Fernando O. Marques

Bio: Fernando O. Marques is an academic researcher from University of Lisbon. The author has contributed to research in topics: Simple shear & Volcano. The author has an hindex of 35, co-authored 124 publications receiving 3016 citations. Previous affiliations of Fernando O. Marques include University of Minho & University of Wisconsin-Madison.

Subduction initiation at passive margins: Numerical modeling

Abstract: [1] Subduction is a key process for terrestrial plate tectonics, but its initiation is still not entirely understood. In particular, despite the abundance of both passive and active continental margins on Earth, no obvious cases of transition between them have been identified so far. It has been shown that at most passive margins, elastic and frictional forces exceed gravitational instability and ridge-push forces, which precludes subduction initiation. Therefore additional factors are needed to start subduction there. We investigated numerically in two dimensions factors controlling passive margins' stability such as age of the oceanic plate, thickness of the continental lithosphere and crust, and density contrast between subcontinental and suboceanic lithospheric mantles. Our numerical experiments show that three subsequent tectonic regimes can develop at a passive margin: (1) stable margin, (2) overthrusting, and (3) subduction. Transition from stable margin to the overthrusting regime is mainly controlled by ductile strength of the lower continental crust. Further transition from overthrusting to the subduction regime is governed by the ductile strength of the subcontinental lithospheric mantle and its chemical density contrast with the suboceanic lithospheric mantle. Our experiments also demonstrate that the age of the oceanic plate is a factor of secondary importance for subduction initiation and only plays a role if other parameters are of critical values. Favorable conditions for subduction initiation thus correspond to passive margins where chemically buoyant (depleted) continental lithosphere becomes thin and hot (Moho temperature >660°C). This situation can be occasionally created by superimposed external processes such as rifting and/or thermal-chemical plume activity.

Is the ‘Azores Hotspot’ a Wetspot? Insights from the Geochemistry of Fluid and Melt Inclusions in Olivine of Pico Basalts

Abstract: The concept of an 'Azores mantle plume' has been widely debated, and the existence of an Azores hotspot questioned. In an effort to shed new light on this controversy, we present He isotope and major, trace and volatile element compositions for basaltic scoriae from five monogenetic cones emplaced along the fissure zone of Pico Island, the youngest island of the Azores archipelago. The bulk scoriae and lavas are moderately alkaline basalts, and their He isotope ratios, determined on olivine crystals, vary between 10*2 and 11*1 ± 0*1 Ra. In contrast, melt inclusions hosted in olivine (Fo76-83*5) span a large range of compositions (K2O = 0*7-1*7 wt %; Ce = 32-65 ppm; Nb = 21-94 ppm), which extends the compositional field of lavas erupted along the Pico fissure zone. This chemical evolution is predominantly controlled by polybaric fractional crystallization. Most melt inclusions share similar enrichments in large ion lithophile and light rare earth elements, and trace element ratios (La/Sm, La/Yb, Sr/Nd, Ta/Th, Zr/Y) with their bulk-rocks. Only a few of them differ in their lower contents of incompatible elements and La/Sm, Li/Ta and Na/K ratios, a feature that is ascribed to distinct conditions of melting. As a whole, the melt inclusions preserve high and variable volatile contents, and contain up to 1*8-2*0 wt % of H2O and 0*4 wt % of CO2. The total fluid pressures, retrieved from the dissolved CO2 and H2O concentrations, and the PCO2 from fluid inclusions, indicate magma ponding and crystallization at the crust-mantle boundary (ca. 18 km deep). The H2O/Cl and H2O/Ce ratios in the inferred parental undegassed basalts of the Pico fissure zone average 0*036 ± 0*006 and 259 ± 21, respectively. The latter value is significantly higher than that reported for typical mid-ocean ridge basalts from the southern Mid-Atlantic Ridge, but is similar to published ratios for submarine undegassed basalts from the Azores platform. Combining the calculated compositions of Pico primary magmas formed by low degrees of melting with recent geophysical data for the Azores, we propose a model for Azores magma generation involving the decompression melting of a water-enriched mantle domain (H2O = 680-570 ppm) with an estimated temperature excess of ≤120°C with respect to the Mid-Atlantic Ridge.

Biochemical Markers of Cardiac Injury in Normal, Surviving Septic, or Nonsurviving Septic Neonatal Foals

Abstract: The cardiac biomarkers cardiac troponin T (cTnT) and I (cTnI) and the cardiac isoenzyme of creatine kinase (CKMB) are used extensively in human medicine to diagnose and provide valuable prognostic information in patients with ischemic, traumatic, and septic myocardial injury. We designed a study to establish normal values for these markers in healthy, neonatal foals and to compare them with values obtained from septic neonates in a referral hospital population. The 25th, 50th, 75th, and 95th percentiles for cTnI and CKMB in the healthy-foal population were 0.08, 0.14, 0.25, 0.49 ng/mL and 1.4, 2.3, 4.0, 7.4 ng/mL, respectively. The values obtained for cTnT were frequently (43/52 foals; 83%) below the lower limit of detection of the assay (0.009 ng/mL), but the median and range were 0.009 and 0.009-0.041 ng/mL, respectively. In the septic foal population, the 25th, 50th, 75th, and 95th percentile values for cTnI and CKMB were 0.05, 0.12, 0.22, and 1.10 ng/mL and 2.0, 4.4, 7.8, and 24 ng/mL, respectively. The values obtained for cTnT were less frequently below the lower limit of detection (23/38 foals; 60%) compared with the healthy foal population, and the median and range were 0.009 and 0.009-0.20 ng/mL, respectively. Significantly higher values were observed for cTnT and CKMB in septic foals compared with the healthy neonatal foal population, but there were no differences among septic foals in survivors compared with nonsurvivors. These findings suggest that myocardial injury occurs during septicemia in neonatal foals but that the injury is not associated with survival among septic foals.

The yield stress—a review or ‘παντα ρει’—everything flows?

Abstract: An account is given of the development of the idea of a yield stress for solids, soft solids and structured liquids from the beginning of this century to the present time. Originally, it was accepted that the yield stress of a solid was essentially the point at which, when the applied stress was increased, the deforming solid first began to show liquid-like behaviour, i.e. continual deformation. In the same way, the yield stress of a structured liquid was originally seen as the point at which, when decreasing the applied stress, solid-like behaviour was first noticed, i.e. no continual deformation. However as time went on, and experimental capabilities increased, it became clear, first for solids and lately for soft solids and structured liquids, that although there is usually a small range of stress over which the mechanical properties change dramatically (an apparent yield stress), these materials nevertheless show slow but continual steady deformation when stressed for a long time below this level, having shown an initial linear elastic response to the applied stress. At the lowest stresses, this creep behaviour for solids, soft solids and structured liquids can be described by a Newtonian-plateau viscosity. As the stress is increased the flow behaviour usually changes into a power-law dependence of steady-state shear rate on shear stress. For structured liquids and soft solids, this behaviour generally gives way to Newtonian behaviour at the highest stresses. For structured liquids this transition from very high (creep) viscosity (>106 Pa.s) to mobile liquid (

Morphology, composition, production, processing and applications of Chlorella vulgaris: A review

Abstract: Economic and technical problems related to the reduction of petroleum resources require the valorisation of renewable raw material Recently, microalgae emerged as promising alternative feedstock that represents an enormous biodiversity with multiple benefits exceeding the potential of conventional agricultural feedstock Thus, this comprehensive review article spots the light on one of the most interesting microalga Chlorella vulgaris It assembles the history and a thorough description of its ultrastructure and composition according to growth conditions The harvesting techniques are presented in relation to the novel algo-refinery concept, with their technological advancements and potential applications in the market

A geodetic plate motion and Global Strain Rate Model

Abstract: We present a new global model of plate motions and strain rates in plate boundary zones constrained by horizontal geodetic velocities. This Global Strain Rate Model (GSRM v.2.1) is a vast improvement over its predecessor both in terms of amount of data input as in an increase in spatial model resolution by factor of ∼2.5 in areas with dense data coverage. We determined 6739 velocities from time series of (mostly) continuous GPS measurements; i.e., by far the largest global velocity solution to date. We transformed 15,772 velocities from 233 (mostly) published studies onto our core solution to obtain 22,511 velocities in the same reference frame. Care is taken to not use velocities from stations (or time periods) that are affected by transient phenomena; i.e., this data set consists of velocities best representing the interseismic plate velocity. About 14% of the Earth is allowed to deform in 145,086 deforming grid cells (0.25° longitude by 0.2° latitude in dimension). The remainder of the Earth's surface is modeled as rigid spherical caps representing 50 tectonic plates. For 36 plates we present new GPS-derived angular velocities. For all the plates that can be compared with the most recent geologic plate motion model, we find that the difference in angular velocity is significant. The rigid-body rotations are used as boundary conditions in the strain rate calculations. The strain rate field is modeled using the Haines and Holt method, which uses splines to obtain an self-consistent interpolated velocity gradient tensor field, from which strain rates, vorticity rates, and expected velocities are derived. We also present expected faulting orientations in areas with significant vorticity, and update the no-net rotation reference frame associated with our global velocity gradient field. Finally, we present a global map of recurrence times for Mw=7.5 characteristic earthquakes.

Porphyroclast systems as kinematic indicators

Abstract: Porphyroclasts of feldspar and other relatively rigid minerals in mylonites commonly have mantles of dynamically recrystallized material that extend as tails into the matrix. The internal shape symmetry of such porphyroclasts is usually orthorhombic or monoclinic; the orientation of the porphyroclast with respect to the foliation (external symmetry) can also be described by these symmetry classes. An identical monoclinic external symmetry of most porphyroclasts in a given sample indicates non-coaxial flow in the matrix during at least the last stages of deformation. Two classes of porphyroclast systems with monoclinic symmetry have been identified on geometrical grounds. sigma-type porphyroclasts are characterized by wedge-shaped tails of recrystallized material. Median lines of the tails lie on opposite sides of, and do not cross, a marker line drawn parallel to the mean foliation. sigma-type porphyroclasts may lie isolated in a homogeneous matrix (sigma/sub a./-type) or may be in clusters associated with shear bands or S-C mylonites (sigma/sub b/-type). delta-type porphyroclasts commonly occur in ultramylonites and have highly attenuated recrystallized tails. Median lines of the tails cross the marker line adjacent to the porphyroclast which results in an embayment of matrix material adjacent to the host grain. More complex porphyroclast systems include ellipsoidal overturned delta-types,more » complex sigma - delta types and folded porphyroclast aggregates. In all cases, the symmetry of porphyroclast aggregates with respect to the foliation can be used to accurately determine the sense of vorticity in the mylonites.« less