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The Fregeneda-Almendra pegmatite field of the Iberian Massif represents a typical expression of peraluminous rare-metal magmatism that occurred over western Europe at the end of the Variscan orogeny. It is the host for two main types of Li-mineralized intrusions, identified at the scale of the Variscan belt, including petalite- or spodumene-rich pegmatites, as well as Li-mica-rich pegmatites, for which the origin of mineralogical-chemical differences is not yet understood. Here, we provide cassiterite and columbite-group mineral (CGM) U-Pb ages along with oxide, mica and phosphate mineral compositions for Li-pegmatites from the Fregeneda-Almendra field in order to assess their petrogenesis and tectonic-magmatic context of emplacement. U-Pb geochronology indicates that petalite-rich and Li-mica-rich pegmatites were mostly emplaced sub-synchronously from 315 ± 6 to 308 ± 6 Ma, during strike-slip deformation and granitic magmatism within an anatectic dome bounding the pegmatite field. U-Pb data and pegmatite geographic zonation suggest that Li-pegmatites were sourced from buried equivalents of leucogranites and migmatites from the dome. Li-pegmatites experienced a complex crystallization including K-feldspar, petalite, topaz, Nb-Ta-Fe-Mn-rich cassiterite, amblygonite-group minerals (AGM) and CGM as early magmatic phases, followed by lepidolite for Li-mica-rich pegmatites. At the magmatic-hydrothermal transition, notably leading to the formation of Nb-Ta-Mn-Fe-poor cassiterite hosting CGM inclusions, earlier minerals were resorbed by muscovite and albite. A later F-rich hydrothermalism is locally reflected by zinnwaldite overgrowths on muscovite. Cassiterite, CGM and micas from petalite-rich pegmatites show lower Mn/Fe ratios and higher Ti contents, along with lower Zr-Ga contents for cassiterite, than that from Li-mica-rich pegmatites. Such behavior is consistent with a magmatic differentiation process whereby Ti content decreased and the degree of Mn-Fe geochemical fractionation and solubilities of Ga and Zr increased in the melts, possibly in relation with high fluorine activity. In Li-mica-rich pegmatites, AGM equilibrated with a melt with up to 2 wt% F, similar to that in equilibrium with lepidolite (1–3 wt%). In petalite-rich pegmatites, the relatively high F concentration of the melts equilibrated with AGM (≤ 1.5 wt% F) contrasts with the liquid equilibrated with muscovite (< 0.5 wt% F). This can be accounted for by muscovite crystallization after the exsolution of a F-rich aqueous phase at the magmatic-hydrothermal transition. Relatively similar F contents in the initial melts of petalite- and Li-mica-rich pegmatites support the hypothesis that the stability of lepidolite does not only involve high F but also a low H2O/F activity ratio. For the Fregeneda-Almendra Li-mica-rich pegmatites, this could be explained by a decrease of melt H2O solubility due to a relatively low pressure of emplacement.

Asparagine (Asn) is a powerful turn-inducer residue, with a large propensity to occupy the second position in the central region of β-turns of proteins. The present work aims at investigating the role of a local anchoring between the Asn side chain and the main chain in this remarkable property. For this purpose, the H-bonding patterns of an asparagine residue in an isolated protein chain fragment forming a γ- or a β-turn have been determined using IR/UV double resonance gas phase spectroscopy on laser-desorbed, jet-cooled short models in conjunction with relevant quantum chemistry calculations. These gas phase data provide evidence for an original double anchoring linking the Asn primary amide side chain (SC), which adopts a gauche+ rotameric form, to its main chain (MC) local environment. From both IR spectroscopic evidence (H-bond induced red shifts) and quantum chemistry, Asn SC is found to behave as a stronger H-bond acceptor than donor, resulting in stronger MC→SC H-bonds than SC→MC ones. These gas phase structural data, relevant to a hydrophobic environment, have been used as a reference to assess the anchoring taking place in high resolution crystallized proteins of the Protein Data Bank. This approach reveals that, when the SC adopts a gauche+ orientation, the stronger MC→SC bonds are preserved in many cases whereas the SC→MC bonds are always disrupted, in qualitative agreement with the gas phase ranking of these interactions. Most interestingly, when Asn occupies the second position of central part of a β-turn (i.e., the very turn-inducer position), the MC→SC H-bonds are also disrupted and replaced by a water-mediated SC to MC anchoring. Owing to the specific features of the hydrated Asn side chain, we propose that it could be a turn precursor structure, able to facilitate turn formation in the early events of the folding process. [ABSTRACT FROM AUTHOR]

The NCI (Non-Covalent Interactions) method, a recently-developed theoretical strategy to visualize weak non-covalent interactions from the topological analysis of the electron density and of its reduced gradient, is applied in the present paper to document intra- and inter-molecular interactions in flexible molecules and systems of biological interest in combination with IR spectroscopy. We first describe the conditions of application of the NCI method to the specific case of intramolecular interactions. Then we apply it to a series of stable conformations of isolated molecules as an interpretative technique to decipher the different physical interactions at play in these systems. Examples are chosen among neutral molecular systems exhibiting a large diversity of interactions, for which an extensive spectroscopic characterization under gas-phase isolation conditions has been obtained using state-of-the-art conformer-specific experimental techniques. The interactions presently documented range from weak intra-molecular H-bonds in simple amino-alcohols, to more complex patterns, with interactions of various strengths in model peptides, as well as in chiral bimolecular systems, where invaluable hints for the understanding of chiral recognition are revealed. We also provide a detailed technical appendix, which discusses the choices of cut-offs as well as the applicability of the NCI analysis to specific constrained systems, where local effects require attention. Finally, the NCI technique provides IR spectroscopists with an elegant visualization of the interactions that potentially impact their vibrational probes, namely the OH and NH stretching motions. This contribution illustrates the power and the conditions of use of the NCI technique, with the aim of providing an easy tool for all chemists, experimentalists and theoreticians, for the visualization and characterization of the interactions shaping complex molecular systems. [ABSTRACT FROM AUTHOR]

Rare-element granites and pegmatites represent important sources of raw materials for “clean, green and high technologies”, such as lithium and tantalum, for example. However, mechanisms of rare-element granites and pegmatite’s origin are still far from being fully understood. Several rare-element pegmatite fields and a rare-element granite are known in the Variscan realms located in Iberia (Spain and Portugal), enhancing the interest of this area for studying the formation of these extremely fractionated melts. In situ U-Pb dating by LA-SF-ICP-MS of columbite-group minerals from rare-element granites and pegmatites of the Iberian Variscan belt provides new constraints on the generation of rare-element melts. Three events have been recognized: (i) Emplacement of the Argemela rare-element granite, in the Central Iberian Zone (CIZ), with an age of 326 ± 3 Ma; (ii) Emplacement of rare-element pegmatites from the Galicia-Trás-os-Montes Zone (GTOMZ), at an average age of 310 ± 5 Ma; (iii) Emplacement of rare-element pegmatites in the CIZ and in the southern GTOMZ at about 301 ± 3 Ma. These two last events are coeval with the two peaks of ages for the late orogenic magmatism at ca. 308 Ma and 299 Ma, and all dated rare-element pegmatites clearly emplaced during the late-orogenic evolution of the Variscan belt. Contemporaneous fields of rare-element pegmatites are arranged in belts following those formed by similar granitoid suites. Pegmatite fields from both the GTOMZ and the CIZ reveal a southward propagation of ages of emplacement, which matches the observed propagation of deformation, metamorphism and magmatism in the two different geotectonic zones. Existence of three successive rare-element events in the Iberian Massif argues against the involvement of lower crustal HP-HT metamorphism in the generation of rare-element melts. Possible sources of rare-element-enriched melts are more likely located in the middle to upper crust, as are the major components of granitic magmatism. Analyses of U and Pb isotopes from columbite-group minerals are very robust and reproducible, making them good candidates for dating ore deposits related to peraluminous magmatism as well as REE- and Nb-bearing deposits.

Paleoclimate reconstructions are generally validated on recent periods. To obtain a set of instrumental records at the regional scale, a time series of monthly mean temperatures in Northeastern Canada were interpolated for the 1961-2000 period. Records were provided by 202 meteorological stations. Temperatures derived from a Canadian regional climate model (Climate Model CRCM 4.2.3 from the AMNO domain produced at ∼50 km resolution) were added as secondary information to take into account local heterogeneity and temporal dependencies. Geostatistical interpolation of the measured temperature was calculated using CRCM modelled data as a covariable and then compared to an ordinary kriging performed on a time series of mean temperature anomalies. Spherical distances between locations were calculated taking into account the curvature of the Earth with monthly semivariances being modelled using Cauchy variograms. Mean absolute error values (1.5 ± 1.2 °C) were calculated for the whole period using cross-validation procedures. Errors were found to have the same order of magnitude in the central part of the study area where few recorded temperatures were available. Monthly mean temperature grids are publicly available through the Institut National de la Recherche Scientifique (http://url.in.rs/3P). Copyright © 2012 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

In order to assess the ability of theory to describe properly the dispersive interactions that are ubiquitous in peptide and protein systems, an isolated short peptide chain has been studied using both gas-phase laser spectroscopy and quantum chemistry. The experimentally observed coexistence of an ex- tended form and a folded form in the supersonic expansion was found to result from comparable Gibbs free energies for the two species under the high-temperature conditions (⩽320 K) resulting from the laser desorption technique used to vaporize the molecules. These data have been compared to results obtained using a series of quantum chemistry methods, including DFT, DFT-D, and post-Hartree-Fock methods, which give rise to a wide range of relative stabilities predicted for these two forms. The experimental observation was best reproduced by an empirically dispersion-corrected functional (B97-D) and a hybrid functional with a significant Hartree-Fock exchange term (M06-2X). In contrast, the popular post-Hartree-Fock method MP2, which is often used for benchmarking these systems, had to be discarded because of a very large basis-set superposition error. The applicability of the atomic counterpoise correction (ACP) is also discussed. This work also introduces the mandatory theoretical examination of experimental abundances. ΔH(0 K) predictions are clearly not sufficient for discussion of folding, as the conformation inversion temperature is crucial to the conformation determination and requires taking into account thermodynamical corrections (ΔG) in order to computationally isolate the most stable conformation. [ABSTRACT FROM AUTHOR]

The W–Sn Panasqueira ore deposit is a magmatic-hydrothermal system, which includes a high-grade quartz-vein type mineralization and a disseminated greisen-type mineralization occurring in the upper part of the Panasqueira two-mica granite. We investigated the genetic and chronological relationships between the greisenization of the Panasqueira granite and the formation of ore-bearing quartz veins by monitoring major and trace elements variations in quartz-white mica assemblages composing the two-mica granite, greisen and W–Sn-bearing quartz veins. The greisen is characterized by an overall depletion in Mg, Ti, Ca, Na, Ba, Sr, REE and enrichment in Fe, Li, Rb, Cs, Sn, W which reflect the breakdown of feldspars and fluid-rock interactions with W–Sn-bearing fluids. White-mica from greisen and mineralized quartz veins are enriched in granophile elements (F, Rb, Cs, Li, Sn, W and Zn) compared to magmatic muscovite from the two-mica granite. Trace elements contents in quartz depict trends which show the progressive enrichment in Ge and B and depletion in Al, Ti and Li from magmatic to hydrothermal quartz that emphasize the progressive evolution and cooling of the magmatic-hydrothermal system of Panasqueira. Geochemical similarities between quartz-white mica assemblages from greisen and wolframite-bearing veins suggest that greisenization and the formation of mineralized veins result from the same hydrothermal event and derived from the same source of hydrothermal fluids. Apatite from greisen and quartz vein yielded U–Pb ages of 292 ± 10 Ma and 295 ± 5 Ma respectively confirming that greisenization and the formation of mineralized veins occurred roughly at the same time. These ages also overlap with the emplacement age of the Panasqueira granite (296 ± 4 Ma), indicating a temporal link between greisenization, W–Sn mineralization and granite crystallization. Temperatures of the magmatic-hydrothermal system constrained by Ti-in quartz thermometry depicts a cooling trend from magmatic quartz of granite (700–600 °C) to hydrothermal quartz of greisen (500–400 °C) and veins (450–350 °C). These results suggest that greisenization and the formation of W–Sn bearing quartz veins occurred at the magmatic-hydrothermal transition, during which orthomagmatic fluids rich in volatils, incompatible elements and W–Sn were exsolved during the final solidification stage of the Panasqueira two-mica granite.

40Ar/39Ar absolute dating on tobelite (an ammonium-rich white mica) has been performed in order to provide geochronological constraints on the Sb ± Au mineralization and hydrothermalism at the Saint-Aubin-des-Châteaux base metal-Sb ± Au occurrence (Variscan Central Armorican Domain, France). The results show that the Sb ± Au deposition occurred at ca. 360 Ma. Coupled with recent results obtained in neighboring areas, this occurrence seems to belong to a large-scale Early Carboniferous economic Sb ± Au mineralizing peak in the southeastern part of the Central Armorican Domain. The emplacement of a coeval widespread mafic magmatism in the region appears to represent a major trigger for this mineralizing system at shallow depths (less than 3 km). In the light of these new data, this Early Carboniferous mafic magmatic event must be considered for the overall understanding of the genesis of mineralizing systems at the scale of the whole Variscan belt. Finally, at Saint-Aubin-des-Châteaux, evidence of an Early Permian hydrothermal event is also reported through LA-ICP-MS U-Pb dating of fluorapatite, arguing for the re-use and re-opening of Early Carboniferous mineralizing plumbing system by late (i.e. Permian) fluid flow pulses although no metal mobilization was associated with this event.

Introduction: Patient-specific evaluation of bone mechanical properties usually relies on the apparent density using clinical Quantitative Computed Tomography (QCT). However, evidence has been reported that bone microarchitecture has an important effect on its mechanical properties. Objective: To study the feasibility of predicting bone morphology from QCT using multi-scale image analysis. Materials and Methods: Two micro computed tomography (μCT) images of a porcine vertebral body were computed. The resolution of the μCT images was reduced to 0.3 mm using a corrected average algorithm in order to get the corresponding macro CT images. A multi-scale geostatisitical simulation algorithm was used to generate 100 equally probable μCT scenarios using only the CT image. Two morphometric parameters were then measured on the original and the simulated μCT images: bone volume (BV) and bone surface (BS). The estimation error of these parameters was then computed. Results: Morphology of trabecular bone could be predicted with an average error of 3% (0.5% to 9.5%). The evaluation of each parameter separately demonstrated that BS had the most error. It could be predicted with an average error of 3.1% (0.5% to 7.0%) while BV could be predicted with an average error of 0.4% (1.6x10-14% to 1.2%). Conclusion: The results show that the proposed method allows predicting bone morphology. However, improvements of the algorithm are required to automatically identify which predicted μCT image is the most similar to the target one. Significance: The non invasive estimation of trabecular architecture using QCT may prove to be useful for the prevention and treatment of bone pathologies. [ABSTRACT FROM AUTHOR]

Mining exploration increasingly relies on large, multivariate databases storing data ranging from drill core geochemical analysis to geophysical data or geological descriptions. Utilizing these large datasets to their full potential implies the use of multivariate statistical analysis such as machine learning. The Random Forest algorithm has proved its efficiency in mining applications. In this study we use it to estimate a key geochemical element, sodium, using a multivariate chemo-physical dataset measured on drill cores in the Matagami mining district of Québec, Canada. Sodium is important to characterize hydrothermal alteration in volcanogenic massive sulfide settings, since Na depletion can be used to vector towards ore, but this element is not readily measured by portable X-ray fluorescence (pXRF). We first test the algorithm on a database of over 8000 traditional laboratory geochemistry analyses and find a correlation of 0.95 between estimated and measured Na. We then test the algorithm on the multi-sensor core logging data, including density, magnetic susceptibility, and 15 geochemical elements by pXRF, but borrowing Na from traditional geochemistry (n = 260). This yields correlations of 0.66 to 0.75 depending on the training and testing sets. Finally the algorithm is applied to the whole multiparameter database (n = 9675) to estimate Na downcore. There is a good general correspondence with the downcore Na patterns seen through traditional geochemistry, and the estimated Na which has much greater spatial resolution. Random Forest appears to be a very good estimation tool when using large amounts of data and variables, as it uses all variables and automatically prioritizes the most useful. This method also allows visualization of the weight of each variable in the estimation. Future studies should compare RF with other methods. • Machine learning helps to exploit large mining exploration databases. • The Random Forest algorithm is used here to estimate sodium, a key missing variable. • Variations in sodium can be used to vector towards VMS deposits. [ABSTRACT FROM AUTHOR]

Abstract Potential impacts of shale gas development on shallow aquifers has raised concerns, especially regarding groundwater contamination. The intermediate zone separating shallow aquifers from shale gas reservoirs plays a critical role in aquifer vulnerability to fluid upflow, but the assessment of such vulnerability is challenging due to the general paucity of data in this intermediate zone. The ultimate goal of the project reported here was to develop a holistic multi-geoscience methodology to assess potential impacts of unconventional hydrocarbon development on fresh-water aquifers related to upward migration through natural pathways. The study area is located in the St. Lawrence Lowlands (southern Quebec, Canada), where limited oil and gas exploration and no shale gas production have taken place. A large set of data was collected over a ∼500 km2 area near a horizontal shale gas exploration well completed and fracked into the Utica Shale at a depth of ≈2 km. To investigate the intermediate zone integrity, this project integrated research results from multiple sources in order to obtain a better understanding of the system hydrodynamics, including geology, hydrogeology, deep and shallow geophysics, soil, rock and groundwater geochemistry, and geomechanics. The combined interpretation of the multi-disciplinary dataset demonstrates that there is no evidence of, and a very limited potential for, upward fluid migration from the Utica Shale reservoir to the shallow aquifer. Microbial and thermogenic methane in groundwater of this region appear to come from the shallow, organic-rich, fractured sedimentary rocks making up the regional aquifer. Nonetheless, diluted brines present in a few shallow wells close to and downstream of a normal fault revealed that some upward groundwater migration occurs, but only over a few hundred meters from the surface based on the isotopic signature of methane. The methodology developed should help support regulations related to shale gas development aiming to protect groundwater. Highlights • This synthesis presents results and benefits from using multi-disciplinary data. • Integrated shallow and deep datasets allowed a holistic study of potential upflow. • Dissolved methane is present throughout the study area, locally at high levels. • Microbial and thermogenic methane in groundwater come from the shallow rock aquifer. • There is no evidence of upward fluid migration over large vertical distances. [ABSTRACT FROM AUTHOR]