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Schubert, Wolfgang; Olesch, Martin (2011): Tab. 1+2: Representative electron-microprobe analyses of minerals from Du Toit Nunataks. PANGAEA,, Supplement to: Schubert, W; Olesch, M (1995): Cordierite in the Shackleton Range, Antarctica: first recorded occurrence. Polarforschung, 63(2/3), 153-164, hdl:10013/epic.29719.d001

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An example of cordierite-bearing gneiss that is part of a high-grade gneiss-migmatite sequence is described from the Hatch Plain in the Read Mountains of the Shackleton Range, Antarctica, for the first time. The cordierite-bearing rocks constitute the more melanosomic portions of the metatectic and migmatitic rocks that are associated with relict granulite facies rocks such as enderbitic granulite and enderbitic garnet granulite. The predominant mineral assemblage in the cordierite-bearing rocks is chemically homogeneous cordierite (XMg 0.61) and biotite (XMg 0.47), strongly zoned garnet (XMg 0.18-0.11), sillimanite, K-feldspar (Or81-94Ab5-18An0.6), plagioclase (An28), and quartz. Inclusions of sillimanite and biotite relics in both garnet and cordierite indicate that garnet and cordierite were produced by the coupled, discontinuous reaction biotite + sillimanite + quartz = cordierite + garnet + K-feldspar + H2O.
Various garnet-biotite and garnet-cordierite geothermometers and sillimanite-quartz-plagioclase-garnet-cordierite geobarometers yield a continuous clockwise path in the P-T diagram. The P-T conditions for equilibrium between garnet core and cordierite and between garnet core and biotite during peak metamorphism and migmatization were estimated to be 690 °C at 5-6 kb. This was followed by cooling and unloading with continuously changing conditions down to 515 °C at 2-3 kb. This low-pressure re-equilibration correlates with the pressure conditions evaluated by SCHULZE (1989) for the widespread granitic gneisses of the Read Group in the Shackleton Range. The associated relict enderbitic granulites representing low-pressure type granulite (8 kb; 790 °C) are comparable to similar low-pressure granulites from the East Antarctic craton. They were either formed by under-accretion processes after collision (WELLS 1979, p. 217) or they are a product of remetamorphism at P-T conditions intermediate between granulite and amphibolite facies. A model of a multiple imbrication zone with crustal thickening (CUTHBERT et al. 1983) is discussed for the formation of the relict granulites of the central and eastern Read Mountains which show higher pressure conditions (8-12 kb, SCHULZE & OLESCH 1990), indicating a Proterozoic crustal thickness of at least 40 km.
Latitude: -80.766700 * Longitude: -25.750000
Hatch_Plain * Latitude: -80.766700 * Longitude: -25.750000 * Location: Du Toi Nunataks, Read Group, Shackleton Range, Antarctia * Method/Device: Geological sample (GEOS)
#NameShort NameUnitPrincipal InvestigatorMethod/DeviceComment
1Mineral nameMineralSchubert, Wolfgang
2Sample code/labelSample labelSchubert, Wolfgang
3CommentCommentSchubert, Wolfgang
4Silicon dioxideSiO2%Schubert, WolfgangMicroprobe
5Titanium dioxideTiO2%Schubert, WolfgangMicroprobe
6Aluminium oxideAl2O3%Schubert, WolfgangMicroprobe
7Chromium(III) oxideCr2O3%Schubert, WolfgangMicroprobe
8Magnesium oxideMgO%Schubert, WolfgangMicroprobe
9Calcium oxideCaO%Schubert, WolfgangMicroprobe
10Manganese oxideMnO%Schubert, WolfgangMicroprobe
11Iron oxide, FeOFeO%Schubert, WolfgangMicroprobe
12Sodium oxideNa2O%Schubert, WolfgangMicroprobe
13Potassium oxideK2O%Schubert, WolfgangMicroprobe
14Barium oxideBaO%Schubert, WolfgangMicroprobe
15SumSum%Schubert, WolfgangMicroprobe
16Number of oxygensNo OSchubert, WolfgangMicroprobe
17SiliconSi%Schubert, WolfgangMicroprobe
18Aluminium (IV)Al(IV)%Schubert, WolfgangMicroprobe
19--Schubert, WolfgangMicroprobe
20Aluminium (VI)Al(VI)%Schubert, WolfgangMicroprobe
21TitaniumTi%Schubert, WolfgangMicroprobe
22ChromiumCr%Schubert, WolfgangMicroprobe
23Iron 3+Fe3+%Schubert, WolfgangMicroprobe
24MagnesiumMg%Schubert, WolfgangMicroprobe
25CalciumCa%Schubert, WolfgangMicroprobe
26ManganeseMn%Schubert, WolfgangMicroprobe
27Iron 2+Fe2+%Schubert, WolfgangMicroprobe
28SodiumNa%Schubert, WolfgangMicroprobe
29PotassiumK%Schubert, WolfgangMicroprobe
30AluminiumAl%Schubert, WolfgangMicroprobe
31BariumBa%Schubert, WolfgangMicroprobe
32SumSum%Schubert, WolfgangMicroprobe
321 data points

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