Oligocene-Miocene burial and exhumation of the Southern Pyrenean foreland quantified by low-temperature thermochronology

International audienceThe central Pyrenees experienced an episode of rapid exhumation in Late Eocene-Early Oligocene times. Erosional products shed from the range during this time were deposited in large palaeovalleys of the southern flank of the Axial Zone, leading to significant sediment accumulation. A recent numerical modelling study of the post-orogenic exhumation and relief history of the central Axial Zone allowed us to constrain this valley-filling episode in terms of timing and thickness of conglomeratic deposits. This paper aims to test these results for the southern fold-and-thrust belt using apatite fission-track and (U-Th)/He analysis on detrital samples from the Tremp-Graus and Ager basins. inverse thermal-history modelling of the low-temperature thermochronology data indicates that the fold-and-thrust belt was covered during the Late Eocene to Miocene by 0.7-1.6 km of sediments and confirms the timing of re-excavation of the valleys during the Miocene. A detailed analysis of the apatite (U-Th)/He results shows that the significant scatter in grain ages can be explained by the influence of alpha-recoil damage with varying effective uranium content together with distinct pre-depositional thermal histories; the age scatter is consistent with initial exhumation of the sediment sources during the Triassic and Early Cretaceous

Innovations in (U–Th)/He, Fission Track, and Trapped Charge Thermochronometry with Applications to Earthquakes, Weathering, Surface‐Mantle Connections, and the Growth and Decay of Mountains

A transformative advance in Earth science is the development of low‐temperature thermochronometry to date Earth surface processes or quantify the thermal evolution of rocks through time. Grand challenges and new directions in low‐temperature thermochronometry involve pushing the boundaries of these techniques to decipher thermal histories operative over seconds to hundreds of millions of years, in recent or deep geologic time and from the perspective of atoms to mountain belts. Here we highlight innovation in bedrock and detrital fission track, (U–Th)/He, and trapped charge thermochronometry, as well as thermal history modeling that enable fresh perspectives on Earth science problems. These developments connect low‐temperature thermochronometry tools with new users across Earth science disciplines to enable transdisciplinary research. Method advances include radiation damage and crystal chemistry influences on fission track and (U–Th)/He systematics, atomistic calculations of He diffusion, measurement protocols and numerical modeling routines in trapped charge systematics, development of 4He/3He and new (U–Th)/He thermochronometers, and multimethod approaches. New applications leverage method developments and include quantifying landscape evolution at variable temporal scales, changes to Earth\u27s surface in deep geologic time and connections to mantle processes, the spectrum of fault processes from paleoearthquakes to slow slip and fluid flow, and paleoclimate and past critical zone evolution. These research avenues have societal implications for modern climate change, groundwater flow paths, mineral resource and petroleum systems science, and earthquake hazards

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

The role of slab geometry in the exhumation of cordilleran-type orogens and their forelands: Insights from northern Patagonia

In cordilleran-type orogens, subduction geometry exerts a fundamental control on the tectonic behavior of the overriding plate. An integrated low-temperature, large thermochronological data set is used in this study to investigate the burial and exhumation history of the overriding plate in northern Patagonia (40°–45°S). Thermal inverse modeling allowed us to establish that a ~2.5–4-km-thick section originally overlaid the Jurassic–Lower Cretaceous successions deposited in half-graben systems that are presently exposed in the foreland. Removal of the sedimentary cover started in the late Early Cretaceous. This was coeval with an increase of the convergence rate and a switch to a westward absolute motion of the South American Plate that was accompanied by shallowing of the subducting slab. Unroofing was probably further enhanced by Late Cretaceous to early Paleogene opening of a slab window beneath the overriding plate. Following a tectonically quiescent period, renewed exhumation occurred in the orogen during relatively fast Neogene plate convergence. However, even the highly sensitive apatite (U-Th)/He thermochronometer does not record any coeval cooling in the foreland. The comparison between Late Cretaceous and Neogene exhumation patterns provides clear evidence of the fundamental role played by inter-plate coupling associated with shallow slab configurations in controlling plate-scale deformation. Our results, besides highlighting for the first time how the whole northern Patagonia foreland was affected by an exhumation of several kilometers since the Late Cretaceous, provide unrivalled evidence of the link between deep geodynamic processes affecting the slab and the modes and timing of unroofing of different sectors of the overriding plate.Fil: Genge, Marie C.. Università di Padova; Italia. Centre National de la Recherche Scientifique; Francia. Université de Lille; Francia. Université du Littoral; FranciaFil: Zattin, Massimiliano. Università di Padova; ItaliaFil: Savignano, Elisa. Università di Padova; ItaliaFil: Franchini, Marta Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Confluencia; Argentina. Universidad Nacional de Río Negro. Sede Alto Valle. Instituto de Investigaciones en Paleobiología y Geología; Argentina. Universidad Nacional del Comahue; ArgentinaFil: Gautheron, Cécile. Université Paris Sud; Francia. Centre D'etudes de Saclay; Francia. Centre National de la Recherche Scientifique; FranciaFil: Ramos, Victor Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Mazzoli, Stefano. Università degli Studi di Camerino; Itali

Differential exhumation driven by Tectonic processes in the Abancay deflection (Peruvian Andes)

The Abancay deflection (12-13.5°S), forming the northern edge of the Altiplano in the Central Andes of Peru, is a remarkable geomorphologic feature marking the along-strike segmentation of the Andes (Dalmayrac et al., 1980). Little is known about the timing and spatial distribution of exhumation in this peculiar part of the Eastern Cordillera for the last 40 Ma; however, it is characterized by 4 km-high relief and 2 km-deep gorges suggesting significant recent incision. To better constrain the exhumation and incision history of this northern edge of the Altiplano, we present apatite and zircon (U-Th)/He and fission-track data from 6 steep altitudinal profiles collected within the deflection (40 sampling sites). Thermochronology results highlight differential exhumation episodes between the Eastern Cordillera and the Altiplano with young thermochronological ages (15 Ma) respectively. We processed these ages into QTQt (Gallagher, 2012) and PECUBE (Braun, 2003) to discuss and unravel the exhumation timing, magnitude and settings of this area. Data inversion reveals the (re)activation of the crustal scale Apurimac fault system tilting the entire deflection like a pop-up structure (< 10 Ma) leading to differential exhumation between the Eastern Cordillera and the Altiplano. We speculate that he Abancay deflection, with its “bulls-eye” morphology and the abrupt increase in exhumation rate < 10 Ma, may represents an Andean proto-syntaxis, somewhat similar to the syntaxes described in the Himalaya or Alaska (Zeitler et al., 2001)

Genetic diversity of[i] Rhizoctonia solani[/i] associated with potato tubers in France

Affiche, résuméThe plant pathogenic soil-borne fungus Rhizoctonia solani causes severe damages in crops all around the world. Tubers of potato are frequently affected by R. solani leading to the downgrading of the production. Generally the isolates involved in the sclerotia occurring at the surface of the tuber are assigned to the anastomosis group (AG) 3 but a more precise characterization of the diversity of this deleterious group is needed to set up appropriate control strategies. The diversity of 73 French isolates from the mains potato seed production areas and 31 isolates originating from 9 other countries was assessed according to 3 molecular approaches. Three phylogenetic trees were built up based on the sequences of the internal transcribed spacer (ITS) region and the gene tef-1α as well as the comparison of the total DNA fingerprints of each strain established by amplified fragment length polymorphism (AFLP). The determination of the AGs of R. solani based on the sequencing of the ITS region showed 3 different AGs among our collection (60 AG 3, 8 AG 2-1 and 5 AG 5). Grouping of the isolates belonging to the same AG was confirmed by the sequencing of the gene tef-1α used for the first time to study the genetic diversity of R. solani. About 42 % of the ITS sequences and 73 % of the gene tef-1α sequences contained polymorphic sites where several nucleotides are possible, suggesting that the cells of R. solani strains contain several copies of ITS and gene tef-1α within the same nucleus or between different nuclei. Phylogenetic trees showed a greater genetic diversity within AGs in tef-1α sequences than in ITS sequences. The AFLP analyses showed an even greater diversity among the strains demonstrating that the French strains of R. solani isolated from potatoes were not a clonal population. Moreover, there was no relationship between the geographical origins of the strains or the potato variety from which they were isolated and their genetic diversity. This important and under evaluated genetic diversity as the lack of population structure suggest important genetic mixings leading to a constant evolution within R. solani and could explain the difficulties to control it successfully

He and Ne isotopic ratios from the Terceira Rift (Azores): Constraints on the boundary between Eurasia and Nubia mantle sources

We present He and Ne isotopic data from subaerial and submarine samples collected along the Terceira Rift. Graciosa Island as well as the western end of S. Miguel Island and D. João de Castro Bank display 4He/3He ratios similar to those observed along the MAR segments located to the north of the Azores Triple Junction area. Conversely, samples from the south Hirondelle Basin display a 4He/3He ratio similar to that of the MAR segments located to the south of the Azores Plateau. The Terceira Rift is thus characterized by the mingling of two different mantle domains referred as ‘Eurasia’ and ‘Nubia’ type. He and Ne systematics shows that the influence of the relatively primitive source sampled by the Azores plume can be followed along the Terceira Rift from the Graciosa Island towards the south Hirondelle Basin. Moreover, samples from the south Hirondelle Basin, D. João de Castro Bank and Graciosa Island cannot be explained by the same hyperbolic mixing model that encloses Terceira data

(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

Control de la exhumación de la deflexión de Abancay (Andes del Perú) por procesos climáticos y/o tectónicos

La deflexión de Abancay se encuentra al norte del Altiplano peruano (12-13.5°S) y marca la transición entre los Andes estrechos del norte y los Andes anchos del sur. Es una anomalía excepcional de escala litosférica. En esta área peculiar de la Cordillera Oriental, numerosos macizos de rocas intrusivas afloran, conformando un relieve abrupto. Las quebradas muestran zonas de knickpoints ≥1000 m de desnivel, estas zonas en muchos casos coinciden con sistema de fallas regionales. Geológicamente, esta zona de transición arqueada, se extiende sobre ~200 km y presenta fallas regionales E-O, que cruzan el eje principal de elongación de la cadena. Esta área se caracteriza también por tener elevaciones >5500 m, siendo el pico más elevado el nevado del Salcantay (6271 m). A pesar de constituir una zona topográficamente importante en los Andes centrales, no existen suficientes trabajos que expliquen los procesos orogénicos de los últimos 40 Ma. En este sentido, es necesario utilizar técnicas modernas que nos permita entender el rol de la tectónica y del clima en la construcción de la topografía durante el Cenozoico. Varios autores desde los primeros tiempos de la geología indican que los paisajes activos a escala orogénica contienen un archivo importante que registra los patrones de la deformación diferencial y la erosión. Siguiendo esta indicación, primero nos enfocamos en cuantificar la exhumación, con el objetivo de determinar el levantamiento de la deflexión de Abancay. Para esto, realizamos trabajos de campo, llegando a obtener 40 muestras, que nos permitirán proporcionar nuevas edades de termocronología de baja temperatura ((U-Th)/He y trazas de fisión enapatitos). También realizamos análisis cuantitativos de geomorfología para estimar el estado de equilibrio del área estudiada a diferentes escalas de tiempo. Nuestros primeros resultados geomorfológicos (knickpoints, Ksn,χ) apuntan a un fuerte desequilibrio en el núcleo de la deflexión de Abancay, lo que sugiere un levantamiento de superficie muy reciente (15 Ma respectivamente