Preliminary results from fault-slip analysis of the Pärvie postglacial fault zone
Abstract
We aim at constraining the paleostress field of a special type of intraplate faulting, triggered by the retreat of continental glaciers along the longest known post-glacial fault (PGF), the Pärvie PGF. It is 155 km long and consists of a series of 3-10 m high fault scarps; most of them west-facing and north-northeast trending. The fault displaces postglacial sediments (Lagerbäck 1979). The displacement is interpreted to have been caused by a great earthquake (M≤8.2; Arvidson 1996) at the end or just after the last glaciation (~10 ky B.P.). The fault zone is still active on the microseismic scale; however, the regional stress field is yet relatively poorly constrained (Lindblom 2011). The PGFs in North Fennoscandia may have formed in the Precambrian (e.g. Olesen et al. 1992). Nevertheless, the stress history of the Pärvie PGF before the last glaciation is poorly known. To reconstruct its stress history, we have performed fault-slip analysis of fault slip data that reactivated the fault. We have collected fault slip data from a profile of outcrops across the Pärvie PGF in the valley wall in the Corruvagge valley in northern Sweden. Cross-cutting relationships, fracture mineralization and brittle behavior of the rock have been used to unravel the brittle history of the fault. At least three paleostress regimes have been identified. Preliminary results indicate that early formed brittle structures where the fracture filling minerals are dominated by amphibole and plagioclase were subjected to a strike-slip stress regime with a small component of extension. The two relatively younger stages of the brittle development of this structure can be related to a compressive respectively an extensional stress-field. The mineral assemblage in the two later brittle deformations is dominated by epidote. Several fractures from the younger stages are cross-cutting and displacing the older events. The mineral assemblages related to the younger stages show several fault-slip indicators and although the tectonic events causing the kinematic indicators are not identified at this stage it should be possible to do so with further analysis. References Arvidsson, R., 1996: Fennoscandian earthquakes: Whole crustal rupturing related to postglacial rebound. Science 274, 744-746. Lagerbäck, R, 1979: Neotectonic structures in northern Sweden. Geologiska Föreningens i Stockholm Förhandlingar (GFF) 100, 263-269. Lindblom, E 2011. Microearthquake Study of End-glacial Faults in Northern Sweden. Uppsala University: Licentiate Thesis, 54 pp. Olesen, O., Henkel, H., Lile, O.B., Mauring, E. & Rønning, J.S., 1992: Geophysical investigations of the Stuoragurra postglacial fault, Finnmark, northern Norway. J. Appl. Geophys. 29, 95-118.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.T23B2674B
- Keywords:
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- 8010 STRUCTURAL GEOLOGY / Fractures and faults;
- 8015 STRUCTURAL GEOLOGY / Local crustal structure;
- 8107 TECTONOPHYSICS / Continental neotectonics;
- 8168 TECTONOPHYSICS / Stresses: general