The foreland-propagating thrust architecture of the East Greenland Caledonides 72°–75°N

Abstract

Systematic geological mapping of the East Greenland Caledonides demonstrates that the orogen is built up of WNW-directed thrust sheets displaced across foreland windows. The foreland windows in the southern half of the orogen are characterized by a thin (220–400 m) Neoproterozoic to Lower Palaeozoic succession, structurally overlain by two major Caledonian thrust sheets (Niggli Spids and Hagar Bjerg Thrust Sheets). The metasediments of the upper-level Hagar Bjerg Thrust Sheet host 940–910 Ma granites and migmatites formed during an early Neoproterozoic thermal or orogenic event, as well as Caledonian 435–425 Ma granites and migmatites. The uppermost unit of the thrust pile, the Franz Joseph Allochthon, comprises a very thick (18.5 km) Neoproterozoic to lower Palaeozoic sedimentary succession (Eleonore Bay Supergroup, Tillite Group, Kong Oscar Fjord Group). Total westward displacement of the thrust sheets was about 200–400 km, with shortening estimated at 40–60%. Major extensional faults post-date thrusting. Restoration of the thrust sheets indicates that the sequence of Caledonian orogenic events now preserved in East Greenland was initiated several hundred kilometres ESE of present-day East Greenland, as Baltica and its marginal assemblage of Early Palaeozoic accretions began to impinge on the Laurentian margin.