Emplacement and deformation of mesozoic Gabbros of the High Atlas (Morocco): paleomagnetism and magnetic fabrics

A paleomagnetic and magnetic fabric study is performed in Upper Jurassic gabbros of the central High Atlas (Morocco). These gabbros were emplaced in the core of preexisting structures developed during the extensional stage and linked to basement faults. These structures were reactivated as anticlines during the Cenozoic compressional inversion. Gabbros from 19 out of the 33 sampled sites show a stable characteristic magnetization, carried by magnetite, which has been interpreted as a primary component. This component shows an important dispersion due to postemplacement tectonic movements. The absence of paleoposition markers in these igneous rocks precludes direct restorations. A novel approach analyzing the orientation of the primary magnetization is used here to restore the magmatic bodies and to understand the deformational history recorded by these rocks. Paleomagnetic vectors are distributed along small circles with horizontal axes, indicating horizontal axis rotations of the gabbro bodies. These rotations are higher when the ratio between shales and gabbros in the core of the anticlines increases. Due to the uncertainties inherent to this work (the igneous bodies recording strong rotations), interpretations must be qualitative. The magnetic fabric is carried by ferromagnetic (s.s.) minerals mimicking the magmatic fabric. Anisotropy of magnetic susceptibility (AMS) axes, using the rotation routine inferred from paleomagnetic results, result in more tightly clustered magnetic lineations, which also become horizontal and are considered in terms of magma flow trend during its emplacement: NW-SE (parallel to the general extensional direction) in the western sector and NE-SW (parallel to the main faults) in the easternmost structures

Mobilisation of rare earth elements in shear zones: insights from the Tabouchent granodioritic pluton (Jebilet massif, Variscan Belt, Morocco)

In the Jebilet massif (Variscan belt, Morocco), two peraluminous granodioritic plutons (the Eastern and Central Jebilet plutons) are spatially associated with a regional shear zone. The Central Jebilet pluton includes the Tabouchent, Bramram and Bamega intrusions, which represent variably eroded portions of an arcuate apical part of the pluton. The intrusions are composed of biotite ± cordierite-bearing granodiorite that is crosscut by tourmaline-bearing leucogranite, which is greisenized in the Bramram cupola. Fluorine, Sn-W (Au) mineralization is present in the pluton while Cu-Au and Pb-Zn-Ag-Au mineralizations are present in the contact metamorphic aureole around the intrusion. Deformation is more homogeneous in the Bramram and Bamega than in the Tabouchent granodioritic intrusion where deformation is very heterogeneous and concentrated within conjugate subvertical meter-scale ductile shear zones that crosscut the intrusion. In the shear zones the breakdown of feldspar and biotite resulted in the transformation of the granodiorite to phyllonites composed of quartz + muscovite ± chlorite. 40Ar/39Ar dating on white mica allowed us to date the regional shearing event to 305.9 ± 0.9 Ma. Fluid-rock interaction in the shear zones resulted in mobilization of rare earth elements (REE) and other major and trace elements. Na and Ca are typically leached from the shear zones while K and volatiles are gained. REE mobilisation was decoupled from that of the major elements and was accompanied by fractionation between light and heavy REE. It was mainly controlled by the alteration of magmatic accessory REE-bearing phases, predominantly monazite, followed by the reprecipitation of syntectonic monazite, xenotime, Th + Ca ± REE phosphate, Ce oxide and REE fluorocarbonates. Other typical changes in the shear zones are enrichments in Sn, W, As and Sb. The mineralogical and chemical changes recorded in the shear zones that crosscut the granodiorite are similar to those associated with the greisenization that affected the Bramram leucogranite. They indicate that the shear zones provide pathways for rising acidic magmatic fluids exsolved from S-type leucogranites

Nonlinear Neural Network for Hemodynamic Model State and Input Estimation using fMRI Data

Originally inspired by biological neural networks, artificial neural networks (ANNs) are powerful mathematical tools that can solve complex nonlinear problems such as filtering, classification, prediction and more. This paper demonstrates the first successful implementation of ANN, specifically nonlinear autoregressive with exogenous input (NARX) networks, to estimate the hemodynamic states and neural activity from simulated and measured real blood oxygenation level dependent (BOLD) signals. Blocked and event-related BOLD data are used to test the algorithm on real experiments. The proposed method is accurate and robust even in the presence of signal noise and it does not depend on sampling interval. Moreover, the structure of the NARX networks is optimized to yield the best estimate with minimal network architecture. The results of the estimated neural activity are also discussed in terms of their potential use

Reply to Comment on “The Jurassic–Cretaceous basaltic magmatism of the Oued El-Abid syncline (High Atlas, Morocco): Physical volcanology, geochemistry and geodynamic implications” by André Michard et al. (2013) [J. Afr. Earth Sci. 88 p.101–105],

International audienceWe welcome the comment by Michard et al. (2013) as it gives us the opportunity to better discuss the Jurassic–Cretaceous magmatism of the High Atlas (Morocco). In their comment, Michard et al. (2013) focus on three main points which are: (i) the age of the basalts from Naour, (ii) the structural history of the Central High Atlas and (iii) the geodynamic significance of the related Jurassic–Cretaceous magmatism. We will address these questions in the following sections