Late stages of continent-continent collision: Timing, kinematic evolution, and exhumation of the Northern rim (Aar Massif) of the Alps

Herwegh, Marco; Berger, Alfons; Glotzbach, Christoph; Wangenheim, Christoph; Mock, Samuel; Wehrens, Philip; Baumberger, Roland; Egli, Daniel; Kissling, Edi

doi:10.1016/j.earscirev.2019.102959

Cited by 45 publications

(64 citation statements)

References 111 publications

(127 reference statements)

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“…It has been suggested that rapid rock uplift of the external Aar Massif (Fig. 1), which is in close proximity to the Thun and Lucerne sections, likely started at ∼ 20 Ma (Herwegh et al, 2017(Herwegh et al, , 2019. However, we do not see a related signal in the detrital zircon U-Pb age patterns (Fig.…”

Section: Abrupt Oligo-miocene Detrital Zircon U-pb Provenance Shiftcontrasting

confidence: 67%

“…1) occurred between 25 and 20 Ma and resulted in a greenschist overprint of the basement in the external massifs (Niggli and Niggli, 1965;Frey et al, 1980;Rahn et al, 1994). A late-stage phase of basement-involved duplexing resulted in the rise of the external massifs and the final shape of the Central Alps (Herwegh et al, 2017;Mair et al, 2018;Herwegh et al, 2019).…”

Section: Alpine Orogenymentioning

confidence: 99%

“…Yet, such insights are of critical importance for reconstructing the causal relationships between orogenic events and the basinal stratigraphic response. In the recent years, advances in isotopic provenance tracing techniques, including detrital mica 40 Ar/ 39 Ar dating (e.g., von Eynatten et al, 1999;von Eynatten and Wijbrans, 2003), zircon fission track dating of detrital clasts (Spiegel et al, 2000), detrital garnet and epidote geochemical analysis (Spiegel et al, 2002;Stutenbecker et al, 2019), and detrital zircon U-Pb geochronology (e.g., Malusà et al, 2016;Anfinson et al, 2016;Lu et al, 2018;Sharman et al, 2018a) have offered more quantitative links to Alpine geodynamic processes, revealed through seismic tomography imaging (Lippitsch et al, 2003;Fry et al, 2010;Hetényi et al, 2018) or bedrock geochronology (synthesized by Boston et al, 2017). In this study, we integrate high-density U-Pb and trace and rare-earth element analysis of detrital zircon from the late-Eocene to mid-Miocene stratigraphic record of the Swiss Molasse Basin to elucidate the tectonic activity and unroofing history of the Central Alps.…”

Section: Introductionmentioning

confidence: 99%

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Tectonic exhumation of the Central Alps recorded by detrital zircon in the Molasse Basin, Switzerland

et al. 2020

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Abstract. Eocene to Miocene sedimentary strata of the Northern Alpine Molasse Basin in Switzerland are well studied, yet they lack robust geochronologic and geochemical analysis of detrital zircon for provenance tracing purposes. Here, we present detrital zircon U–Pb ages coupled with rare-earth and trace element geochemistry to provide insights into the sedimentary provenance and to elucidate the tectonic activity of the central Alpine Orogen from the late Eocene to mid Miocene. Between 35 and 22.5 ± 1 Ma, the detrital zircon U–Pb age signatures are dominated by age groups of 300–370, 380–490, and 500–710 Ma, with minor Proterozoic age contributions. In contrast, from 21 Ma to ∼ 13.5 Ma (youngest preserved sediments), the detrital zircon U–Pb age signatures were dominated by a 252–300 Ma age group, with a secondary abundance of the 380–490 Ma age group and only minor contributions of the 500–710 Ma age group. The Eo-Oligocene provenance signatures are consistent with interpretations that initial basin deposition primarily recorded unroofing of the Austroalpine orogenic lid and lesser contributions from underlying Penninic units (including the Lepontine dome), containing reworked detritus from Variscan, Caledonian–Sardic, Cadomian, and Pan-African orogenic cycles. In contrast, the dominant 252–300 Ma age group from early Miocene foreland deposits is indicative of the exhumation of Variscan-aged crystalline rocks from the Lepontine dome basement units. Noticeable is the lack of Alpine-aged detrital zircon in all samples with the exception of one late Eocene sample, which reflects Alpine volcanism linked to incipient continent–continent collision. In addition, detrital zircon rare-earth and trace element data, coupled with zircon morphology and U∕Th ratios, point to primarily igneous and rare metamorphic sources. The observed switch from Austroalpine to Penninic detrital provenance in the Molasse Basin at ∼ 21 Ma appears to mark the onset of synorogenic extension of the Central Alps. Synorogenic extension accommodated by the Simplon fault zone promoted updoming and exhumation the Penninic crystalline core of the Alpine Orogen. The lack of Alpine detrital zircon U–Pb ages in all Oligo-Miocene strata corroborate the interpretations that between ∼ 25 and 15 Ma, the exposed bedrock in the Lepontine dome comprised greenschist-facies rocks only, where temperatures were too low for allowing zircon rims to grow, and that the Molasse Basin drainage network did not access the prominent Alpine-age Periadriatic intrusions located in the area surrounding the Periadriatic Line.

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Section: Abrupt Oligo-miocene Detrital Zircon U-pb Provenance Shiftcontrasting

confidence: 67%

Section: Alpine Orogenymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Tectonic exhumation of the Central Alps recorded by detrital zircon in the Molasse Basin, Switzerland

et al. 2020

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“…undeformed) Molasse will be essential. Furthermore, we expect that ongoing seismotomographic investigations will disclose further details to constrain the deep-seated driving mechanisms (Hetényi et al, 2018a).…”

Section: The Exceptional Position Of the Bavarian Subalpine Molassementioning

confidence: 97%

Long-wavelength late-Miocene thrusting in the north Alpine foreland: implications for late orogenic processes

et al. 2020

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Abstract. In this paper, we present new exhumation ages for the imbricated proximal molasse, i.e. Subalpine Molasse, of the northern Central Alps. Based on apatite (U-Th-Sm)/He thermochronometry, we constrain thrust-driven exhumation in the Subalpine Molasse between 12 and 4 Ma. This occurs synchronously to the main deformation in the adjacent Jura fold-and-thrust belt farther north and to the late stage of thrust-related exhumation of the basement massifs (i.e. external crystalline massifs) in the hinterland. Our results agree with other findings along the north Alpine foreland. While site-specific variations in the mechanical stratigraphy of the molasse deposits influence the pattern of thrusting at the local scale, we observe that late-Miocene thrusting is a long-wavelength feature occurring along the north Alpine foreland roughly between Lake Geneva and Salzburg. The extent of this thrusting signal as well as the timing suggests that late-Miocene thrusting in the north Alpine foreland coincides with the geometries and dynamics of the attached Central Alpine slab at depth. Interestingly, this implies that the slab geometry at depth does not coincide with the boundary between the Eastern and Central Alps as observed in the surface geology. Using this observation, we propose that thrusting in the Subalpine Molasse and consequently also the late stage of thrust-related exhumation of the external crystalline massifs, as well as the main deformation in the Jura fold-and-thrust belt are at least partly linked to changes in slab dynamics.

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“…The Grimsel area is in the Aar Massif, one of the External Crystalline Massifs of the Alps (Rolland et al, 2009;Herwegh et al, 2020). Here, epidote-quartz veins are common in the Central Aar granite and in the Grimsel granodiorite, which during the earliest Permian intruded into a polycyclic basement bearing evidence of Ordovician metamorphism and Variscan overprint (Schaltegger and Corfu, 1992;Berger et al, 2017).…”

Section: Geological Context and Field Relationsmentioning

confidence: 99%

U–Pb geochronology of epidote by LA–ICP–MS as a tool for dating hydrothermal-vein formation

Peverelli

Ewing

Rubatto

et al. 2020

Preprint

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Abstract. Monoclinic epidote is a low-µ (µ = 283U / 204Pb) mineral occurring in a variety of geological environments, participating in many metamorphic reactions and stable throughout a wide range of pressure–temperature conditions. Despite containing fair amounts of U, its use as a U–Pb geochronometer has been hindered by the commonly high contents of initial Pb with isotopic compositions that cannot be assumed a priori. We present U–Pb geochronology of hydrothermal-vein epidote spanning a wide range of Pb (3.9–190 µg g−1), Th (0.009–38 µg g−1) and U (2.6–530 µg g−1) contents and with µ values between 7–510 from the Albula area (eastern Swiss Alps), from the Grimsel area (central Swiss Alps) and from the Heyuan fault (Guangdong province, China). The investigated epidote samples show appreciable fractions of initial Pb that vary to different extents. A protocol has been developed for in situ U–Pb dating of epidote by spot-analysis laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) with a magmatic allanite as primary reference material. The suitability of the protocol and the reliability of the measured isotopic ratios have been ascertained by independent measurements of 238U / 206Pb and 207Pb / 206Pb ratios respectively by quadrupole and multicollector ICP–MS applied to epidote micro-separates digested and diluted in acids. For age calculation, we used the Tera–Wasserburg (207Pb / 206Pb–238U / 206Pb) diagram, which does not require corrections for initial Pb and provides the initial 207Pb / 206Pb ratio if all intra-sample analyses are co-genetic. Petrographic and microstructural data indicate that the calculated ages date the crystallization of vein epidote from a hydrothermal fluid and that the U–Pb system was not reset to younger ages by later events. Vein epidote from the Albula area formed in the Paleocene (62.7 ± 3.0 Ma) and is related to Alpine greenschist-facies metamorphism. The Miocene (19.1 ± 4.0 Ma and 16.9 ± 3.7 Ma) epidote veins from the Grimsel area formed during the Handegg phase (22–17 Ma) of the Alpine evolution of the Aar Massif. Identical initial 207Pb / 206Pb ratios reveal homogeneity in Pb isotopic compositions of the fluid across ca. 200 m. Vein epidote from the Heyuan fault is Cretaceous in age (108.1 ± 8.4 Ma) and formed during the early movements of the fault. In situ U–Pb analyses of epidote returned reliable ages of otherwise undatable epidote-quartz veins. The Tera–Wasserburg approach has proven pivotal for in situ U–Pb dating of epidote and the decisive aspect for low age uncertainties is the variability in intra-sample initial Pb fractions.

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Late stages of continent-continent collision: Timing, kinematic evolution, and exhumation of the Northern rim (Aar Massif) of the Alps

Cited by 45 publications

References 111 publications

Tectonic exhumation of the Central Alps recorded by detrital zircon in the Molasse Basin, Switzerland

Tectonic exhumation of the Central Alps recorded by detrital zircon in the Molasse Basin, Switzerland

Long-wavelength late-Miocene thrusting in the north Alpine foreland: implications for late orogenic processes

U–Pb geochronology of epidote by LA–ICP–MS as a tool for dating hydrothermal-vein formation

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