The breakdown of potassium feldspar at high water pressures

Thompson, Pauline; Parsons, Ian; Graham, Colin M.; Jackson, B. G.

doi:10.1007/s004100050358

Cited by 32 publications

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“…3, right inset). These are consistent with the observed OH stretching modes of K -cymrite at 3530 cm −1 and 3620 cm −1 by infrared spectroscopy (Thompson et al, 1998). The corresponding Raman peaks for cymrite appear at 3500 cm −1 and 3557 cm −1 (Graham et al, 1992).…”

supporting

confidence: 88%

“…The larger change from 300 °C to 500 °C can be attributed to dehydration. The dehydration temper ature range observed by the Raman modes is consistent with the thermogravimetric analyses of Thompson et al (1998). The curve in Figure 4 likely refl ects kinetic be havior of the dehydration process, and does not represent the equilibrium state.…”

supporting

confidence: 66%

“…Both phases have a unique crystal structure consisting of double -layers of Si(Al)O 4 tetrahedra that are linked together by large cations (K or Ba), with water molecules occupying cages within the double -layers (Fasshauer et al, 1997). When heated at ambient pressure, K -cymrite dehydrates to a metastable anhydrous hexagonal KAlSi 3 O 8 phase while retaining its original structure (Thompson et al, 1998). The latter is isostructural with hexacelsian (BaAl 2 Si 2 O 8 ) (Takéuchi, 1958), although with a different space group.…”

Section: Introductionmentioning

confidence: 99%

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Raman and NMR spectroscopic characterization of high-pressure K-cymrite (KAlSi3O8.H2O) and its anhydrous form (kokchetavite)

Kanzaki

Xue

Amalberti

et al. 2012

Journal of Mineralogical and Petrological Sciences

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To facilitate identification of high -pressure K -cymrite (KAlSi 3 O 8 ·H 2 O) phase and its anhydrous form (kokche tavite) in natural rocks, we have synthesized both phases and have characterized them by micro -Raman and NMR spectroscopy. K -cymrite was synthesized at 5 GPa and 800 °C. Kokchetavite was obtained by dehydrating K -cymrite at ambient pressure and 550 °C. The . The Raman spectrum for kokchetavite is consistent with that previously reported for a natural sample found as inclusions in clinopyroxenes and garnets in a garnet -pyroxene rock. However, the data for K -cymrite are inconsistent with the Raman features of a previously reported "relict K -cymrite in K -feldspar" from an eclogite. Pressure -and temperature -dependencies of the Raman shifts for the strongest peak of both phases are also reported.

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supporting

confidence: 88%

supporting

confidence: 66%

Section: Introductionmentioning

confidence: 99%

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Raman and NMR spectroscopic characterization of high-pressure K-cymrite (KAlSi3O8.H2O) and its anhydrous form (kokchetavite)

Kanzaki

Xue

Amalberti

et al. 2012

Journal of Mineralogical and Petrological Sciences

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“…1). K-cymrite is stable up to about 9 GPa, where it decomposes to K-hollandite [K VI Al Vl Si 3 O 8 ] and fluid (Thompson et al 1998). In a dry system, K-feldspar reacts to K-Si-wadeite [K VI 2 Si IV Si 3 O 9 ], (also termed Si-wadeite; Harlow and Davies 2004;Yong et al 2008) + kyanite + coesite above 5 to 6.5 GPa, 400 to 1000 • C (Yagi et al 1994;Urakawa et al 1994).…”

Section: Introductionmentioning

confidence: 99%

High-pressure ammonium-bearing silicates: Implications for nitrogen and hydrogen storage in the Earth's mantle

Watenphul

Wunder

Heinrich

2009

American Mineralogist

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The ammonium analogues of the high-pressure potassium-bearing silicate phases K-hollandite, K-Si-wadeite, K-cymrite, and phengite were synthesized in the system (NH 4 Ammonium in eclogite facies metasediments is mainly bound in micas and concentrations may reach up to a few thousand ppm. It can be stored to greater depths in high-pressure potassium silicates during ongoing subduction. This possibly provides an important mechanism for nitrogen and hydrogen transport into the deeper mantle.

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“…In the presence of H 2 O-rich fluid, K-feldspar is not stable at pressure greater than 2.5 GPa and will transform into K-cymerite [12,39,40]. In addition, hydrous granitic melts with H 2 O content of c. 10 wt% should occur at the estimated peak metamorphic conditions for the Sulu UHP eclogite (P>3.3 GPa and T=750-850°C) [11,12], implying the high potential in forming K-cymerite in the Dabie-Sulu UHP rocks under UHP conditions.…”

Section: Discussionmentioning

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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The breakdown of potassium feldspar at high water pressures

Cited by 32 publications

References 0 publications

Raman and NMR spectroscopic characterization of high-pressure K-cymrite (KAlSi<sub>3</sub>O<sub>8</sub><sup>.</sup>H<sub>2</sub>O) and its anhydrous form (kokchetavite)

Raman and NMR spectroscopic characterization of high-pressure K-cymrite (KAlSi<sub>3</sub>O<sub>8</sub><sup>.</sup>H<sub>2</sub>O) and its anhydrous form (kokchetavite)

High-pressure ammonium-bearing silicates: Implications for nitrogen and hydrogen storage in the Earth's mantle

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

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