Tectonic Stages Research Articles

The structural evolution of the Messinian evaporites in the Levantine Basin

The Levantine Basin in the South-eastern Mediterranean Sea is a world class site for studying the initial stages of salt tectonics driven by differential sediment load, because the Messinian evaporites are comparatively young, the sediment load varies along the basin margin, they are hardly tectonically overprinted, and the geometry of the basin and the overburden is well-defined. In this study we analyse depositional phases of the evaporites and their structural evolution by means of high-resolution multi-channel seismic data. The basinal evaporites have a maximum thickness of about 2 km, precipitated during the Messinian Salinity Crisis, 5.3–5.9 Ma ago. The evaporite body is characterized by 5 transparent layers sequenced by four internal reflections. We suggest that each of the internal reflection bands indicate a change of evaporite facies, possibly interbedded clastic sediments, which were deposited during temporal sea level rises. All of these internal reflections are differently folded and distorted, proving that the deformation was syn-depositional. Thrust angles up to 14° are observed. Backstripping of the Pliocene–Quaternary reveals that salt tectonic is mainly driven by the sediment load of the Nile Cone. The direction of lateral salt displacement is mainly SSW–NNE and parallel to the bathymetric trend. Apparent rollback anticlines off Israel result rather from differential subsidence than from lateral salt displacement. In the south-eastern basin margin the deposition of the Isreali Slump Complex (ISC) is coeval with the onset of salt tectonic faulting, suggesting a causal link between slumping processes and salt tectonics. The superposition of ‘thin-skinned’ tectonics and ‘thick-skinned’ tectonics becomes apparent in several locations: The fold belt off the Israeli Mediterranean slope mainly results from active strike-slip tectonics, which becomes evident in faults which reach from the seafloor well below the base of the evaporites. Owing to the wrenching of the crustal segments which are bounded by deep-rooted fault lines like the Damietta–Latakia, Pelusium and Shelf Edge Hinge line the setting is transpressional south of 32°N, where the fault lines bend further towards the west. This adds a component of ‘thick-skinned’ transpression to the generally ‘thin-skinned’ compressional regime in the basin. Above 1.5 km of evaporites, a mud volcano is observed with the mud source seemingly within the evaporite layer. At the eastern Cyprus Arc, the convergence zone of the African and the Anatolian plates, deep-rooted compression heavily deformed the base of the evaporites, whereas at the Eratosthenes Seamount mainly superficial compression affecting the Post-Messinian sediments and the top of the evaporites is observed.

Late Cretaceous structural control and Alpine overprint of the high-sulfidation Cu–Au epithermal Chelopech deposit, Srednogorie belt, Bulgaria

The Chelopech epithermal high-sulfidation deposit is located in the Panagyurishte ore district in Bulgaria, which is defined by a NNW alignment of Upper Cretaceous porphyry–Cu and Cu–Au epithermal deposits, and forms part of the Eastern European Banat–Srednogorie belt. Detailed structural mapping and drillcore descriptions have been used to define the structural evolution of the Chelopech deposit from the Late Cretaceous to the present. The Chelopech deposit is characterized by three fault populations including ∼N55, ∼N110, and ∼N155-trending faults, which are also recognized in the entire Panagyurishte district. Mapping and 3-D modeling show that hydrothermal alteration and orebody geometry at Chelopech are controlled by the ∼N55-trending and ∼N110-trending faults. Moreover, the ∼N155-trending faults are parallel to the regional ore deposit alignment of the Panagyurishte ore district. It is concluded that the three fault populations are early features and Late Cretaceous in age, and that they were active during high-sulfidation ore formation at Chelopech. However, the relative fault chronology cannot be deduced anymore due to Late Cretaceous and Tertiary tectonic overprint. Structurally controlled ore formation was followed by Senonian sandstone, limestone, and flysch deposition. The entire Late Cretaceous magmatic and sedimentary rock succession underwent folding, which produced WNW-oriented folds throughout the Panagyurishte district. A subsequent tectonic stage resulted in overthrusting of older rock units along ∼NE-trending reverse faults on the Upper Cretaceous magmatic and sedimentary host rocks of the high-sulfidation epithermal deposit at Chelopech. The three fault populations contemporaneous with ore formation, i.e., the ∼N55-, ∼N110- and ∼N155-trending faults, were reactivated as thrusts or reverse faults, dextral strike–slip faults, and transfer faults, respectively, during this event. Previous studies indicate that the present-day setting is characterized by dextral transtensional strike–slip tectonics. The ∼NE-trending overthrust affecting the Chelopech deposit and the reactivation of the ore-controlling faults are compatible with dextral strike–slip tectonics, but indicate local transpression, thus revealing that the Chelopech deposit might be sited at a transpressive offset within a generally transtensional strike–slip system. The early WNW-trending folds require a roughly NNE–SSW shortening, which is incompatible with the present-day dextral strike–slip tectonic setting and the ∼NE-trending thrust formed during the tectonic overprint of the Chelopech deposit. This reveals a rotation of the principal stress axes after Late Cretaceous high-sulfidation ore formation and post-ore deposition of sedimentary rocks. The nature of the sedimentary rocks interlayered and immediately covering the Upper Cretaceous magmatic rocks hosting the Chelopech deposit indicates sedimentation and associated volcanism in an extensional setting immediately before ore formation. It is concluded that the Chelopech deposit was formed when the tectonic setting changed from extensional during Late Cretaceous basin sedimentation and magmatism, to compressional producing WNW-trending folds under a roughly NNE–SSW compression, possibly in a sinistral strike–slip system. Thus, like other world-class, high-sulfidation epithermal deposits, the Chelopech deposit was formed at the end of an extensional period or during a transient period of stress relaxation, which are particularly favorable tectonic settings for the formation of high-sulfidation epithermal deposits. The exceptional preservation of the Upper Cretaceous Chelopech epithermal deposit is explained by the combined deposition of a thick Senonian sedimentary sequence on top of the Upper Cretaceous magmatic host rocks of the deposit, and the later overthrust of older rock units on top of the deposit. Our study at Chelopech supports previous studies stating that post-ore basin sedimentation and tectonic processes provide the favorable environment to preserve old epithermal deposits from erosion. The tectonic evolution of the Chelopech deposit is similar to that of the entire Panagyurishte ore district. This coherence of the magmatic, hydrothermal, and tectonic events from north to south suggests that the ore deposits of the entire Panagyurishte ore district were formed in a similar tectonic environment.

Global reconstructions of Cenozoic seafloor ages: Implications for bathymetry and sea level

Although accurate estimates of Cenozoic seafloor ages will serve to further our understanding of the relationship between mantle dynamics, plate tectonics, and a variety of surficial geological processes, it is difficult to estimate ages of subducted seafloor. However, given the near-constancy of surface velocities within a tectonic stage, we can estimate Cenozoic plate ages, even for subducted lithosphere. We reconstruct seafloor ages based on the Cenozoic plate reconstructions and absolute rotation poles of Gordon and Jurdy [R.G. Gordon and D.M. Jurdy, Cenozoic Global Plate Motions, J. Geophys. Res. 91 (1986) 12389–12406.]. For the western Pacific, we explore alternative models based on the reconstructions of Hall [R. Hall, Cenozoic geological and plate tectonic evolution of SE Asia and the SW Pacific: computer-based reconstructions, model and animations, J. Asian Earth Sci. 20 (2002) 353–434.]. Both reconstructions indicate an increase in average seafloor age since the early Cenozoic, resulting in an increase in the volume of ocean basins and a decreased sea level since the Early Cenozoic. These trends are more pronounced for the Gordon and Jurdy [R.G. Gordon and D.M. Jurdy, Cenozoic Global Plate Motions, J. Geophys. Res. 91 (1986) 12,389–12,406.] reconstruction because the Hall [R. Hall, Cenozoic geological and plate tectonic evolution of SE Asia and the SW Pacific: computer-based reconstructions, model and animations, J. Asian Earth Sci. 20 (2002) 353–434.] reconstruction retains older seafloor in the western Pacific, which approximately halves the predicted sea level decrease since the early Cenozoic (250 vs. 125 m compared to geologic estimates of ∼150 m). These changes in sea level occur despite decreases in oceanic lithosphere production rates of only about 20% in both models. Thus, the changing distribution of seafloor age has a larger effect on sea level than changes in spreading rates or ridge lengths. These reconstructions can also be used to estimate past heat flow, the volume of subducted buoyancy and changes in the bathymetry of the Cenozoic ocean basins.

Linking regional‐scale lineaments to local‐scale fracturing and groundwater inflow into the Päijänne water‐conveyance tunnel, Finland

ABSTRACTPotential structural or lithological controls of groundwater flow into the mostly rock‐surfaced Päijänne water‐conveyance tunnel in southern Finland were investigated by integrating geological, hydrogeological and aerogeophysical data. Fracture‐zone geometry and distribution, interpreted from processed aeromagnetic images, and topographic and geological information are compared for three different sections of the Päijänne Tunnel. Documented observations on fracturing and ground‐water inflow from inside the tunnel provide subsurface information on the fractures and their hydraulic properties. Topographic and aeromagnetic lineaments both exhibit general NE–SW and NW–SE orientations at a regional scale. Based on the aeromagnetic interpretation, bedrock fractures intersecting the tunnel are part of a regional fracture network and their evolution can be connected to the main tectonic stages in southern Finland. Their distribution is lithologically controlled and reflects the rock type and its structure. For more detailed scales, a superficial deposit relief map is a powerful tool for obtaining a more accurate location of fracture zones and for evaluating their connection to superficial deposits as possible groundwater reservoirs. Depending on the scale, integrated interpretation using both topographic and aeromagnetic data gives the best results, particularly when supported by independent verification such as the observed fracturing inside the tunnel.NW–SE appears to be the most common strike trend among the measured fractures linked with water inflow. In the magnetic data, this orientation is displayed (1) as swarms of short, faint signatures indicating brittle, shallow features, and (2) as extended, broad, linear magnetic gradients denoting block boundaries. Their lengths, of tens to hundreds of kilometres, suggest that they may also be deep‐reaching. The coincidence and the parallel orientation of these two magnetic features of different scales suggest their genetic relationship: the faulted block boundaries were reactivated at later tectonic stages, resulting in brittle fracturing along the same earlier structural weakness zones. Many of the locations where water‐conducting fracturing occurs, or where groundwater inflow has been measured at a larger scale, are associated with intersecting or individual topographically interpreted fracture zones, especially NW–SE trending ones.

Varying tectonic control on basin development at an active microplate margin: Latakia Basin, Eastern Mediterranean

Detailed interpretation of multichannel seismic reflection profiles show that the Latakia Basin evolved in two distinct tectonic stages: southeast-directed contraction that culminated in the latest Miocene, followed in the early–middle Pliocene by progressive transition to partitioned contraction and extension related to the initiation of strike slip along the eastern Anatolian Transform Fault and its marine extensions. The Miocene fold/thrust belt comprises two arcuate culminations enclosing a Miocene piggy-back depocentre situated on the backlimb of the Amanos–Larnaka ramp anticline. In the early–middle Miocene, this piggy-back basin was part of a much wider foredeep that also encompassed the Miocene successions of the Cilicia–Adana basin complex to the north. The Misis–Kyrenia fold/thrust belt evolved in the Tortonian, effectively dividing the foredeep into two large piggy-back basins. Our data demonstrate that a fundamental change in kinematic regime occurred during the Messinian to early Pliocene involving the onset of strike-slip movements resulting in transtension along the northeast-trending portion of the main lineaments bounding the Latakia Basin and continued contraction across the east-trending portion of the lineaments. In the northeastern portion of the Latakia Basin southeast-directed thrusting ceased in the early Messinian and was followed in the lower Pliocene by the development of horst and grabzen structures, bounded by faults linking onland with the strands of the East Anatolian Transform Fault.

Discussion of “The polygenetic Au–Ag bearing veins of Bou Madine (Jbel Ougnat, Eastern Anti-Atlas, Morocco): tectonic control and evolution of a Neoproterozoic epithermal deposit” [Abia et al., Journal of African Earth Sciences, 36 (2003) 251–271

In order to better understand the orogenic evolution of the Rif chain in the Eocene-Miocene interval, we provide new structural and kinematic data for the Jebha area, a key-sector of the Central Rif. Here the thrust sheet superposition occurs along the well-known Jebha-Chrafate lineament, widely considered as a major left-lateral transfer fault that enabled the Miocene westward migration of the internal thrust front. Our structural analysis was mainly focused on (i) the internal deformation of stacked nappes and (ii) the kinematics of the main thrust faults. Five main deformation stages were recognized for the Eocene-Miocene tectonic evolution of this area. The first orogenic pulse (D1), which occurred in the Eocene-Oligocene interval, was responsible for the tectonic stacking of the Ghomaride Nappes. Subsequently between the late Aquitanian and the late Burdigalian, imbrication (stage D2) occurred for some Internal Dorsale Calcaire thrust sheets within a dominant regional ENE-WSW shortening. At the Rif scale, different displacements of the WSW-migrating thrust front were accommodated by transfer structures including the Jebha-Chrafate fault. The following late Burdigalian-Langhian stage (D3) was defined, on the contrary, by a prevalence of the radial thrust front migration. In the Jebha area the early thrusting (stage D3a) was characterized by a main SE-vergence. In this phase the External Dorsale Calcaire and the Maghrebian Flysch Basin Units were included in the accretionary wedge. Two late D3 regional deformation phases were probably related to the buttressing effect that followed the collision of the thrust sheet pile against the crustal ramp of the External Rif domain. The first stage (D3b) consisted of an out-of-sequence thrusting recorded in the western sector of the Jebha area with the superposition of the Ghomaride Unit onto the External Dorsale Calcaire Unit, and in the eastern sector with the stacking of the Internal Dorsale Calcaire Unit directly onto the Predorsalian Unit. The second stage (D3c) included a late back-thrusting affecting the whole orogenic chain and deforming all the tectonic contacts. The fourth stage (D4) was characterized by strike-slip faulting and SW-verging folding. This latter mostly affected the successions located to the East of the Jebha village and was partially synchronous with the D3 stage. It was most probably related to the SW-migration of the internal thrust-front of the Bokkoya Dorsale Calcaire Complex and a renewed activity of the Jebha-Chrafate fault zone. The last tectonic stage (D5) included a radial extension expressed by high and low-angle normal faults.

Deformation of the northeastern Venezuelan Andes. Relationships with the Caribbean overthrusts

The Merida Andes (Venezuela) formed in the middle Miocene due to oblique convergence between the South American plate and the Maracaibo block [Audemard et al., 2002] (figs. 1A and 1B). The study area corresponds to the so-called "Barbacoas platform" [Renz, 1960], which constitutes the northeastern termination of the belt, NE of Valera (fig. 2). It is located in the northeastern part of Trujillo block [Hervouet et al., 2001], considered as an independent block separated from the main Maracaibo block along the Valera fault. According to Stephan [1982], the N170°E-trending Caribbean compression developed in this area from late Cretaceous to Eocene. It was followed by a N105°E-trending compression older than middle Miocene, and finally by the NW-SE Andean compressional stage that lasted till now in most of the chain. However, east of El Empedrado fault, a NNE-SSW compression presently occurs that is oblique to the classical Andean stage. The tectonic evolution of the Andean stage is not well understood. The Merida Andes are mainly composed of Precambrian and Paleozoic rocks. The northern part of the belt only comprises a complete and continuous Jurassic to Paleogene cover. This lithologic pattern is probably a consequence of the tectonic escape of the Maracaibo block, and more particularly of the smaller Trujillo block. The Merida and Carribean belts being close to each other, the influence of the Andean deformation on the Caribbean allochthonous must be taken into account. In order to make a structural analysis at regional scale, we privileged the use of remote sensing data (Landsat, Spot and Radar images) and aerial photographs. This was complemented by structural data obtained in the field, allowing the study of geometric and chronological relationships between the tectonic structures.

The late thermal history of the Ronda area, southern Spain

The Betic–Rif belt, in the western Mediterranean, experienced a pre-Alpine history and was later extensively reworked by major Alpine tectonics. There is abundant data showing that the Betic chain suffered very high cooling rates during its Alpine history, constrained mainly by geochronology using various isotopic systems and by palaeontological age determinations. In the westernmost part of the chain the high closure-temperature isotopic systems recorded Miocene high-grade metamorphism in the country rocks. In order to constrain the later stages of cooling, fission-track analysis has been applied to both zircon and apatite. The results point to extremely high rates of cooling (400 °C/Ma) between 21 and 19 Ma. Rates slowed to 100 °C/Ma for the time period 19 to about 12 Ma. The fission-track analysis also confirms the existence of an extensional tectonic stage between 19 and 17 Ma.

Various mechanisms to induce present-day shallow flat subduction and implications for the younger Earth: a numerical parameter study

Shallow flat subduction is a relatively common feature at present-day subduction zones. Several mechanisms to explain this feature have been proposed, and can be subdivided into three groups: overthrusting of the subducting plate, subduction of a plume-generated oceanic plateau, and slab suction forces. We developed a numerical model to investigate these mechanisms and tested it through a comparison of the model results with the observations of the Peru flat slab where all three mechanisms seem to be contributing. The ratio of contributions of overthrusting continent to plateau subduction is in the range of 1:1 to 1:2, and the role of plate suction forces is likely to be significant. By applying the overthrusting continent and plateau subduction mechanisms separately, we were able to determine the most important model parameters for each of the mechanisms. Overthrusting easily results in flat subduction, and the flat slab length is primarily a function of slab age, overriding plate motion and mantle viscosity. An oceanic plateau is much less likely to cause flat subduction, and favorable conditions for flat subduction include a young slab age, long-lived plateau buoyancy after subduction, a strong mantle, and addition of slab suction forces that are large enough to further reduce the subduction dip angle, once the plateau initiates this flattening. Furthermore, we found that even though today flat subduction can be explained with the dominant model parameters within a reasonable range, for a slightly hotter, younger Earth, these flat subduction conditions are much less favorable, and so this style of subduction was probably not present in the past. This contradicts earlier predictions that flat subduction was a more wide-spread phenomenon in the early stages of plate tectonics in a younger earth.

Late Neoproterozoic strongly peraluminous leucogranites, South Eastern Desert, Egypt ? petrogenesis and geodynamic significance

Late Neoproterozoic garnet-bearing leucogranites are developed locally along thrust faults in the South Eastern Desert, Egypt. This work presents field observations, whole rock major and trace element abundances, Rb–Sr isotope data and mineral chemistry for three occurrences in the Sikait-Nugrus area. Field observations show that the leucogranites cut the faults and their contact with the country rocks is sharp with no indication of contact metamorphism. They were intruded into a low-grade metamorphosed ophiolitic melange and a high-grade metamorphosed metasedimentary succession of biotite schist composition. Numerous biotite schist enclaves, having irregular and diffuse contacts, are recorded within the leucogranites. Whole rock Rb–Sr ages of the leucogranites from two different localities are 610±20 and 594±12 Ma respectively; they are interpreted as emplacement ages. The leucogranites contain more than 70% SiO2, and they are strongly peraluminous (A/CNK>1.1) with low TiO2, Fe2O3*, MgO, CaO, Ba, Sr, LREE, Eu/Eu* and Sr/Ba and high Rb, Rb/Zr, Rb/Sr and Rb/Ba. These geochemical parameters and the low initial 87Sr/86Sr ratios (∼0.703) indicate crustal derivation by dehydration partial melting from a juvenile protolith similar to the exposed biotite-rich metasediments. Models for the tectonic setting of these leucogranites suggest their emplacement during an extensional tectonic stage that follows continental collision. It is proposed that crustal heating, caused by decompression along shear zones, is responsible for the production of these granitic melts. The results support previous hypotheses and further document a regional late Neoproterozoic extensional tectonic event, which is probably related to the initial break-up of Gondwana.

Brittle post-metamorphic tectonics in the Gran Paradiso Massif (north-western Italian Alps)

New geological mapping (1:10.000 scale) and structural analysis in the Orco valley (NW Italian Alps), give insights on the post-metamorphic brittle tectonic evolution of the Gran Paradiso Unit and adjoining Piemonte Ophiolitic Unit and Sesia-Lanzo Unit. According to existing geochronological data, the metamorphic evolution of the studied domain ended in Early Oligocene and was followed by a progressive exhumation during Neogene. This work describes the brittle fault network developed during the post-metamorphic tectonic stages coeval to exhumation. The geometry and kinematics of this fault network allow to interpret the study area as a part of a larger lowstrain, fault-bounded block, whose main bordering discontinuities are located outside the mapped region. The post-metamorphic kinematic evolution was characterised by: (a) ESE-WNW extension, attested by NNE-SSW normal faults and extensional joints; (b) dextral shearing along a major E-W shear zone (Orco shear zone). The individual faults of the studied area are considered as P- or R-shears of the Orco shear zone, which could be in turn a part of a larger NE-SW regional shear zone bounded to the N by the Chamonix-Rhône- Simplon Line.

Regional deformation of the Sierra de San Luis, Argentina: Implications for the Paleozoic development of western Gondwana

Metamorphic and ductile deformation fabrics within the Sierra de San Luis, central Argentina, provide evidence for the Early to Middle Paleozoic development of the paleo‐Pacific margin of Gondwana. Presumed Vendian‐aged metasedimentary rocks within both the Sierra de San Luis and the Sierras de Córdoba preserve early pressure solution cleavage development. Cambrian peak metamorphism in the Sierras de Córdoba and Ordovician peak metamorphism in the Sierra de San Luis indicate that juxtaposition of these two terranes did not occur prior to the Late Ordovician. Peak metamorphism and regional folding of the Sierra de San Luis metasedimentary rocks is equated with early stages of the development and shortening of the Famatinian magmatic arc along the western margin of Gondwana. Extensive, NNE trending zones of upper greenschist‐ to amphibolite‐facies ductile deformation within the Sierra de San Luis and along the western margin of the Sierra de Comechingones record the dextral oblique juxtaposition of the Sierra de San Luis terrane against the southwestern margin of the Sierras de Córdoba, coincident with, or closely followed by, the suture of the exotic Precordillera terrane to the western margin of Gondwana by the Early Devonian. Middle to Late Devonian restricted, lower greenschist‐grade reactivation of ductile faults may record the accretion of the Chilenia terrane, the final stage of Paleozoic convergent tectonism along this segment of western Gondwana.

Consolidation and Break-up of the South American Platform in Southeastern Brazil: Tectonothermal and Denudation Histories

The different tectonic stages that occurred at the end of the Proterozoic and during the Phanerozoic have an important bearing on the tectonothermal history of the South American Platform and its consolidation. Geochronological data (U/Pb monazite, 40Ar/ 39Ar whole rock) and apatite fission-track analysis, from Precambrian rocks of the southeastern Brazilian coastline, permit the modeling of a long-term thermal history of the crust and constrain variable denudation rates. Using these data, a temperature-time diagram reflects a period of accelerated exhumation during the end of the Brasiliano Orogeny, followed by long stability and reactivation of the platform during the Rifting Phase of the South Atlantic Ocean. U/Pb zircon and monazite (blocking temperature of ca. 650° C) data from a series of igneous bodies suggest that a tangential and transpressional tectonic regime occurred between 625 and 610 Ma. During the following escape tectonics, between 610 and 590 Ma the exhumation process indicates cooling rates of ca. 12°C/Ma. 40Ar/ 39Ar biotite ages between 540 and 510 Ma (ca. 300°C) and a corrected fission-track age on apatites (100°C) of 480 Ma indicate an exhumation event related to block tectonics with huge vertical displacement along shear zones. A long stabilization phase, with low exhumation, and cooling rate around 0.25°C/Ma was recorded from the Cambro/Ordovician to the Mesozoic. At 65 Ma an acceleration of the exhumation through denudation and reworking of the South American surface with cooling rate of 1.5°C/Ma is observed. The uplift of the Mantiqueira and Serra do Mar mountain ranges along the southeast Brazilian coastline works as a climatic barrier provoking lateral erosional processes causing long-term scarp retreat, combined with intense, but progressive denudation towards the continent. A denudation of 2.5 to 4 km was calculated for such processes. This lateral retreat of escarpments and flexural response can provide important insights regarding marginal isostatic uplift and the evolution of offshore sedimentary basins of southeast Brazil.

Tectonic stress field and its effect on hydrocarbon migration and accumulation in Mesozoic and Cenozoic in Kuqa depression, Tarim basin

Through rock acoustic emission experiments and structural deformation analysis, the tectonic stages in Meso-Cenozoic in the Kuqa depression of the Tarim basin are firstly divided. Then, combining with rock magnetic fabric analysis and memory information, the distribution characteristics of tectonic stress field of every tectonic stage are quantificationally resumed. At the same time, according to the distribution relation of tectonic stress field of hydrocarbon formation stage by the finite element numerical simulation method and the known hydrocarbon reservoirs, the effects of tectonic stress field on hydrocarbon migration and accumulation are further analyzed. The Kuqa depression has mainly experienced six tectonic movements since Mesozoic. Except that the tectonic stress field of the Early Yanshan stage (208—135 Ma) showed northeast-southwest extensional stress field where the orientation of the maximum principal compressive stress (σ 1 ) was northwest-southeast, the others were compressive stress field where the orientations of the maximum principal compressive stress (σ 1 ) were near north-south. Along with the closure of the paleo-Tethys ocean, the Kuqa depression in the Indosinian stage (250—208 Ma) was in strong compressive circumstance with apparently big maximum principal stress (σ 1 ) magnitude. Due to the equilibrium adjustment of interior Eurasia, the Kuqa depression in the Early Yanshan stage (208—135 Ma) was in weak extensional circumstance with apparently small maximum principal stress (σ 1 ) magnitude. From the Late Yanshan stage (135—65 Ma) on, with a series of collision events occurring at the south edge of Eurasia, the Kuqa depression was in compressive circumstance again in which the maximum principal stress (σ 1 ) magnitude was from small to big in turn. The Late Himalayan stage (2.6—0.7 Ma) was the main tectonic deformation stage with the biggest principal compressive stress (σ 1 ) magnitude. Tectonic stress field plays a dominant role in hydrocarbon formation, it not only forms migration channels and trap structures for hydrocarbon accumulation, but also is the main drive power for hydrocarbon migration vertically along faults.

Tectonique et karstification : le cas de la région de Han-sur-Lesse (Belgique)

Relationship between karst and tectonics in the Han-sur-Lesse area (Luxembourg province, Belgium). The structure of four limestone massifs around Han-sur-Lesse (Belgium) has been studied with the aim of understanding the relationship between karst and tectonics. In the massifs of Han and Wellin, a swallow-hole -resurgence system is observed, on the contrary of Grignaux-Turmont and Resteigne massifs. The structural analysis involves a geometric study of tectonic objects as the faults or the joints, to establish the structural evolution of the massif. With such an analysis, it is possible to describe more accurately the relationships between the tectonic evolution of a massif and its speleogenesis defined by the presence of a structured endokarstic hydrosystem. A study of the karstified joints' directions has showed that the karstogenesis developed during two successive stages. Indeed, we can observe that the Han tectonic network is mainly structured according to two directions : the first one -N50°E -N65°E -was caused by a Mesozoïc extensional tectonic stage, without any hydrodynamic potential. It induced a ghost-rock karstification. The second one -N140°E -is due to another tectonic extensional stage during the Cenozoïc ; this second stage, in relation with the Ardennes uplift is combined with the appearance of a hydraulic gradient, which allows the structuring of karstic systems. The hydraulic gradient together with the extensional tectonics lead to the karstification of Han and Wellin massifs.

Proterozoic basement provinces of southern and southwestern Australia, and their correlation with Antarctica

Abstract Three Precambrian basement provinces extend from the southern coast of Australia into East Antarctica when reconstructed in a Gondwana configuration. These are, from east to west, the Mawson Craton, and the Albany-Fraser and Pinjarra Orogens. The Mawson Craton preserves evidence for tectonic activity from the late Archaean until the earliest Mesoproterozoic. It is exposed in the Gawler Craton of South Australia, the Terre Adélie and King George V Land coastline of East Antarctica, and the Miller Range of the central Transantarctic Mountains. It may form a significant part of the ice-covered East Antarctic Shield, although insufficient data are available to constrain its lateral extent. The Mawson Craton underwent late Palaeoproterozoic tectonism along its eastern margin (the Kimban Orogeny) and the occurrence of c. 1700Ma eclogites in the Transantarctic Mountains implies that this was, in part, a collisional event, although elsewhere it was characterized by low P/T metamorphism. The western margin of the Mawson Craton collided with a continental fragment comprising the Nawa Domain of the Gawler Craton, the Coompana Block and the Nornalup Complex of Western Australia at c. 1560Ma during the Kararan Orogeny. The western edge of the Nornalup Complex later collided with the Biranup and Fraser Complexes and Yilgarn Craton to form the Albany-Fraser Orogen during two stages of tectonism at c. 1350–1260 and 1210–1140Ma. The Pinjarra Orogen truncates the western margin of the Yilgarn Craton and Albany-Fraser Orogen, and contains allochthonous 1100–1000Ma gneissic blocks transported along the craton margin during at least two stages of Neoproterozoic transcurrent movement. It divides East Gondwana into Australo-Antarctic and Indo-Antarctic domains, which are distinct continental fragments with different Proterozoic histories that were juxtaposed by oblique collision at 550–500Ma during the assembly of Gondwana. The path taken by the Pinjarra Orogen beneath the Antarctic ice sheet is unknown, but it is of similar width and length to the East African Orogen, and must have been a fundamental Neoproterozoic boundary of critical importance to supercontinent assembly and breakup.

Late stages of deformation and exhumation of an orogen constrained by fission-track data: A case study in the Western Alps

Research Article| November 01, 2003 Late stages of deformation and exhumation of an orogen constrained by fission-track data: A case study in the Western Alps B. Fügenschuh; B. Fügenschuh 1Department of Earth Sciences, Basel University, Bernoullistrasse 32, 4056 Basel, Switzerland Search for other works by this author on: GSW Google Scholar S.M. Schmid S.M. Schmid 1Department of Earth Sciences, Basel University, Bernoullistrasse 32, 4056 Basel, Switzerland Search for other works by this author on: GSW Google Scholar GSA Bulletin (2003) 115 (11): 1425–1440. https://doi.org/10.1130/B25092.1 Article history received: 20 Dec 2001 rev-recd: 22 May 2003 accepted: 12 Jun 2003 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation B. Fügenschuh, S.M. Schmid; Late stages of deformation and exhumation of an orogen constrained by fission-track data: A case study in the Western Alps. GSA Bulletin 2003;; 115 (11): 1425–1440. doi: https://doi.org/10.1130/B25092.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract New zircon and apatite fission-track data, combined with a structural analysis, provide constraints regarding the large-scale tectonic evolution of part of the French/Italian Alps. The observed migration of cooling toward more external units is interpreted to be due to thrust propagation. In the absence of significant amounts of crustal thinning, the exhumation has been dominantly by erosion.The most internal unit investigated (the Penninic Houillère zone) started to cool at ca. 35 Ma, after an earlier tectonometamorphic event that only affected Penninic units. Fission-track data from the Cheval Noir unit (replacing the Valaisan unit in the south) constrain the age of metamorphism in these frontal Penninic units to be older than 32 Ma. There, cooling started with the onset of a second stage of the tectonic evolution, i.e., with top-to-the-west-northwest movement along the Roselend thrust at ca. 32 Ma. This Oligocene to early Miocene thrusting led to burial and metamorphism in the external massifs and their cover (Dauphinois unit). During a third tectonic stage, thrust-related culminations formed in the external massifs. Between 20 and 15 Ma, this stage led to the onset of exhumation in the Dauphinois and in the northern frontal Penninic units (Valaisan units), caused by erosion that followed tilting in the backlimb of these culminations. Northward-increasing amounts of Miocene– Pliocene shortening in front of and below the external massifs led to significantly higher amounts of exhumation in the north. Finally, and in very recent times (post–5 Ma), the frontal thrust of the Houillère zone was reactivated as a normal fault with moderate offset (<3 km). You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Post-collisional crustal extension setting and VHMS mineralization in the Jinshajiang orogenic belt, southwestern China

The Jinshajiang orogenic belt (JOB) of southwestern China, located along the eastern margin of the Himalayan–Tibetan orogen, includes a collage of continental blocks joined by Paleozoic ophiolitic sutures and Permian volcanic arcs. Three major tectonic stages are recognized based on the volcanic–sedimentary sequence and geochemistry of volcanic rocks in the belt. Westward subduction of the Paleozoic Jinshajiang oceanic plate at the end of Permian resulted in the formation of the Chubarong–Dongzhulin intra-oceanic arc and Jamda–Weixi volcanic arc on the eastern margin of the Changdu continental block. Collision between the volcanic arcs and the Yangtze continent block during Early–Middle Triassic caused the closing of the Jinshajiang oceanic basin and the eruption of high-Si and -Al potassic rhyolitic rocks along the Permian volcanic arc. Slab breakoff or mountain-root delamination under this orogenic belt led to post-collisional crustal extension at the end of the Triassic, forming a series of rift basins on this continental margin arc. Significant potential for VHMS deposits occurs in the submarine volcanic districts of the JOB. Mesozoic VHMS deposits occur in the post-collisional extension environment and cluster in the Late Triassic rift basins.

A Vendian-Cambrian Island Arc System of the Siberian Continent in Gorny Altai (Russia, Central Asia)

An extended Vendian-Cambrian island-arc system similar to the Izu-Bonin-Mariana type is described in the Gorny Altai terrane at the margin of the Siberian continent. Three different tectonic stages in the terrane are recognized. (1) A set of ensimatic active margins including subducted oceanic crust of the Paleo-Asian ocean, the Uimen-Lebed primitive island arc, oceanic islands and seamounts: the set of rocks is assumed to be formed in the Vendian. (2) A more evolved island arc comprising calc-alkaline volcanics and granites: a fore-arc trough in Middle-late Cambrian time was filled with disrupted products of pre-Middle Cambrian accretionary wedges and island arcs. (3) Collision of the more evolved island arc with the Siberian continent: folding, metamorphism and intrusion of granites occurred in late Cambrian-early Ordovician time. In the late Paleozoic, the above-mentioned Caledonian accretion-collision structure of the Siberian continent was broken by large-scale strike-slip faults into several segments. This resulted in the formation of a typical mosaic-block structure.

The Miocene tectono‐sedimentary evolution of the southern Tyrrhenian Sea: stratigraphy, structural and palaeomagnetic data from the on‐shore Amantea basin (Calabrian Arc, Italy)

AbstractWe report on new stratigraphic, palaeomagnetic and anisotropy of magnetic susceptibility (AMS) results from the Amantea basin, located on‐shore along the Tyrrhenian coast of the Calabrian Arc (Italy). The Miocene Amantea Basin formed on the top of a brittlely extended upper plate, separated from a blueschist lower plate by a low‐angle top‐to‐the‐west extensional detachment fault. The stratigraphic architecture of the basin is mainly controlled by the geometry of the detachment fault and is organized in several depositional sequences, separated by major unconformities. The first sequence (DS1) directly overlaps the basement units, and is constituted by Serravallian coarse‐grained conglomerates and sandstones. The upper boundary of this sequence is a major angular unconformity locally marked by a thick palaeosol (type 1 sequence boundary). The second depositional sequence DS2 (middle Tortonian‐early Messinian) is mainly formed by conglomerates, passing upwards to calcarenites, sandstones, claystones and diatomites. Finally, Messinian limestones and evaporites form the third depositional sequence (DS3). Our new biostratigraphic data on the Neogene deposits of the Amantea basin indicate a hiatus of 3 Ma separating sequences DS1 and DS2.The structural architecture of the basin is characterized by faulted homoclines, generally westward dipping, dissected by eastward dipping normal faults. Strike‐slip faults are also present along the margins of the intrabasinal structural highs. Several episodes of syn‐depositional tectonic activity are marked by well‐exposed progressive unconformities, folds and capped normal faults. Three main stages of extensional tectonics affected the area during Neogene‐Quaternary times: (1) Serravallian low‐angle normal faulting; (2) middle Tortonian high‐angle syn‐sedimentary normal faulting; (3) Messinian‐Quaternary high‐angle normal faulting.Extensional tectonics controlled the exhumation of high‐P/low‐T metamorphic rocks and later the foundering of the Amantea basin, with a constant WNW‐ESE stretching direction (present‐day coordinates), defined by means of structural analyses and by AMS data. Palaeomagnetic analyses performed mainly on the claystone deposits of DS1 show a post‐Serravallian clockwise rotation of the Amantea basin.The data presented in this paper constrain better the overall timing, structure and kinematics of the early stages of extensional tectonics of the southern Tyrrhenian Sea. In particular, extensional basins in the southern Tyrrhenian Sea opened during Serravallian and evolved during late Miocene. These data confirm that, at that time, the Amantea basin represented the conjugate extensional margin of the Sardinian border, and that it later drifted south‐eastward and rotated clockwise as a part of the Calabria‐Peloritani terrane.