The supposed thrust fault in the Dyle-Thyle outcrop area (Southern Brabant Massif, Belgium) re-interpreted as a folded low-angle extensional detachment

• Published in: Geologica Belgica Vol. 8; no. 3; pp. 53 - 69
• Main Authors: DEBACKER, Timothy N, HERBOSCH, Alain, SINTUBIN, Manuel
• Format: Journal Article
• Language: English; French
• Published: Bruxelles Geologica Belgica 2005; Université de Liège
• Subjects: Aeromagnetic; Anglo-Brabant deformation belt; Areal geology. Maps; Earth sciences; Earth, ocean, space; Exact sciences and technology; extensional detachment; fold transition zone; Geologic maps, cartography; Geophysics: general, magnetic, electric and thermic methods and properties; Internal geophysics; slate belt; steeply plunging folds; Tectonics. Structural geology. Plate tectonics; Belgium; Brabant Massif; Western Europe; similar folds; folding; plunging folds; transition zones; cleavage; lower Paleozoic; Aeromagnetic; displacements; thrust fault; deformation; fold transition zone; magnetic anomalies; tectonic controls; models; orientation; outcrops; aeromagnetic maps; Upper Cambrian; maps; extensional detachment; Europe; slates; steeply plunging folds; Lower Cambrian; metamorphic rocks; dip faults; Paleozoic; Cambrian; Anglo-Brabant deformation belt; slate belt
• ISSN: 1374-8505; 2034-1954

Since 1943 the anomalous contact in the Dyle-Thyle area between the Lower Cambrian Tubize Formation and older deposits, on the one hand, and the Upper Cambrian Mousty Formation and younger deposits, on the other hand, has been interpreted as a gently N-dipping, large-displacement thrust, the Orne-Noirmont-Baudecet thrust. The irregular fault trace and the presence of a supposed klippe at Court-St.-Etienne are both ascribed to the very gentle fault dip. However, a review of outcrop, borehole and geophysical data shows that there are no convincing arguments for such a gently N-dipping thrust. An alternative model is proposed in which the Orne-Noirmont-Baudecet fault is considered a pre-cleavage and pre-folding low-angle extensional detachment, similar to the Asquempont fault sensu Debacker in the Senne-Sennette area. The irregular subcrop trace of the Orne-Noirmont-Baudecet fault is attributed to the strongly variable fold orientations, associated with a transition zone between steeply plunging and gently plunging folds, similar to what has recently been described in the Senne-Sennette area. Although also this model remains speculative, it is the only model which successfully combines all the data from the Dyle-Thyle area and which is compatible also with the structural architecture of other outcrop and subcrop areas of the Brabant Massif.