Thermobarometric profile through the Caledonian nappe stack of Western Ofoten,North Norway |
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| Authors: | Mark G Steltenpohl John M Bartley |
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| Institution: | (1) Department of Geology, University of North Carolina, 27514 Chapel Hill, NC, USA;(2) Department of Geology and Geophysics, University of Utah, 84112 Salt Lake City, UT, USA;(3) Present address: Alabama Geological Survey, 420 Hackberry Lane, 35486 Tuscaloosa, AL, USA |
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| Abstract: | P-T estimates from pelite thermobarometry along a transect through the Caledonian nappe stack in Ofoten, north Norway (68° 30° N) plot as a trend in P-T space (ranging from 443° C, 6.9 kb, to 688° C, 10.6 kb). The P-T range for each nappe overlaps the others, except for those from the lowest unit (Narvik Group) which has significantly higher values. Within the P-T ranges for each nappe, the position on the trend of a given sample is independent of its tectonic position. Results support our earlier conclusion, based on structural and petrographic grounds, that the regional metamorphic peak was reached during or after stacking of the nappes in the Siluro-Devonian Scandian orogeny.The P-T trend closely resembles a trend reported from the Narvik Group in a nearby area which was interpreted to record varying amounts of retrograde reequilibration during uplift and cooling and thus define a portion of the area's cooling trajectory. However, evidence for an earlier, higher P-T event recorded only in the Narvik Group includes: 1) the Narvik Group gives the only P-T values exceeding 630° C, 9kb; 2) it preserves the only evidence suggesting polymetamorphism; and 3) it underlies an unconformity which has been interpreted on regional grounds to record the Cambro-Ordovician Finnmarkian orogeny. Therefore, the Narvik Group P-T trend probably does not quantitatively constrain the cooling history during uplift but reflects superposition of metamorphism in the Finnmarkian and Scandian orogenies. A Monte Carlo analysis of error propagation applied to the thermobarometric calculations indicates that the trend at least partly resulted due to an artifact of errors introduced by analytical uncertainties in the microprobe analyses. |
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