Tectonic Phases Research Articles

Scapolite metagabbros of the Xambica Suite: A Tonian OIB magmatism in the crustal evolution of the Araguaia Belt

The geological evolution of the Araguaia Belt (AB), an important Neoproterozoic orogen located in central-north Brazil, is marked by different stages in its tectonic evolution. These stages are characterized by various magmatic events represented by felsic alkaline plutons, ophiolitic suites, mafic-ultramafic intrusions, S-type granites, diabase dykes and tholeiitic basalts distributed along its 1200 km N–S long. One of these events was identified in the Xambioá region, in the NW of Tocantins/SE of Pará state, in which dozens of bodies of scapolite metagabbros and amphibolites were identified through mapping and fieldwork, which were gathered in the Xambica Gabbroic Suite (XGS). Field relations and structural observations reveal that they were intrusive bodies in the sedimentary successions of the Estrondo Group before metamorphism. We present complementary studies involving detailed petrographic, lithochemical and geochronological analyses to characterize these rocks and contextualize this magmatic event in AB evolution. The petrographic study allowed to classify the rocks of the XGS into metagabbros with plagioclase and clinopyroxenes relicts, scapolite-hornblende metagabbro, garnet-scapolite metagabbro, amphibolites, and rarely listwanite and steatite. Geochronological dating of zircon crystals from this suite of rocks was performed using two different techniques. Single zircon Pb-evaporation dating of a metagabbro (XL-02) yielded the age of 819 ± 5 Ma. U–Pb zircon dating by LA-MC-ICP-MS of a metagabbro (BV-01) and an amphibolite (XL-09) gave 822 ± 2 Ma and 826 ± 26 Ma, respectively. Two other metagabbro samples (XL-02 and XB-08) yielded concordant ages of 861 ± 21 Ma and 873 ± 15 Ma. The younger concordant ages are interpreted as the crystallization of the gabbroic protoliths in the Tonian, while the older concordant ages are related to the presence of inherited zircon. The geochemical signature of metagabbros and amphibolites is similar to that of ocean island basalts (OIB) related to an intraplate tectonic environment, characterizing an extensional tectonic phase in AB evolution, which differs from other mafic events already recognized in AB of a MORB or tholeiitic signatures. Similar Tonian age are reported in basic to intermediate volcanic secession in the Goiás Magmatic Arc representing a contemporary collisional tectonic event, which reveals a link in the evolution between these two geotectonic units.

Early, far-field and diffuse tectonics records in the North Aquitaine Basin (France)

In Western Europe, the deformations related to the opening of the Bay of Biscay and the formation of the Pyrenean belt are well described in the southern part of the Aquitaine Basin, but little is known about the impact of these geodynamic events towards the Northern Aquitaine Platform. In this paper, we combine field observation with Unmanned Aerial Vehicle (UAV) imagery and calcite U-Pb geochronology to determine precisely the tectonic evolution in the Vendée Coastal domain. We evidence two main tectonic events: (1) At the transition between the Late Jurassic to Early Cretaceous, WNW-ESE striking normal faults formed horsts and grabens at the onset of the opening of the Bay of Biscay. The reactivation of Variscan faults during this tectonic event is consistent with oblique extension. This event triggered ascending fluid flows that mix with Basin fluids responsible for barite-pyrite-quartz mineralizations near the unconformity. (2) During the Late Cretaceous, fractures, wide-open folds, veins, and joints are consistent with the N-S shortening direction during the earliest stages of the Pyrenenan compression. In both cases, the Northern Aquitaine Platform records the early stages of the main regional tectonic events in a far-field position. In the northern Aquitaine Basin, as in many other places in Europe, the tectonic study of sedimentary platforms located far from the plate boundaries provides new constraints on the early diffuse deformation process that predate the main tectonic phases.

New 3D fault model for eastern Flanders (Belgium) providing insights on the major deformation phases in the region since the late Paleozoic

A new 3D fault model was created for the Upper Paleozoic to Cenozoic subsurface in eastern Flanders (Belgium). The model was based on the integration of 2D seismic interpretations, borehole and gravimetric data, as well as coal mining and topographic maps. Four major tectonic phases, taking place during the latest Paleozoic, Jurassic, Late Cretaceous and Cenozoic, shaped the fault network. The latest Paleozoic phase was transpressional and expressed by local folding of the Carboniferous strata underneath the base Permian unconformity. The largest anticlines were asymmetric, with amplitudes of up to 500 m and SSW-NNE oriented axal planes. The subsequent Jurassic phase caused normal faulting across the area, resulting in the development of the northeast-dipping, western border fault systems of the Campine Basin and Roer Valley Graben. Fault strikes were predominantly WNW-ESE to NNW-SSE. Both fault directions were most likely inherited from early Carboniferous and older tectonic phases. Jurassic fault reactivation explains the activity along fault populations with different orientations as well as the linkage of these faults into long (>10 km) systems, despite displaying generally relatively small vertical throws (<500 m). Soft-linked boundaries (accommodation zones) between Jurassic fault domains are located on top of the largest latest Paleozoic transpressional anticlines.The Late Cretaceous major tectonic phase was compressional and involved inversion of the Roer Valley Graben with subsequent subsidence and carbonate deposition in the flanking Campine Block.During the Cenozoic extensional phase, most normal faults that developed were rooted in Jurassic faults and therefore displayed similar WNW-ESE to NNW-SSE strikes. Cenozoic extension was, however, weaker than Jurassic extension; Cenozoic fault numbers, lengths and vertical throws were smaller than during the Jurassic phase. Also during the Cenozoic phase, faulting was more localized onto the pre-existing Roer Valley Graben border fault system compared to the more diffuse Jurassic faulting. The Cenozoic faults were generally planar, whereas some of its Jurassic roots near and in the border fault system of the Roer Valley Graben were listric.

Meta‐analysis of the long‐term stratigraphic evolution of rifted margin basins: The GeoDyNamical Analysis approach applied to the South Atlantic Ocean

AbstractModels of the formation of rifted margins have significantly evolved over the last decades by identifying new styles of crustal thinning and magmatic production. However, the expression of these different processes in the depositional environments of the overlying basins remains to be determined. Using only published data, we integrated the sedimentary evolution of 21 basins of the Equatorial, Central and South segments of the South Atlantic that record various styles of crustal thinning and magmatic production. To compare these basins that underwent rifting at different times, we developed a new type of analysis allowing to evaluate statistically the (dis)similarities in depositional environment trends by normalizing them to the tectonic phases of the basin (syn‐rift, transition and post‐rift) rather than the stratigraphic or absolute ages: The GeoDyNamical Analysis. We show that the timing of the long‐term retrograding mega‐sequence driven by lithosphere thinning depends on the deformation style and magma production. Along oblique margins of the Equatorial Segment, deepening initiated during syn‐rift because their narrow crustal thinning style favours rapid tectonic subsidence surpassing sediment supply. Along wide margins of the Central Segment, deepening is initiated later, at the end of the transition phase, because depth‐dependent thinning favours slow tectonic subsidence and late break‐up. Along magma‐rich margins of the South Segment, deepening is initiated during the transition phase, after volcanics stopped filling accommodation created by subsidence. In the Central Segment, evaporites accumulated during the second half of the transition phase, when crustal thinning ceased in the proximal margin and migrated to its distal part. Immediately before and during evaporites accumulation, sediments recorded continental and coastal depositional environments resulting from the limited thermal subsidence in the proximal margin domain. Evaporite deposition lasted until the initiation of retrograding mega‐sequence, at the onset of the post‐rift phase and the end of crustal thinning in the distal margin.

New Insights into the Genetic Mechanism of the Miocene Mounded Stratigraphy in the Qiongdongnan Basin, Northern South China Sea

The origin of deep-water mounds has been a topic of debate in recent years. In this study, newly collected seismic data were employed to characterize the mounds within the Meishan Formation in the Qiongdongnan Basin and a novel model was proposed. The result showed that pervasive mounds and ‘V’-shaped troughs were alternately distributed at the top of the Meishan Formation. They appeared as elongated ridges flanked by similarly elongated gullies, with the trending parallel with the strike of the basinward slope. The mounded features were considered to be formed in response to the tectonically induced seabed deformation. The differential subsidence steepened the slope that was equivalent to the top of the Meishan Formation (ca. 10.5 Ma), which offered sufficient driving forces triggering the slope’s instability. Correspondingly, the uppermost deposits glided along a bedding-parallel detachment surface, creating a number of listric detachment faults that ceased downward to this surface. The uppermost layer was cut into a range of tilted fault blocks with tops constituting a seemingly mounded topography. Some of the downfaulted troughs between mounds steered the gravity flows and were filled by sand-rich lithologies. The differential subsidence played a decisive role in the formation of a mounded stratigraphy, which in turn acted as clues to the important tectonic phase since the late Miocene.

Neo-Tectonism and Quantitative Morphotectonic Analysis of Roste Valley at Imbricated-Suture Zones, Kurdistan Region, Iraq

The morphotectonic analysis was done of the Roste valley, within the Imbricated and Suture zone of the Zagros Fold,Thrust Belt. The formations of the Imbricate Zone are of Jurassic and Cretaceous ages and the Suture Zone is covered by Zagros nappes of the Tertiary period. The Zagros Fold-Thrust Belt passes through several stages and tectonic phases. During the last stage of the Zagros Fold-Thrust Belt development from the Savian to Valahian and Pasadenian tectonic phases, the study area is influenced by active tectonic activity which is reflected by geomorphic properties in each subbasin. The migration of the Roste stream across oblique fault leaves 7 levels of the river terraces which are also signs of Neotectonics. The study area is divided into 18 subbasins for the morphotectonic analysis through applying geomorphic indices (HI, SL, Vf, Af, Smf, and Bs) and accordingly the index of relative active tectonics was indicted. The morphotectonic study reveals that the index of relative active tectonics is higher in the Suture Zone than in the Imbricated Zone. The index of relative active tectonics of the Suture Zone’s subbasins ranges from high to very high neotectonics activity (1.67-1.17), whereas of the Imbricate Zone’s subbasins ranges from medium to high active tectonic activity (2.33-1.67). The results are related to morphotectonic indices that show the balance between the tectonic and erosion process.

Automatic Zonation and Correlation of Well Logs for a Tectono-Sedimentary Interpretation in the Continental Siliciclastic Basin of Duero River (Iberian Peninsula)

Abstract A procedure to automatically correlate well logs measured in boreholes that are located in continental siliciclastic basins by using two different methods is shown. The first method is applied to the parametric layers that were determined in each borehole starting from the values of their geophysical parameters and consists of correlating, by cross-association, the columns formed by these layers. The second method consists of cross-correlating the geophysical stretches or units, which are established as sets of layers with similar characteristics that are sufficiently different from the average values in the adjacent stretches. The evaluation of the correlation results requires showing the criteria that are used for determining the parametric layers that are obtained from the well logs, the result of which is called segmentation in this study. This evaluation also requires to show the techniques that are used to determine the geophysical stretches by a process that is called stretching in this study. The reason for using different correlation methods is that cross-association of layers provides high resolution but relatively smaller spatial extent, whereas cross-correlations of geophysical stretches provide higher spatial extent but lower resolution. Thus, the cross-association results have been used both to assess the correlations in boreholes that are relatively close (distances&amp;lt;10 km) and to support the establishment of the stretch correlation criteria. The developed methodology is applied to a set of boreholes located in the Duero Basin (Spain). From the results obtained, an evaluation of the correlations with respect to the distances between boreholes was carried out. Furthermore, it is shown that the correlations between geophysical stretches enable identifying the correspondences between these and the tectono-sedimentary sequences (activation-relaxation of a tectonic phase) that are established in the literature.

Neogene-Quaternary evolution of the La Baja Guajira basin, Colombia: Burial and thermal history with implications on petroleum systems

The La Baja Guajira Basin is South America's northernmost part that extends from onshore Colombia into the Caribbean Sea and represents an important gas-producing region in Colombia. The dataset used in this study consists of twenty-four (24) regional 2D seismic-reflection lines integrated with information from nine (9) boreholes across the basin. We present seismic interpretations of key stratigraphic and structural features constrained by 1D basin modeling. This allows us to describe the Neogene-Quaternary evolution of the basin, and understand the possible implications for the hydrocarbon potential.We have interpreted eight (8) seismic units within the La Baja Guajira Basin (acoustic basement to U7) affected by three fault groups: 1) NW-SE-striking basement normal faults, 2) inverted normal faults, and 3) strike-slip faults. Considering the evidence, we propose four tectonic phases along the basin's evolution. The basement was affected by normal faulting as the result of extensional tectonics prior to the deposition of the sedimentary infill (Paleogene?). Another extensional interval occurred during the Early Miocene, triggering a moderate accommodation within the proximal area. Subsequently, extension migrated westwards resulting in the formation of the main La Baja Guajira Basin depocenter. In the Middle Miocene (post-extension), sedimentation was controlled by exhumation pulses in adjacent areas to the basin, which resulted in significant sediment input contemporaneous with rapid tectonic subsidence. Yet, local inversion of NW-SE-oriented basement-rooted faults affected today's offshore domain until the Late Miocene. This inversion can be associated with regional compressive deformation linked to the activity of the Oca and Cuiza faults. A second episode of rapid tectonic subsidence happened in the Early Pliocene. In the south of the basin, rocks were subjected to maximum burial and highest temperatures in recent times, conditions that might lead to hydrocarbon generation. The high Neogene to recent sedimentation rates calculated for the La Baja Guajira Basin support microbial gas generation; structural reactivation in this time supported trap formation, particularly in the offshore parts of the basin.

The effect of tectonic subsidence on the evolution of depocenters and development of the Mundaú sub-basin, Brazilian Equatorial margin

Located on the Brazilian Equatorial Margin, the Mundaú Sub-Basin is the only offshore hydrocarbon-producing region of the Ceará Basin. The origin and evolution of the Mundaú Sub-basin are a consequence of the rupture of the Pangea supercontinent during the Early Cretaceous, which led to the opening and development of the Equatorial Atlantic Ocean. This area has been considered a new exploration frontier, promoting research to be developed in recent years. However, the interactions between transtensive events and spatial-temporal distributions of tectonic subsidence have been poorly studied. To cover this gap, fifty-seven wells and approximately 5800 km of 2D seismic lines were analyzed to understand these events. From these data, stratigraphic and structural interpretations were performed throughout the sub-basin, enabling the construction of 43 pseudo-wells. Using descompactation of the wells and pseudo-wells using the backstripping method, it was possible to reconstruct seven tectonic phases for the Sub-Basin, which correspond to the rift sequence (RP01, RP02, and RP03), the transition sequence (BP01), and the drift sequence (DP01, DP02, and DP03). Four sets of faults of three zones of the three zones (WZ, CZ and EZ) proposed for the Mundaú Sub-Basin were also analyzed. The faults are distributed in two orthogonal families, formed in two distinct events. Older R and P faults, respectively trending NWW-SEE and NNESSW, formed during RP01 (first event). Younger R and P faults, respectively trending NNW-SSE and NEE-SWW, formed during RP02 (second event). Tectonic reconstruction revealed the diachronic formation of two depocenters, one in the West Zone (WZ) during RP01, and the other in the Central Zone (CZ) during RP02. Despite the intense tectonic activity in WZ and CZ, the East Zone (EZ) showed low subsidence rates and little development during the entire rift phase. In turn, BP01 showed faster subsidence rates when compared to RP03, indicating tectonic influence even during the breakup phase. Finally, the drift phase showed the lowest subsidence rates, spatially distributed in an opposite pattern to the rift phase. From these results, a rotation of the Principal Displacement Zone (PDZ) was identified, with initial parallel motion vectors, forming the WZ depocenter and generating the first fault family during RP01; after RP02, motion vectors were oblique, forming the second depocenter in CZ and generating the second fault family. Significant thermal control associated with magmatic events was identified during the drift phase. This study also describes the main structures formed along with the overlap of parallel and oblique PDZ displacement.

Rift-enhanced foredeep and contractional tectonics interplay in the outer Albanides

The Albanides thrust belt is associated with the ENE-ward subduction of the Adriatic lithosphere facing the Peri-Adriatic Basin, a foredeep filled with a Neogene-Quaternary sedimentary sequence more than 6 km thick. This basin segment is anomalously deep, compared to the adjacent foredeeps, and dominated by Neogene strata deposited at a rate of circa 0.3–0.4 mm/yr. Moreover, the Upper Miocene deposits of the Peri-Adriatic Basin lie on deeply eroded anticlines composed of Meso-Cenozoic carbonate units. This observation is in contrast with the expected constant steady-state fold uplift trend generally observed in orogens related to E-NE directed subductions. These observations suggest that following a Late Oligocene to Early-Middle Miocene contractional tectonic phase associated with subaerial erosion, the northern portion of the frontal zone of the outer Albanides accretionary prism was affected by strong subsidence during the Late Miocene. Evidence from field mapping combined with the integration of exploration wells and seismic reflection profiles indicate that this unexpected subsidence may be related to a Miocene extensional/transtensional tectonic phase. The actual anomalously high heat flow (>80 mW/m2) in the offshore depocenter of the Peri-Adriatic Basin also supports this interpretation.This extensional tectonic phase was unrelated to the subduction process, suggested by the obliquely orientation of the new basin with respect to the strike of the Albanides thrust belt, also partially superimposed on it. This Miocene event and the associated thermal pulse could have played a crucial role for the generation of hydrocarbons in the Outer Albanides. The tectonic interplay between this rifting episode and the usual foredeep flexural evolution may explain the peculiar evolution of the Outer Albanides and the associated anomalous foredeep. This basin can be defined as a rift-enhanced foredeep generated by two spatially co-existing, but independent tectonic processes, i.e., by the flexural loading exerted by the orogenic fold-and-thrust system and the rifting in the foreland itself.

Migration and localization of faulting near the intersection of the Dead Sea Fault and the Carmel−Gilboa−Faria Fault System

Crustal deformation and seismicity in the Levant region are mainly related to the plate-boundary Dead Sea Fault (DSF) and the intraplate Carmel−Gilboa−Faria Fault System (CGFS). The intersection between these two major fault systems is generally treated as a ∼35-km-wide deformation belt stretched between the Faria and Gilboa Faults. Here, we present spatial and temporal analysis of faulting near this intersection. Our analysis is based on new geological mapping, new high-resolution airborne light detection and ranging (LiDAR) data, and seismic reflection profiles and indicates northward migration and localization of the intersection over time since the early Miocene. We discovered and mapped outcrops of Miocene, Pliocene, and Pleistocene rock units as well as faults and reconstructed the evolution of deformation. Three main tectonic phases were identified in this area covering the following periods: the early−middle Miocene, the late Miocene−Pliocene, and the Quaternary. During the first phase, the DSF and the CGFS developed, and the CGFS faulted along a series of subparallel grabens and elongated NW−SE, between the southernmost Faria and the northernmost Gilboa faults, over a belt width of ∼35 km. During the second phase, deformation along the CGFS migrated northward and concentrated at an ∼6-km-wide zone in the northern Faria Anticline. During the third stage, small-scale northward migration and localization of the deformation to a width zone of ∼1−2 km at the southern boundary of the Beit She’an Valley occurred. Faults from the third phase reveal both sinistral and normal faulting. We propose that the currently active intersection between the DSF and the CGFS is located east of this localized deformation zone, near a right step of the DSF and the uplifted area of Tel Al-Qarn in the eastern Jordan Valley. We suggest that the northward migration and localization of this intersection are related to regional tectonic changes, spatial variations in the Sinai-Arabia Euler pole, and the localization of deformation along the DSF.

Palaeogeographic evolution of Zealandia: mid-Cretaceous to present

ABSTRACT We present a suite of 15 palaeogeographic maps illustrating the geological evolution of the entirety of Zealandia, from mid-Cretaceous to present, highlighting major tectonic phases, from initial Gondwana rifting through to development of the Neogene plate boundary. They illustrate palaeobathymetric and palaeofacies interpretations along with supporting geological datasets and a synthesis of regional tectonics. The maps are underpinned by a geologically-constrained and structurally-based rigid retro-deformation block model. This model, tied to the global plate circuit, is relatively simple for the main regions of Northern and Southern Zealandia, but breaks central Zealandia into numerous fault-bounded blocks, reflecting complex Neogene deformation associated with the modern plate boundary. Production of maps using GPlates and GIS allows for simple alteration or refinement of the block model and reconstruction of any geological dataset at any time. Reconstructions are within a palaeomagnetic reference frame, allowing assessment of palaeo-latitude, critical for palaeo-climatic and palaeo-biogeographic studies.

The sedimentology and depositional environments of the Bastians Dal and Muslingebjerg formations: evidence for the earliest phases of Jurassic rifting in North-East Greenland

The aim of this study is to elucidate the character of the earliest phases of Jurassic rifting in North-East Greenland. To achieve this, detailed sedimentological analysis and geological mapping were undertaken on the outcrops of central Kuhn Ø (74°53’55’’N,20°20’56”W). In this region the basement is overlain by the fluvial Bastians Dal Formation (Middle Jurassic) which is, in turn, overlain by the coal-bearing Muslingebjerg Formation. A maximum thickness of 140 m is calculated for the Bastians Dal Formation and mapping of stratal geometries demonstrates thinning to both the north and south, confirming that these deposits infill a palaeovalley. Predominantly south-westward palaeocurrent orientations are observed and likely reflect the orientation of the palaeovalley (NE–SW). The overlying Muslingebjerg Formation displays significant lateral variations in thickness as well as facies, thickening from a 5-m-thick coal seam in the north to 50 m in the south. Southern outcrops include two intervals of fine-grained sandstones displaying low-angle and trough cross-bedding some of which contain suggestions of tidal bundling. The arrangement of facies suggests that coal formation occurred in both fluvial- and shallow-marine (tidal?) environments. Coals are similar to those described elsewhere from the Muslingebjerg Formation and display subtle differences consistent with variable degrees of marine influence. Mapping demonstrates the presence of an NE–SW-oriented bounding fault in the south of the region into which the Muslingebjerg Formation thickens. This likely also controlled the orientation of the underlying NE–SW-aligned palaeovalley and is oblique to the proposed overall N–S orientation of faulting related to rifting through the Mid to Late Jurassic. Instead, these alignments resemble those that define pre-Jurassic phases of rifting and may therefore indicate a transitional phase of tectonism. Faulting on a similar alignment can be traced SW, cutting Lindeman Fjord and following the valleys east of the A. P. Olsen Land plateau.

Transitional shale quality and exploration potential: A case study from the Lower Carboniferous Jiusi Formation in northwest Weining, China

The organic-rich shale of the early Carboniferous Jiusi Formation in the Weining area, Southwestern China, has large geological gas reserves, making the Jiusi Formation another target after the Ordovician-Silurian marine shale in South China. The complex superposition of multi-stage tectonic phases since the Himalayan paroxysmal phase has induced a series of controversies in the sedimentology of the Jiui Formation, as only a few drillings were executed. In order to better understand the development potential of the shale associated with the Jiui Formation, five outcrops and a well (YS302) were studied, clarifying the sedimentary evolution of the formation, while two 2D seismic sections were used to analyze the regional structural styles. The result shows that the Jiusi Formation was significantly influenced by the synsedimentary extension of the northwestern margin of the Yadu-Ziyun-Luodian Fault, with the depositional center of the Jiusi Formation extending to well YS302 along a NW direction and asymmetrically thinning in a NE–SW direction. Fifteen lithofacies and three facies associations were identified, from tidal or delta settings to lagoon environments, finally turning into platform facies at the base of the Shangsi Formation. According to the geochemical analysis of 27 core samples and 37 outcrop samples, as well as the well YS302 logging interpretation result. The transitional Jiusi shale in the Weining area has a strong heterogeneity, with high total organic content (TOC) values being mostly provided by the surrounding coal seams. XRD analyses show that the minerals of the transitional shale are dominated by a high clay content (42 wt%). The content of water-sensitive minerals in Jiusi shale is also relatively high, with clay minerals dominated by an illite/smectite mixture (52.8%). When compared with the commercially developed Ordovician-Silurian marine shale, the Jiusi transitional shale shows relatively poor quality, related to dense bioturbation and terrestrial input affecting the preservation of organic matter. Therefore, the evaluation standard for marine shale is difficult to apply to the transitional Jiusi shale. The cumulative thickness of shale in YS302 worthy of shale gas development is nearly 100 m. Meanwhile, considering that the transitional shales are often interlayered with coal, the shale gas and coalbed methane can be developed together.

Cenozoic tectono-sedimentary evolution of the Upper Moulouya continental basins (Moroccan Atlas system): Insights from lithostratigraphy, structural analysis and paleostress reconstruction

The Upper Moulouya massif (UMM) is located at the junction between the Middle and the High Atlas mountain ranges where outcrop a segment of the Moroccan Variscan belt and its unconformably overlying Meso-Cenozoic cover. In this paper, we propose the Cenozoic tectono-sedimentary evolution of the continental series filling the intramontane basins of the UMM using a multidisciplinary approach with multiscale geological-structural and paleostress analyses. The lithostratigraphic study shows that these series correspond to Oligo-Neogene fluvio-lacustrine sequences, alluvial fans deposits, and alluvial outwash plains, associated with volcanic rocks. Structural and paleostress analyses provide a complex tectono-sedimentary evolution marked by the superposition of four tectonic phases with changes in paleostress orientations. These tectonic phases are consistent with strike-slip tectonic regimes associated with compressional, transpressional, transtensional and extensional episodes: (i) the first tectonic phase is characterized by NW-SE trending σ1 axis, and NE-SW trending σ3 axis, with NNW-SSE to N–S sinistral strike-slip faults, ENE-WSW to E-W dextral strike-slip faults, and NE-SW reverse faults cross cutting the Mesozoic and Oligo-Miocene series; (ii) the second tectonic phase is characterized by ENE-WSW to E-W σ1 axis, and NNW-SSE to N–S σ3 axis where the subsidence of Pliocene lake basins is probably controlled by ENE-WSW to E-W extensional faults and NE-SW transtensional faults; (iii) the third phase is marked by NNE-SSW to NE-SW trending σ1 axis, and WNW-ESE to NW-SE trending σ3 axis, with submeridian dextral strike-slip faults, subequatorial sinistral strike-slip faults, NE-SW normal faults, and NW-SE reverse faults; (iv) the last tectonic phase is characterized by NNW-SSE to N–S σ1 axis, and ENE-WSW to E-W σ3 axis responsible for subequatorial reverse faults, submeridian normal faults, NE-SW sinistral strike-slip faults, and NW-SE dextral strike-slip faults.

Structural lineament mapping of Central-Eastern high atlas, Morocco, using ASAR/Envisat and SAR/sentinel 1B data

The Central-Eastern part of the High Atlas is dominated by carbonate of Mesozoic age which is affected by the Alpine Orogeny. The deformation manifest in area by different geological structures. The analysis of these later lead to their classification in different category for understanding the geodynamic of the area. This study focuses to map structural lineaments in the Central-Eastern High Atlas using two types of Radar data: Synthetic Aperture Radar (SAR)/Sentinel 1B with polarization (VV + VH) and Advanced Synthetic Aperture Radar (ASAR)/Envisat with polarization (VV + HH). This research aims to demonstrate the utility of Radar data for extracting structural lineaments in carbonate deposits. In this work, two techniques of processing data are used: First, the automatic extraction technique, we are employing the Algorithm Line Module of PCI Geomatica program, after the enhancement of images by applying the mean Co-occurrence filter. Second, the manual extraction technique, it was accomplished by applying directional filters with four directions (N00°, N45°, N90° and N135°) in order to highlight linear structures, then trace the detected lineaments. The synthetic maps of structural lineaments are developed by the two techniques. They are validated by using the lithologic maps extracted from Landsat Operational Land Imager (OLI), the previous researches in the study area, shaded relief extracted from ASTER Global Digital Elevation Model (GDEM), and field investigation data. The results present a good correlation between the direction of structural lineaments extracted from the satellite images and the field measurements. Therefore, the directions of lineaments extracted are N-S and E-W, NE-SW and NW-SE, especially the abundance of the direction N-S. This last one is perpendicular with the major faults. The density of structural lineaments in the study area is controlled particularly by the lithological nature and dynamic evolution, where the concentration is high in the Liassic carbonates. The geostatistical and spatial distribution of the structural lineaments led us to conclude that different tectonic factors are responsible for the distribution of lineaments in the surface of the study area. The comparison of two types of radar data shows that Envisat data is more efficient in the manual extraction than Sentinel 1B data. However, Sentinel 1B data is more efficient in the automatic extraction than Envisat data. This work identifies several families of structural lineaments which can be determined the tectonic phases of the Alpine orogeny affected the intracontinental Atlas basin.

Geodynamic framework of the magmatic activity of Cretaceous Léré basin (Southwestern Chad, Central Africa)

Numerous 5 to 20 m-wide dolerite dykes crosscut vertically to sub-vertically basement granitoids around and within the Cretaceous Léré basin, SW Chad (Central Africa). They extend along strike on several hundred meters length. Léré dolerites exhibit various textures, from classical doleritic texture to sub-ophitic via ophitic and intersertal textures. They are composed of euhedral and subhedral crystals of andesine and labradorite, anorthoclase, augite, olivine, ilmenite and Ti-magnetite. Calcite and amphibole are present. Estimated crystallization temperatures are between 1050 and 1105 ± 50 °C. Occurrence of dyke swarms in Léré basin is controlled by Pan-African strike-slip faults created during an extensional tectonic phase during Paleozoic to Early Mesozoic. These lavas, analyzed with ICP-MS and ICP-AES, are basalt, trachybasalt and basaltic trachyandesite with some continental tholeiite affinity. Dolerites of Léré basin have evolved by limited fractional crystallization differentiation, accompanying by minor assimilation process. Three groups of rocks are identified (according to Y/Nb ratios), linked to different mantle sources which have intermediate compositions between E-MORB and OIB.

3D digital outcrop model-based analysis of fracture network along the seismogenic Mt. Vettore Fault System (Central Italy): the importance of inherited fractures

The Mt. Vettore area is located in the Central Apennines (Italy), a region characterized by intense seismic activity that has recorded multiple moderate-to-high magnitude seismic sequences. The seismic activity is due to the presence of normal fault systems, among which is the Mt. Vettore Fault System (VFS), which was last activated during the 2016-17 Central Italy seismic sequence.. Moreover, the region has experienced three major tectonic phases over geological history, thus it is important to unravel their contribution to the current fracture network. Based on the integration of field observation with Unmanned Aerial Vehicle - Digital Photogrammetry data, we aim to analyze the fracture network on eight different outcrops located at different structural positions with respect to VFZ. Results show that the Late Miocene−Early Pliocene compressional phase deeply affected the present-day fracture pattern, which is especially related to the evolution of the Mt. Sibillini regional thrust and its related anticline. The present-day Quaternary extensional phase, and the associated normal faults, mostly reactivate some of the pre-existing fracture sets.

Late Famatinian (440–410 Ma) overprint of Grenvillian metamorphism in Grt‐St schists from the Sierra de Maz (Argentina): Phase equilibrium modelling, geochronology, and tectonic significance

AbstractThe analysis of major and trace elements in zoned minerals is useful for deciphering parts of the tectonothermal evolution of polymetamorphic tarrain. We applied this approach to the Maz Metasedimentary Series in Western Sierras Pampeanas of Argentina, where polymetamorphism resulted in the overprinting of a Grenvillian basement (the Maz Complex) during the pervasive Rinconada tectonic phase of the Famatinian orogeny. The older metamorphism (M1) is assigned to the youngest Grenvillian metamorphic event recognized in this basement at c. 1035 Ma, whereas the Rinconada metamorphism (M2) was Silurian to early Devonian, essentially between 440 and 410 Ma. The latter resulted from oceanward migration of the orogenic front relative to earlier late Cambrian to Ordovician (490–470 Ma) tectonic phases of the Famatinian orogeny. The M1 and M2 metamorphic events have been recognized in a staurolite‐garnet schist from the Maz Metasedimentary Series. Most metamorphic minerals from this rock were formed during the M2 event which was of the Barrovian type (±kyanite). Part of the metamorphic P–T evolution is recorded in the complex compositional zoning of garnet porphyroblasts. Three types of garnet were identified based on texture and chemistry, including trace elements (REEs). Phase equilibrium analysis, compositional isopleth, and multi‐equilibrium thermobarometry were applied in order to establish the P–T history. M1 is represented by preservation of Grt1 ± Kfs ± Sil, with peak P–T condition of 790°C and 5.2 kbar, that is, granulite facies. This early metamorphic event was related to a deformational D1 episode represented by a relict S1 foliation. The latter is preserved as aligned inclusions in staurolite porphyroblasts and as relics of an older crenulated foliation in microlithons from the matrix. M2 followed a clockwise P–T path with three mineral growth stages. The earliest occurred at ~585°C and ~8.7 kbar and is represented by Grt2 ± St1 ± Bt1 + Qz. Grt2 was partially coeval with growth of St1, which was stable at ~625°C and 9.0 kbar. Grt2 + St1 are syn‐kinematic to the main S2 foliation (D2 episode). Subsequently, decompression (D3) started as St2 (+ Bt2 + Ms1 + Qz + Pl) crystallized, and garnet was partially consumed at ~612–620°C and ~7.3–7.7 kbar. St3 + Grt3 crystallized at ~608°C and ~6.8 kbar at the end of D3. Increasing P–T conditions during the earlier M2 growth stage suggest burial of the Maz Metasedimentary Series, probably linked to tectonic thickening by underthrusting (tectonic phase D2). Peak metamorphic conditions were attained during thrust stacking. The tectonic phase (D2) was responsible for the main S2 foliation, which was penetrative at all scales. The nearly isothermal decompression path is compatible with exhumation, probably resulting from extension along discrete shear zones (tectonic phase D3) that produced a mylonitic foliation S3.

Mid-Miocene to recent tectonic evolution of the Punta Stilo Swell (Calabrian Arc, southern Italy): An effect of Calabrian Arc migration

The development of Punta Stilo Swell (PSS), a submerged lobate-shaped promontory located in the Crotone-Spartivento Basin, is inferred to be closely linked to the Calabrian Arc kinematics since mid-Miocene onward. The latter consists of an alternation between long-term phases of subsidence related to forward migration of the Calabrian accretionary complex, and short-term compressional-transpressional phases, characterized by episodes of uplift and formation of regional unconformities, in a context of stopping or slowdown of Calabrian accretionary complex migration. In particular, the study area is supposed to have respectively experienced phases of compressional and extensional tectonics during late Messinian and early Pliocene, which likely produced a reactivation of inherited compressional and extensional structures. Late Pliocene/Pleistocene transtensional tectonics is documented along the offshore extension of the Soverato-Lamezia Fault Zone (SLFZ), in the N sector of the PSS. The resulting physiographic modifications associated with such compressional, extensional and transtensional tectonics is believed to have controlled the accumulation of the thick Plio-Pleistocene succession of the PSS. The northern continental slope is inferred to be the result of late Pliocene/Pleistocene transtensional tectonics occurred along the SLFZ, whereas the shelf break is considered the result of an early Pliocene extensional tectonics. The considerable steepness (>10°) of the southern and eastern continental slope of the PSS is associated with the late Messinian compressional tectonic activity and is marked by the occurrence of slope failure-associated events.