Ages radiometriques (K/Ar) de feldspaths potassiques et de micas neoformes dans le Trias de Tunisie septentrionale

Bellón, Hervé; Perthuisot, V.

doi:10.2113/gssgfbull.s7-xix.5.1179

Cited by 10 publications

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“…The HP/LT thermobarometric results in the Ichkeul marbles indicate that the epizonal dome reached a typical orogenic P‐T gradient of approximately 13°C/km during a HP‐LT metamorphic event and was exhumed from under approximately 26 km overburden provided by the Tell‐Flysch nappe stack. The exhumation path of the Ichkeul marbles is marked by the growth of biotite defining the main S‐L S 1 fabric and dated between 23 and 17 Ma (Bellon & Perthuisot, 1977). Thus, this process may reflect early Miocene syn‐orogenic exhumation in the subduction channel as proposed for other Western Mediterranean nappe belts (Booth‐Rea et al., 2015; Ryan et al., 2021).…”

Section: Discussionmentioning

confidence: 99%

“…Integrating our new rutile results with previously published radiometric dating indicates a polymetamorphic evolution for the Tunisian Tell, similar to the one observed at the opposite end of the Maghrebian Alpine chain, in the Rif (Jabaloy et al., 2015; Vázquez et al., 2013). The only existing radiometric ages in metamorphic minerals of the Tunisian Tell are K‐feldspar and phlogopite K‐Ar ages from metabasites and marbles from different outcrops that give late Cretaceous (97 ± 5 to 67 ± 3 Ma), Palaeocene (65 ± 3 Ma), Oligocene (27 ± 1 to 25 ± 1 Ma) and Miocene ages (23 ± 1.2 to 17.6 ± 0.9 Ma) (Bellon & Perthuisot, 1977) (Figure 3). Although, this age dispersion was interpreted as a result of Cretaceous extensional‐sedimentary load related metamorphism, mixed with radiometric resetting by late Neogene magmatic heating in the region (Bellon & Perthuisot, 1977), we provide a new alternative scenario.…”

Section: Discussionmentioning

confidence: 99%

“…Metamorphic minerals have been dated in the Tunisian Tell and Atlas. K‐Ar ages on K‐feldspar and phlogopite in metabasites and marbles give different age populations (Figure 3), including late Cretaceous to Paleocene ages (97–64 Ma) in Le Kef diapir, younger late Oligocene to early Miocene (25–18 Ma) ages in more internal Triassic outcrops, and only early Miocene ages (23–17 Ma) in the deeper Ichkeul massif (Bellon & Perthuisot, 1977). This age disparity has been interpreted as mixed Cretaceous rifting ages with late Miocene magmatic or hydrothermal‐related thermal resetting by Bellon and Perthuisot (1977).…”

Section: Geological Settingmentioning

confidence: 99%

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Metamorphic Domes in Northern Tunisia: Exhuming the Roots of Nappe Belts by Widespread Post‐Subduction Delamination in the Western Mediterranean

et al. 2023

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Cenozoic extension in the Western Mediterranean has been related to the dynamics of back-arc domains. Although, in most of its orogenic belts extension propagated into the fore-arc nappe domains. Here we revisit the structure, metamorphism and radiometric ages of the Tunisian Tell, where HP/LT rocks (350°C at 0.8 GPa), were exhumed by the sequential activity of extensional detachments after heating and decompression (410°C-440°C at 0.6-0.3 GPa) in a plate convergent setting. Normal faults thinning the Tunisian Tell detached at two different crustal levels. The shallower one cuts down into the Atlas Mesozoic sequence, involving Tellian Triassic evaporites in the hanging-wall forming halokinetic structures in the Mejerda basin late Miocene. The deeper-detachment bounds metamorphic domes formed by marbles and metapsammites from the Atlas domain. Illite crystallinity on Triassic rocks shows epizonal to anchizonal values, at deep and intermediate structural depths of the Tell-Atlas nappe belt, respectively. New U-Pb 49.78 ± 1.28 Ma rutile ages from Tellian metabasites, together with existing phlogopite 23-17 Ma K-Ar ages in Atlas marbles from the footwall of the deepest detachment, indicate a polymetamorphic evolution. The Tell rocks underthrusted the Kabylian flysch in the early Eocene. Further, early Miocene shortening thrusted the metabasites over lower-grade sediments, producing HP/LT metamorphism and ductile stretching at the base of the Atlas belt. The exhumation of midcrustal roots of Western Mediterranean nappe belts after tectonic shortening is a common feature related to tearing at the edges of the subduction systems and inboard delamination of their subcontinental lithospheric mantle.Plain Language Summary Mountain belts are formed by shortened sedimentary rocks. The Tell cordillera in Northern Tunisia is interpreted as a classic mountain belt developed through protracted shortening from the late Cretaceous until Present, formed by folded and overthrusted rocks, and intruded by salt bodies. However, we show here that conversely, some of the supposed salt bodies are formed by metamorphic rocks that were originally buried at depths of approximately 26 km. Moreover, the remaining salt structures in the Tunisian Tell formed in relation to the late-stage thinning and collapse of the mountain belt, as they intrude through extensional faults into late Miocene sediments. We characterize the temperature and pressure conditions reached by the metamorphic rocks and obtain a 49 Ma age of an early metamorphic event by radiometric dating of rutile. Metamorphic rocks where also exhumed in other Western Mediterranean mountain belts like the Betics, Rif, Algerian Tell after the main shortening stage. We relate this process to delamination, a deep mantle tectonic mechanism, which strips the nappe belt crustal domain from its underlying mantle root.BOOTH REA ET AL.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Geological Settingmentioning

confidence: 99%

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Metamorphic Domes in Northern Tunisia: Exhuming the Roots of Nappe Belts by Widespread Post‐Subduction Delamination in the Western Mediterranean

et al. 2023

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“…These minerals are probably products of metasomatic reactions triggered by Si-, K-, and Mg-rich fluids circulating throughout the salt deposits [147]. K/Ar dating on metasomatic feldspars indicates that metasomatic processes may have occurred in a time lapse between 97 Ma and 18 Ma [150]. A Triassic age is generally suggested for Tunisian diapirs [151], although no geophysical data nor core drillings can substantiate such an assumption.…”

Section: Salts In Central Part Of the Mediterranean Margin Of Africa mentioning

confidence: 99%

Tracking the Serpentinite Feet of the Mediterranean Salt Giant

2018

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Interpretation of seismic profiles and results of scientific drillings in the Mediterranean subseafloor provided indication of gigantic salt deposits which rarely crop out on land, such as in Sicily. The salt giants were ascribed to the desiccation, driven by the solar energy, of the entire basin. Nevertheless, the evaporite model hardly explains deep-sea salt deposits. This paper considers a different hypothesis suggesting that seawater reached NaCl saturation during serpentinization of ultramafic rocks. Solid salts and brine pockets were buried within the serpentinite bodies being later (e.g., in the Messinian) released, due to serpentinite breakdown, and discharged at seafloor as hydrothermal heavy brines. Therefore, sea-bottom layers of brine at gypsum and halite saturation were formed. The model is applicable to the Mediterranean area since geophysical data revealed relicts of an aged (hence serpentinized) oceanic lithosphere, of Tethyan affinity, both in its western “Atlantic” extension (Gulf of Cádiz) and in eastern basins, and xenoliths from Hyblean diatremes (Sicily) provided evidence of buried serpentinites in the central area. In addition, the buoyant behavior of muddled serpentinite and salts (and hydrocarbons) gave rise to many composite diapirs throughout the Mediterranean area. Thus, the Mediterranean “salt giant” consists of several independent geobodies of serpentinite and salts.

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“…The Oxfordian‐Kimmeridgian, exposed at the eastern extremity of the massif, consists of cherts, dolomite marls, siliceous limestones and shales intercalated by cinerites enriched in mica, feldspar and quartz. Radiometric (K/Ar) dating of phlogopites at Jebel Ichkeul yielded ages ranging from 17.6 to 23 Ma (Bellon & Perthuisot, ).…”

Section: Geological Settings and Mineralizationmentioning

confidence: 99%

Geochemistry of Triassic Carbonates: Exploration Guide to Pb–Zn Mineralization in North Tunisia

et al. 2016

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The Triassic carbonate rocks in Northern Tunisia (Nappes, Domes, Jurassic Mountains zones), consist of massive carbonates, clays and gypsum with authigenic minerals. These are associated with several Pb-Zn deposits and occurrences. At Jebel Ichkeul, Bechateur and Oum Edeboua, these Triassic carbonates exhibit enrichment in Pb (0.32 to 228 ppm), Zn (17 to 261 ppm), Cd (5 to 6 ppm) and Co (0.3 to 89.5 ppm), with respect to their average contents in crustal carbonates. The enrichment is more pronounced at Oum Edeboua (near the ore zone). Permeability is one of the most effective factors of dispersion of metallic trace elements, causing the development of geochemical halos. The genetic relationship of the Triassic carbonate rocks with the ore deposits was controlled by diapirism and tectonic movements, which favored mineralization along the Triassic-cover contact as well as the remobilization of metals from the mineralized rocks. Analysis of metallic trace elements in Triassic rocks provides clues to the presence of possible mineral deposits. These could be effectively used for both geochemical interpretation and mineral exploration. Carbon and O-isotope data (-9.3‰ < δ 13 C < +3‰; +21.9 < δ 18 O < +31‰) suggest that the Triassic carbonates of all study areas have marine carbonates as their origin; some of them show significantly lower δ 18 O values indicating some exchange with hydrothermal fluids. Calcites associated with mineralization at Oum Edeboua have δ 13 C of -6.2‰ to -8.22‰ and δ 18 O of +24.88‰ to +25‰. The C-isotope compositions of these calcites are 13 C depleted, indicating an organic origin.

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Ages radiometriques (K/Ar) de feldspaths potassiques et de micas neoformes dans le Trias de Tunisie septentrionale

Cited by 10 publications

References 0 publications

Metamorphic Domes in Northern Tunisia: Exhuming the Roots of Nappe Belts by Widespread Post‐Subduction Delamination in the Western Mediterranean

Metamorphic Domes in Northern Tunisia: Exhuming the Roots of Nappe Belts by Widespread Post‐Subduction Delamination in the Western Mediterranean

Tracking the Serpentinite Feet of the Mediterranean Salt Giant

Geochemistry of Triassic Carbonates: Exploration Guide to Pb–Zn Mineralization in North Tunisia

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