Water Incorporation in Garnet: Coesite versus Quartz Eclogite from Erzgebirge and Fichtelgebirge

Gose, Jürgen; Schmädicke, Esther

doi:10.1093/petrology/egy022

Cited by 18 publications

(82 citation statements)

References 68 publications

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“…In the course of this study, it turned out that garnetite nodules are not so rare as previously thought (Schmädicke & Evans, 1997), but occur as agglomerates in different parts of the quarry. Although garnet peridotite and pyroxenite (Schmädicke & Gose, 2019) as well as gneiss‐hosted eclogite (Gose & Schmädicke, 2018; Schmädicke & Gose, 2017) were subject to recent studies on water in garnet, this investigation focuses on garnetite (metarodingite) and peridotite‐hosted eclogite.…”

Section: Geological Settingmentioning

confidence: 99%

“…This type of amphibole is a typical feature of Erzgebirge UHP eclogite as it was never found in HP eclogite. Its growth is attributed to eclogite facies recrystallization at pessures of 25–28 kbar (Gose & Schmädicke, 2018; Schmädicke et al., 1992). Post‐eclogitic recrystallization is almost absent as symplectite after omphacite is present only in very small amounts («1 vol.%).…”

Section: Sample Descriptionmentioning

confidence: 99%

“…The amount of water in the garnet structure (= structural water or ‘SW’) was inferred from the absorption of bands with maxima in the range between 3,460 and 3,670 cm ‐1 and calculated by applying the mineral‐specific molar absorption coefficient of Bell, Ihinger, and Rossman (1995). For spectra fitting, deconvolution, baseline correction and quantification of H 2 O, the method used for garnet from Erzgebirge eclogite (Gose & Schmädicke, 2018; Schmädicke & Gose, 2017) and GBU from Erzgebirge and LA (Schmädicke & Gose, 2019) was adopted here. The total uncertainty of the contents of SW (Table 4) is estimated to be 20% in most cases.…”

Section: Analytical Detailsmentioning

confidence: 99%

“…Nevertheless, garnet is usually well preserved, even in strongly serpentinized samples with very few olivine and pyroxene relics, and can be used as a proxy for water in the peak assemblage. In addition, garnet is present in all types of Erzgebirge GBU (peridotite, pyroxenite and garnetite; Schmädicke & Evans, 1997) as well as in eclogite (Gose & Schmädicke, 2018; Schmädicke & Gose, 2017). Therefore, it is the ideal mineral to compare the different rock types with respect to their water content.…”

Section: Introductionmentioning

confidence: 99%

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Water in garnet of garnetite (metarodingite) and eclogite from the Erzgebirge and the Lepontine Alps

Schmädicke

Gose

2020

Journal Metamorphic Geology

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Section: Geological Settingmentioning

confidence: 99%

Section: Sample Descriptionmentioning

confidence: 99%

Section: Analytical Detailsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Water in garnet of garnetite (metarodingite) and eclogite from the Erzgebirge and the Lepontine Alps

Schmädicke

Gose

2020

Journal Metamorphic Geology

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“…The former are often characterized, for example, by a prominent OHmode at 3570 cm -1 (Bell and Rossman 1992b). It goes without out saying that pyropes from Earth's mantle, as found in various xenoliths from kimberlites (e.g., Bell and Rossman 1992b;Matsyuk et al 1998), and in other types of eclogites (e.g., Schmädike et al 2015;Liu et al 2016;Gose and Schmädicke 2018;Zhang et al 2019) and pyroxenites (Li et al 2018), have a completely different petrologic origin than those found in the UHP whiteschists and quartzites at Dora Maira. The chemistries of mantle garnets are more complex and varied, as they contain a number of chemical components (Dawson and Stephens 1975).…”

Section: There Are Pyropes and There Are Pyropes: Differences In Compmentioning

confidence: 99%

Micro- and nano-size hydrogrossular-like clusters in pyrope crystals from ultra-high-pressure rocks of the Dora-Maira Massif, western Alps

Geiger

Rossman

2020

Contrib Mineral Petrol

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The supracrustal metamorphic rocks of the Dora-Maira Massif, western Alps, have been intensively studied. Certain ultrahigh-pressure lithologies contain coesite and nearly end-member composition pyrope, Mg 3 Al 2 Si 3 O 12 , making this locality petrologically and mineralogically unique. Structural OH-, loosely termed "water", in pyrope crystals of different composition has been investigated numerous times, using different experimental techniques, by various researchers. However, it is not clear where the minor OHis located in them. IR single-crystal spectra of two pyropes of composition {Mg 2.79 ,Fe 2+ 0.15 , Ca 0.04 } Σ2.98 [Al] 2.02 (Si) 2.99 O 12 and {Mg 2.90 ,Fe 2+ 0.04 ,Ca 0.02 } Σ2.96 [Al] 2.03 (Si) 3 O 12 were recorded at room temperature (RT) and 80 K. The spectra show five distinct OHbands located above 3600 cm-1 at RT and seven narrow bands at 80 K and additional fine structure. The spectra were curve fit and the OHstretching modes analyzed and assigned. It is argued that OHis located in microscopic-and nano-size Ca 3 Al 2 H 12 O 12-like clusters. The basic substitution mechanism is the hydrogarnet one, where (H 4 O 4) 4-⇔ (SiO 4) 4-, and various local configurations containing different numbers of (H 4 O 4) 4groups define the cluster type. The amounts of H 2 O range between 5 and 100 ppm by weight, depending on the IR calibration adopted, and are variable among crystals. Hydrogrossular-like clusters are also present in a synthetic pyrope with a minor Ca content grown hydrothermally at 900 °C and 20 kbar, as based on its IR spectra at RT and 80 K. Experiment and nature are in agreement, and OHgroups are partitioned into various barely nano-size hydrogrossular-like clusters. This proposal is new and significant mineralogical, petrological, and geochemical implications result. Ca and proton ordering occur. Hypothetical "defect" and/or coupled-substitution mechanisms to account for structural OHare not needed to interpret experimental results. OHincorporation in pyrope of different generations at Dora-Maira is discussed and OHcould potentially be used as an indicator of changing P H 2 O (a H 2 O)-T conditions in a metamorphic cycle. Published experimental hydration, dehydroxylation, and hydrogen diffusion results on Dora-Maira pyropes can now be interpreted atomistically.

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Inhibited hydrogen uptake in metasomatised cratonic eclogite

Aulbach,

Gies,

Linckens

et al. 2024

Contrib Mineral Petrol

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Water occurs in Earth’s interior mostly as trace hydroxyl in nominally anhydrous minerals. Clinopyroxene is known to be an important water carrier in the uppermost mantle, and eclogite, which forms a subordinate part of the cratonic lithosphere, contains some 50% of jadeite-rich clinopyroxene, making this potentially a significant H2O reservoir in the bulk lithospheric mantle. Mantle metasomatism, in particular by small-volume melts like kimberlite, is known to enrich the lithosphere in highly incompatible components, but its effect on H2O contents in cratonic eclogite remains unclear. We report H2O concentrations for clinopyroxene and garnet in eclogite and pyroxenite xenoliths from several African kimberlites, obtained by Fourier-Transform Infrared Spectroscopy (FTIR). Except one sample showing evidence for minor within-grain variability of H2O concentrations (< 15%), FTIR images demonstrate that H2O is homogeneously distributed in optically clear areas of clinopyroxene fragments mounted for this study. The samples were variably metasomatised by a kimberlite-like melt, as evidenced by elevated MgO contents and abundances of highly incompatible elements (e.g., Sr, Ce, Th). Although metasomatised eclogites and pyroxenites on average show higher H2O abundances than pristine ones, mantle metasomatism decreases the Al2O3 content in clinopyroxene, which is known to enhance hydrogen incorporation in this mineral. As a consequence, hydrogen incorporation is inhibited, and c(H2O) becomes increasingly decoupled from other highly incompatible components, such as LREE. Thus, eclogite – metasomatised or not - does not significantly contribute to the H2O inventory in the bulk cratonic mantle.

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Water Incorporation in Garnet: Coesite versus Quartz Eclogite from Erzgebirge and Fichtelgebirge

Cited by 18 publications

References 68 publications

Water in garnet of garnetite (metarodingite) and eclogite from the Erzgebirge and the Lepontine Alps

Water in garnet of garnetite (metarodingite) and eclogite from the Erzgebirge and the Lepontine Alps

Micro- and nano-size hydrogrossular-like clusters in pyrope crystals from ultra-high-pressure rocks of the Dora-Maira Massif, western Alps

Inhibited hydrogen uptake in metasomatised cratonic eclogite

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