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Conodont geothermometry and tectonic overburden in the northernmost East Greenland Caledonides

JAN AUDUN RASMUSSEN^* and M. PAUL SMITH^,

^* Geological Survey of Denmark and Greenland, Thoravej 8, DK-2400 Copenhagen NV, Denmark
School of Earth Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK

Author for correspondence: m.p.smith{at}bham.ac.uk

Kronprins Christian Land lies at the northernmost limit of the East Greenland Caledonides, and may be divided into four main tracts: foreland, parautochthon, thin-skinned thrust sheets containing Neoproterozoic sediments, and thick-skinned thrust sheets of crystalline basement. The eastern part of the foreland and the parautochthon are composed of Ordovician–Silurian shelf carbonates overlain by Llandovery–lower Wenlock turbidites deposited at the southern margin of the Franklinian Basin. Deformation of the parautochthon occurred beneath a major detachment, the Vandredalen thrust, with Neoproterozoic sediments of the Rivieradal Group lying in the hanging wall. The Rivieradal Group was deposited in an E-facing half-graben and was displaced westwards across its rift shoulders during Caledonian thrusting. Extensive sampling for conodonts has been carried out within the Lower Palaeozoic rocks of the foreland and parautochthon in order to increase the precision of structural interpretations and to provide data on maximum burial temperature and, in turn, the thickness of overburden. In contrast to earlier studies, conodont colour alteration indices (CAI) show a gradual and continuous increase from CAI 3 in the eastern part of the foreland to CAI 5+ in the easternmost parts of the parautochthon. The isopleths are not disrupted or truncated by thrusting, as previously suspected, indicating that the heating is not attributable to pre-thrusting stratigraphic overburden. Furthermore, considerations of the regional geology indicate that there was no significant accumulation of sedimentary overburden in post-Caledonian time; the predominant component is thus considered to be loading by thrust sheets. Modelling of the overburden thickness suggests that, prior to erosion, it increased from 3.9 km (CAI 3) in the easternmost foreland to a maximum of 12.5 km beneath the Vandredalen thrust sheet in the easternmost part of the area, providing constraints for restoring cross-sections across the orogen.

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