Partial melting, fluid supercriticality and element mobility in ultrahigh-pressure metamorphic rocks during continental collision

Zheng, Yong‐Fei; Xia, Qiong‐Xia; Chen, Ren‐Xu; Gao, Xiao‐Ying

doi:10.1016/j.earscirev.2011.04.004

Cited by 336 publications

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“…Polyphase inclusions consisting of hydrous, Ti-bearing and P-bearing minerals in HP to UHP phases in the eclogites from Donghai, Jiangsu Province, indicated the presence of supercritical fluids at UHP conditions or at the earliest stages of rapid exhumation [16,47]. Liu et al [48] found Cl-bearing hornblende in the Sulu eclogite and interpreted that they were formed from aqueous fluids rich in Cl produced by hydration of phengite and normally anhydrous minerals (NAM) (e.g.…”

Section: Discussionmentioning

confidence: 99%

“…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].…”

mentioning

confidence: 99%

“…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%

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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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Section: Discussionmentioning

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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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“…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 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%

“…It is widely accepted that the breakdown of phengite and zoisite play a key role in partial melting of UHP rocks [14]. Thus, it is important to investigate the dehydration melting of hydrous minerals under various P-T conditions and their implications for initial melting of host rocks.…”

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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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Integrated geophysical-petrological modeling of lithosphere-asthenosphere boundary in central Tibet using electromagnetic and seismic data

Vozár

Jones

Fullea

et al. 2014

Geochem. Geophys. Geosyst.

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We undertake a petrologically driven approach to jointly model magnetotelluric (MT) and seismic surface wave dispersion (SW) data from central Tibet, constrained by topographic height. The approach derives realistic temperature and pressure distributions within the upper mantle and characterizes mineral assemblages of given bulk chemical compositions as well as water content. This allows us to define a bulk geophysical model of the upper mantle based on laboratory and xenolith data for the most relevant mantle mineral assemblages and to derive corresponding predicted geophysical observables. One-dimensional deep resistivity models were derived for two groups of MT stations. One group, located in the Lhasa Terrane, shows the existence of an electrically conductive upper mantle layer and shallower conductive upper mantle layer for the other group, located in the Qiangtang Terrane. The subsequent one-dimensional integrated petrological-geophysical modeling suggests a lithosphere-asthenosphere boundary (LAB) at a depth of 80-120 km with a dry lithosphere for the Qiangtang Terrane. In contrast, for the Lhasa Terrane the LAB is located at about 180 km but the presence of a small amount of water in the lithospheric mantle (<0.02 wt%) is required to fit the longest period MT responses. Our results suggest two different lithospheric configurations beneath the southern and central Tibetan Plateau. The model for the Lhasa Terrane implies underthrusting of a moderately wet Indian plate. The model for the Qiangtang Terrane shows relatively thick and conductive crust and implies thin and dry Tibetan lithosphere.

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Partial melting, fluid supercriticality and element mobility in ultrahigh-pressure metamorphic rocks during continental collision

Cited by 336 publications

References 332 publications

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

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

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

Integrated geophysical-petrological modeling of lithosphere-asthenosphere boundary in central Tibet using electromagnetic and seismic data

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