Fernando O Marques

• PhD
• Retired at University of Lisbon

Mass controls two major processes in volcanic islands: large-scale collapse and vertical movements. Therefore, large islands like Hawaii are gradually subsiding and have undergone massive landsliding. What if the mass is much smaller, and there is good evidence that the vertical movement is more complex than simple loading-related subsidence? Here,...

We chose the Jatobá Basin (JB) in the Borborema Province in northeastern Brazil to address two outstanding problems, basin tectonic inversion and stress propagation, because (a) evidence of tectonic inversion is conspicuous in the JB, and (b) the basin sits on intracontinental northeastern Brazil, far from plate boundaries and the most obvious stre...

Mass controls two major processes in volcanic islands: large-scale collapse and vertical movements. Therefore, large islands like Hawaii are gradually subsiding and have undergone massive landsliding. What if the mass is much smaller, and there is good evidence that the vertical movement is more complex than simple loading-related subsidence? Here,...

The most important form of plate evolution occurs where three tectonic plates meet, a triple junction ¹ (TJ). Ridge-ridge-ridge (RRR) TJs are unique because they are stable at all ridge configurations and spreading velocities ¹ . This idealised and simplified RRR TJ with three straight rifts is challenged here by showing that it does not apply if a...

The late Quaternary paleoclimate of the North Atlantic region has been widely studied, but the local terrestrial response to broader climatic variations remains underexplored. The Azores Archipelago, influenced by the North Atlantic Oscillation (NAO) and the Azores High, is a strategic target to investigate such interactions. Here, paleosols develo...

Large-scale flank collapses are one of the main hazards associated with the evolution of volcanic islands. Precisely dating such events is critical to evaluate the frequency of destabilization episodes and further assess the triggering mechanism(s) associated with internal and/or external factors, such as volcano dynamics, regional tectonics, and g...

Volcanic islands evolve through complex interactions between volcano growth and surface processes. Climate changes impact the physical and chemical processes that drive weathering and denudation. While global paleoclimate has been extensively studied for the late Quaternary, elucidating the local climatic response to global forcing on such islands...

Volcanic ocean island collapse is a gravitational process, which means that mass is a key variable. Here we show that small volcanic islands (small mass) usually considered stable can undergo full flank collapse (i.e. full flank plus summit), and we also evaluate the most likely collapse mechanisms by numerical modelling. Santa Maria Island (Azores...

Paleosols (PSs) contain valuable information about the climatic conditions under which they formed and constitute an outstanding archive of past weathering processes. Nevertheless, paleosol dating over most of the Quaternary remains challenging. Volcanic environments are unique sites for such purposes, as precise radiometric age determination can b...

Most intraplate areas worldwide are under compression characterized by thrust and strike-slip deformations. The sources of the stresses in these regions are a combination of far-field (regional) stresses (e.g., ridge push, slab pull, lithospheric drag) and near-field (local) stresses (e.g., topography, lateral and vertical anisotropy of strength or...

The exceptionally dynamic eruption of La Palma in 2021 represents a unique window to look deep into the lithosphere and the mechanics of an eruptive process. Magma ascent is powered by overpressure (dynamic/lithostatic pressure > 1), meaning that thermodynamically estimated pressure cannot be directly converted to depth. The problem is that the amo...

The Newfoundland-Iberia rift, which includes the Lusitanian Basin (LB), has been considered the archetype of a magma-poor rift, but its main steps are still debated. The new data reported here indicate that the LB’s eastern border comprises two contrasting types of contact between continental sediments and Variscan basement: major angular unconform...

Hydrothermal silicification and deformation bands influence the physical properties of porous siliciclastic rocks. However, the impacts generated by the coexistence of these two processes on fault zone flow properties, such as porosity and permeability reductions, are still debatable. We integrated structural, geomechanical, and petro-physical data...

Volcanic ocean island collapse is a gravitational process, therefore mass is a key variable. Based on this premise, islands much smaller than Hawaii are believed to be not prone to collapse. Here we show that they can collapse, and more than once, like in Santa Maria Island (Azores), 170 times smaller than Hawaii, as inferred from onshore data and...

The control of normal fault growth by preexisting basement structures is still a worldwide matter of debate. The objectives of the present study are (i) to investigate where rift faults nucleate in continental-scale ductile shear zones and how these zones influence fault architecture; (ii) how subvertical basement fabric controls listric fault geom...

The age of breakup which formed the Central-North Atlantic has been debated for many decades and is still subject to debate: from ca. 150 Ma to 110 Ma. To address this issue, we have carried out a thermochronological study of the eastern margin of the rifted Iberia-Newfoundland sector. New apatite fission-track (AFT) data acquired on samples from t...

Exhumation of the roots of collapsing orogens is a key process in the evolution of mountain belts, which is critical for the understanding of orogenic cycles. From new structural analyses, KAr and ⁴⁰Ar/³⁹Ar on muscovite, biotite and K-feldspar, and available UPb ages, we constrain the cooling and exhumation history of granitic batholiths from the m...

The Pico-Faial ridge is a steep WNW-ESE volcanic ridge that has developed within the Nubia-Eurasia diffuse plate boundary, close to the Azores Triple Junction. The ridge comprises two islands, Pico and Faial, separated by a shallow (< 100 m depth) and narrow (< 8 km) channel. Despite some similarities, the two islands show contrasting features stil...

The Ossa-Morena Zone (OMZ) has a complex geological history including both Cadomian and Variscan orogenic events. Therefore, the OMZ plays an important role in understanding the geodynamic evolution of Iberia. However, the P–T–t evolution of the OMZ is poorly documented. Here, we combine structural and metamorphic analyses with new geochronological...

Common basin models assume that the post‐rift tectonic evolution of most basins is usually associated with tectonic quiescence. However, tectonic inversion during the post‐rift phase has been proposed for several sedimentary basins worldwide, but how and why it happens is still a matter of debate, especially in intracontinental settings where the l...

We present paleomagnetic and geochronological data of twenty-five stacked lava flows from São Miguel Island (Azores) that were emplaced during the last geomagnetic reversal (Matuyama-Brunhes, M-B). The characteristic direction of natural remanent magnetization was isolated through alternating field and/or thermal demagnetization. From bottom to top...

Santa Maria is the oldest island in the Azores, formerly belonging to the Eurasia plate and currently the only one sitting on the Nubia Plate, thus sharing a geodynamic evolution with the Azores Triple Junction. It is therefore important to evaluate the effects of active tectonics on the evolution of Santa Maria, for example on its vertical movemen...

Dated paleosea level markers and eustatic sea level changes are necessary but not sufficient information to calculate vertical motion rates on oceanic islands. Therefore, we use a procedure in which we work progressively back in time to incorporate the more recent vertical motion rates implied by the youngest paleoshorelines into the vertical motio...

The target of this study is the Fogo Island in Cape Verde, where the hazards (caldera and/or flank collapse) and the timing (120 ka or younger?) are still controversial. Using high-resolution DEM, field geological and structural analysis, and high-precision K-Ar dating, we produced an age-calibrated volcanic stratigraphy of Fogo’s summit (Chã das C...

Contrary to the classical modes of basin formation based on far-field stresses, here we report on a new mechanism of basin generation by near-field (internal) stresses based on scaled laboratory experiments: basins forming atop a relaxing buckled elastic layer following a far-field compressional event. This investigation builds on the works by Marq...

We report a new paleomagnetic and rock magnetic volcanic record of the Matuyama-Brunhes (M-B) transition in a sequence of 28 lava flows from the Azores Island. We sampled a 100-m thick succession of lavas incised by a deep creek. More than 250 paleomagnetic samples were analyzed using both alternating field up to 120 mT and thermal stepwise demagne...

Small intra-plate volcanic islands (total height above seafloor <2500 m) have been considered gravitationally stable. Topographic, stratigraphic, structural and new K/Ar data show that the small island of Flores (Azores) is strongly asymmetric and made up of nested volcanic successions. Along the northwestern coastline, ca. 1.2 Ma lava flows are in...

The Himalayas are the archetype of continental collision, where a number of long-standing fundamental problems persist in the Greater Himalayan Sequence (GHS): (1) contemporaneous reverse and normal faulting, (2) inversion of metamorphic grade, (3) origin of high- (HP) and ultrahigh-pressure (UHP) rocks, (4) mode of ductile extrusion and exhumation...

The Himalayas are the archetype of continental collision, where a number of long-standing fundamental problems persist in the Greater Himalayan Sequence (GHS): (1) contemporaneous reverse and normal faulting; (2) inversion of metamorphic grade; (3) origin of high- (HP) and ultra-high (UHP) pressure rocks; (4) mode of ductile extrusion and exhumatio...

The S. Jorge Island in the Azores lies on a peculiar setting, the southern shoulder of the Terceira Rift (TR), which raises a series of questions that we address in this study. We first established the main volcanic stratigraphy by recognizing, in the field, the main unconformities/discontinuities and their meaning (major erosion surfaces and fault...

In dynamic geological settings, the total pressure (P) comprises dynamic and (litho)static (PL) components, which are indistinguishable when pressure is estimated thermodynamically. The difference between the two components is called tectonic overpressure (here defined as TOP = P/PL), the magnitude of which has been debated for decades in geodynami...

The morphology of volcanic oceanic islands results from the interplay between constructive and destructive processes, and tectonics. In this study, the analysis of the paleomagnetic directions obtained on well-dated volcanic rocks is used as a tool to assess tilting related to tectonics and large-scale volcano instability along the Pico-Faial linea...

The Macaronesia islands (Canary and Cape Verde archipelagos) have experienced intense seismic and volcanic activity that may in the near future put in risk people and goods. It is important to implement measurement strategies to monitor the seismic activity and the surface deformation. Synthetic Aperture Radar interferometry (SAR) has proven to be...

The critical taper theory of Coulomb wedges has been classicaly applied to compressive regimes (accretionary prisms / fold-and-thrust belts), and more recently to gravitational instabilities. Following the initial hypothesis of the theory, we provide an alternative expression of the exact solution for a non-cohesive wedge by considering the balance...

By physical modelling we investigated the buckling and post-buckling behaviour of an elastic layer hosted in a viscous medium, as analogue of the elastic response of crustal rocks. The experiments were performed by embedding thin elastic layers of finite length in a linear viscous medium, and in two successive stages: a first stage of layer-paralle...

Several processes concur to shape an oceanic volcanic island, in particular the insular shelves, but the dominant process will be the one with the highest rate for a given period of time. Therefore, one has to estimate rates in order to conclude for the dominant process. We take advantage of the contrasting tectonic settings of two islands in the A...

The evolution of hyperslow oceanic rifts, like the Terceira Rift (TR) in the Azores, is still poorly understood. Here we examine the distribution of strain and magmatism in the portion of the TR making up the Nubia-Eurasia plate boundary. We use São Miguel Island because it stretches most of the TR width, which allows to investigate the TR's archit...

The solid-state flow of rocks commonly produces a parallel arrangement of elongate minerals with their longest axes coincident with the direction of flow – a mineral lineation. However, this does not conform to Jeffery's theory of the rotation of rigid ellipsoidal inclusions (REIs) in viscous simple shear, because rigid inclusions rotate continuous...

The physics of subduction initiation can be studied with numerical models of lithosphere dynamics, to the extent where we can now test the potential consequences of a catastrophic subduction initiation event on the Earth System. The South American Atlantic passive margin is here used to show that, once subduction has catastrophically initiated ther...

In Sibrant et al. (2014), we reconstructed the evolution of Graciosa Island (Azores). We extensively discussed the nature and the meaning of the destruction episodes, either tectonics or gravitational, and concluded that the island has evolved through major landslides. In their comment, Quartau et al. conclude that: (1) “Sibrant et al. (2014) is ba...

The interpretation of high-resolution topography/bathymetry, GPS and InSAR data, and detailed structural geology indicate that: (1) Terceira developed at the intersection of two major volcano-tectonic lineaments: WNW-ESE (local TR’s direction) and NNW-SSE (submarine chain of volcanoes, here firstly recognized and coined Terceira Seamount Chain). (2...

The breakup of Pangea in the Mesozoic placed the South American and African plates under horizontal extension, which triggered rifting and the formation of intracontinental basins in NE Brazil. The subsequent geodynamic evolution changed the forces acting upon the South American plate because of the simultaneous development of the Mid-Atlantic Ridg...

The growth and decay of oceanic volcanoes developed close to plate boundaries are intrinsically related to a competition between construction and destruction processes, partly controlled by tectonic strain and stresses. From morphologic, stratigraphic, tectonic and new high-precision K-Ar data, we present a comprehensive picture of the volcano-tect...

The study of volcanism near unstable plate triple junctions (TJs) offers a unique opportunity to investigate the interactions between mantle dynamics and lithospheric deformation in relation to short-term plate reconfiguration. From combined geochronological and geochemical analyses on Terceira, S. Jorge and Faial volcanic islands, we evidence cont...

The study of volcanism near unstable plate triple junctions (TJs) offers a unique opportunity to investigate the interactions between mantle dynamics and lithospheric deformation in relation to short-term plate reconfiguration. From combined geochronological and geochemical analyses on Terceira, S. Jorge and Faial volcanic islands, we evidence cont...

With very few exceptions, M > 4 tectonic earthquakes in the Azores show normal fault solution and occur away from the islands. Exceptionally, the 1998 shock was pure strike-slip and occurred within the northern edge of the Pico-Faial Ridge. Fault plane solutions show two possible planes of rupture striking ENE-WSW (dextral) and NNW-SSE (sinistral)....

Many are the situations in Geology in which non-deformable and deformable inclusions are carried about in suspension by the motion of a fluid, or a rock behaving like a fluid. Therefore, it is of crucial importance to Geosciences to understand the rotational behaviour of inclusions in viscous flow, and the effects in the matrix deformation. A major...

Subduction initiation at straight passive margins can be investigated with two-dimensional (2-D) numerical models, because the geometry is purely cylindrical. However, on Earth, straight margins rarely occur. The construction of 3-D models is therefore critical in the modeling of spontaneous subduction initiation at realistic, curved passive margin...

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...

Large-scale flank collapses are common in the geological evolution of volcanic ocean islands in the Atlantic. To date, catastrophic lateral collapses in the Azores Islands have been difficult to identify, leading to suggestions that a lack of events may relate to the relatively small size of the islands. Here we show evidence for two major collapse...

A rock salt-lamprophyre dyke contact zone (sub-vertical, NE-SW strike) was investigated for its petrographic, mechanic and physical properties by means of anisotropy of magnetic susceptibility (AMS) and rock magnetic properties, coupled with quantitative microstructural analysis and thermal mathematical modelling. The quantitative microstructural a...

The evolution of volcanic islands is generally marked by the interplay between construction and destruction processes. Large-scale flank collapses episodes, especially, constitute a major threat, because they can generate fast-running debris-avalanches and trigger destructive tsunamis. The Azores islands are located on the triple junction between N...

We use GPS, bathymetric/structural, and seismic data to define the pattern of present deformation along the northern half of the Azores plateau, where the Nubia-Eurasia plate boundary terminates at the axis of the Mid-Atlantic Ridge (MAR). New and existing campaign GPS velocities from the Azores islands reveal extension oblique to a series of en éc...

This study revisits the palaeomagnetism of the Sines massif (similar to 76 Ma) in the southwestern Iberian Margin (Portugal). The palaeomagnetic analysis was complemented by a comprehensive study of the magnetic mineralogy by means of rock magnetic measurements and petrographic observations. The overall dispersion of palaeomagnetic directions (decl...

We investigate the evolution of uplifted areas in NE Brazil, which have been considered as residual landforms. The study focuses on the 130 km-long, 41 km-wide Pereiro Massif (PM). The structural control and the age of this uplift are the problems addressed in this study. We carried out topographic analysis, geomorphological and geological mapping,...

Motivated by the need for halite rheology, we investigated the stress/strain/strain rate behaviour of halite to high shear strains in torsion, using polymer jackets whose strength does not influence halite rheology. The experimental results show that: (1) halite strength decays exponentially with temperature increase, being very weak at 300 °C (ca....

The morpho-structural evolution of oceanic islands results from competition between volcano growth and partial destruction by mass-wasting processes. We present here a multi-disciplinary study aimed at recovering the successive stages of development of Faial (Azores) during the last 1 Myr. Using high-resolution digital elevation model (DEM), new K/...

We report evidence for ongoing lateral slump of part of the southeastern flank of the Pico volcanic ridge in the Azores. Data from a high-resolution digital elevation model, field work, GPS, and radar interferometry show that: (1) the slumping sector is several cubic kilometers in size; (2) the structure involves several curved scars with normal fa...

The motivation to carry out this study stemmed from the generalized perception that nowadays youth lacks the skills for the 21st century. Especially the high-level competences like critical thinking, problem solving and autonomy. Several tools can help to improve these competences (e.g. the SCRATCH programming language), but, as researchers and edu...

Eye and sheath folds are described from the turbidites of the Aberystwyth Group, in the Silurian of west Wales. They have been studied at outcrop and on high resolution optical scans of cut surfaces. The folds are not tectonic in origin. They occur as part of the convolute-laminated interval of each sand-mud turbidite bed. The thickness of this int...

On the one hand, it is not yet understood why transform faults commonly form orthogonal to rifts, because this cannot be explained by simple theories of fracture mechanics. On the other hand, rock experimental data have shown that a very strong layer (elastic core) should exist between brittle and ductile layers of the lithosphere. Therefore, we in...

Deformation of rocks produces structures at all scales that are in many cases periodic (folding or boudinage), with variable amplitude and wavelength. Here we focus on boudinage, a process of primordial importance for tectonics. In the present study, we carried out measurements of natural boudins and experimentally tested the effects of two variabl...

We present a palaeomagnetic study on 38 lava flows and 20 dykes encompassing the past 1.3 Myr on S. Jorge Island (Azores Archipelago—North Atlantic Ocean). The sections sampled in the southeastern and central/western parts of the island record reversed and normal polarities, respectively. They indicate a mean palaeomagnetic pole (81.3°N, 160.7°E, K...

We report evidence for ongoing lateral slump of part of the southeastern fl ank of the Pico volcanic ridge in the Azores. Data from a high-resolution digital elevation model, fi eld work, GPS, and radar interferometry show that: (1) the slumping sector is several cubic kilometers in size; (2) the structure involves several curved scars with normal...