transfers, indicating subduction of continental crustal rocks to mantle depths of over 100 km. The UHP terranes are characterized by minor occurrences of mafic eclogites and ultramafic peridotites that are hosted by felsic gneisses. Such UHP eclogite-facies parageneses are absent in Pacific-type subduction zones [2]. These UHP rocks are of crustal and mantle protoliths and now occur together with their lower pressure counterparts in continental collision orogens [3]. It is intriguing how the continental crust is subducted to mantle depths for UHP metamorphism, how UHP slices are exhumed from mantle depths to crustal levels, and how metamorphic rocks of different P-T conditions occur together in the same orogens. The property of plate interface in subduction zones is a key to physical and chemical interactions at interplate boundaries. Physical and chemical transfers at convergent plate margins can occur on various spatial and temporal scales, which is fundamental to subduction-zone processes. Like the plate tectonic theory, the concept of subduction channel was originally developed from the tectonics of oceanic subduction zone [4][5][6]. It was primarily focused on the plate interface interaction in ocean...

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“…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 rocks in collisional orogenic belts [12][13][14]. So far, some aspects related to dehydration melting of UHP rocks are still open to discussion, including petrological evidence [15][16][17][18][19][20], conditions and degrees of melting, the differences among various rock units, element partitioning and coupling of lithological strength during melting. …”

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confidence: 99%

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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Synexhumation anatexis of ultrahigh-pressure metamorphic rocks: Petrological evidence from granitic gneiss in the Sulu orogen

Cited by 96 publications

References 121 publications

Geochemistry of continental subduction-zone fluids

Geochemistry of continental subduction-zone fluids

Continental subduction channel processes: Plate interface interaction during continental collision

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

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