Devonian basin initiation in East Greenland: a result of sinistral wrench faulting and Caledonian extensional collapse

Abstract

Following the Caledonian orogeny, large scale ESE–WNW extensional faulting and N–S directed sinistral wrenching affected East Greenland leading to the initiation of the Devonian basin. The NNE–SSW trending extensional faults have very large downthrows to the east exceeding 10 km and separate up to 90 km wide fault blocks, which during deformation were tilted approximately 12°. The tilting of one of the fault blocks led to uplift of deep-seated hot crystalline rocks in the eastern part causing contact metamorphism in the adjacent downfaulted block to the east. Based on K-Ar cooling ages, the faulting seems to have taken place during the Middle Devonian around 385 Ma, coinciding with the initiation of deposition within the Devonian basin. A N–S trending sinistral wrench fault zone developed in addition to the extensional faults leading to formation of synthetic and antithetic Riedel shears along the present-day western border of the Devonian basin. The timing of the wrench displacement cannot be younger than Middle Devonian. The extension faults and the wrench fault can be followed as regional structures in East Greenland and can be compared to similar Devonian extensional structures in northern Great Britain and to the major wrench faults in Scotland. No clear separation in time is possible between the extension and the wrenching, and a transtensional kinematic history is the most plausible. The basin-forming tectonic evolution in East Greenland during Middle Devonian can be related to an extensional collapse of an overthickened Caledonian crustal welt associated with wrench deformations due to late Caledonian shear displacements along plate boundaries. This evolution is analogous to the Devonian basin formation in northern Great Britain.

Laurentian margin evolution and the Caledonian orogeny—A template for Scotland and East Greenland

“…Larsen and Bengaard (1991) tentatively linked the Western fault zone with the Storstrømmen Shear Zone to the north and with the Great Glen Fault to the south. Dewey and Strachan (2003) argued that relative motion between Laurentia and Avalonia/Baltica changed from sinistrally transpressive collision at about 425 Ma to more orogen parallel sinistrally transtensional movements which persisted until c. 400…”

“…In central East Greenland, mid-Devonian continental sediments were deposited on the eroded Caledonian orogen; sedimentation was controlled, in part, by sinistral displacements along the Western fault zone (Larsen and Bengaard, 1991;Olsen, 1993). Larsen and Bengaard (1991) tentatively linked the Western fault zone with the Storstrømmen Shear Zone to the north and with the Great Glen Fault to the south.…”

CRUSMID-3D: Crustal Structure and Mineral Deposit Systems

“…The sequence was widely deformed by N-S syn-sedimentary open folding, westward thrusting and by uplift. Transtensional pull-apart basins started to form in Middle to Late Devonian with large scale ESE-WNW extensional faulting that displaced the Caledonian thrust units north of Kong Oscar Fjord (Higgins et al, 2004), and N-S directed sinistral wrench faulting (Larsen and Bengaard, 1991). The stress pattern shifted from oblique to a more orthogonal rifting in latest Devonian leading in late Carboniferous-early Permian to rotational block faulting along the new half graben basin margins (Fig.…”

“…ref.). Upper Carboniferous to lower Permian continental sedimentation took place within the wide tilted blocks (Larsen and Bengaard, 1991). Upper Permian sediments are observed both along the Post-Devonian Main Fault System on the western margin of Jameson Land and in Wegener Halvø showing that the original basin was more than 80 km wide (Henriksen, 1986).…”

The Tooth of Time: Lauge Koch's Last Lecture

“…The weakly metamorphosed Neoproterozoic succession is overlain by nearly 3 km of Cambrian and Ordovician carbonates, mostly limestone (Cowie and Adams 1957;Smith and Rasmussen 2008). An angular unconformity separates the mainly marine Neoproterozoic and early Paleozoic strata from terrestrial redbeds, including coarsegrained conglomerates, of Devonian age (Larsen and Bengaard 1991;Hartz 2000;Larsen et al 2008). Still younger rocks occur along the outer coast, including outliers of the great Paleogene igneous province south of Scoresby Sound (Noe-Nygaard 1976).…”