Reconciling late faulting over the whole Alpine belt: from structural analysis to geochronological constrains

Bertrand, Audrey; Sue, Christian

doi:10.1007/s00015-017-0265-4

Cited by 10 publications

(8 citation statements)

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“…Concurrently to the Miocene progradation of the collision front towards the external zones, the inner part of the belt was affected by orogen-parallel extension, crosscutting earlier compressional structures and resulting in intertwined networks of normal and strike-slip faults (e.g. Champagnac et al 55 (2006); Sue and Tricart (2003); Bertrand and Sue (2017)). A late phase of orogen-perpendicular extension developed in the core of the Western Alps during the Plio-Pleistocene (Bilau et al, 2020;Sue et al, 2007), leading to the extensional reactivation of the FPT .…”

Section: Introductionmentioning

confidence: 99%

Present-day geodynamics of the Western Alps: new insights from earthquake mechanisms

Mathey¹,

Sue²,

Pagani³

et al. 2020

Preprint

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Abstract. Due to the low to moderate seismicity of the European Western Alps, few focal mechanisms are available to this day in this region, and the corresponding current seismic stress and strain fields remain partly elusive. The development of dense seismic networks in the past decades now provides a substantial amount of seismic records down to low magnitudes. The corresponding data, while challenging to handle due to their amount and relative noise, represent a new opportunity to increase the spatial resolution of seismic deformation fields. The aim of this paper is to quantitatively assess the current seismic stress and strain fields within the Western Alps, from a probabilistic standpoint, using new seismotectonic data. The dataset comprises more than 30,000 earthquakes recorded by dense seismic networks since 1989 and more than 2200 focal mechanisms newly computed in a consistent manner. The global distribution of P and T axes plunges confirms a majority of transcurrent focal mechanisms in the overall alpine realm, combined with pure extension localized in the core of the belt. We inverted this new set of focal mechanisms through several strategies, including a seismotectonic zoning scheme and grid procedure, revealing extensional axes oriented obliquely to the strike of the belt. The Bayesian inversion of this new dataset of focal mechanisms provides a probabilistic continuous map of the style of seismic deformation in the Western Alps. Extension is found clustered, instead of continuous along the backbone of the belt. Compression is robustly retrieved only in the Po plain, which lays at the limit between the Adriatic and Eurasian plates. High frequency spatial variations of the seismic deformation are consistent with surface horizontal GNSS measurements as well as with deep lithospheric structures, thereby providing new elements to understand the current 3D dynamics of the belt. We interpret the ongoing seismotectonic and kinematic regimes as being controlled by the joint effects of far-field forces –imposed by the counterclockwise rotation of Adria with respect to Europe- and of buoyancy forces in the core of the belt, which together explain the high frequency patches of extension and of marginal compression overprinted on an overall transcurrent tectonic regime.

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Section: Introductionmentioning

confidence: 99%

Present-day geodynamics of the Western Alps: new insights from earthquake mechanisms

Mathey¹,

Sue²,

Pagani³

et al. 2020

Preprint

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“…A Miocene age has been proposed for the onset of the extensional activation of the PFT based on AFT dating on both sides of this major fault, i.e. in the Pelvoux external crystalline massif and in the Champsaur sandstones to the west and in the Briançonnais zone to the east (Tricart et al, 2001(Tricart et al, , 2007Beucher et al, 2012). The Briançonnais zone corresponds to the east hang-Figure 6.…”

Section: Discussionmentioning

confidence: 99%

“…In this compartment, AFT ages ranging from 30 to 20 Ma are interpreted as the exhumation age of this area related to the compressional activity of the PFT during the Alpine collision, the motion of which is constrained by direct 40 Ar/ 39 Ar dating on phengite at 35-25 Ma (Simon-Labric et al, 2009;Bellanger et al, 2015). To the west (footwall of the PFT), the AFT ages range from 13 to 4 Ma in the Pelvoux external crystalline massif (Beucher et al, 2012) and from 9 to 4 Ma in the Champsaur sandstones (Tricart et al, 2007), and are interpreted as the extensional reactivation of the PFT by the latter authors. As the AFT dates record an exhumation age associated with cooling below ∼ 100 • C (Ault et al, 2019), they may not correspond to an age of PFT activity but rather record an erosion process that is related to both climatic and tectonic processes (e.g.…”

Section: Discussionmentioning

confidence: 99%

Extensional reactivation of the Penninic frontal thrust 3 Myr ago as evidenced by U–Pb dating on calcite in fault zone cataclasite

et al. 2021

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Abstract. In the Western Alps, the Penninic frontal thrust (PFT) is the main crustal-scale tectonic structure of the belt. This thrust transported the high-pressure metamorphosed internal units over the non-metamorphosed European margin during the Oligocene (34–29 Ma). Following the propagation of the compression toward the European foreland, the PFT was later reactivated as an extensional detachment associated with the development of the High Durance extensional fault system (HDFS). This inversion of tectonic displacement along a major tectonic structure has been widely emphasized as an example of extensional collapse of a thickened collisional orogen. However, the inception age of the extensional inversion remains unconstrained. Here, for the first time, we provide chronological constraints on the extensional motion of an exhumed zone of the PFT by applying U–Pb dating on secondary calcites from a fault zone cataclasite. The calcite cement and veins of the cataclasite formed after the main fault slip event, at 3.6 ± 0.4–3.4 ± 0.6 Ma. Cross-cutting calcite veins featuring the last fault activity are dated at 2.6 ± 0.3–2.3 ± 0.3 Ma. δ13C and δ18O fluid signatures derived from these secondary calcites suggest fluid percolation from deep-seated reservoir at the scale of the Western Alps. Our data provide evidence that the PFT extensional reactivation initiated at least ∼ 3.5 Myr ago with a reactivation phase at ∼ 2.5 Ma. This reactivation may result from the westward propagation of the compressional deformation toward the external Alps, combined with the exhumation of external crystalline massifs. In this context, the exhumation of the dated normal faults is linked to the eastward translation of the HDFS seismogenic zone, in agreement with the present-day seismic activity.

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“…Post‐orogenic brittle tectonics in the Eastern Alps has been the object of several paleostress studies focused on the poly‐phase kinematics of major fault zones and ductile shear zones overprinted by brittle faulting (e.g., Sue & Tricart, 2003). We build a database trying to homogenize all the paleostress data in study area that as far as we know have been published (pink triangles in Figure 1; e.g., Agliardi et al., 2009; Bartel et al., 2014; Bertrand & Sue, 2017; Castellarin & Cantelli, 2000; Luth et al., 2013; Ortner, 2003; Pischinger et al., 2008; Prosser, 1998, 2000; Scardia et al., 2014; Verwater et al., 2021; Viola et al., 2001; Zago, 2012). The extent and complexity of the study area make the acquisition of new data possible only in limited sectors (yellow triangles in Figure 1), where we focused on some major faults close to the western rim of the Dolomites Indenter—DI (Section 4.4).…”

Section: Methodsmentioning

confidence: 99%

Stress Patterns and Crustal Anisotropy in the Eastern Alps: Insights From Seismological and Geological Observations

Villani,

Antonioli,

Pastori

et al. 2024

Tectonics

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In the Eastern Alps, the indentation of the Adriatic promontory since the Cenozoic affected the kinematics of separate crustal domains bounded by faults that accommodate lateral extrusion processes and differential shortening. Deciphering the pattern of crustal stresses in the orogen interior is challenging, due to the lack of in situ stress measurements at crustal depths. We define stress regimes and the orientations of the most‐compressive horizontal stress (SHmax) by integrating published results with new data, including stress analysis from fault plane solutions, estimation of crustal anisotropy through the shear wave splitting analysis, paleostress determination from fault slip data, and computation of cumulative seismic displacements. The retrieved regional SHmax are generally consistent with N‐S convergence. In the northern part of the study area, current stress orientations are almost parallel to paleo‐SHmax, suggesting a rather uniform compressional regime since the late Cenozoic. Conversely, sharp deflections and divergence with paleo‐SHmax appear at the western border of the Adriatic promontory across major transpressive and extensional shear zones and in the Southalpine domain, indicating a change in tectonically induced second‐order stresses. A current strike‐slip regime with subordinate orogen‐parallel seismic displacements affects a belt to north of the Periadriatic Lineament and NE‐extension characterizes the Ortles‐Engandine region. Seismic anisotropy locally exhibits fault‐parallel fast axes (Brenner‐Giudicarie fault‐systems, Dinaric and Southalpine thrusts), whereas stress‐induced anisotropy parallel to SHmax characterizes the southern part of the orogen. Cumulative seismic displacements are small compared to geodetic ones, and unravel partitioning of deformation into second‐order transpressive and extensional belts in response to indentation.

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Reconciling late faulting over the whole Alpine belt: from structural analysis to geochronological constrains

Abstract: International audienc

Cited by 10 publications

References 123 publications

Present-day geodynamics of the Western Alps: new insights from earthquake mechanisms

Present-day geodynamics of the Western Alps: new insights from earthquake mechanisms

Extensional reactivation of the Penninic frontal thrust 3 Myr ago as evidenced by U–Pb dating on calcite in fault zone cataclasite

Stress Patterns and Crustal Anisotropy in the Eastern Alps: Insights From Seismological and Geological Observations

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