Extended data for: Impact of sub-basalt thrust systems on the Faroe continental shelf for the late Paleoproterozoic–Cenozoic tectonic evolution of the margin

High-resolution version of the seismic reflection data off the Faroe Islands from TGS presented in "Impact of sub-basalt thrust systems on the Faroe continental shelf for the late Paleoproterozoic–Cenozoic tectonic evolution of the margin". The data were acquired by Western Geophysical in 1994-1995 and reprocessed by TGS between April 2011 and January 2012 (Nicholson, 2012; internal reprocessing report accessible upon contacting TGS). Nicholson, A.: Final Report Seismic Data Re-processing Offshore Faroes, April 2011-January 2012, Project No. 624, Project Code OF9495RE11, 2012. (2024-08-09)

Extended data for "Impact of sub-basalt thrust systems on the Faroe continental shelf for the late Paleoproterozoic–Cenozoic tectonic evolution of the margin". The dataset includes the following: -Figure_2a: Interpreted (up) and uninterpreted (down) Figure 2a: NNE–SSW-trending seismic transect west of the Faroe Islands showing the occurrence of major NNE-dipping, top-SSW thrust systems below Cenozoic lavas off the Faroe Islands. The thrust systems consist of major mylonitic shear surfaces (red lines) and of tightly folded bedding or foliation surfaces (yellow lines). Relatively small (kilometer to hundreds of meters wide) features of interest include asymmetric (up to isoclinal recumbent) folds, duplexes, and antiformal thrust stacks. The vergence of asymmetric fold structures (and mylonitic shear surfaces) is opposite on either side of major ridges and highs, e.g., at Wyville–Thomson Ridge, suggesting limited amounts of movement. There are Z-shaped reflections in the lower part of the Suðurøy and West Faroe fault zones suggesting extensional reactivation of the fault zones. -Figure_2b: Interpreted (up) and uninterpreted (down) Figure 2b: NE–SW-trending seismic transects showing the continuation of the top-SSW Wyville–Thomson fault zone at Wyville–Thomson Ridge. -Figure_2c: Interpreted (up) and uninterpreted (down) Figure 2c: NE–SW-trending seismic transects showing the continuation of the top-SSW Wyville–Thomson fault zone at Wyville–Thomson Ridge. -Figure_2d: Interpreted (up) and uninterpreted (down) Figure 2d: NE–SW-trending seismic transects showing the continuation of the top-SSW Wyville–Thomson fault zone at Wyville–Thomson Ridge. -Figure_2e: Interpreted (up) and uninterpreted (down) Figure 2e: WNW–ESE-trending seismic section along the Wyville–Thomson Ridge showing tens of kilometers wide, open, NNE–SSW-striking macrofolds deforming the top-SSW Wyville–Thomson fault zone. The opposite sense of shear is indicated by asymmetric folds and minor brittle thrusts on either limbs of the macrofolds, which suggests limited amount of tectonic displacement. In the northwest, the section displays gently northwest-dipping, moderate-amplitude reflections (blue lines), curving-downward reflections (black lines), and southeast-dipping disruption surfaces (black lines) interpreted respectively as SDRs, saucer-shaped sills, and dykes and sills. The later crosscut the folded Wyville–Thomson fault zone. The Wyville–Thomson fault zone and related asymmetric folds extend below and northwest of the SDRs suggesting that the Iceland–Faroe Ridge consists (at least partly) of continental crust. -Figure_2f: Interpreted (up) and uninterpreted (down) Figure 2f: ENE–WSW-trending seismic section at the Munkagrunnur Ridge showing asymmetric folds indicating top-east kinematics along the Munkagrunnur fault zone. The Z-shaped reflections suggest extensional reworking of the fault zone. -Figure_2g: Interpreted (up) and uninterpreted (down) Figure 2g: NE–SW-trending seismic transect at Munkagrunnur Ridge showing the dominance of top-NNE kinematic indicators (e.g., NNE-verging folds and top-NNE minor brittle thrusts) along the Munkagrunnur fault zone. -Figure_2h: Interpreted (up) and uninterpreted (down) Figure 2h: NW–SE-trending transect along the Munkagrunnur Ridge showing the reworking of the Munkagrunnur fault zone by a tens of kilometers wide, NNE–SSW-striking, SSW-plunging macrofold with opposite sense of shear on either flanks. -Figure_2i: Interpreted (up) and uninterpreted (down) Figure 2i: Folded portion of the West Faroe fault zone that was overprinted by a top-northwest Caledonian thrust. The listric, post-Caledonian, brittle, normal fault, which offsets the Top-basement reflection by ca. 1 second (TWT) merges with the top-northwest thrust at depth suggesting it formed along preexisting zones of weakness in the crust. (2024-12-02)

Abstract of the revised, accepted version of the related manuscript "Impact of sub-basalt thrust systems on the Faroe continental shelf for the late Paleoproterozoic–Cenozoic tectonic evolution of the margin".

Background The Faroe margin in the northeastern Atlantic is segmented by margin-orthogonal, WNW–ESE-striking lineaments extending several hundred kilometers out to the continent–ocean transition. Despite several earlier studies speculating that these features are the product of reactivation of pre-Cenozoic basement-seated structures at depth, the thick Cenozoic volcano-sedimentary sequences deposited along the margin mask the underburden, thus rendering the identification and interpretation of such structures and resolving the pre-Cenozoic history of the area challenging. The present study documents for the first time the existence of margin-orthogonal basement-seated thrust systems and describes their detailed geometry, kinematics, and tectonic evolution.

Methods We interpreted basement-seated tectonic structures on seismic reflection data from TGS on the Faroe Platform and the Wyville–Thomson and Munkagrunnur ridges using the newly established seismic facies of major thrust systems.

Results The data show that the Wyville–Thomson Ridge, Munkagrunnur Ridge, and Faroe Platform are cored by WNW–ESE-striking thrust systems hundreds of kilometers long and 30–50 km wide, showing dominantly top-SSW kinematics. The thrusts were reworked into NE–SW-striking folds during the Caledonian Orogeny and controlled the formation of Caledonian thrusts, which in turn controlled the formation of post-Caledonian faults. The pre-Caledonian nature of the WNW–ESE-striking thrusts and their geometry and kinematics suggest a relationship with late Paleoproterozoic Laxfordian shear zones onshore northern Scotland and the continuation of the coeval Nagssugtoqidian Orogen in southeastern Greenland, the Ammassalik Belt. The thrust systems also align with the Tornquist Zone in eastern Europe and the North Sea, thus suggesting either that they controlled the formation of the Tornquist Zone or a possibly much longer (Paleoproterozoic?) tectonic history for the Tornquist Zone.

Conclusions The Faroe Island margin is crosscut by late Paleoproterozoic Laxfordian–Nagssugtoqidian thrust systems, which controlled further tectonic development of the margin.

(2024-12-02)