Some geometrical characteristics of inversion

Abstract

Summary The inversion of extensional fault systems results in the reversal of slip on the faults and expulsion of the synrift fill. During inversion the beds in the cover sequence shorten before the net extension at the basement level has been cancelled. Shortening of the sedimentary cover generates folding and backthrusting in the still downthrown hanging wall block. Intracratonic inverted basins in different parts of the Alpine Foreland show similar structural geometries with the major extensional faults which controlled basin development reactivated during subsequent compression. We use examples from the Western Approaches and offshore Holland (Broad Fourteens Basin) to illustrate the structural styles developed during inversion. The fundamental control on compressional structural geometry exerted by pre-existing extensional structures is also visible in more complexly deformed orogenic belts, like the Western Alps and the Pyrenees. In these areas inversion also occurs, but more commonly extensional faults which may not have inverted act as an indirect control on the location of ramps, and/or thrust orientation. Seismic data are normally required to establish these effects with certainty. However, as the body of knowledge builds up, it is possible to recognize certain geometrical characteristics which suggest the control of extensional faults in thrust belts. These include footwall shortcuts, out of sequence structures and arcuate thrust-fold traces.

The role of inherited extensional fault segmentation and linkage in contractional orogenesis: a reconstruction of Lower Cretaceous inverted rift basins in the Eastern Cordillera of Colombia

“…In addition, the polarity of normal faults, associated disparities in syntectonic sediment thickness, and existence of extensional transfer structures may exert an important control on orogenic evolution during contraction (e.g. Hayward & Graham, 1989).…”

“…In the more severely inverted basins of many orogens, however, detailed ¢eld-based accounts regarding the mechanical interaction of segmented former extensional faults, the nature of displacement transfer, and how such structures are incorporated into the orogenic realm are rare (Hayward & Graham, 1989;Garc|¤ a Senz, 2002;Kley et al, 2005;Monaldi et al, 2008). These problems are often compounded by a general lack of good seismic images with unequivocal extensional features.…”

Positive inversion of extensional footwalls in the southern Serra do Espinhaço, Brazil - insights from sandbox laboratory experiments

“…Only a few studies have described the inversion of a half-graben by the movement of the extensional footwall (e.g. McClay et al 1989, Butler 1989, Hayward and Graham 1989, Knott et al 1995. Their theoretical interpretations present some fea- 'pop-up' structure; and F-combined model. tures that were also produced in our experiments, such as the trapping of the rift fi lls in the hinterland of the inverted basin, the development of a thrust system in the foreland and the introduction of prerift sheets into the synrift sequence.…”

“…Both architectures are in good agreement with our experiment II. In addition, McClay et al (1989), Hayward and Graham (1989) and Knott et al (1995) proposed that, during the progressive evolution of basin inversion, rotation of the normal detachment ramp occurs until complete inversion. The evolution of an " overturned normal fault" can be seen in our physical model II (Fig.…”

The role of backstop shape during inversion tectonics physical models

“…and Hayward and Graham (1989), the basement, either in the hanging wall or in the footwall of the extensional detachment, may produce buttressing structures in the syn-rift sequence either by folding and associated cleavages, rotation in the foreland or backward propagating displacements.…”