Showing papers in "International Journal of Earth Sciences in 1992"
TL;DR: The Central High Atlas is characterized by a relatively mild deformation, with a local development of a more or less penetrative cleavage in the axial part of the belt as mentioned in this paper.
Abstract: The Central High Atlas is characterized by a relatively mild deformation, with a local development of a more or less penetrative cleavage in the axial part of the belt. Locally, this cleavage and the plutonic bodies which outcrop in the core of most of the north-east trending anticlines (ridges »with intrusions«) are overlain by a disconformable sequence that comprises red clastic deposits which are capped by Cenomano-Turonian limestones. The age of these red deposits are bracketted between Bathonian to Mid-Cretaceous. Therefore, the spatial relationship of the cleavage with mafic intrusions, in the axial part of the Central High Atlas, suggests that it developed contemporaneously with the emplacement of magmas, probably during Mid-Jurassic times. During this period, the structural inversion occurred, from a transtensional regime to a transpressive regime. There are few indications that an important shortening persisted within the axial part of the Central High Atlas after the end of the Jurassic. Along the northern and the southern borders of the belt, however, Cretaceous and Cenozoic strata were deposited. Their sedimentary facies bear witness of successive stages of the Atlas evolution. Especially, the rapidly coarsening up of the clastic deposits since the Oligocene in these marginal basins indicates the onset of the rising up of the belt, i. e. the orogenic inversion.
110 citations
TL;DR: The High and Middle Atlas are intracontinental mountain belts situated within the mobile foreland of the Mediterranean Rif orogen. as discussed by the authors has recently revealed there a flat layered structure of the crust with several low velocity zones.
Abstract: The High and Middle Atlas are intracontinental mountain belts situated within the mobile foreland of the Mediterranean Rif orogen. They developed in three stages. The first period (Permian — Bathonian) culminated during the Lias with extended rift grabens and tholeiite extrusions. From Callovian to Eocene, the tectonic activity and the rates of sedimentation were reduced, both pointing to a cooling of the lithosphere. Since the Oligocene, the whole region is submitted to compressional stress. The High and the Middle Atlas were uplifted within two phases, which were correlated with main phases of Rif orogenesis. Refraction seismic measurements have recently revealed there a flat layered structure of the crust with several low velocity zones. The deepest one coincides with a layer of high electric conductivity, which is interpreted as a zone of detachment.
97 citations
TL;DR: In 1986 explosion seismic investigations have been carried out along a traverse of about 350 km length running from NNW to SSE crossing the High and Middle Atlas as discussed by the authors, and two further profiles run E/W through the Middle and NW-SE through the High Atlas.
Abstract: In 1986 explosion seismic investigations have been carried out along a traverse of about 350 km length running from NNW to SSE crossing the High and Middle Atlas. Two further profiles run E/W through the Middle and NW-SE through the High Atlas.
88 citations
TL;DR: The origin and development of Early Devonian (late Pragian to late Zlichovian) mud mounds of the Hamar Laghdad area in the eastern Antiatlas, Morocco, are controlled by extrinsic and intrinsic factors as discussed by the authors.
Abstract: The origin and development of Early Devonian (late Pragian to late Zlichovian; predominantly uppermost Zlichovian as indicated by conodont faunas) mud mounds of the Hamar Laghdad area in the eastern Antiatlas, Morocco, are controlled by extrinsic and intrinsic factors. Extrinsic factors include the existence of a paleohigh (Lochkovian volcaniclastics), unidirectional currents and repeated storm events as well as sea level fluctuations. Intrinsic, biologically induced factors are the preferred growth of organisms on the top and the flanks of the mounds because of more favourable ecological conditions, and a rapid synsedimentary lithification of the steep mound flanks by interskeletal cementation of auloporid tabulate corals. The mounds developed in an epicontinental basin below the wave base but within the range of storms. The formation of the mounds started within the uppermost part of the bedded crinoid facies of the Kess-Kess Formation with the hydrological accumulation of a bioclastic pile. This elevation became settled by crinoids and high-diverse tabulate corals producing bioclastic sediment. Binding activities of the organisms were missing, calcareous algae and stromatoporoids are completely absent. Baffling by thamnoporid tabulate corals might have occurred locally but was not important for the development of the mounds. Steep slopes to the north and less steep slopes to the south may be the result of north-northwest to south-southeast trending currents, derived from orientation patterns of orthocone nautiloids in the uppermost beds of the Kess-Kess Formation. A synsedimentary cementation of the flanks, possibly triggered by submarine interskeletal cementation of patchily distributed auloporid colonies, protected the bioclastic sediment against redistribution by frequent storms (indicated by densely spaced eventstone intervals and partly also by the common >>Stromatactis<<-like structures within the mound facies). Accumulation of more parautochthonous bioclastic sediment within the mounds as compared to the intermound area, therefore, is caused by a self-sustaining system of hydrologic piling of sediment triggered by storms, preferred settlement of organisms upon these piles, producing bioclastic sediment and coeval biocementation of the growing mound flanks. This model differs from existing mud mound models in the lack or only minor significance of binding and baffling, in the lack of mound facies sequences and in the greater importance of extrinsic control factors.
84 citations
TL;DR: From Central Morocco (Central High Atlas, Middle Atlas, Haute Moulouya) continental tholeiites were investigated geochemically and geochronologically as mentioned in this paper, where the major, trace and rare earth element contents classify these volcanic rocks as basaltic to andesitic-basaltic, quartz-normative tholeIites.
Abstract: From Central Morocco (Central High Atlas, Middle Atlas, Haute Moulouya) continental tholeiites were investigated geochemically and geochronologically. These tholeiites are intercalated within continental redbeds of the Early Mesozoic (Triassic-Liassic). The major, trace and rare earth element contents classify these volcanic rocks as basaltic to andesitic-basaltic, quartz-normative tholeiites. Some trace element ratios (e.g. Zr/Nb, Zr/ Y, Y/Nb, Ti/V) suffer a heterogeneous source with a composition similar to MORB (P- to N-type). The enriched LILE contents, the negative Nb anomaly and the inital87Sr/86Sr ratios (0.7064–0.7069) reveal the presence of a crustal component up to 13–17 wt%.87Sr/86Sr ratios of carbonate mineral separates from different lava flows show different cycles of alteration; however, the major and trace element chemistry together with Sr isotope evidence, indicate that the alteration phases are not submarine in origin.40Ar/39Ar age determinations on translucent plagioclase phenocrysts yield extrusion ages which range between 210.4 ± 2.1 Ma and 196.3 ± 1.2 Ma. These ages correspond to a stratigraphic period between the Norian (Rhaetian?) and the Upper Sinemurian.
79 citations
TL;DR: In this paper, structural evidence and Rb/Sr data of quartzdiorites were used for the age attribution of the Saghro hills in the Moroccan Anti-Atlas.
Abstract: The Saghro hills constitute the northern branch of the Panafrican mobile belt in the eastern part of the Moroccan Anti-Atlas The Precambrian terranes are predominantly composed of volcaniclastic and volcanic series witnessing a mainly explosive volcanism, intruded by diorites and granites Their age attribution is problematic, and has been reconsidered in the present study based on structural evidence and Rb/Sr data of quartzdiorites: penetratively deformed volcano-sedimentaries intruded by these plutons aged between 754 and 722 Ma are now considered as Lower Precambrian II The Upper PII series have been reattributed, and only formations overlying a basal conglomerate and angular disconformity are considered PIII
77 citations
TL;DR: The most important, often interacting, global tectonic determinants are: taphrogenesis of the NW-African continental margin lasting until the Early Cretaceous (Triassic rifting and subsequent mid-Atlantic spreading), strike-slip-faulting at the Newfoundland-Gibraltar fault zone (Liassic) as discussed by the authors.
Abstract: Plate tectonic processes in the Atlantic and western Tethyan realm directed the post-Variscan sedimentary and structural evolution of the High Atlas and Middle Atlas intracontinental mountain ranges of Morocco. Plate movements caused a reactivation of an inherited pan-African or Hercynian fault pattern by the variation of stress regimes through time. This resulted in strike-slip as well as vertical tectonics. During times of relative tectonic quiescence eustatic sea-level changes governed the sedimentary development. The most important, often interacting, global tectonic determinants are: taphrogenesis of the NW-African continental margin lasting until the Early Cretaceous (Triassic rifting and subsequent mid-Atlantic spreading), strike-slip-faulting at the Newfoundland-Gibraltar fault zone (Liassic — earliest Eocene), and continental convergence between Europe (Iberia) and Africa which started in the Late Cretaceous and reached its acme in the Neogene. In the realm of the Central High Atlas and the Middle Atlas the interaction of these processes triggered continental rifting (Triassic) and subsequent marine flooding of the intergrown riftgrabens prograding from the Tethys realm (Early Jurassic — earliest Middle Jurassic). After its abortion, the former Atlas rift was filled up with marine sediments (Bajocian — Bathonian), followed by continental redbeds and final uplift (late Mid Jurassic — late Early Cretaceous). Eustatic sea-level changes mostly governed the sedimentary evolution from Aptian to latest Mid Eocene. After a first weak uplift of the central High Atlas during the Senonian major uplift of the intracontinental chains commenced at the Mid/ Late Eocene transition. Diastrophism of the Atlas ranges during the Miocene and Pliocene coincided with the main orogenic movements of the Betico-Rifean arc.
71 citations
TL;DR: In this article, the limit between the West Asturian-Leonese and Central-Iberian zones in the NW of the Iberian Peninsula is described in the area of Caurel-Truchas (Provinces of Orense and Leon).
Abstract: The limit between the West Asturian-Leonese and Central-Iberian Zones in the NW of the Iberian Peninsula is described in the area of Caurel-Truchas (Provinces of Orense and Leon). From the distribution of the sedimentary formations and the Variscan structures it is inferred that the transition between the two zones was a fault system, which was active during, at least, the Ordovician and Lower Silurian. The faults were supposedly normal, though they had probably some strike-slip component, and gave rise to a half-graben in which a syn-rift sequence was deposited. The latter underwent inversion at the onset of the Variscan tectonism, producing a ramp anticline-syncline pair that forms the more important folds in the area. The varying geometry of these folds is interpreted partly as being due to the existence of previous en echelon folds related to the strike-slip component of the faults and, partly, as a result of the variable intensity of the shear strain undergone during the first variscan phase.
67 citations
TL;DR: In this article, a series of 8 new seismic refraction profiles were computed as extensions of the borehole controlled reflection profiles of the Po plain into the northern Apennines and the Ligurian Alps.
Abstract: A series of 8 new seismic refraction profiles were computed as extensions of the borehole controlled reflection profiles of the Po plain into the northern Apennines and the Ligurian Alps. They help to more clearly define the subsurface structure of this intricate ‘Ligurian knot’. In particular, it has been possible to identify a number of high velocity bodies, and they may be correlated with such geological entities as the Adriatic Mesozoic, ophiolites of the Apenninic Liguride nappes, and ophiolites or Mesozoic carbonates underlying the Antola flysch in the Alpine part of the knot. When combining the refraction and reflection lines, these bodies appear to be bounded by important dislocation surfaces, such as the Padanide sole thrust (Plio-Pleistocene), the Villalvernia Varzi line (Oligo-Miocene), the Ottone-Levanto line (Oligo-Miocene), and the Volpedo-Valle Salimbene fault (Oligo-Miocene; reactivated as a transfer fault in the Plio-Pleistocene). The 3D geometry may be interpreted in terms of regional kinematics and is compatible with a model that envisages an Oligo-Early Miocene NW translation of the Adriatic indenter, coupled with collapse in the Provencal-Ligurian sea and rotation of the Sardinia-Liguria complex into the roll-back of the Adriatic subduction zone. The refraction interpretations, extending to a depth of 15 km, are supplemented by data on the Moho configuration obtained for the European Geotraverse. The Moho appears to be dissected into a series of patches which may be interpreted in terms of the shallow crustal configuration and its history. In particular, the deepest patch appears to be terminated by the Volpedo-Valle Salimbene fault, which consequently would displace the entire crust.
63 citations
TL;DR: In this article, the authors describe a complicated block structure (horst-and-graben pattern) dominated by the NNW-SSE Struma and Vardar lineaments, the WNW-ESE Sava and Marica lineaments and the Middle Mesta and North Anatolian fault zones.
Abstract: The neotectonic movements on the Balkan Peninsula occurred after the last intense thrusting (Early Miocene), and after the Early — Middle Miocene planation. They were controlled by extensional collapse of the Late Alpine orogen, and by extension behind the Aegean arc, and were influenced by the complicated vertical and horizontal movements in the Pannonian region. The Stara-planina and Dinarian-Hellenic linear neotectonic morphostructures inherited the Alpine orogenic zones (Balkanides and Dinarides-Hellenides) and bounded the Central-Balkan neotectonic region. The linear morphostructures were tilted towards the Pannonian and Euxinian basins and the North-Aegean trough. The Central-Balkan neotectonic region has a complicated block structure (horst-and-graben pattern) dominated by the NNW-SSE Struma and Vardar lineaments, the WNW-ESE Sava and Marica lineaments, and the Middle-Mesta and North Anatolian fault zones. The dominating Serbo-Macedonian neotectonic swell was rifted, and subsided along the Struma and Vardar lineaments. The range of the vertical neotectonic displacements reached a maximum of 3–4 km, and even up to 6 km at the edges of the Pannonian and Aegean basins. The general doming of the region was controlled by the isostatic uplift of a thickened crustal lens (Rhodope Massif) in the southern margin of the Eurasian plate. The collapse of the complicated domal structure began along the main (Struma, Vardar and Marica) lineaments in the central parts of the dome, and continued in the Pliocene and Quaternary along a more external contour bounded by the Stara-planina and Dinarian-Hellenic linear morphostructures.
59 citations
TL;DR: In this paper, structural analysis indicates that the Saraya batholith corresponds to a composite body consisting of several coalescent plutons and interfering diapirs, and that the structural fabric patterns in these plutsons and in the host-rocks constitutes the basis of a hypothetical model of initiation, ascent and emplacement.
Abstract: The large Saraya batholith intruded the Lower Proterozoic sequences of Eastern Senegal. Structural analysis indicates that this large granitic batholith corresponds to a composite body consisting of several coalescent plutons and interfering diapirs. Interpretation of the structural fabric patterns in these plutons and in the host-rocks constitutes the basis of a hypothetical model of initiation, ascent and emplacement as follows: (1.) development of a deep N-S granitic ridge controled by a major crustal fracture generated by an earlier extensional phase re-activated by a strike-slip fault which, probably, would facilitate segregation, collection and ascent of magmas; (2.) intrusion and splitting up of the ridge into several diapirs which ascended simultaneously and separately in a setting of a N-S sinistral transcurrent deformation inducing a transverse NW-SE shortening and forceful emplacement of plutons and (3.) final emplacement characterized by interference between regional deformation and pluton ‘ballooning’, the latter leading to the coalescence of intrusions and to the formation of a larger, apparently homogeneous body.
TL;DR: In this paper, a survey of recently active faults in Morocco is presented, where a map of vertical deformation was established from the elevations of summit level surfaces, and an analysis was made of the drainage pattern.
Abstract: A survey has been done of recently active faults in Morocco. In addition to field observations, morphometric methods were applied and an analysis was made of the drainage pattern. In the morphometric analysis, a map of vertical deformation was established from the elevations of summit level surfaces. This enables the recognition of neotectonic discontinuities and lithological contrasts; the actual discrimination of different rock-types can only be achieved by comparison with field observations. The analysis of drainage patterns — including their perturbations and anomalies — can also reveal the presence of features due to neotectonics, structural control or lithological variation. Certain faults can be detected which correspond to structures known from field geology or remote sensing (NE-SW and NW-SE oriented sets). Some new faults are observed which belong to these sets, as well as others which define a new N-S trending set. The present analysis leads to a distinction between ancient faults and currently active faults. The results of this study are shown on a map of recently active faults where the respective vertical displacements are also indicated.
TL;DR: Within the fracturai pattern of Morocco, 35-45° and 70-90° directions are predominant Most of the faults originated already during the Upper Palaeozoic and were repeatedly reactivated, later on Two of the large fracture systems are considered here as discussed by the authors.
Abstract: Within the fracturai pattern of Morocco, 35–45° and 70–90° directions are predominant Most of the faults originated already during the Upper Palaeozoic and were repeatedly reactivated, later on Two of the large fracture systems are considered here The South Atlas fault system (SAF) is composed of different faults with directions varying between 45–90° They were not functionally connected to the southern hinge of the High Atlas until its Miocene uplift Today, it seems to be inactive on the whole Both the tectonic data and the facies distribution of Mesozoic strata contradict clearly the interpretation that the SAF is a huge wrench-fault or even the Mesozoic plate margin of Africa The SW striking Transalboran fault system (TAF) is still active It crosses Morocco from Melilla to Agadir, showing again singular faults which are unified to extended lineaments only in a few areas The intervals between the faults are bridged by linear arrangements of earthquake hypocenters Sinistral massflow within the deeper parts of the lithosphere seems to be compensated at the surface by movements along pre-existing faults For the Moroccan segment of the TAF, a sinsitral displacement is testified at least since the Oligocene, while the northeastern segments from the Rif to Spain did not even originate until the Pliocene This would mean that sinistral shear was transmitted from Africa into the accreted Alboran and Iberia blocks after the Miocene collision
TL;DR: In this paper, a compilation of heavy mineral data and pebble analysis in the various turbiditic fan systems was presented, which indicated that the heavy minerals primarily reflect the nature of basement rocks exposed in the source terrains.
Abstract: The Polish Outer Carpathians consist of several flysch series of unknown original basement They were deposited from Late Jurassic to Miocene in a large basin dissected by tectonically uplifted ridges (cordillieras) which acted as source terrains The actual nappe pile is correlated with palaeogeographic basin realms From N to S the Skole, Silesian, Dukla and Magura basins are distinguished Our paper presents a first compilation of heavy mineral data and pebble analysis in the various turbiditic fan systems It is assumed that the heavy minerals primarily reflect the nature of basement rocks exposed in the source terrains The individual flysch basins were supplied generally from unmetamorphosed granitic to highgrade metamorphic continental basement series But staurolite-bearing high-grade metamorphics appear to have been present only in the northernmost provenance area (Silesian and Subsilesian ridges) A few reworked chromian spinel mineral grains in the northern parts of the basin were derived from small Caledonian/Variscan ultrabasic sutures present in the source ridges Increased chromian spinel contents are revealed in the southern part of the basin (Maastrichtian-Eocene Magura series) and in Cretaceous Pieniny Klippen belt flysch formations The chromian spinel in the Magura series was derived, either directly from Alpine oceanic crust obducted in the southern part of the Pieniny realm, or from re-eroded Pieniny flysch series Hence, our heavy mineral data indicate that in the Outer Carpathian basin during Cretaceous convergence no Alpine ophiolitic crust was obducted Therefore, an ophiolitic basement to the individual basins appears inprobable The Outer Carpathians presumably occupied, with respect to the internal suture zone, the position of a deep continental basement floored foreland basin
TL;DR: In this article, the dextral Budaors shear zone and the Buda imbricate stack are localised in the Dextral dextrals and the latter is underlain by blind reverse faults probably merging into a detachment fault at shallow depths.
Abstract: The Upper Eocene sequence of the Buda Hills consists of fluvial and shallow marine conglomerates, sandstones, bioclastic shallow-water limestone, marlstone and pelagicGlobigerina marl. The succession illustrates rapid, overall subsidence of the area, from terrestrial environments to bathyal depths. Sedimentation occurred on slopes situated on the flanks of synsedimentary basement antiforms. Vertical growth of antiforms caused progressive tilting of beds, layer-parallel extension by boudinage and faulting, and induced redeposition by mass flow. Antiforms are localised in the dextral Budaors shear zone and in the Buda imbricate stack, which accommodated the dextral displacement. The latter is underlain by blind reverse faults probably merging into a detachment fault at shallow depths. These structures were formed by WNW-ESE oriented compression and NNE-SSW directed tension. The morphological expression of the imbricate stack is the SE-facing Buda slope. The Bakony unit, while “escaping” from the Alps, was bordered by a northern sinistral and a southern dextral shear zone. Synsedimentary tectonics in the Buda Hills demonstrates the style of deformation inside the escaping block, close to the southern border zone. Tectonically controlled sedimentation suggests that escape tectonics was active as early as Late Eocene time.
TL;DR: Geological studies of the tectonic zones of eastern Albania indicate that they represent the passive margin to a Neotethyan Mirdita ocean basin, situated on the western margin of the Korab-Pelagonian microcontinent as discussed by the authors.
Abstract: Geological studies of the tectonic zones of eastern Albania indicate that they represent the passive margin to a Neotethyan Mirdita ocean basin, situated on the western margin of the Korab-Pelagonian microcontinent.
TL;DR: In this article, the effects of the Mg2+ ion concentration and the ionic products of carbonate upon the induction time for the onset of precipitation and the different mineralogies of calcium carbonates were studied.
Abstract: The effects of the Mg2+ ion concentration and the ionic products of carbonate upon the induction time for the onset of precipitation and the different mineralogies of calcium carbonates were studied. It was shown that Mg2+ ions delay the spontaneous precipitation of calcium carbonate from supersaturated solutions (e.g. seawater) with respect to calcium carbonate mineral to such an extent that only biogenic removal of skeletal calcium carbonate is possible from the open ocean. Low concentrations of magnesium ions in solution favor calcite formation while aragonite is formed at high magnesium concentrations. The mole% of MgCO3 in magnesian calcite increases with the increase of (Mg2+) in solution and with the increase of (CO32−) in the presence of (Mg2+) in solution.
TL;DR: In this paper, an orthogneissamphibolite complex, weakly deformed low grade sediments (?Devonian and Visean), and a number of different syn-to post-orogenic granodioritic to granitic intrusives, all crosscut by Late Lower Carboniferous undeformed lamprophyric dikes and unconformable overlain by Permian sediments and volcanics.
Abstract: Several small outcrops along the western Rhinegraben escarpment expose rocks which represent the western prolongation of the so-called Mid-German Crystalline Rise. This basement ridge separates the Rhenohercynian and Saxothuringian zones of the Variscan belt of Europe and thus marks the boundary between the external and the internal zones. The variable rock association includes an orthogneissamphibolite complex, weakly deformed low grade sediments (?Devonian and Visean), and a number of different syn- to post-orogenic granodioritic to granitic intrusives, all crosscut by Late Lower Carboniferous undeformed lamprophyric dikes and unconformable overlain by Permian sediments and volcanics. Largely isothermal decompression during coaxial fabric evolution in the orthogneiss complex marks an early stage of deformation possibly due to crustal attenuation. Peak metamorphism (amphibolite/greenschist facies) in the other sequences with only minor orogenic shortening is succeeded by retrogressive strike-slip deformation associated to peak intrusive activity. The encountered typically low-P high-T metamorphism, the predominant strike-slip type kinematic pattern, and the preservation of parts of the Devono-Carboniferous sedimentary cover of the Rise preclude major crustal thickening and subsequent exhumation. An exception is the probably thrust-bounded juxtaposition of the Albersweiler orthogneisses and Burrweiler schists which is supported by their respective PT-paths. The orogenic imprint in the sedimentary cover of the crystalline rise appears to be thermal rather than strain-induced, suggesting a dominant role of the abundant pre- to late-orogenic intrusives. The essential aspects of this sequence of related structural and thermal events as well as the rock type association suggest a largely submarine incipient magmatic arc type of orogenic environment for this part of the Variscan belt. Its evolution probably started during the Upper Devonian on a disintegrating continental platform and proceeded through the Lower Carboniferous continental collision with the Rhenohercynian zone entailing a concomittant switch in deformation mode of the upper plate.
TL;DR: The electrical resistivity structure of the crust and upper mantle of the Atlas Mountain System was studied using magnetotelluric and geomagnetic deep soundings in this paper, where a mid-crustal low resistivity layer with total conductance (thickness-resistivity ratio) of about 2000 Siemens stretches from the southern border of the High Atlas towards the Middle Atlas.
Abstract: The electrical resistivity structure of the crust and upper mantle of the Atlas Mountain System was studied using magnetotelluric and geomagnetic deep soundings. Field experiments were done in eastern Morocco along a traverse from the Anti Atlas to the Rides Rifaines in two campaigns in 1983 and 1988. Zones of very low electrical resistivity could be identified in the various structural settings at different depth ranges, most likely connected directly to the tectonic evolution of the mountain belts. A mid-crustal low resistivity layer with total conductance (thickness-resistivity ratio) of about 2000 Siemens stretches from the southern border of the High Atlas towards the Middle Atlas. This layer seems to characterize the base of crustal detachment, e.g., the plane for large horizontal overthrusting, and supports the idea of thick- and thin-skinned tectonics involved in Atlasic mountain building. In the western Middle Atlas an upper-crustal low resistivity layer (at depth < 10 km) was found in the area where volcanic activity was present, pointing towards a direct relation between low electrical resistivity and volcanic or postvolcanic events. North of the Middle Atlas resistivity structures change totally: The Pre and parts of the Sub-Rif have a highly conductive cover, presumably connected to the molasse basin. Total conductance was calculated to reach 6000 Siemens. No further conductive structures, like, e.g., the ones found beneath the High and Middle Atlas, are seen within the resistive crust, but at much greater depth within the upper mantle.
TL;DR: The Western Ligurian Flysch Units represent an Upper Cretaceous to Paleogene accretionary prism overthrust onto the paleo-European continental margin during the collisional stages of the Alpine orogeny (Eocene) as mentioned in this paper.
Abstract: The Western Ligurian Flysch Units represent an Upper Cretaceous to Paleogene accretionary prism overthrust onto the paleo-European continental margin during the collisional stages of the Alpine orogeny (Eocene). Their precollisional evolution has been reconsidered according to the data collected through extensive field mapping, the study of lowgrade metamorphism and by considering more strictly the processes documented in modern convergent zones.
TL;DR: The Świetokrzyski Horst, created during the Laramide phase, is situated in the central part of the Mid Polish Uplands as mentioned in this paper, composed of folded Paleozoic rocks partly covered by Mesozoic sediments.
Abstract: The Świetokrzyski Horst, created during the Laramide phase, is situated in the central part of the Mid Polish Uplands. It is composed of folded Paleozoic rocks partly covered by Mesozoic sediments. In this area two tectonostratigraphic units can be distinguished: the Kielce Unit to the S and the Łysogory Unit to the N.
TL;DR: In this article, the authors point out that a rift stage (Permian to Early Jurassic) in the tectonic history of the Western High Atlas was followed by a gulf stage (Late Jurassic to Middle Cretaceous) until later the high mountain range generated by inversion in Late Cretages and Neogene to recent times.
Abstract: Angular unconformities, time gaps, and progressive increase of thickness in the Mesozoic sedimentary pile of the Western High Atlas, Morocco, point to mid-Jurassic tectonic pulses in this area. Red beds, Middle Jurassic in age, were deposited in the nearshore Agadir-Essaouira basin in contrast to transgressive tendencies of the eustatic curve. These phenomena are easily explained by uplift and erosion in the central part of the mountain belt even in the Middle Jurassic. Thus, a rift stage (Permian to Early Jurassic) in the tectonic history of the Western High Atlas was followed by a gulf stage (Late Jurassic to Middle Cretaceous) until later the high mountain range generated by inversion in Late Cretaceous and Neogene to recent times. Tensional forces that created the mobile rift belt were superimposed by vertical uplift during the Middle Jurassic that gave rise to a NNE-SSW stretching high. Even in the present-day high mountain range this area, called the »ancient massif«, is strongly elevated. Thus, the evaluation of the geological history of the Western High Atlas seems much complicated.
TL;DR: In this article, two distinct nappe emplacement vectors are identified in the Argolis Peninsula of southern Greece, located at the southern end of the Pelagonian continental terrane, confirm that this block was rifted from Gondwana in mid Triassic times.
Abstract: Continental collision in the Aegean area has produced a collage of micro-continental blocks, which were accreted to the active margin of Eurasia in Early Tertiary times. Studies undertaken in the Argolis Peninsula of southern Greece, located at the southern end of the Pelagonian continental terrane, confirm that this block was rifted from Gondwana in Mid Triassic times. By Mid Jurassic times at the latest, actively spreading oceanic basins had opened in both the Pindos and Vardar Zones on either side of this block. Identification of Late Cretaceous oceanic basalts within an accretionary complex in the eastern Argolis Peninsula extends the history of the Neotethys beyond Late Jurassic ophiolite emplacement, previously believed to be the result of continental collision. The Cretaceous ocean basins were relict Jurassic features, as no rifting event is known which can account for their formation following ophiolite obduction. After a phase of Late Cretaceous oceanic spreading in the eastern Vardar oceanic basin, Early Tertiary collision occurred as a result of northeast-dipping subduction along the eastern margins of both Pindos and Vardar branches of the Neotethys. Two distinct nappe emplacement vectors are identified in the Argolis Peninsula. After accounting for Neotectonic rotations these are interpreted to reflect SW-directed orthogonal collision in the west and NW-directed emplacement in the east, resulting from tranpressional collision along the southern end of the Pelagonian block.
TL;DR: In this article, the thermal histories of Tertiary basins situated around and within the Eastern Alps were examined using coalification data, and the data suggest that the basins' thermal histories are intimately related to late Alpidic geodynamics of the eastern Alps.
Abstract: The thermal histories of Tertiary basins situated around and within the Eastern Alps are examined using coalification data.Waples' method is used to estimate paleogeothermal conditions. The data suggest that the basins' thermal histories are intimately related to late Alpidic geodynamics of the Eastern Alps.
TL;DR: In this article, an umfassende analyse and modellierung der Entwicklungsgeschichte des Saar-Nahe-Beckens in SW Germany wird bislang dadurch erschwert, das erhebliche Teile der ursprunglichen permokarbonen Beckenfullung bereits erodiert sind.
Abstract: Eine umfassende Analyse und Modellierung der Entwicklungsgeschichte des Saar-Nahe-Beckens in SW-Deutschland wird bislang dadurch erschwert, das erhebliche Teile der ursprunglichen permokarbonen Beckenfullung bereits erodiert sind. Zur Quantifizierung der maximalen Uberlagerung des heutigen Aufschlusniveaus wurde der Kompaktionsgrad von Tonsteinen mit Hilfe geophysikalischer Bohrlochmessungen untersucht. Es kann eine maximale Uberlagerung bestimmt werden, die im SW des Saar-Nahe-Beckens 1950 m und im NE 2400 m betragt (bezogen auf heutiges Meeresspiegelniveau). Aufgrund palaogeographischer Argumente lassen sich diese Uberlagerungswerte nur durch eine Sedimentabfolge mit permokarbonem bzw. permischem Alter erklaren. Eine maximale Versenkung im Mesozoikum oder Tertiar kann ausgeschlossen werden. Durch die Quantifizierung und zeitliche Einstufung der maximalen Versenkungstiefe kann die Subsidenz- und Hebungsgeschichte des Saar-Nahe-Bekkens seit dem Karbon luckenlos rekonstruiert werden.
TL;DR: In this article, the structural development of the Middle Atlas and the central High Atlas was controlled by a pre-existent fault pattern, which was reactivated repeatedly in various manners, such as earthquakes and volcanic eruptions.
Abstract: Since the beginning of the Mesozoic the structural development of the Middle Atlas and the central High Atlas was controlled by a pre-existent fault pattern, which was reactivated repeatedly in various manners.
TL;DR: Three tectonometamorphic events have been recognized in the crystalline rocks of the Catherine mantled gneiss dome (CD) in the central Erzgebirge as mentioned in this paper.
Abstract: Three tectonometamorphic events have been recognized in the crystalline rocks of the Catherine mantled gneiss Dome (CD) in the central Erzgebirge. The first tectonometamorphic event is characterized by the acquisition of a S1–S2 metamorphic foliation, development of F2 isoclinal partly syn-schistose folding and intrusion of early synkinematic granites. P-T conditions correspond to higher amphibolite facies metamorphism and culminate in anatexis. A diapiric intrusion of Cambro-Ordovician muscovite-biotite porphyritic granite has verticalized the S2 foliation and is responsible for the genesis of the classical mantled gneiss dome. Oblate strain and orthorhombic diffuse c-axis patterns are typical of the marginal parts of the dome.
TL;DR: The relative size of glass rims coating crystals in the matrix ash provides a semi-quantitative measure of abrasion of ash grains in pyroclastic flows as mentioned in this paper, showing that fine ash in distal deposits are due to diminishing elutriation rather than high rate of attrition.
Abstract: The relative size of glass rims coating crystals in the matrix ash provides a semi-quantitative measure of abrasion of ash grains in pyroclastic flows. Median abrasion indices (= areacrystal / areaglass rim) are 8.4 to 18.5 in Laacher See pyroclastic flow units but only 4 to 6.3 in assocciated fallout, showing stronger abrasion of ash particles in the pyroclastic flows. All pyroclasts undergo strong attrition in the vent but clasts in pyroclastic flows undergo a second major phase of abrasion during high-energy near-vent flow. Abrasion of ash particles is weaker during lower-energy higher-strength motion further downstream, suggesting that high contents of fine ash in distal deposits are due to diminishing elutriation rather than high rate of attrition.
TL;DR: In this article, the paleoenvironment of the southwestern portion of the Paleogene Moroccan phosphate sea has been reconstructed in detail by microfacies studies for a complete transgressive-regressive cycle.
Abstract: The paleoenvironment of the southwestern portion of the Paleogene Moroccan phosphate sea has been reconstructed in detail by microfacies studies for a complete transgressive-regressive cycle. In front of the Anti-Atlas, forming the southern border of the Atlantic gulf, a bioclastic and phosphatic carbonate ramp extended to the north. The ramp was a homoclinal, very gentle dipping surface. Four stages of ramp evolution can be distinguished. They are (1) the marginal marine initial stage, (2) the marine transgressive stage, (3) the marine regressive stage and (4) the final silting up stage. The ramp is characterized by a distinct facies zonation. A sabkha plain, documented by mudstones and dolocretes, was situated between the arid hinterland and the ramp. Nearshore, open lagoons existed, populated by chlorophycean algae and miliolid foraminifera. These environments were protected from the open sea by a chain of oyster banks. A belt of echinoid enrichments probably marked the wave base. Sea areas with deeper and only temporarily, highly-agitated water are characterized by a benthic faunal assemblage of varied molluscs, with bryozoans becoming more abundant to the east. The carbonates are intensively bioturbated and interfinger with phosphorite sands, which dominated in the deepest part of the ramp. All phosphorites studied are clastics, poor in matrix and are not associated with phosphate source rocks. A process of extensive reworking, transport and redeposition, which is related to transgressions and regressions, has to be assumed.