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The Kopet Dagh mountains in NE Iran exhibit a 7-km-thick continu-ous sedimentary sequence recording detritus from exposed surrounding terranes from the last 175 Ma. This work presents a multi-disciplinary geochronologic and provenance analysis in an attempt to identify and date major geologic events along the northern segment of the Tethys and reconstruct the regional tectonic history from Gondwana-related rifting until the Alpine orogeny. Sandstone framework, heavy mineral analysis, U-Pb dating of detrital zircons, and Hf-isotope ratio meas-urements on dated zircons from Triassic to Paleocene sandstones indicate three main tectonic events that include Early Silurian intracontinental rifting (opening of Paleo-Tethys), Early Carboniferous rifting of a back-arc basin (Aghdarband Complex), and Late Triassic collisional to post-collisional magmatism (Paleo-Tethys collision). Mineralogical and age peak considerations indicate that detritus was supplied from the south into the extensional Kopet Dagh Basin during Middle Jurassic, while Cretaceous to Paleocene sandstones show signs of increas-ing recycling. ISSN:1945-452X ISSN:0002-9599

We present an integrated analysis of the geophysical parameters of the lithosphere of Black Sea basin obtained as a result of the interpretation of magnetic, gravity, thermal, deep seismic sounding and seismic-tomographic data. It first demonstrates inherent significant differences in geophysical parameters of lithosphere in the Western and Eastern Black Sea subbasins existing from the prerift stage. The set of reviewed parameters responsible for formation of the present-day lithosphere includes types of crust, depths to acoustic basement, configuration of subbasins, depths to Moho, heat flow and relief of the thermal-asthenosphere boundary (LAB), trends of main deep faults of the crystalline crust, their kinematic types, occurring linear magnetic anomalies, velocity pattern of subcrustal mantle. The above-mentioned parameters of the lithosphere are indicators of the age, geodynamics and driving mechanisms for opening of a subbasins. Oblique trends of the subbasins and the topography of Moho discontinuity in the west and east domains, oblique striking of pre-rifting Istanbul zone and the Shatsky Ridge and different trends of deep faults in the crystalline crust suggest distinct lithospheric structure existing from pre-opening of the Black Sea subbasins and different geodynamical conditions of its formation. The Odesa-Sinop-Ordu deep fault zone as a direct continuation of the Golovanivskaya suture zone of the Ukrainian shield and its slope, probably is of the Precambrian age. So it could be the tectonic boundary between two segments of pre-rift continental crust and between future subbasins. The examples illustrate how indicated parameters of the lithosphere can geophysically confirm the basic ideas of available models for geodynamics of the Black Sea., Представлено комплексний аналіз результатів інтерпретації даних магнітного, гравітаційного, теплового полів, глибинного сейсмічного зондування і сейсмічної томографії. Він вперше демонструє, що суттєві відмінності геофізичних параметрів літосфери Західного та Східного Чорноморських суббасейнів існують від дорифтової стадії. Набір розглянутих параметрів, відповідальних за формування сучасної літосфери, включає типи кори, глибини до акустичного фундаменту, конфігурацію суббасейнів, глибини до Мохо, рельєф границі термоастеносфери (ЛАГ), простягання основних глибинних розломів кристалічної кори, їхні кінематичні типи, лінійні магнітні аномалії, швидкісну картину підкорової мантії. Параметри літосфери є індикаторами віку, геодинаміки та механізмів розкриття суббасейнів. Простягання рельєфу Мохо під кутом один до одного в суббасейнах і передрифтової Стамбульської зони і хребта Шатського, різнонаправлені простягання глибинних розломів обох суббасейнів указують на відмінну будову літосфери від дорифтової стадії. Одесько-Синопська зона глибинних розломів як безпосереднє продовження Голованівської сутури Українського щита і його схилу є докембрійського віку і може бути тектонічною межею між двома сегментами дорифтової континентальної кори і майбутніми суббасейнами. Наведено приклади як параметри літосфери підтверджують базові ідеї геодинаміки Чорного моря

The Red Sea is an ideal location for studying rifting processes, offering a young and active intra‐continental rift at the final stages of breakup. We explore the 3D lithospheric structure of the Red Sea by analyzing the gravity response of four end‐member models of rift architecture, including two end‐member types margin architecture Type I—narrow margins and exhumed lithospheric mantle, and Type II—(ultra)wide margins and removal of lithospheric mantle. Additionally, we test two options for the distribution of the oceanic crust (a) limited, that is, confined only to regions of magnetic stripes, and (b) extended, that is, available in vast areas within the basin. South of latitude 23°N, our results suggest the presence of ultrawide margins and limited oceanic crust. North of this latitude, the model of exhumed mantle and limited oceanic crust has minimized residuals compared to the observed gravity field, and agrees with a previously published regional tomographic model. Additionally, we find evidence for the presence of a high‐density body along the southern Arabian coast, probably associated with magmatic underplating. We discuss the lithospheric structure of the Red Sea with respect to the nearby Afar plume, agreeing that the close proximity of the central‐southern regions to the plume promoted a reduction in the strength of the lithosphere, and led to the development of ultrawide margins in these areas., Plain Language Summary: The Red Sea is a young example of continental break‐up, a process in which a continent disintegrate into smaller pieces and an ocean is formed between them. We explore the sub‐surface structure of the Red Sea, down to 140 km, aiming to better understand the mechanisms that allowed the Arabian plate to separate from Africa ∼23 million years ago. We examine the gravity response of four end‐member models of rift structures and compare them to the gravity signal measured in this region. We find that the sub‐surface structure in the central‐southern region is different than in the northern regions. Toward the south, the crust is thin and stretched, the lithospheric mantle is absent, and the asthenosphere is rising in a wide region. In the north the lithospheric mantle is exhumed and the asthenosphere is rising in narrow regions below the center of the basin. We discuss the reasons for these differences and support the possibility that the Afar Plume, currently located to the south of the Red Sea, had a thermal weakening effect on the central‐southern regions of the Red Sea, which allowed the lithosphere to deform more easily, having direct implications in the present‐day architecture of the Red Sea., Key Points: Gravity modeling in the Red Sea suggests a contrasting rift architecture in the central‐southern regions and in the northern regions. In the central‐southern regions, ultrawide margins and thinned continental crust are underlaid by a broad asthenosphere upwelling. In the northern regions, we infer exhumed mantle lithosphere and a narrow asthenosphere upwelling., Minerva Foundation http://dx.doi.org/10.13039/501100001658, Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659, http://icgem.gfz-potsdam.de/calcgrid, https://www.gebco.net/data_and_products/gridded_bathymetry_data/#global, https://ngdc.noaa.gov/mgg/sedthick/, https://ds.iris.edu/ds/products/emc-af2019/, https://zenodo.org/record/5771863#.Y6gmBHZBzfs, https://zenodo.org/record/4482096#.Y6gnPHZBzfs, https://igmas.git-pages.gfz-potsdam.de/igmas-pages/

The Ural mobile belt is an intracontinental epioceanic orogen that has already gone through all stages of the geodynamic development. Igneous rocks formed during each stage are important indicators for understanding the evolution of this belt and determining potential ore contents of its segments. We consolidated large datasets on petrogeochemistry and isotope geochronology of the Paleozoic (490–250 Ma) granitoids associated with the opening and evolution of the Ural paleoocean and the subsequent formation of the collisional orogen. Using these data, we have revised the ages of several tectono-magmatic events, clarified the paleogeodynamic settings for the generation of granitoids of different compositions, and described the roles of mantle-crust interactions and the plume factor in the formation of the mature continental crust in the study area. The results can be useful for geological mapping and improving the assessment of the potential ore contents in granitoid complexes that differ in origin and composition.

International audience; Phylogenetic studies of present-day terrestrial organisms suggest that faunal dispersals between South America and the Greater Antilles may have occurred during the Cenozoic through the Lesser Antilles. However, because of the lack of geological data to unravel the areas that may have emerged along the Lesser Antilles trench, the migration paths used by their ancestors remain unknown. Here, we present novel paleogeographic maps of the central Lesser Antilles (extending from Guadeloupe to Martinique islands) which are built on the basis of onshore and offshore stratigraphic correlations (50 seismic lines, biostratigraphy of 9 dredged and 29 field samples, six sedimentary logs). We find that repetitive episodes of uplift and drowning have occurred in the central part of the Lesser Antilles during the Neogene. Offshore, the Marie-Galante Basin comprises three sedimentary megasequences that deposited between: (i) the Oligocene and Early Miocene, including the extinct arc, (ii) the Middle and Late Miocene and (iii) the latest Miocene and Holocene. These sediments infill a NNW-SEE trending forearc rift that opened during the Early Miocene. The megasequences are separated by subaerial regional unconformities that affect the rift shoulders. Onshore, we show that the lower part of the carbonate platform in Guadeloupe and La Désirade has deposited during the late Messinian. In Martinique, we refine the age of the carbonate deposits belonging to the extinct arc to the Chattian-Burdigalian, and evidence a major subaerial unconformity corresponding to the Middle Miocene. We propose that between Anguilla and Martinique, from north to south, large archipelagos, which are now drowned, have existed during the early Middle Miocene and the latest Miocene. We suggest that during the Miocene, the Lesser Antilles may have been used as a pathway for land-faunal dispersals from South America.

Significance This article tackles the longstanding question of why some continental rifting was associated with major pulses of excess volcanism that formed “volcanic rifted margins,” yet other rifting, even nearby, was not. After reviewing the South Atlantic rifting exemplar, we present results from an improved type of three-dimensional calculation of mantle flow that avoids many of the artificial boundary condition-related pitfalls in prior numerical studies that did not predict asymmetric rift-related volcanism. Our experiments match the observed development of asymmetric volcanism during South Atlantic rifting, with important implications for plume-influenced rifting of continents. In particular, the scenario does not require a conventionally assumed “starting plume head” to provide the hotter-than-average mantle that induces excess rift magmatism., Volcanic rifted margins are typically associated with a thick magmatic layer of seaward dipping reflectors and anomalous regional uplift. This is conventionally interpreted as due to melting of an arriving mantle plume head at the onset of rifting. However, seaward dipping reflectors and uplift are sometimes asymmetrically distributed with respect to the subsequent plume track. Here we investigate if these asymmetries are induced by preexisting lateral variations in the thickness of continental lithosphere and/or lithospheric stretching rates, variations that promote lateral sublithospheric flow of plume material below only one arm of the extending rift. Using three-dimensional numerical experiments, we find that South Atlantic rifting is predicted to develop a strong southward asymmetry in its distribution of seaward dipping reflectors and associated anomalous relief with respect to the Tristan Plume that “drove” this volcanic rifted margin, and that the region where plume material drains into the rift should experience long-lived uplift during rifting—both as observed. We conclude that a mantle plume is still needed to source the anomalously hot sublithospheric material that generates a volcanic rifted margin, but lateral along-rift flow from this plume, not a broad starting plume head, is what controls when and where a volcanic rifted margin will form.

The study was focused on the tectonic structure features of the Gulf of Aden, which includes three provinces. The western, central and eastern provinces differ in morphostructural segmentation of the spreading ridge of the Gulf of Aden, which took place in different geodynamic regimes of their formation and development. In our study, physical modeling was performed to investigate the segmentation mechanisms of the three parts and the formation of the marginal plateau and the island of Socotral. In experiments, an elastic-plastic plate lying on a liquid base (simulating melt) was subjected to normal or oblique stretchig. Plate sections imitating the continental or oceanic lithosphere in the model had different thicknesses. Various heterogeneities, such as cuts, linear weakened zones (rift heating zones) etc., were set in the plate sections in accordance with natural analogues. The modeling results show that morphostructural segmentation of the spreading axis in the Gulf of Aden depends on the degree of heating and the thickness of the lithosphere, associated with different distances from the Afar plume and local thermal anomalies, spreading obliquity and the existence of structural inhomogeneities with increased lithosphere strength, which are associated in this case with the presence of Mesozoic grabens on the pre-breakup basement. The smaller is the lithosphere thickness, the smaller is the size of the segments. The sharper is the angle, the more pronounced is segmentation. The study of the connection of the Gulf of Aden continental rift with the rift zone of the Carlsberg ridge suggests that during their development, these rift fractures propagated towards each other. The experiment results show that in case of a «sharp» boundary between blocks that differ in thickness, a shear zone is likely to occur. Such a case is applicable, for example, to the Alula-Fartak fracture zone, or to Owen’s fracture zone. With a less ‘sharp’ boundary, overlapping structures are often formed, such as microplates or microblocks enclosed between two rift fissures. In such case, one microblock then dies, while the other develops into a spreading ridge. Apparently, such a microblock is represented by the marginal plateau and the island of Sokotra. As shown by the modeling, propagation of the two rifts towards each other was important for the formation of the plateau and the island of Socotra. Moreover, a significant role was played by the initial geometry of the rift zones and their initial positioning separate from each other.

Continent-derived tectonic units in the Tauern Window of the Alps exhibit stratigraphic and structural traces of extension of continental margins eventually leading to the opening of the Alpine Tethys. In this study, we reassess lithostratigraphic data from the central part of the Tauern Window to reconstruct the post-Variscan evolution of this area, particularly the rift-related geometry of the European continental margin. The lithostratigraphy of the Alpine nappes reflects systematic variations of the structure of the European margin. The lowest tectonic units (Venediger nappe system, Eclogite Zone and Trögereck Nappe) are characterized by a thick succession of arkose-rich Bündnerschiefer-type sediments of probably Early Cretaceous age that we interpret as syn-rift sequence and which stratigraphically overlies thinned continental basement and thin pre-rift sediments. In contrast, the highest tectonic unit derived from Europe (Rote Wand Nappe) preserves a thick pre-rift sedimentary sequence overlying thinned continental basement, as well as a thick syn- to post-rift succession characterized by turbiditic Bündnerschiefer-type sediments of probable Cretaceous age. These observations point towards a highly segmented structure of the European rifted margin. We propose that this involved the formation of an outer margin high, partly preserved in the Rote Wand Nappe, that was separated from the main part of the European margin by a rift basin overlying strongly-thinned continental crust. The along-strike discontinuity of the Rote Wand Nappe is proposed to reflect the lateral variation in thickness of the outer margin high that resulted from margin-parallel segmentation of the European continental crust during highly oblique rifting antecedent to the opening of Alpine Tethys.

The Oligocene-Recent Red Sea rift is one of the preeminent examples of lithospheric rupture in the recent geological past, forming the basis for many models of how continental breakup occurs and progresses to the formation of new oceanic crust. Utilisation of low-temperature thermochronology in the Red Sea Rift since the 1980s has been key to constraining its spatio-temporal evolution, providing constraints for the propagation of strain and geomorphological development of its margins where datable syn-tectonic strata and/or markers are absent. We review the wealth of published apatite fission track and (U-Th-Sm)/He data from along the Red Sea, affording insights into the Oligocene-Recent thermo-tectonic evolution of the Nubian and Arabian margins. A regional interpolation protocol was employed to synthesise time-temperature reconstructions generated from the mined thermochronology data and burial histories produced from vitrinite reflectance and well data. These cooling-heating maps record a series of pronounced episodes of upper crustal thermal flux related to the development of the Oligocene-Recent Red Sea Rift. Assimilation of these regional thermal history maps with paleogeographic reconstructions and regional magmatic and strain histories provide regional perspectives on the roles of tectonism and geodynamic activity in Red Sea formation and their effects on rift margin development.

In the West of the aHochthon of Magnitogorsk zone thrusted onto the Precambrian complexes of the Uraltau zone, the Devonian island-arc complexes overlap stratigraphicalry the Ordovician and Silurian chert-basalt sequences and serpentine melange. Melange and Ordovician strata are intruded by dyke swarms and sheeted dykes («dyke in dyke») which are composed of mafic and ultramafic rocks. The dykes, composed by gabbro-dolerite, amphibole K-feldspar gabbro, hornblendite, picrite and lamprophyre, predominate. The composition of the ultramafic rocks corresponds to the composition of picrite and komatiite. The 40Ar/39Ar age of the magmatic amphibole from gabbro is 357 ± 8 m.y. The formation of dykes is related to the Early Carboniferous rift-related magmatism on an active continental margin.

International audience; We investigated the variability of the first-order crustal structure and early post-rift stratigraphy of six segments of the African Equatorial Atlantic margin using sub-surface data (seismic and wells). Extension obliquity of the segments varies from 0° for the West Ivory Coast and Ghana transform segments to 30° for the Togo-Benin oblique segment and 75° for the East Ivory Coast normally divergent segment. The Sierra Leone and Liberia segments underwent probably deformation during both the early Jurassic rifting of the Central Atlantic and the early Cretaceous rifting of the Equatorial Atlantic with contrasted divergence obliquities. For segments that underwent a single rifting, we show that, the higher the obliquity, the wider the crustal thinning domain. This has a major influence on the first-order geometry of all the post-rift horizons, including the present-day slope: the lower the obliquity, the larger the differential subsidence across the margin and the steeper the present-day slopes of post-rift horizons. This also has a major influence on the flexural isostatic response of the lithosphere to thermal- and erosion/sedimentation- driven (un)loads during the early post-rift. Narrow (transform) segments underwent higher flexural (and/or thermal) uplifts in the proximal domain than wider divergent segments. Along the same margin, divergent segments therefore may preserve early post-rift deposits in their proximal domains, whereas they are not preserved on nearby transform segments.

The structure of the eastern part of the Gulf of Aden is peculiar for the presence of a submerged plateau and the island of Socotra, which were formed at the initial stage of its formation. With the beginning of continental rifting in the Oligocene-Miocene, more ancient riftogenic structures of the Mesozoic age were reactivated. This was most revealed in the relief in the Guardafuy graben, which cuts off the base of the Socotra plateau from the shelf of the modern eastern tip of the Horn of Africa. During tension, there were significant rotational deformations of the entire plateau. Socotra Island is divided into two parts by the large Hadibo transfer zone. The morphostructure of the elevated eastern part is determined by the asymmetric arch-like Hajhir Mountains. The western part is deformed much more strongly than the eastern part and is strongly broken by steeply falling faults. The continental margins of Socotra Island in the eastern province of the Gulf of Aden are amagmatic, asymmetrical and fractured by a series of faults and detachments. The difference in their structure is explained by the peculiarity of the transition from continental rifting to spreading, associated with the hyper-extension of the continental crust. In order to understand the conditions of riftogenesis, under which the formation of the continental block of the submerged marginal plateau and the island of Socotra is possible, the authors carried out a physical simulation, the results of which are presented in Article 2.

The Eocene-Miocene successions recovered at DSDP sites on the Jan Mayen Ridge (NE Atlantic) and on the adjacent East Greenland margin provide a sedimentary record of the rifting and separation of the Jan Mayen Microcontinent from East Greenland. A combination of palynology, conventional heavy mineral analysis, single-grain major and trace element geochemistry and radiometric dating of amphibole and zircon has revealed a major change in sediment provenance took place at the Early/Late Oligocene boundary corresponding to a prominent seismic reflector termed JA. During the Eocene and Early Oligocene, lateral variations in provenance character indicate multiple, small-scale transport systems. Site 349 and Kap Brewster were predominantly supplied from magmatic sources (Kap Brewster having a stronger subalkaline signature compared with Site 349), whereas Site 346 received almost exclusively metasedimentary detritus. By contrast, Late Oligocene provenance characteristics are closely comparable at the two Jan Mayen sites, the most distinctive feature being the abundance of reworked Carboniferous, Jurassic, Cretaceous and Eocene palynomorphs. The Site 349 succession documents an evolution in the nature of the magmatic provenance component. Supply from evolved alkaline magmatic rocks, such as syenites, was important in the Middle Eocene and lower part of the Early Oligocene, but was superseded in the later Early Oligocene by mafic magmatic sources. In the latest Early Oligocene, the presence of evolved clinopyroxenes provides evidence for prolonged magmatic fractionation. Initial low degrees of partial melting led to generation of alkaline (syenitic) magmas. The extent of partial melting increased during the Early Oligocene, generating basaltic rocks with both subalkaline and alkaline compositions. Towards the end of the Early Oligocene, the amount of partial melting and magma supply rates decreased. In the Late Oligocene, there is no evidence for contemporaneous igneous activity, with scarce magmatic indicator minerals. The provenance change suggests that the hiatus at the Early/Late Oligocene boundary represents the initiation of the proto-Kolbeinsey Ridge and separation of the Jan Mayen Microcontinent from East Greenland.

Volcanic rocks of the Zamoranos Formation exposed in the Betic Cordillera of southern Spain reveal Late Triassic CAMP volcanism extending from southwest to southeast of the Iberian massif. Comparison with volcanic rocks from the Upper Triassic of the Algarve region in Portugal enables correlation between these different magmatic provinces based on the striking geochemical similarity. The studied mafic magmatic rocks in the Betic Cordillera reveal three volcanic episodes during the deposition of the Zamoranos Formation with two types of geochemical affinity: alkaline (Group 1) and sub-alkaline (Group 2 and 3). The sub-alkaline rocks resemble the studied Triassic rocks of Portugal and the magmatism described as CAMP on a global scale. In the present study, the identification of alkaline rocks preceding the main CAMP sub-alkaline phase by ca. 15 Ma, is the first evidence of alkaline precursors prior to CAMP magmatism and indicates a change from a prior deeper enriched mantle source to a subsequent, shallower one. The temporal evolution of alkaline magmatism followed by a CAMP-type sub-alkaline magmatism is best explained in a context of initial rifting during Norian-Rhaetian times. It is inferred that rifting gradually developed from west to east in the southern area of Iberia., This research was funded by Projects PID2019-104625RB-I00 and PGC2018-098272-B-I00 (Secretaría de Estado de I+D+I, Spain), B-RNM-072-UGR18 ( FEDER Andalucía), RNM-208 and P18-RT-4074 (Junta de Andalucía). A.C. acknowledges the research grant provided by the Alexander von Humboldt Foundation for a post-doctoral fellowship at Bochum and the Juan de la Cierva program funded by The Ministry of Science and Innovation (Spain).

International audience; Synrift stratigraphy and the distribution of breakup-related erosional unconformities vary vastly between passive margins and cannot be explained by classical rifting models. Here we use numerical modeling to predict their spatiotemporal distribution. We show that synrift stratigraphy mimics rift architecture, which is controlled by lithospheric strength. Basinward rift migration during extension produces (1) oceanward younging, syntectonic and posttectonic sequences, (2) rift migration unconformities, RMUs, predating breakup, and (3) a breakup unconformity, BU, that only extends over the outermost margins, since breakup is not linked with a sudden stress drop. With small synrift sedimentation, the RMUs and BU laterally merge to form a margin-wide unconformity. In symmetric, wide conjugate margins, which arise for weak lithospheres such as the South China Sea, a long phase of distributed deformation with little subsidence results in early synrift sediment over most of the margins. RMUs merge into a single event that marks the subsequent focusing of deformation into a narrow breakup area, which experiences short-lived intense thinning and subsidence. In asymmetric conjugate margins, lateral rift migration transports shallowly deposited, early synrift sediments from the narrow to the wide, hyperextended margin, leading to a condensed syntectonic sequence and a single BU in the narrow margin and a series of RMUs in the wide one. For very weak lower crusts, lateral rift migration generates large synrift sag basins in the wide margin, as in Angola and Congo margins. Our models resemble the observed margins tectonic diversity and may be used as templates for interpreting their distal, unexplored areas.

Three crustal-scale sequentially restored cross-sections along the Central External Betic Cordillera enable us to pinpoint the role of extreme crustal thinning, tectonic inheritance and salt tectonics during the evolution of the South-Iberian paleomargin from Mesozoic rifting to Cenozoic continental subduction. This interpretation puts forward the existence of a former highly extended Mesozoic rift system, namely the Subbetic Basin. The basin comprises three main domains that coincide with the classical zoning of the External Betics: (i) The Intermediate units in the northern basin margin represent primary thick minibasins separated by salt walls; (ii) the External Subbetic units attest an inflated salt body in a central trough; and (iii) the Median and Internal Subbetic units in the southern basin margin are analogous to a group of primary minibasins with intercalations of submarine volcanic rocks overlying hyperextended crust. Shortening led to the extrusion of a salt canopy and the development of secondary minibasins. Furthermore, the tectonic inversion of the Subbetic Basin created two major thrusts sheets detached at the Upper Triassic evaporites, accommodating a shortening of approximate to 100-145 km at early Eocene-middle Miocene time. Compression reshaped the hyperextended domain into a subduction trench, and the former transfer faults into tear faults. Ongoing shortening led to the subduction of the South-Iberian paleomargin beneath the Alboran Domain lithosphere. Our results provide a new perspective on the inversion of segmented rift basins partly floored by mantle rocks and call for a major reconsideration on the tectonic architecture and evolution of the Betic-Rif Cordillera., This work has been funded by the projects “Tectonic map of the Iberian Peninsula and the surrounding cordilleras” included into the Spanish National Cartographic Plan, and A-RNM-005-UGR18 of the Programa Operativo FEDER Andalucía 2014–2020. The geophysical data are available on the IGME website at http://info.igme.es/SIGEOF/.

The present study focuses on the petrographic and petrological characteristics of mantle bodies included in Upper Cretaceous sedimentary melanges of the External Ligurian units (Northern Appennine), within the Monte Gavi and Monte Sant'Agostino areas. Two distinct pyroxenite-bearing mantle sections were recognized, mostly based on their plagioclase-facies evolution. The Monte Gavi mantle section is nearly undeformed and records a process of melt infiltration and reaction under plagioclase-facies conditions. The melt-rock interaction event involved both peridotites (mostly harzburgites) and enclosed spinel pyroxenite layers, and is estimated to have occurred at 0.7-0.8 GPa. In the Monte Gavi peridotites and pyroxenites, the spinel-facies clinopyroxene was partially replaced by plagioclase and new orthopyroxene (± secondary clinopyroxene). The reactive melt migration led to relatively high TiO2 contents in relict clinopyroxene and spinel (up to 2.3 wt% and 1.0 wt%, respectively, in the pyroxenites), with the latter also having high Cr# (up to 35 in the peridotites). The Monte Sant'Agostino mantle section displays a widespread ductile shearing and no evidence for melt-rock interaction under plagioclase-facies conditions. The main deformation phase recorded by the Monte Sant'Agostino peridotites (mostly lherzolites) is estimated to have occurred at 750-780 °C and 0.3-0.6 GPa, and gave rise to protomylonitic to ultramylonitic textures characterized by 10-50 ?m neoblasts. The enclosed pyroxenite layers yielded relatively high temperature and pressure estimates (870-930 °C and 0.8-0.9 GPa). Presumably, in the Monte Sant'Agostino mantle section, plagioclase crystallization occurred earlier in the pyroxenites than in enclosing lherzolites, thereby enhancing strain localization and formation of mylonite shear zones in the entire mantle section. We propose that subcontinental mantle section from the External Ligurian units consists of three distinct mantle domains, developed in response to the rifting evolution that ultimately formed a Middle Jurassic ocean-continent transition: (1) a spinel tectonite domain that underwent no significant deformation and melt-rock reaction under plagioclase-facies conditions, characterized by static plagioclase development, (2) a plagioclase mylonite domain experiencing melt-absent deformation, and (3) a nearly undeformed domain that underwent melt infiltration and reaction under plagioclase-facies conditions. We relate mantle domains (1,2) to a rifting-driven uplift in the late Triassic accommodated by large-scale shear zones consisting of plagioclase mylonites.

The northernmost outcrops of the Triassic extensional Cuyo basin in western Argentina reveal a basal coarse conglomerate overlain by a thinning-fining upward siliciclastic red-bedded section with subordinated tuffs and microbial-rich carbonates (Cerro Puntudo Formation), unconformably covered by a second coarse conglomerate (El Relincho Formation), which were previously interpreted as two rifting events. An integrated analysis of facies associations, stacking patterns, paleocurrent and provenance was carried out in order to reveal the rift sedimentation using a source-to-sink approach. Besides the traditional controls in continental basins (e.g., sedimentation, tectonics and climate), this study considers possible drainage pattern evolution in order to differentiate isolated versus integrated depocenter stages. U-Pb zircon data corroborate our analysis and reveal a volcanic basement source of 256.8 ± 3.5 Ma (Permian/Lopingian) and a sedimentation age of 249.8 ± 2.5 Ma (Early Triassic) for a tuff interbedded within the Cerro Puntudo Formation, complementing previous age of 243.8 ± 1.9 Ma (Middle Triassic) at the top of this unit. Stratigraphic stacking allows the interpretation of three evolutionary stages. A first stage, represented by thick massive boulder-volcanic-rich conglomerates characterizing alluvial fan deposition, indicates strong tectonic activity of border faults (first rifting event). These features suggest high surface gradient and high available space controlling accommodation and dispersal of gravity and debris-flow deposits. Paleocurrents to the east reveal largely north-south normal faults located to the west and sediment supply from a proximal volcanic source area. A second stage, represented by a notable fining-thinning upward facies, including fluvial and palustrine (stromatolites with pedogenetic features) deposits, indicates a transition to tectonic quiescence. These facies associations developed in a context of low sedimentation rate, limited tectonic relief and low accommodation space. A third stage is represented by greenish well-rounded coarse-grained polymictic conglomerates of El Relincho Formation that unconformably truncate the Cerro Puntudo Formation. These conglomerates are interpreted as perennial braided fluvial systems (with paleocurrents to the northwest) indicating drainage reorganization primarily influenced by climate change and combined tectonic reactivation, previously considered the second rifting event. Climate change affected sediment delivery and allowed regionally connectivity and overfilling of the depocenters. In this last stage, northwest axial transport from variable sources within the Precordillera (to the southeast) is inferred from provenance analysis indicating open linked-depocenters. This study suggests a new stratigraphic correlation for the northern part of the Cuyo basin, implying that during the first rifting event a semi-arid climate prevailed with development of isolated and independent depocenters (first and second stages), whereas above the unconformity initiating the second rifting event (third stage) depocenters were interconnected. In the light of our source-to-sink analysis, such paleogeographic change allowed overfilling and laterally linkage of separate half-grabens along the Cuyo basin. Whereas tectonic reactivation may better explain renewed conglomerate deposition, climate change toward more humid conditions allowed previously separated depocenters to be connected through axial drainages. Fil: Teixeira, Bárbara M. N.. Petrobras. Petróleo Brasileiro S. A; Argentina Fil: Astini, Ricardo Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Gomez, Fernando Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Morales, Norberto. Universidade Estadual Paulista. Instituto de Geociências e Ciências Exatas; Brasil Fil: Pimentel, Marcio. Universidade do Brasília; Brasil

In the modern structure of the East European platform (EEP) an important role is played by long-lived dislocation zones, complicating the complexes of the platform’s cover and the basement. They are organized non-linearly, form a large vortex megastructure twisted clockwise, and are characterized by an inhomogeneous structure in the vertical and lateral directions. In the stages of their development, numerous dynamic (kinematic) inversions are observed, which are associated with the periodic manifestation and repetition of various geodynamic settings: collision, rifting, transpression and transtension. The processes of alternating rotation of EEP using “iris diaphragm” model explain many development laws of long-lived tectonic zones and vortex megastructure.

The Alleppey Platform is an important morphological feature located in the Kerala-Konkan basin off the southwest coast of India. In the present study, seismic reflection data available in the basin were used to understand the sedimentation history and also to carry out integrated gravity interpretation. Detailed seismic reflection data in the basin reveals that: (1) the Alleppey Platform is associated with a basement high in the west of its present-day geometry (as observed in the time-structure map of the Trap Top (K/T boundary)), (2) the platform subsequently started developing during the Eocene period and attained the present geometry by the Miocene and, (3) both the Alleppey platform and the Vishnu fracture zone have had significant impact on the sedimentation patterns (as shown by the time-structure and the isochron maps of the major sedimentary horizons in the region). The 3-D sediment gravity effect computed from the sedimentary layer geometry was used to construct the crustal Bouguer anomaly map of the region. The 3-D gravity inversion of crustal Bouguer anomaly exhibits a Moho depression below the western border of the platform and a minor rise towards the east which then deepens again below the Indian shield. The 2-D gravity modelling across the Alleppey platform reveals the geometry of crustal extension, in which there are patches of thin and thick crust. The Vishnu Fracture Zone appears as a crustal-scale feature at the western boundary of the Alleppey platform. Based on the gravity model and the seismic reflection data, we suggest that the basement high to the west of the present day Alleppey platform remained as a piece of continental block very close to the mainland with the intervening depression filling up with sediments during the rifting. In order to place the Alleppey platform in the overall perspective of tectonic evolution of the Kerala-Konkan basin, we propose its candidature as a continental fragment. (C) 2017, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V.

International audience; The stunningly increased resolution of the deep crustal levels in recent industrial seismic profiles acquired along most of the world's rifted margins leads to the unraveling of an unexpected variety of structures. It provides unprecedented access to the processes occurring in the middle and lower continental crust. We present a series of so far unreleased profiles that allows the identification of various rift-related geological processes such as crustal boudinage, ductile shear and low-angle detachment faulting, and a rifting history that differs from the classical models of oceanward-dipping normal faults. The lower crust in rifted margins appears much more intensely deformed than usually represented. At the foot of both magma-rich and magma-poor margins, we observe clear indications of ductile deformation of the deep continental crust along large-scale shallow dipping shear zones. These shear zones generally show a top-to-the-continent sense of shear consistent with the activity of Continentward Dipping Normal Faults (CDNF) observed in the upper crust. This pattern is responsible for a migration of the deformation and associated sedimentation and/or volcanic activity toward the ocean. We discuss the origin of these CDNF and investigate their implications and the effect of sediment thermal blanketing on crustal rheology. In some cases, low-angle shear zones define an anastomosed pattern that delineates boudin-like structures. The maximum deformation is localized in the inter-boudin areas. The upper crust is intensely boudinaged and the highly deformed lower crust fills the inter-boudins underneath. The boudinage pattern controls the position and dip of upper crustal normal faults. We present some of the most striking examples from the margins of Uruguay, West Africa, South China Sea and Barents Sea, and discuss their implications for the time-temperature history of the margins.

The NW-SE striking Otway Basin in southeastern Australia is part of the continental rift system that formed during the separation of Australia from Antarctica. The development of this sedimentary basin occurred in two phases of Late Jurassic-Early Cretaceous and Late Cretaceous rifting. The evolution of this basin is mainly associated with extensional processes that took place in a pre-existing basement of Archean, Proterozoic to Paleozoic age. In this study, the total amounts of extension and stretching factor (β factor) have been measured for six transects across the entire passive margin of the Otway Basin region. The results show significant variation in extensional stretching along the basin, with the smallest stretching factors in the easternmost (β = 1.73, 1.9) and westernmost part of the basin (β = 2.09), and the largest stretching factors in the central part (β = 2.14 to 2.44). The domain with the lowest β factor is underlain mostly by thicker lithosphere of the Delamerian Orogen and older crustal fragments of the Selwyn Block. In contrast, the region with the largest β factor and amount of extension is related to younger and thinner lithosphere of the Lachlan Orogen. The main basement structures have been mapped throughout eastern South Australia and Victoria to examine the possible relationships between the younger pattern of extensional faults and the older basement fabrics. The pattern of normal faults varies considerably along onshore and offshore components of the Otway Basin from west to east. It appears that the orientation of pre-existing structures in the basement has some control on the geometry of the younger normal faults across the Otway Basin, but only in a limited number of places. In most areas the basement fabric has no control on the younger faulting pattern. Basement structure such as the north-south Coorong Shear Zone seems to affect the geometry of normal faults by changing their strike from E-W to NW-SE and also, in the easternmost part of the basin, the Bambra Fault changes the strike of normal faults from NW-SE to the NE-SW. Our results imply that the properties of the continental lithosphere exert a major influence on the β factor and amount of crustal extension but only a minor influence on the geometry of extensional faults.

The initiation, growth and interaction of faults within an extensional rift is an inherently four dimensional process where connectivity with time and depth aredifficult to constrain. A 3D discrete element model is employed that represents the crust as a two-layered brittle-ductile system in which faults nucleate, propagate and interact in response to local heterogeneities and resulting stresses. Faults nucleate in conjugate sets throughout the model brittle crust; they grow through a combination of tip propagation and interaction of co-linear segments to form larger normal faults. Segment linkage occurs by merging of adjacent fault segments located along-strike, down-dip or oblique to one another. Finally, deformation localises onto the largest faults. Displacement distribution on faults is highly variable with marked along-strike and temporal variations in displacements rates. Displacement maxima continuously migrate as smaller fault segments interact and link to form the final fault plane. As a result, displacement maxima associated with fault nucleation sites are not coincident with the location of the maximum finite displacement on a fault where segment linkage overprints the record. The observed style of fault growth is consistent with the isolated growth model in the earliest stages which then gives way to a coherent (constant-length) fault growth model at greater strains.

Rift structures are considered as elements of the composite structural parageneses of deformations in the crust and lithosphere with respect to kinematic types of such deformations. Most of the studied rift systems are associated with shear zones that contain extension faults with normal fault components, as well as strike-slip and compression structures. The regular structural pattern on the Earth surface and its relation to the distribution of the mantle density variations reflect the deformation of the Earth as a triaxial rotating ellipsoid.

New marine geophysical data acquired across the partly ice‐covered northern East Greenland continental margin highlight a complex interaction between tectonic and magmatic events. Breakup‐related lava flows are imaged in reflection seismic data as seaward dipping reflectors (SDRs), which are found to decrease in size both northwards and southwards from a central point at 75° N. We provide evidence that the magnetic anomaly pattern in the shelf area is related to volcanic phases and not to the presence of oceanic crust. The remnant magnetization of the individual lava flows is used to deduce a relative timing of the emplacement of the volcanic wedges. We find that the SDRs have been emplaced over a period of 2‐4 Ma progressively from north to south and from landward to seaward. The new data indicate a major post‐middle Eocene magmatic phase around the landward termination of the West Jan Mayen Fracture Zone. This post‐40 Ma volcanism likely was associated with the progressive separation of the Jan Mayen microcontinent from East Greenland. The break‐up of the Greenland Sea started at several isolated seafloor spreading cells whose location was controlled by rift structures and led to the present‐day segmentation of the margin. The original rift basins were subsequently connected by steady‐state seafloor spreading that propagated southwards, from the Greenland Fracture Zone to the Jan Mayen Fracture Zone. Key Points Polyphase Cenozoic volcanic rifting and consecutive emplacement of breakup‐related lava flows units along the northern East Greenland margin Breakup along restricted margin segments is followed by north to south directed progressive opening of the Greenland Sea Widespread post‐middle Eocene (< 40 Ma) offshore magmatism, associated with the breakup of the Jan Mayen microcontinent from East Greenland

The South China Sea, as ‘a non-volcanic passive margin basin’ in the Pacific, has often been considered as a small-scale analogue of the Atlantic. The recent ocean drilling in the northern South China Sea margin found, however, that the Iberian model of non-volcanic rifted margin from the Atlantic does not apply to the South China Sea. In this paper, we review a variety of rifted basins and propose to discriminate two types of rifting basins: plate-edge type such as the South China Sea and intra-plate type like the Atlantic. They not only differ from each other in structure, formation process, lifespan and geographic size, but also occur at different stages of the Wilson cycle. The intra-plate rifting occurred in the Mesozoic and gave rise to large oceans, whereas the plate-edge rifting took place mainly in the mid-Cenozoic, with three-quarters of the basins concentrated in the Western Pacific. As a member of the Western Pacific system of marginal seas, the South China Sea should be studied not in isolation on its origin and evolution, but in a systematic context to include also its neighboring counterparts.

Passive margins around the world commonly feature evidence of syn-rift small scale contractional deformation, such as reverse faulting and low amplitude folding, as well as evidence of basin depth inversions. Often, these features have no corresponding change in plate motion, and seem in conflict with the kinematic understanding that areas undergoing continental rifting should record only extensional deformation and subsidence. It has been proposed that syn-rift basin inversion may form as a result of gravitational body forces developing because of the upwelling asthenospheric dome beneath the rifted region, known as rift push. The aim of this thesis is to investigate the role these gravitational forces can play on the evolution of passive margins during rifting, and to quantify the role the upwelling asthenosphere plays in this process. To achieve this, we use high-resolution thermomechanical numerical modelling in both two and three dimensions, with non-linear, temperature, stress, and strain-dependent rheologies, to map the evolution of the stress regime throughout the lithosphere as the margins develop. Two dimensional numerical experiments show that the upwelling asthenosphere is capable of driving rift opening, and that transient compressional stress of up to 30 MPa develop within localized regions of the passive margin. When coupled with simplified surface processes allowing the formation of sedimentary basins, the experiments show that rift basins can undergo multiple phases of compression with no change to the applied rift kinematics, as they tend to localise compressive stress. We also explore the role of rift-push in the fundamentally three-dimensional context of continental rifting close to an Euler pole. It has been proposed that diachronous upwelling of the asthenosphere could induce compressional structures along the strike of the rift axis. Our experiments show that as the asthenosphere reaches break-up earlier at one end of the rift, a component of rift-push force is orthogonal to the rift axis (as per the previous experiments), and a second component is parallel to the rift axis, as the relatively unthinned areas of lithosphere are juxtaposed against the upwelled asthenospheric dome along the strike of the rift. In combination, these force components produce transcurrent and compressional stress within the developing passive margins, which matches earthquake focal mechanism data from similar realworld examples. Finally, to facilitate the access of thermo-mechanical modelling to a broader community of structural geologists and tectonicists, we have designed a prebuilt toolbox named the Lithospheric Modelling Recipes which includes a customizable 2D and 3D lithospheric model. In doing so, we aim to a) give structural geologists and tectonicists a user-friendly self-consistent framework to test their conceptual ideas, b) expand the pool of expertise and ideas tapping into geodynamic modelling, and c) enable a large number of geoscientists to critically assess geodynamic models, and d) contribute to the reproducibility of thermo-mechanical modelling.

The age and style of opening of the Havre Trough back-arc system is uncertain due to a lack of geochronologic constraints for the region. 40Ar/39Ar dating of 19 volcanic rocks from across the southern Havre Trough and Kermadec Arc was conducted in three laboratories to provide age constraints on the system. The results are integrated and interpreted as suggesting that this subduction system is young (

Эта работа основана исключительно на эксплуатации 1500 км мультитрековых сейсмических профилей. Эти профили получены из нескольких сейсморазведочных работ, которые обычно проводились в 1970-х годах на границе Абиджана. Анализ нескольких сейсмических профилей, полученных в результате 2D сейсмического отражения, позволил изучить структурную основу окраины Абиджана (Кот-д’Ивуар) в нижнем меловом периоде. Основные структурные особенности, нормальные разломы, наклонные блоки, грабены, листовые разломы и структуры в «цветке» и «хвостике», наблюдаемые в основном в осадочных сериях Альба, указывают на то, что этот регион окраины Кот д’Ивуара является результатом многофазной геологической истории в связи с обоими крупномасштабными внешнее разделительное движение и растяжение. Таким образом, эти структуры, унаследованные от разрыва дивергенции, происходят от компонента растяжения первоначального разделения между Африкой и Америкой. Поэтому цель этой работы – дать подробные сведения о тектоническом компоненте восточной части Абиджанской окраины. И показать, что осадочный бассейн Кот д’Ивуара начался с «pull-apart». Для достижения нашей цели мы будим изучать карты сейсмических отражений восточного участка осадочного бассейна Кот д’Ивуара, то есть часть окраины Абиджан., This work is based exclusively on the operation of 1,500 km of multitrack seismic profiles. These profiles are derived from several seismic surveys, which were usually carried out in the 1970s at the Abidjan border. An analysis of several seismic profiles obtained from 2D seismic reflection made it possible to study the structural basis of the Abidjan margin (Côte d’Ivoire) in the lower Cretaceous period. The main structural features, normal faults, inclined blocks, grabens, leaf faults and structures in the “flower” and “tail”, observed mainly in the Alba sedimentary series, indicate that this region of the Cote d’Ivoire margin is a result of a multiphase geological history due to both large-scale external separation movement and stretching. Thus, these structures, inherited from the divergence gap, derive from the stretching component of the initial separation between Africa and America. Therefore, the purpose of this work is to provide detailed information about the tectonic component of the eastern part of the Abidjan margin. And to show that the sedimentary basin of Côte d’Ivoire began with a “pull-apart”. To achieve our goal, we will study the seismic reflection maps of the eastern portion of the Ivorian sedimentary basin, that is, part of the Abidjan margin.

International audience; We compile field data collected along the eastern part of the North Pyrenean Zone (NPZ) to point to a tectonic evolution under peculiar thermal conditions applying to the basin sediments in relation with the opening of the Cretaceous Pyrenean rift. Based on this compilation, we show that when thinning of the continental crust increased , isotherms moved closer to the surface with the result that the brittle-ductile transition propagated upward and reached sediments deposited at the early stage of the basin opening. During the continental breakup, the pre-rift Mesozoic cover was efficiently decoupled from the Paleozoic basement along the Triassic evaporite level and underwent drastic ductile thinning and boudinage. We suggest that the upper Albian and upper Creta-ceous flysches acted as a blanket allowing temperature increase in the mobile pre-rift cover. Finally, we show that continuous spreading of the basin floor triggered the exhumation of the metamorphic, ductily sheared pre-rift cover, thus contributing to the progressive thinning of the sedimentary pile. In a second step, we investigate the detailed geological records of such a hot regime evolution along a reference-section of the eastern NPZ. We propose a balanced restoration from the Mouthoumet basement massif (north) to the Boucheville Albian basin (south). This section shows a north to south increase in the HT Pyrenean imprint from almost no metamorphic recrystallization to more than 600 °C in the pre-and syn-rift sediments. From this reconstruction, we propose a scenario of tectonic thinning involving the exhumation of the pre-rift cover by the activation of various detachment surfaces at different levels in the sedimentary pile. In a third step, examination of the architecture of current distal passive margin domains provides confident comparison between the Pyrenean case and modern analogs. Finally, we propose a general evolutionary model for the pre-rift sequence of the Northeastern Pyrenean rifted margin.

The transition from the Cambrian to Ordovician in Morocco is known to be characterized by a frequent Furongian hiatus, restricted extension of the Tremadocian marine deposits, and frequent unconformities at the base of the transgressive upper Floian deposits. In the present work, we first highlight the occurrence of Fe- and mica-rich, red silty/sandy formations in the Central and Eastern High Atlas between the Middle Cambrian and Upper Floian sequences. In the Tislyt type-locality, a synsedimentary hemigraben structure is defined, within which the red beds show frequent slump folds, debris flows and internal unconformities. The correlation with several coeval series of the Meseta domain allows us to define a shallow marine, ferruginous clastic Atlas-Meseta Red Beds (AMRB) basin during the Tremadocian-early Floian. The AMRB basin extended between the Meseta coastal block and the Anti-Atlas domain, being limited by the fault zones that became the West Meseta shear zone and the South Meseta fault, respectively, in the Variscan orogen. The AMRB basin compares with the coeval rifted basins of the central Iberian and Armorican massifs. The red beds were likely sourced from the east, from both the Precambrian basement and Early Ordovician magmatic rocks, contrary to the Ordovician deposits of the Sahara platform sourced from the south. Subsidence of the AMRB and central Iberian-Armorican basins of the NW-Gondwana border aborted during the Floian, whereas the opening of the Rheic ocean went on more to the west.

The North Atlantic, extending from the Charlie Gibbs Fracture Zone to the north Norway-Greenland-Svalbard margins, is regarded as both a classic case of structural inheritance and an exemplar for the Wilson-cycle concept. This paper examines different aspects of structural inheritance in the Circum-North Atlantic region: 1) as a function of rejuvenation from lithospheric to crustal scales, and 2) in terms of sequential rifting and opening of the ocean and its margins, including a series of failed rift systems. We summarise and evaluate the role of fundamental lithospheric structures such as mantle fabric and composition, lower crustal inhomogeneities, orogenic belts, and major strike-slip faults during breakup. We relate these to the development and shaping of the NE Atlantic rifted margins, localisation of magmatism, and microcontinent release. We show that, although inheritance is common on multiple scales, the Wilson Cycle is at best an imperfect model for the Circum-North Atlantic region. Observations from the NE Atlantic suggest depth dependency in inheritance (surface, crust, mantle) with selective rejuvenation depending on time-scales, stress field orientations and thermal regime. Specifically, post-Caledonian reactivation to form the North Atlantic rift systems essentially followed pre-existing orogenic crustal structures, while eventual breakup reflected a change in stress field and exploitation of a deeper-seated, lithospheric-scale shear fabrics. We infer that, although collapse of an orogenic belt and eventual transition to a new ocean does occur, it is by no means inevitable.

Sedimentary rocks in the Alanya Window document pulsed Permian-Triassic rifting in a proximal basin setting, adjacent to the Tauride continental unit (Geyik Dağ). Late Cambrian-Early Ordovician clastic sediments accumulated along the north margin of Gondwana on a variable shallow-marine shelf. Above an unconformity related to rift-shoulder uplift, Late Permian facies document shallow-marine to evaporitic environments during regional tectonic subsidence (first main rift pulse). Above a second unconformity (both extension and sea-level controlled), Early Triassic carbonates and mudrocks accumulated on an unstable, gently subsiding shelf. Mudrocks, sandstones and lithoclastic debris-flows, derived from the underlying succession, accumulated during the Middle Triassic (Anisian-early Ladinian), implying strong tectonic subsidence and flank uplift (second main rift pulse). Radiolarian mudstones accumulated during late Middle Triassic-early Late Triassic in a well-oxidised, organically productive, but relatively quiescent, deep-water basin above the carbonate compensation depth (CCD). Thick (100s m) lithoclastic sandstone turbidites (commonly plant-rich) and localised debris-flows accumulated during the Late Triassic (Carnian), together with detached blocks of underlying lithologies (third main rift pulse, with regional uplift). Alkaline basaltic sills were intruded locally. Final continental break-up to create the Southern Neotethys took place regionally during the Late Triassic (Carnian). Latest Triassic-Late Cretaceous deposition records passive margin subsidence. Variable low-grade metamorphism and two-stage tectonic emplacement (southwards(?) then northwards) took place during latest Cretaceous and Eocene, respectively. The tectonic-sedimentary development of the Antalya Complex provides insights into rift/continental break-up processes that differ from the recently well-documented Alpine-North Atlantic region. Publisher PDF

Reconstructions of the opening of the North Atlantic Ocean generally result in the Orphan Basin, offshore Newfoundland, Canada, lying approximately conjugate to the rift basins on the Irish Atlantic margin at the onset of seafloor spreading toward the end of the Early Cretaceous. Most of these plate reconstructions have involved rigid plates with plate motions based solely on the interpretation of oceanic magnetic anomalies. In particular, these reconstructions often show the Rockall Basin, west of Ireland, forming a continuous Mesozoic basin with the West Orphan Basin, offshore Newfoundland. However, more recent plate reconstructions involving deformable plates have called this conjugate relationship into question. The goal of this study is to investigate the validity of this potentially continuous basin system by reconstructing and restoring present-day seismically-constrained geological models both spatially and temporally back to their original configurations pre-rift. By comparing the reconstructions in terms of sedimentary package thicknesses and crustal thicknesses in 3D, using both rigid and deformable plate reconstructions to orient the reconstructed models, we are able to test different basin connectivity scenarios using a multidisciplinary approach. Our analysis provides subsurface geophysical support for the hypothesis that the Rockall Basin was originally conjugate to and continuous with the East Orphan Basin during Jurassic rifting, later linking to the West Orphan Basin as rifting evolved during the Early Cretaceous. This complex basin evolution example highlights the need for using 3D rifting mechanism models to properly understand the fundamental driving forces during rifting and has significant implications for assessing basin prospectivity across conjugate margin pairs.

Understanding dikes is vital as they serve both as bodies that build the crust and as conduits that feed eruptions, and must be monitored to evaluate volcanic hazard. During the 2014–15 Barðarbunga rifting event, Iceland, intense seismicity accompanied the intrusion of a ∼50 km lateral dike which culminated in a 6 month long eruption. We here present relocations of earthquakes induced by the lateral dike intrusion, using cross-correlated, sub-sample relative travel times. The ∼100 m spatial resolution achieved reveals the complexity of the dike propagation pathway and dynamics (jerky, segmented), and allows us to address the precise relationship between the dike and seismicity, with direct implications for hazard monitoring. The spatio-temporal characteristics of the induced seismicity can be directly linked in the first instance to propagation of the tip and opening of the dike, and following this – after dike opening – indicate a relationship with magma pressure changes (i.e. dike inflation/deflation), followed by a general ‘post-opening’ decay. Seismicity occurs only at the base of the dike, where dike-imposed stresses – combined with the background tectonic stress (from regional extension over >200 yr since last rifting) – are sufficient to induce failure of pre-existing weaknesses in the crust, while the greatest opening is at shallower depths. Emplacement oblique to the spreading ridge resulted in left-lateral shear motion along the distal dike section (studied here), and a prevalence of left-lateral shear failure. Fault plane strikes are predominately independent of the orientation of lineations delineated by the hypocenters, indicating that they are controlled by the underlying host rock fabric. This high-resolution study provides unprecedented opportunity for comparison with both geodetic and field (frozen dike) observations, and development and consolidation of analytical and analogue models, with implications for rifting processes and real-time monitoring of magma intrusion.

North America's ~1.1‐Ga failed Midcontinent Rift (MCR) is a striking feature of gravity and magnetic anomaly maps across the continent. However, how the rift affected the underlying lithosphere is not well understood. With data from the Superior Province Rifting Earthscope Experiment and the USArray Transportable Array, we constrain three‐dimensional seismic velocity discontinuity structure in the lithosphere beneath the southwestward arm of the MCR using S‐to‐P receiver functions. We image a velocity increase with depth associated with the Moho at depths of 33–40 ± 4 km, generally deepening toward the east. The Moho amplitude decreases beneath the rift axis in Minnesota and Wisconsin, where the velocity gradient is more gradual, possibly due to crustal underplating. We see hints of a deeper velocity increase at 61 ± 4‐km depth that may be the base of underplating. Beneath the rift axis further south in Iowa, we image two distinct positive phases at 34–39 ± 4 and 62–65 ± 4 km likely related to an altered Moho and an underplated layer. We image velocity decreases with depth at depths of 90–190 ± 7 km in some locations that do not geographically correlate with the rift. These include a discontinuity at depths of 90–120 ± 7 km with a northerly dip in the south that abruptly deepens to 150–190 ± 7 km across the Spirit Lake Tectonic Zone provincial suture. The negative phases may represent a patchy, frozen‐in midlithosphere discontinuity feature that likely predates the MCR and/or be related to lithospheric thickness., Key Points S‐to‐P receiver functions constrain a Moho, crustal underplating and midlithosphere discontinuities beneath the Midcontinent RiftThe Moho and crustal underplating directly beneath the rift axis vary in character from north to southMidlithospheric discontinuities predate the rifting event and seem unperturbed by rift‐related activity

Although structural inheritance is a fundamental factor in the tectonic evolution of the crust, few studies have been aimed at understanding in detail the interaction between pre-existing normal faults in a rift zone and successive dominant strike-slip (transtensional) movements. Firstly, we present the complex pattern of faults and tension fractures of the western, pre-Holocene part of the N-S Theistareykir Fissure Swarm (ThFS - Northern Iceland Rift), crossed by the NW-SE striking, right-lateral, Husavik-Flatey Fault (HFF), and we integrate previous observations with new field data that reveal Holocene motions along the N-S faults near the HFF. Secondly, we propose a set of analogue experiments that reproduce the N-S rifting followed by superimposed transtensional faulting along the HFF. In a first set of experiments, we tested the effect of an initial extension at the shallow crustal level by forming a rift zone. During this rifting phase, we modelled the presence of a sub-orthogonal discontinuity that represents the structural inheritance of the HFF (that is older than the ThFS), but without any imposed “regional” transtensional movement along it. After that, we superimposed a dominant right-lateral movement along the HFF on the modelled rift faults in order to assess the effect of the inheritance of the rift plus the HFF. Our results show that during rifting, a series of elongated and depressed areas develop along the initial HFF discontinuity (that is locally reactivated by the rift opening), in agreement with field data. During the second experimental set of exclusively shear deformation along the HFF, the models show the development of Riedel shears at the HFF, contemporaneous to the local reactivation of normal faults and tension fractures in the previous rift zone. This reactivation occurs by block rotation, incremental dip-slip motions on pre-existing fault scarps, widening of tension fractures and development of new structures. We conclude that transversal basins can develop from the early stages of rift development, and that the structures of a pre-existing rift may reactivate under a local stress state induced by incremental transtensional motions.

The Triassic geodynamic evolution of the Pontides Belt, which geographically corresponds to northern Anatolia, is still a matter of debate. We present and interpret geological, petrographical, geochemical, and geochronological data from small, discordant, metagabbroic rocks exposed in the Tokat Massif. Field and petrographic characteristics distinguish four subgroups: (i) medium-grained, slightly lineated, clinopyroxene-rich metagabbros; (ii) fine-grained, nonlineated, clinopyroxene-rich metagabbros; (iii) medium-grained, nonlineated, brown amphibole-rich metagabbros; and (iv) medium-grained, slightly lineated, brown and blue amphibole-rich metagabbros. Magmatic kaersutites give Ar-39/Ar-40 plateau ages of 244.60.5 and 243.160.92Ma and overlap the U-Pb age of titanite from a clinopyroxene-rich sample. Inherited zircons (similar to 460, similar to 880, and similar to 2600Ma) in fine-grained clinopyroxene-rich metagabbros indicate interaction with a range of crustal rocks during the intrusion. The blue amphiboles are magnesioriebeckites that formed during metamorphism or late-stage crystallization. Geochemical data, including whole rock major and trace element concentrations, and Sr-Nd-Pb isotope compositions reveal that both clinopyroxene- and amphibole-rich metagabbros are alkaline in composition but derived from distinct mantle sources. They are compositionally distinct from mafic igneous rocks in the contemporaneous Permo-Triassic Karakaya Complex that is well exposed in the western part of the Pontides Belt. Considering all data, we suggest that the Pontides Belt was shaped above a south dipping subduction zone during Permo-Triassic and the alkaline gabbros that were emplaced into crustal rocks during Early Triassic back-arc rifting of the northern margin of Gondwana.

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International audience; Recent studies proposing pre-orogenic mantle exhumation models have helped renew the interest of the geosciences community in the Pyrenees, which should be now interpreted as a hyper-extended passive margin before the convergence between Iberia and Eurasia occurred. Unresolved questions of the Pyrenean geology, as well as the understanding of the formation of hyper-extended passive margins, are how the crust was thinned, and when, where and how the crustal breakoff occurred. The study of the Variscan and pre-Variscan Pyrenean basement is thus critical to document and understand this Cretaceous crustal thinning. In order to specify the timing of Mesozoic metasomatism and the associated deformation in the pre-Mesozoic basement of the Pyrenees, we carried out a U–Th–Pb laser ablation ICP–MS study on a large panel of REE and titanium-rich minerals (titanite and rutile) from talc–chlorite ores from the eastern Pyrenees, with a special emphasis on the Trimouns deposit, the world’s largest talc quarry. Our results suggest that the Trimouns talc formation was restricted to the upper Aptian–Cenomanian time, while the talc and chlorite formation in the eastern Pyrenees occurred during several distinct Permian, Jurassic and Cretaceous episodes. These results give strong constraints on the tectonic setting of the Pyrenean domain during the transition between the Variscan and Alpine orogenic cycles, and particularly on when and how the upper crust was thinned before the crustal breakoff and the final mantle exhumation.

Mantle-derived serpentinites have been detected at magma-poor rifted margins and above subduction zones, where they are usually produced by fluids released from the slab to the mantle wedge. Here we show evidence of a new class of serpentinite diapirs within the external subduction system of the Calabrian Arc, derived directly from the lower plate. Mantle serpentinites rise through lithospheric faults caused by incipient rifting and the collapse of the accretionary wedge. Mantle-derived diapirism is not linked directly to subduction processes. The serpentinites, formed probably during Mesozoic Tethyan rifting, were carried below the subduction system by plate convergence; lithospheric faults driving margin segmentation act as windows through which inherited serpentinites rise to the sub-seafloor. The discovery of deep-seated seismogenic features coupled with inherited lower plate serpentinite diapirs, provides constraints on mechanisms exposing altered products of mantle peridotite at the seafloor long time after their formation., Understanding subduction zone mechanics and resulting volcanism remains challenging. Here, the authors present seismic reflection profiles from the Mediterranean Sea where serpentinite diapirs are present on the external subduction system of the Calabrian Arc and may be linked to recent volcanism at Etna.

La convergencia cretácica a paleógena entre las placas del Caribe y de Suramérica involucra deformaciones penetrativas en rocas mesozoicas del Graben de Cosinas. Como consecuencia, se proponen múltiples modelos estructurales contrastantes, donde no existe coherencia en la identificación de pliegues, desplazamiento de fallas, espesores y facies de las unidades; de manera tal que los esquemas tanto estratigráficos como estructurales actuales, se basan en una componente conceptual que no satisface las observaciones fotogeológicas y de campo. Por lo tanto, se enfoca en elucidar el estilo y las características del plegamiento del lado sur del trazo de la Falla Cuisa en la Serranía de Cosinas, y determinar su relación con la convergencia y obducción de la Placa Caribe. Abstract: The Cretaceous to Paleogene convergence between the Caribbean and South American plates involves penetrative deformations in Mesozoic rocks of the Cosinas Graben. Therefore, multiple contrasting structural models proposed, without coherence in the identification of folds, faults displacements, thicknesses and facies of the units. In that case, the current stratigraphic and structural schemes are based on a conceptual component that does not satisfy photogeological and field observations. Therefore, it focuses on elucidating the style and characteristics of the folding of the south side of the Cuisa Fault line in the Serranía de Cosinas, and determining its relationship with the convergence and obduction of the Caribbean Plate. Maestría

The Aravalli–Delhi and Satpura Mobile Belts (ADMB and SMB) and the Eastern Ghat Mobile Belt (EGMB) in India form major Proterozoic mobile belts with adjoining cratons and contemporary basins. The most convincing features of the ADMB and the SMB have been the crustal layers dipping from both sides in opposite directions, crustal thickening (∼45 km) and high density and high conductivity rocks in upper/lower crust associated with faults/thrusts. These observations indicate convergence while domal type reflectors in the lower crust suggest an extensional rifting phase. In case of the SMB, even the remnant of the subducting slab characterized by high conductive and low density slab in lithospheric mantle up to ∼120 km across the Purna–Godavari river faults has been traced which may be caused by fluids due to metamorphism. Subduction related intrusives of the SMB south of it and the ADMB west of it suggest N–S and E–W directed convergence and subduction during Meso–Neoproterozoic convergence. The simultaneous E–W convergence between the Bundelkhand craton and Marwar craton (Western Rajasthan) across the ADMB and the N–S convergence between the Bundelkhand craton and the Bhandara and Dharwar cratons across the SMB suggest that the forces of convergence might have been in a NE–SW direction with E–W and N–S components in the two cases, respectively. This explains the arcuate shaped collision zone of the ADMB and the SMB which are connected in their western part. The Eastern Ghat Mobile Belt (EGMB) also shows signatures of E–W directed Meso–Neoproterozoic convergence with East Antarctica similar to ADMB in north India. Foreland basins such as Vindhyan (ADMB–SMB), and Kurnool (EGMB) Supergroups of rocks were formed during this convergence. Older rocks such as Aravalli (ADMB), Mahakoshal–Bijawar (SMB), and Cuddapah (EGMB) Supergroups of rocks with several basic/ultrabasic intrusives along these mobile belts, plausibly formed during an earlier episode of rifting during Paleo–Mesoproterozoic period. They are highly disturbed and deformed due to subsequent Meso–Neoproterozoic convergence. As these Paleoproterozoic basins are characterized by large scale basic/ultrabasic intrusives that are considerably wide spread, it is suggested that a plume/superplume might have existed under the Indian cratons at that time which was responsible for the breakup of these cratons. Further, the presence of older intrusives in these mobile belts suggests that there might have been some form of convergence also during Paleoproterozoic period.

The article presents recent results of seismogeological, seismological and engineering seismological studies conducted by the Laboratory. Specific features of seismicity in regions of Russia are reviewed. Space-and-time and energy patterns of seismicity and the state of stresses of the lithosphere are analysed. It is forecasted how foundations of buildings and structures located in the Baikal rift zone may be affected by potential strong earthquakes.

[1] Lithosphere necking evolution determines the 3-D architecture of crustal and upper mantle thinning and related basins, and the heat flow distribution in rifted regions. Despite a large number of studies, lithosphere necking evolution is still a matter of debate. We present the result from lithospheric-scale analog models designed for investigating the necking shape during extension and the vertical distribution of finite deformation in the mechanical lithosphere. In our experiments, lithosphere necking is asymmetric and, in particular, the 3-D distribution of thinning is cylindrical in the crust and very heterogeneous in the mantle. Overall, the evolution of rifting and necking progresses from delocalized to localized deformation.

The South Atlantic rift basin evolved as branch of a large Jurassic-Cretaceous intraplate rift zone between the African and South American plates during the final breakup of western Gondwana. By quantitatively accounting for crustal deformation in the Central and West African rift zone, we indirectly construct the kinematic history of the pre-breakup evolution of the conjugate West African-Brazilian margins. Our model suggests a causal link between changes in extension direction and velocity during continental extension and the generation of marginal structures such as the enigmatic Pre-salt sag basin and the S\~ao Paulo High. We model an initial E-W directed extension between South America and Africa (fixed in present-day position) at very low extensional velocities until Upper Hauterivian times ($\approx$126 Ma) when rift activity along in the equatorial Atlantic domain started to increase significantly. During this initial $\approx$17 Myr-long stretching episode the Pre-salt basin width on the conjugate Brazilian and West African margins is generated. An intermediate stage between 126.57 Ma and Base Aptian is characterised by strain localisation, rapid lithospheric weakening in the equatorial Atlantic domain, resulting in both progressively increasing extensional velocities as well as a significant rotation of the extension direction to NE-SW. Final breakup between South America and Africa occurred in the conjugate Santos--Benguela margin segment at around 113 Ma and in the Equatorial Atlantic domain between the Ghanaian Ridge and the Piau\'i-Cear\'a margin at 103 Ma. We conclude that such a multi-velocity, multi-directional rift history exerts primary control on the evolution of this conjugate passive margins systems and can explain the first order tectonic structures along the South Atlantic and possibly other passive margins., Comment: 46 Pages, 22 figures. Submitted to Solid Earth (http://www.solid-earth.net). Abstract shortened due to arXiv restrictions. New version contains revisions and amendments as per reviewers requests. Supplementary data is available at http://datahub.io/en/dataset/southatlanticrift

The Afar triple junction, where the Red Sea, Gulf of Aden and African Rift System extension zones converge, is a pivotal domain for the study of continental-to-oceanic rift evolution. The western margin of Afar forms the southernmost sector of the western margin of the Red Sea rift where that margin enters the Ethiopian flood basalt province. Tectonism and volcanism at the triple junction had commenced by similar to 31 Ma with crustal fissuring, diking and voluminous eruption of the Ethiopian-Yemen flood basalt pile. The dikes which fed the Oligocene-Quaternary lava sequence covering the western Afar rift margin provide an opportunity to probe the geochemical reservoirs associated with the evolution of a still active continental margin. Ar-40/Ar-39 geochronology reveals that the western Afar margin dikes span the entire history of rift evolution from the initial Oligocene flood basalt event to the development of focused zones of intrusion in rift marginal basins. Major element, trace element and isotopic (Sr-Nd-Pb-Hf) data demonstrate temporal geochemical heterogeneities resulting from variable contributions from the Afar plume, depleted asthenospheric mantle, and African lithosphere. The various dikes erupted between 31 Ma and 22 Ma all share isotopic signatures attesting to a contribution from the Afar plume, indicating this initial period in the evolution of the Afar margin was one of magma-assisted weakening of the lithosphere. From 22 Ma to 12 Ma, however, diffuse diking during continued evolution of the rift margin facilitated ascent of magmas in which depleted mantle and lithospheric sources predominated, though contributions from the Afar plume persisted. After 10 Ma, magmatic intrusion migrated eastwards towards the Afar rift floor, with an increasing fraction of the magmas derived from depleted mantle with less of a lithospheric signature. The dikes of the western Afar margin reveal that magma generation processes during the evolution of this continental rift margin are increasingly dominated by shallow decompressional melting of the ambient asthenosphere, the composition of which may in part be controlled by preferential channeling of plume material along the developing neo-oceanic axes of extension. (C) 2012 Elsevier Ltd. All rights reserved.

The article provides information about “Continental rifting, accompanying processes” Symposium dedicated to the memory of N.A. Logachev and E.E. Milanovsky, ‘Academicians of Rifting’. The symposium took place on 20–23 August 2013. It was initiated and arranged by the Institute of the Earth's Crust SB RAS and the Geological Faculty of the Irkutsk State University (Irkutsk) with participation of the Geological Faculty of Moscow State University. Topics of the symposium are reviewed.