The fracture network, a proxy for mesoscale deformation: Constraints on layer parallel shortening history from the Malargüe fold and thrust belt, Argentina

Abstract

An analysis was performed of the fracture networks in the N-S trending thick-skinned Malargüe fold and thrust belt (MFTB). A total of 2000 planar structures including joints and veins were measured in different structural domains ranging from surficial thin-skinned systems detached in the cover to large-scale structures such as basement-cored folds. The investigated stratigraphic section ranges from the Middle Jurassic (Cuyo Group) to the Paleocene (Malargüe Group), including sandstones, siltstones, shales, and limestones. Four main fracture sets are identified trending, E-W, NW-SE, NE-SW, and N-S. The abutting relationships provide a reliable chronology between the four fracture sets which are ubiquitously found in the MFTB throughout the various structural domains. Due to this observation, we assume the fracture signal to be regional and developed in response to both large-scale processes and folding. In particular, based on a fold test and the characteristics of data dispersion, the fracture sets I, II, and III exhibit a prefolding origin, while set IV shows a synfolding origin. A regional interpretation of the various fractures is proposed, involving several stages of fracture formation from compaction to folding, including prefolding layer parallel shortening. The fracture signal yields useful insights about the structural history of the MFTB and the spatiotemporal evolution of the foreland tectonic regime since Late Cretaceous times. We then place the various identified fracture sets into the known pattern of geodynamic evolution since the Late Cretaceous.

Evidence of active shortening along the eastern border of the San Rafael basement block: characterization of the seismic source of the Villa Atuel earthquake (1929), Mendoza province, Argentina

“…Considering the Southern Andes and the particular case of the Malargue Fold–Thrust Belt, a systematically compressive regime recorded in the development of inverted basement structures in the foreland basin (Strecker et al 2011; this study), in the transmission of the crustal shortening in the intrabelt sedimentary cover (Branellec et al 2015 a , Branellec et al this issue) and in the record by meso- and microscale strain indicators such as fracture sets and matrix-scale strain (Branellec et al 2015b) is suggested. This pattern of deformation is also clearly evidenced further north in the Sierra Pampeanas (e.g.…”

Syn‐orogenic fluid flow in the Jaca basin (south Pyrenean fold and thrust belt) from fracture and vein analyses

“…Fractures networks of foreland settings can either be inherited from former orogenic episodes of deformations, developed during early compression by layer parallel shortening (LPS), or during further sediment burial stages (Engelder & Peacock, ; Bergbauer & Pollard, ; Bellahsen et al ., ; Tavani et al ., ; Branellec et al ., ). In our study, fractures originated from Pyrenean orogeny because studied rocks are syn‐orogenic (upper Cretaceous to upper Eocene).…”

“…LPS is widely recognized in foreland basin and fold‐and‐thrust belts (e.g. Bellahsen et al ., ; Beaudoin et al ., ; Branellec et al ., ). In response to LPS, transverse fractures develop before and during early folding.…”

“…Fractures are grouped in sets based (i) on their orientation, (ii) on their dip with respect to bedding, (iii) on their chronological timing of emplacement as determined by their abutting and crosscutting relationships, and (iv) by the presence of mineralization, or slicken fibres (e.g. Branellec et al ., ). The type of opening mode of fractures, mode I vs. mode I + II, is determined thanks to field observation and thin‐section analysis.…”

Vein formation during progressive Paleogene faulting and folding within the lower Cook Inlet basin, Alaska

“…The K parameter was used to evaluate the degree of clustering during each step of rotation (cf. Branellec et al, 2015) for each vein set using Fisher statistics (Fisher et al, 1987b). K is a dispersion or concentration factor defined by:…”