Unravelling the Temporal and Chemical Evolution of a Mineralizing Fluid in Karst-Hosted Deposits: A Record from Goethite in the High Atlas Foreland (Morocco)

Timing and duration of ore deposit formation are crucial to understanding the mineralization process. To address this, the geochronological (U-Th)/He method, geochemical and H- and O-isotope compositions of pure goethite formed in the Imini karst-hosted Mn district (High Atlas, Morocco) were examined in detail. Two main generations of cavity-filling and fracture-filling goethite are identified, and both precipitated prior to the massive Mn oxide ore. The δD and δ18O values reveal that the mineralizing fluid of cavity and fracture-filling goethite is meteoric-derived but enriched in 18O due to fluid–rock interactions with the host rock dolostone or mixing with O2-rich surface water resident in an open karst system. The cavity-filling goethite precipitated between 95 to 80 Ma, whereas fracture-filling goethite formed between 80 to 50 Ma. Ore deposition occurred discontinuously during the early Atlas doming associated with one or more early compressional events in the Atlas tectonism. The increase in δD values and depletion in U content result from a change in the mineralizing fluid within the karst system. At about 50 Ma, the fluid is notably enriched in U, Cu and trace metals

(U-Th)/He dating of supergene iron (oxyhydr-)oxides of the Nefza-Sejnane district (Tunisia):new insights into mineralization and mammalian biostratigraphy

The mining district of Nefza-Sejnane (Tunisia) encloses numerous ores and raw material deposits, all formed in relation with successive Fe-rich fluids of meteoric and/or hydrothermal origins. Here, for the first time in Tunisia, (U-Th)/He ages were obtained on supergene goethite from various localities/deposits of the district highlight direct dating of significant weathering episodes during late Tortonian and late Pleistocene. These weathering events are most likely associated with favorable conditions that combine (i) wet climate displaying sufficient meteoric water/fluid; and (ii) regional exhumation, due to large-scale vertical lithospheric movements enhancing the percolation of fluids. Matched with previous works, these results refine the stratigraphic frame for the polymetallic mineralization and clay deposits in the district, confirming the influence of meteoric fluids circulation during the late Cenozoic. As a consequence of the new (U-Th)/He data, we moreover propose a taxonomic and stratigraphic revision of the well-known mammalian fauna from the Fe-rich Douahria locality, suggesting an early Tortonian age for the fossils, i.e., prior to the first episode of meteoric event in the area

Burial in the western Central Andes through Oligocene to Miocene ignimbrite flare-ups recorded by low-temperature thermochronology in the Cañete Canyon, Peru

Thermochronological data are essential to constrain thermal and exhumation histories in active mountain ranges. In the Central Andes, bedrock outcrops are rare, being blanketed by widespread late Palaeogene–Neogene and younger volcanic formations. For this reason, the exhumation history of the Western Cordillera (WC) in the Peruvian Andes has only been investigated locally along the mountain range. Dense thermochronological data are only available in canyons of the Arequipa (16° S) and Cordillera Negra regions (10° S). We present new apatite (U-Th)/He and fission-track data from the 1 km deep Cañete Canyon (13° S), where the Oligo-Miocene deposits are preserved lying conformably on an Eocene palaeo-topographic surface. Thermal modelling of thermochronological data indicate that the 30–20 Ma ignimbrite deposits overlying the bedrock were thick enough to cause burial reheating. We demonstrate that burial associated with thick volcanic formations should be taken into account when interpreting thermochronological data from the WC or in similar volcanic-arc settings

Cenozoic (U-Th)/He ages in Lofoten - Vesterålen islands, Northern Norway

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Climate control on Early Cenozoic denudation of the Namibian margin as deduced from new thermochronological constraints

International audienceThe processes that control long term landscape evolution in continental interiors and, in particular, along passive margins such as in southern Africa, are still the subject of much debate (e.g. Braun, 2018). Although today the Namibian margin is characterized by an arid climate, it has experienced climatic fluctuations during the Cenozoic and, yet, to date no study has documented the potential role of climate on its erosion history. In western Namibia, the Brandberg Massif, an erosional remnant or inselberg, provides a good opportunity to document the Cenozoic denudation history of the margin using the relationship between rock cooling or exhumation ages and their elevation. Here we provide new apatite (U–Th–Sm)/He dates on the Brandberg Inselberg that range from 151 ± 12 to 30 ± 2 Ma. Combined with existing apatite fission track data, they yield new constraints on the denudation history of the margin. These data document two main cooling phases since continental break-up 130 Myr ago, a rapid one (∼10 °C/Myr) following break-up and a slower one (∼1–2 °C/Myr) between 65 and 35 Ma. We interpret them respectively to be related to escarpment erosion following rifting and continental break-up and as a phase of enhanced denudation during the Early Eocene Climatic Optimum. We propose that during the Early Eocene Climatic Optimum chemical weathering was important and contributed significantly to the denudation of the Namibian margin and the formation of a pediplain around the Brandberg and enhanced valley incision within the massif. Additionally, aridification of the region since 35 Ma has resulted in negligible denudation rates since that time

Unravelling the temporal and chemical evolution of a mineralizing fluid in karst-hosted deposits:a record from goethite in the High Atlas foreland (Morocco)

Timing and duration of ore deposit formation are crucial to understanding the mineralization process. To address this, the geochronological (U-Th)/He method, geochemical and H- and O-isotope compositions of pure goethite formed in the Imini karst-hosted Mn district (High Atlas, Morocco) were examined in detail. Two main generations of cavity-filling and fracture-filling goethite are identified, and both precipitated prior to the massive Mn oxide ore. The δD and δ18O values reveal that the mineralizing fluid of cavity and fracture-filling goethite is meteoric-derived but enriched in 18O due to fluid–rock interactions with the host rock dolostone or mixing with O2-rich surface water resident in an open karst system. The cavity-filling goethite precipitated between 95 to 80 Ma, whereas fracture-filling goethite formed between 80 to 50 Ma. Ore deposition occurred discontinuously during the early Atlas doming associated with one or more early compressional events in the Atlas tectonism. The increase in δD values and depletion in U content result from a change in the mineralizing fluid within the karst system. At about 50 Ma, the fluid is notably enriched in U, Cu and trace metals

Erratum to “Climate control on Early Cenozoic denudation of the Namibian margin as deduced from new thermochronological constraints” [Earth Planet. Sci. Lett. 527 (2019) 115779]

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Thermal record of the building of an orogen in the retro‐foreland basin: Insight from basement and detrital thermochronology in the eastern Pyrenees and the north Pyrenean basin (France)

International audienceAn understanding of the evolution of foreland basins improves our knowledge of how mountain belts have grown and helps us to decipher events which may not be preserved in the orogen. The infilling of the north Pyrenean retro-foreland basin (Aquitaine Basin, France) during the main exhumation of the Pyrenees and its corresponding thermal history have not been fully investigated. We applied apatite fission track (AFT) and (U-Th-Sm)/He (AHe) methods coupled with inverse thermal modelling on both the detrital Eocene (47 to 33 Ma) syn-orogenic Palassou conglomerates of the eastern part of the Aquitaine Basin and basement samples from the North Pyrenean Zone and the Axial Zone of the Pyrenees. Apatite crystals were separated from granitic cobbles found in the conglomerates. AFT ages for detrital samples range from 27 ± 2 to 43 ± 4 Ma, and AHe ages from 13 ± 1 to 76 ± 5 Ma. For in situ massifs AFT ages range from 35 ± 2 to 90 ± 17 Ma and AHe ages from 39 ± 2 and 80 ± 5 Ma. AFT ages for detrital samples are close to deposition ages, whereas AHe ages are older and younger than deposition ages and show a partial thermal resetting due to burial. A detailed analysis of the ages obtained and thermal histories derived from modelling shows that ages reflect (a) exhumation from 70 to 55 Ma revealed by a long stay in the partial retention zone (PRZ), (b) a Palaeocene–Eocene cooling in the Pyrenees, (c) a post-depositional episode of moderate heating of the sediments in the basin represented by partially reset young AHe and AFT ages compared to deposition ages and (d) an early to mid-Miocene final exhumation of the basin deposits as evidenced by young AHe ages and geological constrains. These results reflect a common event with the south Pyrenean foreland basin that is characterized by high piedmont aggradation from the late Eocene to the Miocene. The aggradation of sediments is possibly connected with well-known high elevation low relief surfaces in the core of the Pyrenees and followed by a Miocene exhumation event that is already observed on the southern flank. However, the timing of the aggradation and exhumation events could be different between the north and the south. Erosion occurred most probably during the early to mid-Miocene in the north and during the late Miocene–early Pliocene in the south