Zircon as a provenance tracer: Coupling Raman spectroscopy and Usingle bondPb geochronology in source-to-sink studies

Usingle bondPb zircon geochronology is one of the most widely used techniques in sedimentary provenance analysis. Unfortunately, the ability of this method to identify sediment sources is often degraded by sediment recycling and mixing of detritus from different source rocks sharing similar age signatures. These processes create non-unique zircon Usingle bondPb age signatures and thereby obscure the provenance signal. We here address this problem by combining detrital zircon Usingle bondPb geochronology with Raman spectroscopy. The position and width of the Raman signal in zircon scales with its degree of metamictization, which in turn is sensitive to temperature. Thus, combined U-Pb + Raman datasets encode information about the crystallization history of detrital zircons as well as their thermal history. Using three borehole samples from Mozambique as part of a source-to-sink study of interest for hydrocarbon exploration, we show that zircon populations with similar Usingle bondPb age distributions can exhibit different Raman signatures. The joint U-Pb + Raman analysis allowed us to identify three different annealing trends, which were linked to specific thermal events. Thus we were able to differentiate a dominant Pan-African Usingle bondPb age peak into several sub-populations and highlight the major effect of Karoo tectono-magmatic events. In our case study, we used Raman also as a means to systematically identify all zircon grains in heavy-mineral mounts, resulting in considerable time savings. Raman spectroscopy is a non-destructive and cost-effective method that is easily integrated in the zircon Usingle bondPb dating workflow to augment the resolution power of detrital zircon Usingle bondPb geochronology

Toward Robust Interpretation of Low‐Temperature Thermochronometers in Magmatic Terranes

Many regions central to our understanding of tectonics and landscape evolution are active or ancient magmatic terranes, and robust interpretation of low‐temperature thermochronologic ages in these settings requires careful attention to the drivers of rock heating and cooling, including magmatism. However, we currently lack a quantitative framework for evaluating the potential role of magmatic cooling—that is, post‐magmatic thermal relaxation—in shaping cooling age patterns in regions with a history of intrusive magmatism. Here we use analytical approximations and numerical models to characterize how low‐temperature thermochronometers document cooling inside and around plutons in steadily exhuming environments. Our models predict that the thermal field a pluton intrudes into, specifically the ambient temperatures relative to the closure temperature of a given thermochronometer, is as important as the pluton size and temperature in controlling the pattern and extent of thermochronometer resetting in the country rocks around a pluton. We identify one advective and several conductive timescales that govern the relationship between the crystallization and cooling ages inside a pluton. In synthetic vertical age‐elevation relationships (AERs), resetting next to plutons results in changes in AER slope that could be misinterpreted as past changes in exhumation rate if the history of magmatism is not accounted for. Finally, we find that large midcrustal plutons, such as those emplaced at ~10–15‐km depth, can reset the low‐temperature thermochronometers far above them in the upper crust—a result with considerable consequences for thermochronology in arcs and regions with a history of magmatic activity that may not have a surface expression.Key PointsIntrusive magmatism may produce important first‐order effects on patterns of low‐temperature thermochronometer coolingAnalytical approximations and numerical models predict cooling ages in and around crustal plutons in steadily exhuming environmentsLarge plutons emplaced in the middle crust at 10–15‐km depth can reset low‐temperature thermochronometers in the upper crustPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146628/1/ggge21696.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146628/2/ggge21696_am.pd

Bias in detrital zircon geochronology and thermochronometry

Detrital studies that utilise zircon U-Pb geochronology and fission-track (FT) thermochronometry are subject to a range of potential sources of bias that should be properly evaluated and minimised. Some of them are common to any single-grain mineral analysis (e.g., variable bedrock mineral fertility, hydraulic sorting during transport, selective grain loss during sample processing), whereas others are intrinsic to zircon, and are related to radiation damage and age discordance. In this article, we quantify the impact of intrinsic bias on detrital studies thanks to the analysis of modern detritus shed from the European Alps, and illustrate the general implications on geological interpretations. We show that detrital zircon U-Pb age distributions based on statistically robust datasets are highly reproducible and representative of the parent bedrock ages in the catchment. Arbitrary or selective removal of discordant grain ages can be minimised by using the Kolmogorov-Smirnov test to identify an appropriate cutoff level. Loss of metamict (α-damaged) zircon has a minor impact on data representativeness, and is mainly controlled by regional metamorphism rather than by mechanical abrasion during river transport. Zircon FT grain-age distributions were found to have poor reproducibility, although age spectra are consistent with bedrock data. However, unlike the U-Pb datasets, U-rich zircon grains (> 1000 ppm) are systematically missed, and undatable grains may exceed 50%. We identify two major sources of distribution bias specific to zircon FT datasets: (i) sediment sources dominated by U-rich zircon grains are markedly underrepresented in the detrital record, because such grains often have uncountable high densities of fission tracks (“U concentration bias”); (ii) sediment sources that shed zircon grains with high levels of α-damage are underrepresented, because these grains are lost during chemical etching for FT revelation (“etching bias”). In case of multimethod dating on the same grains (e.g. FT and U-Pb double dating), bias affecting detrital zircon FT dating propagates to the entire dataset. These effects may not impact on exhumation-rate studies that utilise the youngest grain ages (i.e., lag-time approach). However, they represent a limiting factor for conventional provenance studies, and generally preclude application of zircon FT dating to sediment budget calculations

Short-term impact of two liquid organic fertilizers on Solanum lycopersicum L. rhizosphere Eubacteria and Archaea diversity

This study evaluates the effect of two different kinds of liquid organic fertilizers and a mineral fertilizer on microbial populations (Eubacteria and Archaea) living in the tomato rhizosphere. The organic fertilizers comprised a stillage from bakery yeasts production, characterized by acidic pH and high organic nitrogen content, as well as a vermicompost extract with alkaline pH and low nitrogen content. The number of operational taxonomic units (OTUs) of Archaea species significantly increased after the addition of both the organic and mineral fertilizers, in comparison to the unfertilized control. Eubacteria OTUs increased only in plants treated with the stillage. T-RFLPs profiles identified different clusters of soil rhizospheric Archaea and Eubacteria in treatments of both organic and mineral fertilizers. However, multivariate analyses performed on indicators of genetic diversity, based on the T-RFLPs profiles, and Shannon and equitability indexes of the Archaea and Eubacteria communities, pointed out marked differences between the control (or the mineral fertilization) and the organic fertilizers. The latter treatments induced also a higher root growth and a modification of the root architecture in comparison to both control and mineral fertilizer. The results are discussed with reference to the effect of the organic products on rhizospheric soil characteristics and the relationships between the plant and the rhizospheric microorganisms

Production of renewable energies and biomolecules from livestock and agro-industrial waste: the BIOMOLENER Project

The BIOMOLENER project is focused in the combination of physical and biological treatments of livestock effluents and whey to exploit their potential as a direct source of commodity chemicals, or as a pabulum for fermentations, aimed at reaching biofuels or microbial biomasses from which biomolecules can be extracted. Processing of these waste give a contribution to the reduction of polluting characteristics

The Gediz supradetachment system (SW Turkey). Magmatism, tectonics and sedimentation during crustal extension

Unraveling the evolution of supradetachment basins developed in the hanging wall of low‐angle detachment faults may be an invaluable tool in reconstructing the tectonic evolution of highly extended terrains. These basins may record major regional tectonic events related to the exhumation of metamorphic core complexes, and the reconstruction of their evolution helps to quantify the amount of extension accommodated by such processes. Here we present stratigraphic and structural field evidence and micropaleontological constraints to the Neogene‐to‐Quaternary evolution of the supradetachment Gediz Graben that developed on top of the exhuming Central Menderes Massif (SW Turkey). This basin displays three different structural styles during its evolution: (i) it initiated as a ramp basin following the activation of the Gediz Detachment in the Middle Miocene, (ii) evolved as a half graben during the late Miocene following the activation of high‐angle brittle faults at its southern margin, and (iii) reached its final symmetric graben configuration in Late Pliocene (?)‐Quaternary times following the activation of its northern margin. New micropaleontological data document a short‐lived upper Tortonian marine episode in the basin, and major along‐strike variations in exhumation are documented on its southern margin. Our reconstruction shows how sedimentary basins originally formed in the hanging wall of detachment faults may eventually end up in tectonic contact with the mylonitic footwall. Finally, we highlight the importance of magmatism in localizing the deformation in highly extended terrains and in controlling the evolution of supradetachment systems