Abstract
Ultrahigh-pressure metamorphism in the Greenland Caledonides; microstructural and thermobarometric evidence
Abstracts with programs - Geological Society of America, Vol.33(6), pp.382-383
Geological Society of America, 2001 annual meeting
11/2001
Abstract
The first evidence for ultrahigh-pressure metamorphism (UHPM) in the Greenland Caledonides has been found in kyanite eclogites and associated host gneisses on a remote island in Jokelbugt (78 degrees 00'N, 18 degrees 04'W). The UHP locality lies at the eastern edge of the North-East Greenland eclogite province, which constitutes a coherent 400 km long slab of MT/HP, Laurentian continental crust. The kyanite eclogites form a 2 km long string of boudins; individual blocks are 50X100 m and lie within clinopyroxene-bearing, quartzofeldspathic gneisses. Polycrystalline quartz inclusions in garnet, omphacite and kyanite are surrounded by radial fractures. Some inclusions contain a palisade quartz outer rim that encircles a region of very fine-grained subgrains to coarser, polygonized recrystallized grains of quartz. Palisade quartz is diagnostic of quartz pseudomorphs after coesite, thus providing textural evidence for UHP conditions. Geothermobarometry on the mineral assemblage garnet+omphacite+kyanite+quartz/coesite+ or -phengite confirms the microstructural interpretation of UHPM. P-T estimates are based on a combination of the garnet-clinopyroxene Fe-Mg exchange thermometer and internally consistent calibrations derived from the net-transfer reactions: (1) grossular+pyrope+2 coesite/quartz = 3 diopside+2 kyanite, and (2) 3 celadonite+2 grossular+pyrope = 6 diopside+3 muscovite. We used the most sodic omphacite, garnet with maximum (XCa2)(XMg), and white mica with the highest Si content to calculate peak P conditions for three eclogite samples. The samples define maximum P conditions of 3.6-4.2 GPa at temperatures ranging from 928-972 degrees C. These PT estimates fall well within the coesite stability field. Temperatures are probably overestimated because of the assumption that all Fe in omphacite is ferrous; however, any Fe3+ in omphacite would only increase the pressure estimates because of the negative slope of reaction (1). The host gneisses are more retrogressed than the kyanite eclogites and only record HP conditions of 2.5 GPa at 826 degrees C; but garnet contains polycrystalline quartz inclusions with radial fractures that are evidence for UHPM. If our research develops as in other UHP terranes (e.g. Western Gneiss Region, Dora Maira, Erzbebirge), then we have begun to define a UHP province in Greenland.
Details
- Title: Subtitle
- Ultrahigh-pressure metamorphism in the Greenland Caledonides; microstructural and thermobarometric evidence
- Creators
- Jane A Gilotti - University of Iowa, Department of Geoscience Iowa City, IA USA United StatesErling J Krogh-Ravna - University of Tromso NOR Norway
- Resource Type
- Abstract
- Publication Details
- Abstracts with programs - Geological Society of America, Vol.33(6), pp.382-383
- Conference
- Geological Society of America, 2001 annual meeting
- Publisher
- Geological Society of America (GSA)
- ISSN
- 0016-7592
- Alternative title
- Geological Society of America, 2001 annual meeting
- Language
- English
- Date published
- 11/2001
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984240781602771
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