Triangle zones – Geometry, kinematics, mechanics, and the need for appreciation of uncertainties

Hagke, Christoph von; Malz, Alexander

doi:10.1016/j.earscirev.2017.11.003

Cited by 54 publications

(42 citation statements)

References 106 publications

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“…20 Ma and 12 Ma (von Hagke et al, 2014;Kempf et al, 1999;Ortner et al, 2015). Despite the uncertainty in the shortening estimates within the Subalpine Molasse (Burkhard and Sommaruga, 1998;von Hagke and Malz, 2018;Ortner et al, 2015), we observe that late Miocene cumulative shortening of the Subalpine Molasse and the Jura FTB decreases constantly from the west to the east from >30 km near Geneva to 20 km near Lake Constance, before finally decreasing to <1 km near Salzburg (12.8° E; Fig. 5b).…”

Section: Late Miocene Shortening Estimatesmentioning

confidence: 78%

Late Miocene thrusting in the North Alpine foreland: Driven by a deep-seated process and shaped by the local mechanical stratigraphy

Mock

Hagke

Schlunegger

et al. 2019

Preprint

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Abstract. Besides classical emplacement and accretion related nappe tectonics, the Oligocene to middle Miocene post-collisional evolution of the central European Alps was also characterized by pronounced vertically directed tectonics. These are expressed by backthrusting along the Insubric Line and the subsequent uplift of the External Crystalline Massifs (ECMs). During late Miocene times, the Central Alps experienced lateral growth when deformation propagated into the external parts of both the pro- and retro-side of the orogen. For the North Alpine foreland, pro-wedge propagation of deformation has been kinematically and spatially linked to the uplift and exhumation of the ECMs. In this paper, we investigate the young exhumation history of the North Alpine foreland. Based on low-temperature apatite (U-Th-Sm)/He thermochronometry, we constrain thrusting in the Subalpine Molasse between 12 Ma and 5 Ma, thus occurring coeval to the main deformation phase in the adjacent Jura fold-and-thrust belt (FTB) and late stage exhumation of the ECMs. However, this pattern of tectonic activity is not restricted to areas which are bordered by the ECMs, but is consistent along the entire front of the Central Alps, regardless of its hinterland architecture. The local-scale pattern of strain partitioning and style of deformation is governed by lateral variations in the sedimentary foreland basin architecture. We suggest that the large-scale constant tectonic signal is the response to a shift in tectonic forces caused by a deep-seated geodynamic process. This resulted in a change from dominantly vertical to orogen-scale horizontal tectonics and an associated orogen-perpendicular growth of crustal thickening. We constrain the onset of this major tectonic change to ca. 15 Ma in the Southern Alps and ca. 12 Ma in the North Alpine foreland, where it results in (re-)activation of thrusts in the Subalpine Molasse and folding in the Jura FTB.

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Section: Late Miocene Shortening Estimatesmentioning

confidence: 78%

Late Miocene thrusting in the North Alpine foreland: Driven by a deep-seated process and shaped by the local mechanical stratigraphy

Mock

Hagke

Schlunegger

et al. 2019

Preprint

Self Cite

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“…The signal of a decreasing amount of horizontal shortening seems to be robust, despite the admittedly large uncertainties with respect to estimates in the Subalpine Molasse (see e.g. Burkhard and Sommaruga, 1998;von Hagke and Malz, 2018;Ortner et al, 2015). As stated below (see next comment), there is no evidence for late Miocene shortening further east than ca 12.8 • E as shown by the studies of Hinsch (2013) and Beidinger and Decker (2014).…”

Section: Interactive Commentmentioning

confidence: 74%

Reply to Nicola Levi's 'Review of Mock et al.'

Mock¹

2019

Preprint

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We appreciate the referee's detailed and constructive comments on our manuscript. We are pleased to see that most of the comments are minor in nature. The referee's major points of concerns are (1) the ambiguity regarding to where the focus of the study is throughout the manuscript and the somewhat unclear terminology regarding the geographical and tectonic descriptions (e.g. Central vs. Eastern Alps), and (2) the lack of data to justify the along-strike comparison which we aim for in the manuscript.

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“…They also differ from triangle zones that are formed above a single detachment (i.e., the type I triangle zone; Fig. 1A), which are simpler structures that can only accommodate very limited shortening (von Hagke and Malz, 2018). In contrast, the type 1 triangle zone in fold 3 shown here likely overlies deeper structures above the basal detachment (Figs.…”

Section: Implications For Triangle Zone Structuresmentioning

confidence: 75%

“…Triangle zones are "structures with a triangular shape in section view accommodating shortening by coeval activity of a basal thrust and an associated backthrust of opposite vergence (e.g., Fig. 1; von Hagke and Malz, 2018). This study provides new details of triangle zone and wedge thrust structures within a submarine fold belt formed across multiple detachments within overpressured shales, especially in the third dimension (i.e., along strike).…”

Section: Implications For Triangle Zone Structuresmentioning

confidence: 84%

Growth of triangle zone fold-thrusts within the NW Borneo deep-water fold belt, offshore Sabah, southern South China Sea

McClay

Vera

2019

Geosphere

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The NW Borneo deep-water fold-and-thrust belt, offshore Sabah, southern South China Sea, contains a structurally complex region of three to four seafloor ridges outboard of the shelf-slope break. Previous studies have suggested the seafloor ridges formed either above shale diapirs produced by mass movement of overpressured shales (i.e., mobile shale) or above an imbricate fold-and-thrust array. Here, we performed tectonostratigraphic analyses on a petroleum industry three-dimensional (3-D) seismic volume that imaged the full growth stratal record. We show fold growth history, deformation styles, along-strike structural variabilities, and synkinematic sedimentation during triangle zone–style fold growth. Nine seismic horizons within growth strata were mapped and correlated to petroleum industry seismostratigraphy. Synkinematic sedimentation interactions with growing folds and near-surface strains were analyzed from seismic attribute maps. We interpret that the seafloor structures were formed by imbricate thrusts above multiple detachments. We estimate ∼8 km minimum shortening since the late Miocene ca. 10 Ma. The folds show oversteepened fold forelimbs, back-rotated backlimbs, and forward-vergent (NW to NNW) “blind” thrust ramps that terminate within the growth strata. Fold cores show evidence of internal shear. Immature folds show detachment fold geometries, whereas mature folds show forelimb break thrusts, type I triangle zones, and rotated forward-vergent roof thrusts. Thrust linkages spaced ∼10 km apart were exploited as thrust top synkinematic sedimentation pathways; the linkages also partition near-surface strains. Our comprehensive, three-dimensional documentation of triangle zone fold growth and sedimentation in a deep-water fold belt highlights internal shear, multiple detachments, and opposite thrust vergence; mobile shales are not required to explain the deformation.

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Triangle zones – Geometry, kinematics, mechanics, and the need for appreciation of uncertainties

Cited by 54 publications

References 106 publications

Late Miocene thrusting in the North Alpine foreland: Driven by a deep-seated process and shaped by the local mechanical stratigraphy

Late Miocene thrusting in the North Alpine foreland: Driven by a deep-seated process and shaped by the local mechanical stratigraphy

Reply to Nicola Levi's 'Review of Mock et al.'

Growth of triangle zone fold-thrusts within the NW Borneo deep-water fold belt, offshore Sabah, southern South China Sea

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