Shear zone memory revealed by in-situ Rb-Sr and 40Ar/39Ar dating of Pyrenean and Alpine tectonic phases in the external Alps

International audienceThe combination of Rb-Sr and $^{40}$Ar/$^{39}$Ar dating methods with high-resolution mineralogical investigation allows deciphering the multiphase history of shear zones and serves as a tool for tectonic reconstructions. However, the interpretation of dates obtained by these two methods in relation to cooling, fluid circulation or to deformationinduced (re)crystallization remains controversial. Here, we apply the in situ 87 Rb/ 87 Sr and $^{40}$Ar/$^{39}$Ar dating methods to shear zone minerals used together with step heating $^{40}$Ar/$^{39}$Ar dating in several case studies with contrasting structural and metamorphic histories along the External Crystalline Massifs (ECMs) of the SW Alps. Our results emphasize polyphase deformation and highlight a variable behaviour of Rb-Sr and K-Ar systems in shear zones. This study provides new constraints about the timing, conditions and mechanisms of deformation in the southern ECMs of the Western Alps. The inherited crustal-scale Variscan shear zones have been reactivated several times in a thick-skin mode since the Late Cretaceous. An early N-S compressional phase impacted the SW Alps mainly at around ~80-70 and ~40 Ma in the Argentera and Pelvoux shear zones, but this signal is not documented further north. This signal is better preserved in the southern Pelvoux massif, with a Rb-Sr age of 79.7 ± 3.7 Ma. There is also a significant compressional deformation on the W-Alpine scale at 34-32 Ma, associated with underthrusting beneath the Penninic Frontal Thrust (PFT). Two compressional deformation pulses occur at 26 and 22-20 Ma in the southern Argentera Massif, corresponding to the onset of transpressive deformation induced by the anti-clockwise rotation of the Adriatic Plate. Finally, the last phase of deformation around 18-15 Ma concerns only the NW Alps, in the Beaufortain massif, which was buried under the Mont-Blanc massif, during the propagation of deformation leading to the development of the frontal fold and thrust belt of the SW Alps. Our results also show that the southern Pelvoux massif already reached a temperature around 300°C at a depth of 10-15 km depth during the Late Cretaceous. This range of temperature and pressure conditions is broadly similar to that reached in the ECMs during the Cenozoic deformation stages

Active Learning of Intuitive Control Knobs for Synthesizers Using Gaussian Processes

Typical synthesizers only provide controls to the low-level parameters of sound-synthesis, such as wave-shapes or filter envelopes. In contrast, composers often want to adjust and express higher-level qualities, such as how ‘scary ’ or ‘steady’ sounds are perceived to be. We develop a system which allows users to directly control abstract, high-level qualities of sounds. To do this, our system learns functions that map from synthesizer control settings to perceived levels of high-level qualities. Given these functions, our system can generate high-level knobs that directly adjust sounds to have more or less of those qualities. We model the functions mapping from control-parameters to the degree of each high-level quality using Gaussian processes, a nonparametric Bayesian model. These models can adjust to the complexity of the function being learned, account for nonlinear interaction between control-parameters, and allow us to characterize the uncertainty about the functions being learned. By tracking uncertainty about the functions being learned, we can use active learning to quickly calibrate the tool, by querying the user about the sounds the system expects to most improve its performance. We show through simulations that this model-based active learning approach learns high-level knobs on certain classes of target concepts faster than several baselines, and give examples of the resulting automaticallyconstructed knobs which adjust levels of non-linear, highlevel concepts