40Ar/39Ar dating of fault : Evidence of an Eo-alpine event (128 Ma) in Greater Kabylia (Algeria): Geodynamic consequences

Cheilletz, Alain; Ruffet, Gilles; Marignac, C.; Kolli, Omar; Gasquet, Dominique; Féraud, Gilbert; Bouillin, Jean-Pierre

doi:10.1007/bf02891382

Cited by 6 publications

(6 citation statements)

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“…Consequently, these rocks too do not seem to have been affected by ductile deformation and dynamic recrystallisation related to the strike-slip fault, the movement of which is dated by synkinematic 277 Ma-old granites (Wang et al 2008a, this issue). Cheilletz et al (1999) and Alexandrov et al (2002) have pointed out that saddle-shaped age spectra, similar to the one obtained for muscovite XJ679, may result from the presence of different reservoirs in partially recrystallised mica grains with distinct argon compositions that degas over a different energy interval: a primary, unrecrystallised or inherited domain (low and high temperature steps) and a newly formed or recrystallised one (saddle minimum in the intermediate to high temperature steps). As suggested by Castonguay et al (2007), the younger subdomains formed by growth or recrystallisation could characterise the last isotopic record during a protracted (re)crystallisation history.…”

Section: Meaning Of Permian 40 Ar/ 39 Ar Agesmentioning

confidence: 74%

New 40Ar/39Ar age constraints on the Late Palaeozoic tectonic evolution of the western Tianshan (Xinjiang, northwestern China), with emphasis on Permian fluid ingress

Jong

Wang

Faure

et al. 2008

Int J Earth Sci (Geol Rundsch)

151

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International audienceLaser-probe dating of mylonite whole-rock samples from the North Tianshan—Main Tianshan fault zone that cross-cuts the North Tianshan domain's southern margin yielded 40Ar/39Ar spectra with 255–285 Ma ages. Biotite from an undeformed, Early Carboniferous granite, which cuts the steep mylonitic foliation in the Proterozoic basement of the Yili arcs's southern margin, gave a 263.4 ± 0.6 Ma plateau age (1σ). Pre-Carboniferous metasediments overlying this basement yielded plateau ages (1σ) of 253.3 ± 0.3 (muscovite) and 252.3 ± 0.3 (biotite) Ma. The Permian ages of mylonites date movement on these ductile, dextral strike-slip shear zones, whereas the mica ages are interpreted by recrystallisation as a result of fluid flow around such transcurrent faults. We propose that the Tianshan's Permian syn-tectonic bimodal magmatism was created in a non-plume-related Yellowstone-like extensional–transtensional tectonic regime. Gold mineralisation, tracing aqueous flow in the crust, peaked in Permian time and continued locally into the Triassic. The picture is emerging that a convective fluid system partly driven by magmatic heat, existed in a strongly fractured and weakened crust with an elevated heat flow, leading to regional-scale isotope resetting. We suggest that surprisingly young isotopic ages in the literature for early orogenic (ultra)high-pressure metamorphism are similarly due to fluid-mediated recrystallisation

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Section: Meaning Of Permian 40 Ar/ 39 Ar Agesmentioning

confidence: 74%

New 40Ar/39Ar age constraints on the Late Palaeozoic tectonic evolution of the western Tianshan (Xinjiang, northwestern China), with emphasis on Permian fluid ingress

Jong

Wang

Faure

et al. 2008

Int J Earth Sci (Geol Rundsch)

151

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“…The age scattering is significantly higher than the error margins of the calculated plateau ages, even in the same sample, and thus should have a geological significance. Even though they allow plateau age calculation, muscovite 40 Ar/ 39 Ar ages around the Joyeuse fault give saddle and staircase shaped spectra, which have been interpreted by many authors as the result of mixing of inherited and neocrystallized white micas due to partial recrystallization (Dunlap et al 1991;Dunlap 1997;Cheilletz et al 1999;Castonguay et al 2001;Alexandrov et al 2002) rather than excess argon component (McDougall and Harrison 1999). Dunlap et al (1991) and Cheilletz et al (1999) argued that the saddle-shaped age spectra could result from the mixing of mineral phases, e.g.…”

Section: Age Distribution Around the Joyeuse Faultmentioning

confidence: 97%

Exhumation processes during post-collisional stage in the Variscan belt revealed by detailed 40Ar/39Ar study (Tanneron Massif, SE France)

Corsini

Bosse

Féraud

et al. 2008

Int J Earth Sci (Geol Rundsch)

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International audienceDetailed 40Ar/39Ar geochronology on single grains of muscovite was performed in the Variscan Tanneron Massif (SE France) to determine the precise timing of the post-collisional exhumation processes. Thirty-two plateau ages, obtained on metamorphic and magmatic rocks sampled along an east–west transect through the massif, vary from 302 ± 2 to 321 ± 2 Ma, and reveal a heterogeneous exhumation of the lower crust that lasted about 20 Ma during late Carboniferous. In the eastern part of the massif, the closure of the K–Ar isotopic system is at 311–315 Ma, whereas in the middle part of the massif it closes earlier at 317–321 Ma. These cooling paths are likely to be the result of differential exhumation processes of distinct crustal blocks controlled by a major ductile fault, the La Moure fault that separates both domains. In the western part of the massif, the ages decrease from 318 to 303 Ma approaching the Rouet granite, which provides the youngest age at 303.6 ± 1.2 Ma. This age distribution can be explained by the occurrence of a thermal structure spatially associated to the magmatic complex. These ages argue in favour of a cooling of the magmatic body at around 15 Ma after the country rocks in the western Tanneron. The emplacement of the Rouet granite in the core of an antiform is responsible for recrystallization and post-isotopic closure disturbances of the K–Ar chronometer in the muscovite from the host rocks. These new 40Ar/39Ar ages clearly outline that at least two different processes may contribute to the exhumation of the lower crust in the later stage of collision. During the first stage between 320 and 310 Ma, the differential motion of tectonic blocks limited by ductile shear zones controls the post-collisional exhumation. This event could be related to orogen parallel shearing associated with crustal-scale strike-slip faults and regional folding. The final exhumation stages at around 300 Ma take place within the tectonic doming associated to magmatic intrusions in the core of antiformal structures. Local ductile to brittle normal faulting is coeval to Upper Carboniferous intracontinental basins opening

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“…Plateau ages were calculated if 70% or more of the 39 Ar K was released in at least three or more contiguous steps that yielded apparent ages within the 1σ of the integrated age of the plateau segment. Pseudoplateau ages were defined with the same criteria if the plateau segment contained less than 70% of the 39 Ar K released (Cheilletz et al 1999), such that the amount of 39 Ar K released is not a disqualifying criterion (Fleck et al 1977). The errors on the 40 Ar*/ 39 Ar K ratio and age of the monitor and decay constants were included in the final calculation of the errors of the (pseudo-)plateau ages.…”

Section: K-mn Oxide Geochronologymentioning

confidence: 99%

Multistage genesis of the late Cretaceous manganese karst-hosted Tasdremt deposit (High Atlas, Morocco)

et al. 2020

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The eastern part of the Souss Basin (Morocco) contains several Mn deposits in the Tasdremt district. Three Mn orebodies occur within the Cenomanian-Turonian dolostones and the Senonian (Coniacian to Maastrichtian) detrital series, the main orebody being located at the boundary between them. The Mn ores consist of coronadite group minerals, mostly coronadite and hollandite, in a karstified dolostone. New field observations, petrographic analyses, and geochemical data define the Tasdremt deposits as a karst-hosted accumulation (11-60 wt.% Mn), particularly enriched in Ba (1.5-8.2 wt.%) and Pb (1.0-5.0 wt.%) with poor contaminations in Al, Fe, and P. This study shows that the ore-forming process is similar to that occurring in the Imini C3 level, located~100 km to the northeast. Such similarities with the high-grade pyrolusite-bearing ore suggest that the Tasdremt deposit is a lateral equivalent of the Imini deposits. However, the scarcity of pyrolusite in Tasdremt results in lower Mn grades, the Tasdremt ores being considered an aborted/ incomplete system in comparison with the Imini deposits. 40 Ar/ 39 Ar geochronology of K-bearing Mn oxides yields late Cretaceous ages, defining three phases at~91.5 Ma,~77.5-82 Ma, and~65-67 Ma. Although the source of metals remains hypothetical, mineralizing fluids were carried by O 2-free groundwater that mixed with O 2-rich shallow meteoric waters at the Tasdremt depositional site. The dissolution of the host dolostones and the karst environment have provided suitable conditions for the precipitation of Mn oxides, causing the coeval increase of pH and Eh, respectively. The Early Atlasic deformation during the Late Cretaceous is associated with mineralization events and was responsible for creation of low stand reliefs from Tasdremt to Imini. This period enabled karstification and mineralization. Connecting the Tasdremt deposits to other African Mn deposits is difficult since the latter consist of laterite resting above Paleoproterozoic Mn protores, and consequently formed under different conditions from karst-hosted deposits. It is likely that other Mn occurrences formed along the Atlas belt in similar settings.

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40Ar/39Ar dating of fault : Evidence of an Eo-alpine event (128 Ma) in Greater Kabylia (Algeria): Geodynamic consequences

Cited by 6 publications

References 0 publications

New 40Ar/39Ar age constraints on the Late Palaeozoic tectonic evolution of the western Tianshan (Xinjiang, northwestern China), with emphasis on Permian fluid ingress

New 40Ar/39Ar age constraints on the Late Palaeozoic tectonic evolution of the western Tianshan (Xinjiang, northwestern China), with emphasis on Permian fluid ingress

Exhumation processes during post-collisional stage in the Variscan belt revealed by detailed 40Ar/39Ar study (Tanneron Massif, SE France)

Multistage genesis of the late Cretaceous manganese karst-hosted Tasdremt deposit (High Atlas, Morocco)

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