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The paleogeographic position of the central Dodecanese Islands at the transition between the Aegean and Anatolian plates plays a considerable role in understanding the link between both geologically unique domains. In this study, we investigate the tectonic history of the central Dodecanese Islands and the general correlation with the Aegean and western Anatolian and focus on the poorly studied islands of Kalymnos and Telendos. Three different major tectonic units were mapped on both islands from bottom to top: (1) The Kefala Unit consists of late Paleozoic, fossil-rich limestones, which have been deformed into a SE-vergent fold-and-thrust belt sealed by an up to 200-m-thick wildflysch-type olistostrome with marble and ultramafic blocks on a scale of tens of meters. (2) The Marina Basement Unit consists of a Variscan amphibolite facies basement with garnet mica schists, quartzites, and amphibolites. (3) Verrucano-type formation violet shales and Mesozoic unmetamorphosed limestones form the Marina Cover Unit. Correlation of these units with other units in the Aegean suggests that Kalymnos is paleogeo-graphically located at the southern margin of the Pelagonian domain, and therefore it was in a structurally upper tectonic position during the Paleogene Alpine orogeny. New white mica 40Ar/39Ar ages confirm the Carboniferous deformation of the Marina Basement Unit followed by a weak Triassic thermal event. Single-grain white mica 40Ar/39Ar ages from pressure solution cleavage of the newly defined Telendos Thrust suggest that the Marina Basement Unit was thrusted toward the north on top of the Kefala Unit in the Paleocene. Located at a tectonically upper position, the units exposed in the central Dodecanese escaped subduction and the syn-orogenic, high-pressure metamorphism. However, these units were affected by post-orogenic extension, and the contact between the Marina Basement Unit and the non-metamorphic Marina Cover Unit has been reactivated by the cataclastic top-to more...

The breakup of Eastern Gondwana started during the Early Jurassic with the separation of Antarctica and Madagascar from Africa. While margins architecture has been described along the Western Somalia Basin and the central Mozambique, the spatial extent of rifting further south – i.e. the Natal Valley – remains poorly documented. Seismic reflection profiles interpretation, 40Ar/39Ar ages and isotopic data show the existence of a plume related magma-rich margin – the Natal segment – characterized by a large volume of seaward dipping reflectors inferred to be basalts. In particular, the contrast in lithosphere rheology, probably caused by a Meso-Neoproterozoic belt between the Kaapval and Grunehogna Archean cratons, favored extension and upwelling from a deep mantle thermomechanical anomaly, the so-called Karoo superplume that started at around 180 Ma. Further, the presence of stretched continental crust at around 30°S implies a more southerly position of Antarctica which will need to be considered in future kinematic models. more...

The breakup of Eastern Gondwana started during the Early Jurassic with the separation of Antarctica and Madagascar from Africa. While margins architecture has been described along the Western Somalia Basin and the central Mozambique, the spatial extent of rifting further south – i.e. the Natal Valley – remains poorly documented. Seismic reflection profiles interpretation, 40Ar/39Ar ages and isotopic data show the existence of a plume related magma-rich margin – the Natal segment – characterized by a large volume of seaward dipping reflectors inferred to be basalts. In particular, the contrast in lithosphere rheology, probably caused by a Meso-Neoproterozoic belt between the Kaapval and Grunehogna Archean cratons, favored extension and upwelling from a deep mantle thermomechanical anomaly, the so-called Karoo superplume that started at around 180 Ma. Further, the presence of stretched continental crust at around 30°S implies a more southerly position of Antarctica which will need to be considered in future kinematic models. more...

A variety of structures results from the interplay of evolving far field forces, plate kinematics and magmatic activity during continental break-up. The east Limpopo transform margin, offshore northern Mozambique, formed as Africa and Antarctica separated during the mid-Jurassic period break-up of the Gondwana supercontinent. The nature of the crust onshore has been discussed for decades in an effort to resolve issues with plate kinematic models. Two seismic refraction profiles with coincident multichannel seismic reflection profiles allow us to interpret the seismic velocity structures across the margin, both onshore and offshore. These seismic profiles allow us to (1) delineate the major regional crustal domains; (2) identify widespread indications of magmatic activity; and (3) map crustal structure and geometry of this magma-rich transform margin. Careful examination of the profiles allows us to make the following observations and interpretations: (1) on land, continental crust is overlain by a >10 km thick volcano-sedimentary wedge related to an early rifting stage, (2) offshore, thick oceanic crust formed due to intense magmatic activity, and between the two (3) a 50-60 km wide transform zone where the crustal structures are affected by intense magmatic activity and faulting. The prominent presence of intrusive and extrusive igneous units may be attributed the combination of a deep-seated melting anomaly and a trans-tensional fault zone running through thinned lithosphere that allowed melt to reach the surface. A comparison of the crustal thinning along other transform margins shows a probable dependence with the thermal and/or tectonic history of the lithosphere. more...

The rifted continental margins of Mozambique provide excellent examples of continental passive margins with a significant structural variability associated with magmatism and inheritance. Despite accumulated knowledge, the tectonic structure and nature of the crust beneath the South Mozambique Coastal Plain (SMCP) are still poorly known. This study interprets high-resolution seismic reflection data paired with data from industry-drilled wells and proposes a structural model of the Limpopo transform margin in a magma-rich context. Results indicate that the Limpopo transform margin is characterized by an ocean-continent transition that links the Beira-High and Natal valley margin segments and represents the western limit of the continental crust, separating continental volcano-sedimentary infilled grabens from the oceanic crust domain. These basins result from the emplacement of the Karoo Supergroup during a Permo-Triassic tectonic event, followed by an Early Jurassic tectonic and magmatic event. This latter led to the establishment of steady-state seafloor spreading at ca.156 Ma along the SMCP. A Late Jurassic to Early Cretaceous event corresponds to formation of the Limpopo transform fault zone. Which accommodated the SSE-ward displacement of Antarctica with respect to Africa. We define a new type of margin: the magma-rich transform margin, characterized by the presence of voluminous magmatic extrusion and intrusion coincident with the formation and evolution of the transform margin. The Limpopo transform fault zone consists of several syn-transfer and -transform faults rather than a single transform fault. The intense magmatic activity was associated primarily with mantle dynamics, which controlled the large-scale differential subsidence along the transform margin. more...

A variety of structures results from the interplay of evolving far field forces, plate kinematics and magmatic activity during continental break-up. The east Limpopo transform margin, offshore northern Mozambique, formed as Africa and Antarctica separated during the mid-Jurassic period break-up of the Gondwana supercontinent. The nature of the crust onshore has been discussed for decades in an effort to resolve issues with plate kinematic models. Two seismic refraction profiles with coincident multichannel seismic reflection profiles allow us to interpret the seismic velocity structures across the margin, both onshore and offshore. These seismic profiles allow us to (1) delineate the major regional crustal domains; (2) identify widespread indications of magmatic activity; and (3) map crustal structure and geometry of this magma-rich transform margin. Careful examination of the profiles allows us to make the following observations and interpretations: (1) on land, continental crust is overlain by a >10 km thick volcano-sedimentary wedge related to an early rifting stage, (2) offshore, thick oceanic crust formed due to intense magmatic activity, and between the two (3) a 50-60 km wide transform zone where the crustal structures are affected by intense magmatic activity and faulting. The prominent presence of intrusive and extrusive igneous units may be attributed the combination of a deep-seated melting anomaly and a trans-tensional fault zone running through thinned lithosphere that allowed melt to reach the surface. A comparison of the crustal thinning along other transform margins shows a probable dependence with the thermal and/or tectonic history of the lithosphere. more...

The rifted continental margins of Mozambique provide excellent examples of continental passive margins with a significant structural variability associated with magmatism and inheritance. Despite accumulated knowledge, the tectonic structure and nature of the crust beneath the South Mozambique Coastal Plain (SMCP) are still poorly known. This study interprets high-resolution seismic reflection data paired with data from industry-drilled wells and proposes a structural model of the Limpopo transform margin in a magma-rich context. Results indicate that the Limpopo transform margin is characterized by an ocean-continent transition that links the Beira-High and Natal valley margin segments and represents the western limit of the continental crust, separating continental volcano-sedimentary infilled grabens from the oceanic crust domain. These basins result from the emplacement of the Karoo Supergroup during a Permo-Triassic tectonic event, followed by an Early Jurassic tectonic and magmatic event. This latter led to the establishment of steady-state seafloor spreading at ca.156 Ma along the SMCP. A Late Jurassic to Early Cretaceous event corresponds to formation of the Limpopo transform fault zone. Which accommodated the SSE-ward displacement of Antarctica with respect to Africa. We define a new type of margin: the magma-rich transform margin, characterized by the presence of voluminous magmatic extrusion and intrusion coincident with the formation and evolution of the transform margin. The Limpopo transform fault zone consists of several syn-transfer and -transform faults rather than a single transform fault. The intense magmatic activity was associated primarily with mantle dynamics, which controlled the large-scale differential subsidence along the transform margin. more...

Slab tearing below western Turkey had first-order tectonic and magmatic consequences by inducing a lateral gradient of extension in the upper plate and toroidal flow of asthenosphere that affected the typology and distribution of melts at the surface. But the coupling mechanisms between the 3D mantle flow at depth and deformation in the upper plate above a slab tear have received little attention so far. This paper is focused on the description of the distribution and kinematics of deformation in the eastern part of the Aegean Sea, within the transition zone between the Cyclades and the Menderes Massif, which have been little studied. By investigating the Dodecanese and Eastern Aegean islands, we thus complete the description of the extensional strain field in the overriding plate around the slab tear. There, extension related to slab retreat and tearing keeps a constant NNE-SSW direction accommodating the difference in finite rates of extension, without localized crustal-scale strike-slip faults and block rotations above the tear. In addition, despite the complexity involved in the Aegean-Anatolian orogenic wedge, a similar structural position is recognized through the entire region. From top to bottom, we found that (i) the Lycian units which were exhumed earlier, in the Late Cretaceous, (ii) the higher-pressure and higher-temperature units (i.e. the Upper Cycladic Blueschist Nappe), with exception of the Vourliotes nappe in Samos, and finally (iii) the colder units such as Amorgos unit, the Menderes and its cover before the Main Menderes Metamorphism overprint and the Lower Cycladic Blueschist Nappe (e.g. Milos, Folegandros, a part of the Dodecanese and Fourni islands). © 2019 Elsevier B.V. more...

Slab tearing below western Turkey had first-order tectonic and magmatic consequences by inducing a lateral gradient of extension in the upper plate and toroidal flow of asthenosphere that affected the typology and distribution of melts at the surface. But the coupling mechanisms between the 3D mantle flow at depth and deformation in the upper plate above a slab tear have received little attention so far. This paper is focused on the description of the distribution and kinematics of deformation in the eastern part of the Aegean Sea, within the transition zone between the Cyclades and the Menderes Massif, which have been little studied. By investigating the Dodecanese and Eastern Aegean islands, we thus complete the description of the extensional strain field in the overriding plate around the slab tear. There, extension related to slab retreat and tearing keeps a constant NNE-SSW direction accommodating the difference in finite rates of extension, without localized crustal-scale strike-slip faults and block rotations above the tear. In addition, despite the complexity involved in the Aegean-Anatolian orogenic wedge, a similar structural position is recognized through the entire region. From top to bottom, we found that (i) the Lycian units which were exhumed earlier, in the Late Cretaceous, (ii) the higher-pressure and higher-temperature units (i.e. the Upper Cycladic Blueschist Nappe), with exception of the Vourliotes nappe in Samos, and finally (iii) the colder units such as Amorgos unit, the Menderes and its cover before the Main Menderes Metamorphism overprint and the Lower Cycladic Blueschist Nappe (e.g. Milos, Folegandros, a part of the Dodecanese and Fourni islands). more...

Slab tearing below western Turkey had first-order tectonic and magmatic consequences by inducing a lateral gradient of extension in the upper plate and toroidal flow of asthenosphere that affected the typology and distribution of melts at the surface. But the coupling mechanisms between the 3D mantle flow at depth and deformation in the upper plate above a slab tear have received little attention so far. This paper is focused on the description of the distribution and kinematics of deformation in the eastern part of the Aegean Sea, within the transition zone between the Cyclades and the Menderes Massif, which have been little studied. By investigating the Dodecanese and Eastern Aegean islands, we thus complete the description of the extensional strain field in the overriding plate around the slab tear. There, extension related to slab retreat and tearing keeps a constant NNE-SSW direction accommodating the difference in finite rates of extension, without localized crustal-scale strike-slip faults and block rotations above the tear. In addition, despite the complexity involved in the Aegean-Anatolian orogenic wedge, a similar structural position is recognized through the entire region. From top to bottom, we found that (i) the Lycian units which were exhumed earlier, in the Late Cretaceous, (ii) the higher-pressure and higher-temperature units (i.e. the Upper Cycladic Blueschist Nappe), with exception of the Vourliotes nappe in Samos, and finally (iii) the colder units such as Amorgos unit, the Menderes and its cover before the Main Menderes Metamorphism overprint and the Lower Cycladic Blueschist Nappe (e.g. Milos, Folegandros, a part of the Dodecanese and Fourni islands). more...

Slab rollback results in the development of low-angle normal faults (detachments) and metamorphic core complexes (MCCs) in back-arc domains. Although the mechanical consequences of slab dynamics on lithospheric and crustal behaviors have already been studied, thermal effects have not been investigated yet. This study shows that slab rollback produces lithospheric-scale thermal perturbations intrinsically associated with emplacement of amagmatic high-enthalpy geothermal systems. Using a multi-scale numerical modeling approach, with lithospheric-scale 3-D thermo-mechanical models of subduction, and 2-D models of fluid flow at the scale of detachments, we demonstrate that subduction-induced extensional tectonics controls the genesis and distribution of crustal-scale thermal domes from the base of the crust, and the location of high-energy geothermal systems. We find that when slab tearing occurs, Moho temperatures can temporarily increase by up to 250 °C due to significant shear heating in the flowing upper mantle. Associated thermal anomalies (with characteristic width and spacing of tens and hundreds of km, for crustal and lithospheric scales, respectively) then migrate systematically toward the retreating trench. These thermal domes weaken the crust, localize deformation and enhance the development of crustal-scale detachments. These thermo-mechanical instabilities mimic genesis of high-temperature MCCs with migmatitic cores in the back-arc domain, such as those of the Menderes (western Anatolia, Turkey) and Larderello (southern Tuscany) provinces in the Mediterranean realm, and those in the Basin and Range (western United States), where detachments control the bulk of the heat transport. At the scale of MCCs, the bulk fluid flow pattern is controlled by topography-driven flow while buoyancy-driven flow dominates within the permeable detachments, focusing reservoir location of high-energy geothermal systems at shallow depth beneath the detachments. more...

Ultrafine-grained and heterostructured materials are currently of high interest due to their superior mechanical and functional properties. Severe plastic deformation (SPD) is one of the most effective methods to produce such materials with unique microstructure-property relationships. In this review paper, after summarizing the recent progress in developing various SPD methods for processing bulk, surface and powder of materials, the main structural and microstructural features of SPD-processed materials are explained including lattice defects, grain boundaries and phase transformations. The properties and potential applications of SPD-processed materials are then reviewed in detail including tensile properties, creep, superplasticity, hydrogen embrittlement resistance, electrical conductivity, magnetic properties, optical properties, solar energy harvesting, photocatalysis, electrocatalysis, hydrolysis, hydrogen storage, hydrogen production, CO2 conversion, corrosion resistance and biocompatibility. It is shown that achieving such properties is not limited to pure metals and conventional metallic alloys, and a wide range of materials are currently processed by SPD, including high-entropy alloys, glasses, semiconductors, ceramics and polymers. It is particularly emphasized that SPD has moved from a simple metal processing tool to a powerful means for the discovery and synthesis of new superfunctional metallic and nonmetallic materials. The article ends by declaring that the borders of SPD have been extended from materials science and it has become an interdisciplinary tool to address scientific questions such as the mechanisms of geological and astronomical phenomena and the origin of life. more...