NE-SW Orientation Research Articles

Gravity study of the Douala sub-basin (Cameroon) using Euler 3D deconvolution, source edge detection (SED) and special function analysis

Gravity data over an extending section of the north west portion of the Douala sedimentary sub-basin have been processed for both shallow and deep geologic contacts. Qualitative analysis, Euler 3D deconvolution, source edge detection (SED) and analysis of some special functions (horizontal gradient magnitude, analytic signal and the local wavenumber) have been carried out. One major peak and two minor peaks were highlighted on the anomaly maps as well as three major zones of anomaly which move from a very high positive anomaly zone in the center through an average positive zone to an average negative zone. Results of Euler 3D deconvolution and SED emphasized the presence of the underlying intrusive body to depths greater than 4 km in this study area and also suggested other geologic contacts above it. Solutions of special function analysis indicated that these geological contacts consist of some major faults with N–S, NE–SW, NW–SE and E–W orientations as well as some minor faults with NW–SE, E–W and NE–SW orientations having dip directions generally pointing away from the center of the study area. The faults and contacts were shown to be buried at a minimum depth of about 2 km with the majority having a structural index value in the range − 0.8 to 0.

Morphology of fore-reef slopes and terraces, Takapoto Atoll (Tuamotu Archipelago, French Polynesia, central Pacific): The tectonic, sea-level and coral-growth control

A dataset of 41 bathymetric profiles detected by satelline imagery and echo-sounding to a maximum depth of 38 m along the fore-reef slopes of Takapoto Atoll (Tuamotu Plateau, French Polynesia, central Pacific) were qualitatively and quantitatively analyzed in order to identify the main geomorphological features. In addition, scuba-diving investigations from a selected site resulted in defining coral composition and cover rate. Six distinct fore-reef sectors were morphologically differentiated on the basis of seaward extension and slope gradient. Only the north end, and a restricted area of the mid-south-east side extend seawards over an average distance of 150 m, with a relatively low gradient (23°–38°). Most of the outer-slope areas are narrow (<100 m on average) and steep (average slope equals to 45° to up to 70°). Geomorphic features include spur-and-groove systems, sub-horizontal to gently dipping terraces (23–45 m wide) ending seawards in vertical steps (<10 m high) and drop-offs (>10 m high), outer-reef crest-like reliefs (0.5 m–1.5 m high), pinnacles (2 m–17 m high), coral heads (<2 m high), trenchs and concave scars. The recognized seven terrace levels occur at the respective depths of about −5 m, −10 m, −15 m, −20 m, −24 m, −30.5 m and −38 m. Based on comparison with subsurface chronostratigraphy of drilled reef sequences from some other Pacific atolls, the terraces are interpreted as remnants of reef tracts formed during Pleistocene interglacial, high sea-stands, respectively during MIS substage 5e (about −125 ka), MIS substages 7a (about −195 ka), 7c (about −210 ka), 7e (about −240 ka) and 9e (−330 ka). After depth correction of ground lowering during periods of emergence and subsidence effects, terrace elevations were expected to indicate eustatic sea-level positions at each identified high sea-stand, at approximately 7 m (MIS 5e) and 2.2 m (MIS 7a) above present sea level and 9.5 m (MIS 7c), 11 m (MIS 7e) and 8.6 m (MIS 9e) below present sea level. During the post-glacial sea-level rise, from about 9.5 ky, the studied portions of fore-reef slopes were re-flooded. It was assumed that coralgal deposits in the form of thin veneers, coral heads, outer-reef crest-like reliefs and pinnacles have simply overlapped pre-existing structures. Locally, the fore-reef zones are carved by trenchs, i.e. incipient detachment faults, and scars, i.e. imprints of former landslides. Similarly, some drop-offs may be regarded as fault walls. The prevailing direction of faulting–collapsing surfaces is consistent with the SW–NE orientation of the main axis of the atoll and submarine ridges rising up from the north-western floor of the Tuamotu Plateau. Analysis of the composition and distribution of coral communities to −30 m depth revealed high, downslope-increasing coral coverage (24% to 67% on average) and the sharp replacement of robust-encrusting Pocillopora by sub-massive to plate-like Porites from depths greater than −10 m. Significant inter-regional differences were detected with atolls in west Pacific, probably due to local ecological constraints.

An Ordovician carbonate reservoir in strike-slip structures producing from fault-associated fracture systems, 3D seismic region of Northern Shun 8 block (Tarim Basin)

The fault system in the 3D seismic region of northern Shun 8 block (Tarim Basin) is mainly composed of NNW-SSE and NE-SW orientation faults. The No.7 fault zone in the NNW-SSE orientation extends linearly on the plane. It partially exhibits segmentation characteristics. According to the fault plane spread feature of the partial extensional section, the No.7 fault zone is the left-order left-lateral strike-slip fault. The SHB7 well on the No. 7 fault zone was drilled to the vicinity of the extensional section. The successive strike-slip stress field generated multiple sets of fractures in different orientations. The integration of 3D seismic, image logs and production logging analysis reveals the clustering of productive fractures around the fault zone. These open to semi-open production fractures are inconsistent with the tectonic stress state of the present day acting in this part of the Tarim Basin, indicating that the present-day tectonic play no role in production rate. The Build-up tests show three main types of responses: (1) A-type displays a radial flow and there is no test boundary for a longer period of time, (2) B-type displaying a short radial flow period followed by bilinear flow and (3) C-type is only related to bilinear flow. These three flow responses are linked with structural models of fault associated production fractures. Analysis of geological and production data indicates that the spatial distribution of productive fracture zones is primarily controlled by open fractures. A better understanding of the production system allows us to optimize the drilling location and select the appropriate well production zonees.

Structure and emplacement of the Coastal Deccan tholeiitic dyke swarm in Goa, on the western Indian rifted margin

Mafic dyke swarms, when controlled by a regional stress field, are emplaced perpendicular to the minimum principal compressive stress direction. However, mafic dyke swarms may also exploit pre-existing structural fabric in their host rocks. Distinguishing between the two scenarios is important for correct geodynamic understanding of magmatic events. Continental flood basalt provinces such as the Deccan Traps of India represent huge fissure eruptions produced by swarms of mafic dykes. The Coastal dyke swarm of the Deccan, along the western Indian rifted margin, is one of its three major dyke swarms. We present a field study of the Goa dykes, part of the Coastal swarm. The dykes are typical dolerites and basalts exposed in Proterozoic-age basement; lava flows which these dykes may have once fed have been stripped away by erosion, though exposed in the Western Ghats escarpment ~ 100 km to the east. The Goa dyke swarm contains 60 dykes, some of which form larger multiple-injection dykes. The dykes are short compared to typical (kilometers or tens of kilometers long) dykes in flood basalt provinces such as the Deccan or Iceland, and range in length from ~ 15 to ~ 220 m and in thickness from 3 cm to 20 m. Most dykes are vertical and the others dip steeply in various directions. Their structural attributes and internal features (such as vesicular zones and columnar jointing) provide clues to the processes of magma flow and solidification in the dykes. Field measurements yield an average crustal dilation of 8% due to dyke emplacement. Calculations of magmatic overpressures and magma chamber depths generally yield unrealistic values owing to the low aspect ratios of the dykes. Based on comparisons between the dyke trends and the host rock joint trends, we consider that a few of the Goa dykes were emplaced along pre-existing fractures, but the orientations of the great majority of the dykes reflect contemporaneous stress fields. Based on crosscutting relationships, we infer that the regional minimum horizontal compressive stress (σ3) changed over time from a ~E-W orientation to a ~NE-SW orientation and finally to a ~N-S direction.

Biogeostatistics confirm: Even a low total number of red wood ant nests provide new information on tectonics in the East Carpathian Orogen (Romania)

Recent statistical analyses revealed that the spatial distribution of nests of red wood ants (RWA; Formica rufa-group) and actively degassing fault zone are strongly correlated. We now applied the modified Hough Transform (mHT) and Iterative Mode Detection (IMD) to RWA nest positions in four study areas of the Eastern Carpathian Orogen. The aim of this analysis was (1) to evaluate relationships between spatial distribution of RWA nests and complex tectonic stress regimes in the Eastern Carpathian Orogen, (2) to test if this procedure is also applicable even when only a low total number of RWA nests is available, and (3) to further verify the validity of this statistic approach. By applying a double-blind study, we minimized bias by researchers’ preconceptions. Since irregular shapes of the study areas were found to strongly influence the findings of distribution patterns, all subsequent analyses were carried out for circular areas. Statistical results substantiated our hypothesis that RWA nest distributions clearly show very pronounced directions even in complex tectonic environments such as the Eastern Carpathian Orogen. Dominant NW-SE directions (scattering between 120° and 150°) are corresponding to the 1st order regional stress field in the East Carpathians. Additionally, our analyses revealed the 2nd order stress field in NE-SW orientation. Furthermore, directions of re-activated shear systems, e.g. from Late Miocene and Pliocene that had been modified by overprinting due to changes of the main stress field, could be identified. For the Moldavian and East European Platform, which are characterized by thick sediment cover, our analyses could significantly contribute to otherwise concealed tectonics. Furthermore, the mode of some faults identified in previous tectonic studies could be complemented and specified and assigned to the corresponding tectonic regime. Our study thus confirms the validity of our statistic approach even when the total number of RWA nests is low.

Unconventional hydrocarbon prospects in Ordovician and Silurian mudrocks of the East European Craton (Poland): Insight from three-dimensional modelling of total organic carbon and thermal maturity

Three-dimensional, structural and parametric numerical modelling was applied to unravel the unconventional hydrocarbon potential of a W-dipping, Lower Palaeozoic mudrock succession, which subcrops for some 700 km in the Baltic, Podlasie and Lublin basins across the SW margin of East European Craton in Poland. Input data comprised structural and thickness maps of Ordovician and Silurian strata and the results of thermal maturity (mean vitrinite-equivalent reflectance, % Ro) and total organic carbon (TOC, % wt.) modelling. A new, spatial interpretation of vitrinite-reflectance variability indicates that the regional, W-increasing thermal maturity pattern breaks into a series of domains, bounded by abrupt maturity variations. In total, 14 tectono-thermal domains were recognised and their boundaries traced to known and inferred faults, mostly of NW‒SE and NE‒SW orientations. On the basis of a combination of thermal maturity and total organic carbon levels (0.6% &gt; Ro&lt;2.4%, and TOC &gt;1.5% wt.), good-quality, unconventional reservoirs can be expected in the Sasino Formation (Caradoc) and Jantar Formation (early Llandovery) in the central and western Baltic Basin. The Jantar Formation also is likely to be prospective in the western Podlasie Basin. Marginal-quality reservoirs may occur in the Sasino and Jantar formations within the Podlasie and Lublin basins and in the Pasłęk Formation (late Llandovery) across all basins. Poorto moderate-quality, unconventional reservoirs could be present in the Pelplin Formation (Wenlock) in the Lublin and southern Podlasie basins. In spite of a considerable hydrocarbon loss during multiphase basin inversion, the Ordovician and Silurian mudrocks still contain huge quantities of dispersed gas. Successful exploitation of it would require the adoption of advanced fracking methods.

2.5D Modelling of Aeromagnetic Data and their Mining Implications over the Ngaoundere Area (Adamawa Province, Cameroon)

This study is based on the analysis and interpretation of aeromagnetic data using version 8.4 of the Geosoft Oasis Montaj Software, to map the subsurface or deep geological structures that affected the geological formations of the Ngaoundere area. The use of the standard aeromagnetic methods made it possible to draw up the maps of the residual magnetic field reduced to the equator (RTE), the horizontal gradient (HG), the analytical signal (AS) and that of the Euler solutions (ED) to find the main magnetic facies corresponding to these structures. The geological formations of the studied area thus appear to be intensely fractured by a NE-SW (N45°E) and ENE-WSW (N70°E) main orientation fault system, the depth of which has been estimated by combining the three-analytical methods HG, AS and ED. Advanced magmatic map analysis revealed dikes associated with vertical faults in the studied area. The development of an interpretative geological map taking into account the basic geology, the deep faults, the identified dikes and the mineralization index made it possible to extract a correlation between geological structures and mineralization of the studied area. The 2.5D modelling of two magnetic profiles plotted on the reduced residual map at the equator was performed to approximate the geometry and depth of the dikes sector, which are potential sources of mineralization here.

Geologia, Petrologia e Evolução Magmática das Rochas Alcalinas Félsicas da Ilha de Vitória, São Paulo, Brasil

This paper presents geological, petrographic, geochemical characteristics and radiometric ages for the felsic alkaline rocks of the Vitoria Island Intrusive Complex, Sao Paulo State, Brazil, and discusses its geochemical evolutionary processes. This intrusive body is about 3 km in diameter and the emerged island areas correspond to its northeastern border. The main intrusion is constituted by nepheline syenite at the central zone, nepheline-bearing syenite at the outer zone, syenite at the border, and quartz syenite at the contact zone with alkali feldspar represented by orthoclase. Clinopyroxene vary from hedenbergite, soda-augite to aegirine-augite, and some crystals have resorption shape and amphibole reaction rim. They are intruded by phonolite, trachyte and lamprophyre dykes. Based on the intrusion relation, the dykes are subdivided into two generations: the first one encompass a radial system and the second a parallel system with NE-SW orientation and sinistral displacement. The alkaline rocks vary from silica undersaturated to oversaturated, show peralkaline to peraluminous compositions and belong to the potassic series. The K-Ar ages for amphibole of the nepheline-bearing syenite and syenite are 89.58 ± 3.18 Ma and 84.35 ± 3.92 Ma, respectively. The rocks are strongly fractionated with high differentiation index (DI) of 88.15 in average, indicating mafic minerals fractionation. K 2 O/(K 2 O+Na 2 O) ratios are low, in average 0.51, in accordance to crystallization of pseudo leucite and potassic feldspar the last observed in thin sections.

Impact of pre-existing fabrics and multi-phase oblique extension on Cenozoic fault patterns, Wichianburi sub-basin of the Phetchabun rift, Thailand

Cenozoic fault patterns associated with rift development in the Wichianburi Sub-Basin show a wide range of controls at different scales including influence by the margin of a Permian basin, and NW-SE to NE-SW trending Triassic folds and faults. During the Late Oligocene-Early Miocene phase 1 normal faults (NNW-SSE to NNE-SSW trends) developed in response to ∼ E-W extension. Faults predominantly trend NNW-SSE to N-S during this phase. During the Middle Miocene-Pliocene the extension direction rotated to a more NW-SE orientation. The old fault orientations were reactivated, and new faults also developed with predominantly NNE-SSW to NE-SW orientations. Many new faults nucleated within the syn-rift section and were not directly influenced by pre-existing fabrics in the pre-rift section. Four types of phase 2 fault can be identified: Type 1 = newly formed faults that strike sub-orthogonal to the phase 2 extension direction, Type 2 = newly formed faults that strike between the phase 1 fault orientations and Type 1 faults. Type 3 = newly formed faults that strike at angles greater than 90° with respect to the phase 2 extension direction. Type 4 = reactivated phase 1 faults. Local stress rotations, and fault linkage rotations explain many of the Type 2 and 3 fault orientations. The stress rotation in the Middle Miocene is observed in other basins in Central Thailand, notably the Suphan Buri and Phitsanulok Basins, where a range of fault patterns are produced by the effects of inherited fabrics plus multi-phase rifting.

Strain monitoring of active faults in the central Apennines (Italy) during the period 2002–2017

We present the results of 3-D monitoring of strain along active faults outcropping in the central Apennines, where recent and historical strong earthquakes occurred, using TM-71 extensometers during the period 2002–2017. We discuss the fault slip development as well as kinematics particularly in the light of local recent seismicity. The recorded fault slip corresponds to the minimum and maximum principal stress with a SW-NE orientation and slightly dipping to SW. Moreover, the detected fault slip is non-linear and affected by remarkable transient periods of acceleration, which lasted up to several months. The recorded accelerations were induced by alternation of extensional, reverse and horizontal displacement due to switching extensional and compressional stress/strain state and coincide with periods of major seismic events that recently affected the central Apennines. This phenomenon is being investigated. In the case of the moderate L'Aquila 2009 and Norcia 2016 earthquakes, the recorded fault slips can be characterized as pre-seismic.

3D structural modeling of the Upper Bahariya Member in Abu Gharadig oil and gas field, North Western Desert, Egypt

Abu Gharadig Field lies in the central portion of Abu Gharadig Basin of the northern part of the Western Desert of Egypt, about 256 km west of Cairo. Abu Gharadig Basin is considered as an E-W trending intracratonic basin. The Upper Bahariya Member is a clayey reservoir and represents one of the Late Cretaceous units. There is a need for identifying whether the petrophysical parameters of this member are related to the facies changes or the present structures. Therefore, detailed structural and petrophysical studies are required. The structural configuration of the Upper Bahariya Member is studied in the present case and the results of this study will form the basis for future petrophysical studies. The present study includes the delineation of the main structural elements of the studied member within the study area. The aim of the present study was achieved through building a 3D structural model using Petrel™ Schlumberger Modeling software by integrating twenty 2D seismic sections with four digital well logs and a check-shot survey. The interpretation of the resulted model shows that the Upper Bahariya Member was folded into doubly plunging anticline with a gentle plunge to SW and a relatively steep plunge to NE. The fold was dissected by a series of normal faults trending E-W to NW-SE. The anticline is asymmetric and exhibits sigmoidal shape. The axis has mainly a NE-SW orientation and exhibits changing of this orientation in the NE part to be ENE-WSW and in the SW part to be also ENE-WSW, relating to the effect of a rotational stress. Growth faulting and thinning of the studied member at the crest of the anticline suggest the syn-sedimentary tectonics. Thus, these structures are related to the Late Cretaceous right-lateral shear which led to the opening of the North Atlantic.

Parabolic megadunes in a subtropical Quaternary inland dune field, southwestern Pampas, Argentina

The Utracán paleo-dune field (La Pampa Province, Argentina, southern South America) was examined by remote sensing, morphometric analyses and field surveys as a case study of complex megadunes of inland deserts. The paleo-dune field is within the Utracán-Argentino valley, one of the transverse valleys of La Pampa Province excavated into a regional structural plain. Similar paleo-dune fields occur within these valleys. Utracán dunes are mostly stabilized by grasses, deeply disturbed by cattle grazing and agriculture. The paleo-dune field is formed by complex parabolic megadunes with superimposed dunes. Parabolic megadunes present lengths of trailing arms of 3.3–12.9 km, widths between them of 2–2.9 km and heights of 7–38 m. The position of the dune noses at the northeastern tip of the bedform and measured SW-NE orientation of arms indicate a mean transport direction to azimuth 68.2°. Above the parabolic arms, and isolated in the paleo-dune field, there are compound blowout dunes (clusters of several blowouts forming a larger bedform). They show the depositional lobes to the NE, with a measured mean transport direction to azimuth 58.1°. The SW-NE longitudinal length varies between 324 and 1302 m and the NW-SE transverse length between 114 and 622 m. Other parabolic arms show low (<3 m) barchanoid dunes, with crest lengths of 48–811 m, a mean crest spacing of 74 m and a transport direction to azimuth 28.2°. The paleo-dune field also shows smaller, simple parabolic and blowout dunes. We hypothesize that the parabolic and blowout dunes are the basic bedforms that emerged under the boundary conditions of the Utracán dune field, related to a high sediment supply coupled with a partial vegetation cover, in a valley that provided accommodation space by means of well-defined depression and wind deceleration due to a change in the longitudinal valley slope direction. The west-to-east spatial progression of dune morphologies along the Utracán-Argentino valley, the general transport direction of dunes to the NE, and the petrographic sand composition allow us the infer that the transverse valleys of La Pampa Province worked as sand transport pathways. These pathways transferred fine to very fine sand from the eastern Andean piedmont to the Pampean plain, likely during the Quaternary.

Geoimaging of subsurface fabric in Awgbagba, Southwestern Nigeria using geomagnetic and geoelectrical techniques

The heterogeneous nature of the earth has given rise to variations experienced in the subsurface. Some parts are good for hydrological exploration while others are good for civil engineering activities. These variations experienced in the subsurface could not be detected except through geophysical survey and analysis. Integration of ground magnetic and Vertical Electrical Sounding (VES) techniques were carried out in Awgbagba to image the subsurface fabric with a view to mapping subsurface geological features, such as the weak and competent zones, to determine the overburden thickness, and suitability of Awgbagba for civil engineering and hydrogeological purposes. Ten ground magnetic traverses were established in W-E and N-S azimuths. Twenty VES points were randomly sounded for the study in order to cover the entire study area. The magnetic residual field anomaly values ranged from -1, 600 to 700 nT. The study area is grouped into low, average, and high magnetic zones. The depth to magnetic sources ranged from 8.1 to 48.9 m with a mean value of 17.4 m. Three planar feature orientations in the study area are in NE-SW, NW-SE, and SE-NW orientations. VES results showed 7 QH-curve type, 6 HA-curve type, 4 KH-curve type, 1 AA-curve type, 1 HK-curve type and 1 QQ-curve type respectively. The ratio of thin-to-thick overburden and fresh-to-fractured bedrock are 3:7 and 2:3 respectively. It is concluded that the study area cannot withstand high-rise building constructions. However, the mapped fracture zones in the study area would serve as promising zones for borehole development.

Development possibilities of rural tourism activities in the Almaj Valley area, Caras-Severin County

Rural tourism and agrotourism have an extremely important contribution in rural area’s development, not only in financial terms but also in terms of increasing and improving the quality of life of residents from these areas. So, the development of these forms of tourism is required in the rural area, both economically and socially. Known as an important ethnographic area of the country, with traditional elements specific, Almaj Valley through natural and cultural potential available, it stands more and more lately by intensifying rural tourist and ecotourist activity. However, tourist infrastructure is very underdeveloped, to rural communities returning the mission to get more involved in this purpose, having in view, the national and international recognition of the high tourism potential of this area&#x0D; Romanian area still retains, quite well, the traditional, cultural, ethnographic and folklore valences specific to rural areas, providing favorable conditions for development of rural tourism and agrotourism. Romanian villages have a rich tourist potential, having diversified tourist resources: traditions, customs and folk values, cultural monuments, historical and art and an unpolluted natural environment with a rich natural tourism potential.&#x0D; Almajului Depression known as well as the Almaj Country, Almajului Valley or Bozovici Depression is situated in the South-East side of Banat Mountains, in the south of Caras-Severin county, near the Parallel 45°, being an intramountainous depression, of ellipsoidal form of NE-SW orientation, belonging to Nera basin.

Structural control and hydrothermal evolution model of unusual, high-grade metasandstone-hosted iron deposits, mesoproterozoic eastern chapada diamantina, Brazil

The Ibicoara high-grade, hypogene hematite deposits are located in the São Francisco Craton, in the Chapada Diamantina Fold Thrust belt. Iron mineralization host rocks are quartz and arkose sandstones from the Tombador Formation, which present planar stratification. Regionally, three deformational phases are identified. The first D1 phase developed kink with subordinate chevron folds, shear zones related to flexural slip with S/C structures, stretch lines (LX1), slickenlines and slickensides. The second phase D2 is represented by dextral and sinistral, reverse high-angle shear zones with NNW-SSE and NW-SE orientation trends, respectively, high-angle tension fractures with an ENE-WSW orientation. During the third deformation phase D3, dextral and sinistral shear zones with ENE-WSW and NE-SW orientations are developed. The richest hematite domains are massive, having Fe2O3total contents to 98%. These irregular-massive domains are distributed along the primary sedimentary foliation (plane-parallel stratification and tangential cross-bedding), of D2 shear zones, or tension fractures generated during D2. The irregular-massive hematite domains grade laterally into platy and stringer domains. In addition, there are vein, stockwork and breccia mineralization styles that crosscut irregular-massive domains or host rock. Chemical analyses of hematite in irregular-massive domains show that Fe2O3 correlates negatively with SiO2, Zr, Th, Sr, Nb, Hf and Ba. On the other hand, it correlates positively with Zn, V, U, Cu, Co, and with the sum of rare earth elements (REE). When normalized to the post-Archean Australian Shale (PAAS), the distribution of REE generally show negative Eu anomalies, and a weak enrichment of light rare earth elements (LREE) compared to the heavy rare earth elements (HREE). The paragenetic succession shows the existence of three groups of hematite. Groups 1 and 2 are mainly related to the irregular-massive domains controlled by rock stratification and the S0//S2 foliation in shear zones. The distinction between them is given by the finer grain size of the first generation of hematite and the presence of breccia domain in the second group. The third group is related to massive-vein domains. For each group, the hematite grain size increases successively, and there is a relative increase in the HREE in relation to the LREE. Furthermore, similarities between the chemical signatures of the first groups 1 and 2 hematite generation with the signatures of the host rock reveal an important influence of the chemical composition of the original rock. This is not the case for the late hematite of massive domains, as well as vein-style hematite, suggesting high fluid-rock conditions. The hematite hydrothermal alteration at Ibicoara has structural control, with dilational structures associated with D2 shear zones. The host lithotype was also a contributing factor due to its porosity and permeability, and the presence of sedimentary structures that favored flow of the hydrothermal fluid from shear zones. Replacement and direct precipitation took place and are responsible for the transfer of solutions and formation of hematite-rich areas. The hydrothermal fluid probably leached components from the Espinhaço Supergroup metasedimentary units and dikes that are regionally present, and carried these during the deformational phases that inverted the Paramirim Aulacogen. The Espinhaço Supergroup is characterized by a sequence of siliciclastic rocks, predominantly metasandstones, and felsic metavolcanic rocks, sterile in iron, which were deposited between the Statherian and Stenian periods. In the Chapada Diamantina area, the Espinhaço Supergroup is comprised from base to top by the Serra da Gameleira Formation and the Rio dos Remédios, Paraguaçu, and Chapada Diamantina groups. The Chapada Diamantina Group contains the Tombador Formation that hosts the high-grade iron deposits investigated in the present study. In light of the tectonic context, and existence of shear-related gold and baryte hydrothermal deposits nucleated during the Paramirim Aulacogen inversion, the Chapada Diamantina Thrust and Fold Belt is considered a potential regional exploration target.

Numerical simulation of 3-D mantle flow evolution in subduction zone environments in relation to seismic anisotropy beneath the eastern Mediterranean region

Seismic anisotropy is a key parameter in understanding subduction zone dynamics in relation to the recent deformation history. It is usually controlled by the mantle flow patterns resulting from the dynamic interactions between a relatively dense subducting oceanic plate and the surrounding mantle. A proper modelling of mantle flow in subduction systems helps our understanding of the seismic anisotropy source, strength and evolution in time. This study further examines shear wave splitting parameters, one of the most well established measuring methods of seismic anisotropy, and their anisotropy source, based on 3-D geodynamic modelling, applied to the eastern Mediterranean Sea and Anatolia. Our model setting is chosen to be a first order representation of the present-day tectonic setting as it consists of a deforming Anatolian micro-plate, that is indented by slow moving African and Arabian plates, and an oceanic plate in between. The retreat of the slab in the Aegean region, the alleged tear in the subducting slab close to the Cyprus trench and the break-off in the slab in eastern Anatolia are considered in our modelling study in order to further explore their influence on mantle flow and splitting parameters. The synthetically calculated fast polarization directions (FPDs) mostly showed a reasonable matching with those inferred from previous seismological observations that are mainly SKS splitting measurements. Regions of FPD similarities between synthetic and observed shear waves mostly indicate N–S to NE–SW orientations of fast shear waves, which are parallel to the extension in the back-arc region and in general perpendicular to the trench. The pattern of FPDs seems to be more complex nearby the trench. Our modelling results suggest that the development of a tear in the African slab and the detachment occurring within the Arabian plate (break-off) appear to have a significant influence on the FPDs due to stronger mantle flow through the slab windows. The mantle flow through the tear close to Cyprus and the break-off in the East can be identified clearly, despite their recent appearances. A circular pattern around the edges of the slab can be observed as well as disruptions of the overall general fast polarization direction due to the flow through the tear.

Earthquake dynamics in the Central India Tectonic Zone

We refine the 1-D velocity model of the Central India Tectonic Zone (CITZ) using well-selected arrival times of P- and S-phases of 354 local earthquakes of magnitude (Mw) between 2.0 and 5.8, recorded by national seismic network from May 1997 to March 2016. Further, we have determined the source mechanisms of 26 selected local events using moment tensor inversion to characterize the dynamics beneath the CITZ. The best-fit simulation between observed and synthetic waveforms obtained the nodal and auxiliary planes of the each faults associated with the earthquake moment magnitude (Mw) for each event. Depth of the fault plane along the CITZ varies from 5 to 38 km. From this study, we found that the western part along the CITZ shows minimum focal depth and reaches maximum 38 kms at Jabalpur in the eastern part. This complex nature of earthquake dynamics occurrence along the CITZ. We propose that the curviplanar the CITZ dominated with sinistral curvature is subjected to compression along the longer ~E–W segments and transtension along shorter segments with ~NE–SW orientations. The occurrences of normal faulting, intrusion of mafic plutons and CLVD mechanisms for earthquakes are interpreted to be linked to the transtension zones and reverse mechanisms associated with the compressions along ~E–W segments.

Contemporaneous alkaline and calc-alkaline series in Central Anatolia (Turkey): Spatio-temporal evolution of a post-collisional Quaternary basaltic volcanism

This study focuses on spatio-temporal evolution of basaltic volcanism in the Central Anatolian post-collisional Quaternary magmatic province which developed along a NE-SW orientation in Turkey. This magmatic province consists of the stratovolcanoes Erciyes (ES) and Hasandag (HS), and the basaltic volcanic fields of Obruk-Zengen (OZ) and Karapınar (KA). The investigated samples range between basic to intermediate in composition (48–56wt% SiO2), and exhibit calc-alkaline affinity at ES whereas HS, OZ and KA are alkaline in composition. Based on new KAr ages and major element data, the oldest basaltic rock of ES is 1700±40ka old and exhibits alkaline character, whereas the youngest basaltic trachyandesite is 12±5ka old and calc-alkaline in composition. Most ES basaltic rocks are younger than 350ka. All samples dated from HS are alkaline basalts, ranging from 543±12ka to 2±7ka old. With the exception of one basalt, all HS basalts are ~100ka or younger in age. KAr ages range from 797±20ka to 66±7ka from OZ. All the basalt samples are alkaline in character and are older than the HS alkaline basalts, with the exception of the youngest samples. The oldest and youngest basaltic samples from KA are 280±7ka and 163±10ka, respectively, and are calc-alkaline in character. Based on thermobarometric estimates samples from OZ exhibit the highest cpx-liqidus temperature and pressure. For all centers the calculated crystallization depths are between 11 and 28km and increase from NE to SW. Multistage crystallization in magma chamber(s) located at different depths can explain this range in pressure. Harker variation diagrams coupled with least-squares mass balance calculations support fractional crystallization for ES and, to lesser extend for HS, OZ and KA. All basaltic volcanic rocks of this study are enriched in large-ion lithophile elements (LILE) and light rare earth elements (LREE). The lack of negative anomalies for high field strength elements (HFSE; Y, Yb) and the La/Nb >1 favor a shallow lithospheric source for ES, HS, OZ and KA basaltic volcanic rocks, whereas some samples bear the trace element signature of an asthenospheric mantle source. The lithospheric mantle beneath Central Anatolia may have not been affected from asthenospheric mantle directly. Negative Nb-Ta-Ti anomalies and a positive Pb spike of ES, HS, OZ and KA may be ascribed to crustal contamination or as the imprints of the previous subduction processes. According to this study, and previous studies, the effect of subduction and/or crustal contamination in Central Anatolia decreased from the Miocene to the Quaternary, and the origin of the Quaternary basaltic rocks mainly derived from subduction-related magmas enriched with sediment input rather than to slab-derived fluids. Our calculated eruption ages for the four basaltic complexes show that spatial differences predominate, whereas temporal trends are difficult to discern due to limited age resolution. According to the available geochronological, petrological and geochemical data, alkaline and calc-alkaline volcanism occurred simultaneously from distinct parental magmas.

Seismic anisotropy in central North Anatolian Fault Zone and its implications on crustal deformation

We investigate the crustal seismic structure and anisotropy around the central portion of the North Anatolian Fault Zone, a major plate boundary, using receiver function analysis. The characterization of crustal seismic anisotropy plays a key role in our understanding of present and past deformation processes at plate boundaries. The development of seismic anisotropy in the crust arises from the response of the rocks to complicated deformation regimes induced by plate interaction. Through the analysis of azimuthally-varying signals of teleseismic receiver functions, we map the anisotropic properties of the crust as a function of depth, by employing the harmonic decomposition technique. Although the Moho is located at a depth of about 40 km, with no major offset across the area, our results show a clear asymmetric distribution of crustal properties between the northern and southern blocks, divided by the North Anatolian Fault Zone. Heterogeneous and strongly anisotropic crust is present in the southern block, where complex intra-crustal signals are the results of strong deformation. In the north, a simpler and weakly anisotropic crust is typically observed. The strongest anisotropic signal is located in the first 15 km of the crust and is widespread in the southern block. Stations located on top of the main active faults in the area indicate the highest amplitudes, together with fault-parallel strikes of the fast plane of anisotropy. We interpret the origin of this signal as due to structure-induced anisotropy, and roughly determine its depth extent up to 15–20 km for these stations. Away from the faults, we suggest the contribution of previously documented uplifted basement blocks to explain the observed anisotropy at upper and middle crustal depths. Finally, we interpret coherent NE-SW orientations below the Moho as a result of frozen-in anisotropy in the upper mantle, as suggested by previous studies.

Style and intensity of late Cenozoic deformation in the Nagoorin Basin (eastern Queensland, Australia) and implications for the pattern of strain in an intraplate setting

AbstractEastern Australia was affected by late Cenozoic intraplate deformation in response to far-field stress transmitted from the plate boundaries, but little is known about the intensity and pattern of this deformation. We used recently surveyed two-dimensional seismic reflection lines and aeromagnetic data, and data from the recently released Australian Stress Map, to investigate the structure of the Nagoorin Basin in eastern Queensland. The western margin of the Nagoorin beds was displaced by the Boynedale Fault, which is a NNW-striking SW-dipping oblique strike-slip reverse fault with a vertical throw ofc.900 m andc.16 km sinistral displacement. A significant part of this large sinistral displacement is interpreted to have occurred prior to late Cenozoic time. Several low-angle (&lt;30°) thin-skinned thrusts with a flat-ramp geometry also displaced the Nagoorin beds, which are interpreted to have developed along detachment surfaces in oil shales and claystone. The Boynedale Fault is a segment within longer NNW-striking faults that include the North Pine and West Ipswich fault systems in eastern Queensland. These NNW-striking faults are potentially active, and may accommodate neotectonic thrust movement in response to the present-day NE–SW orientation of SHmax. Results of this study, in conjunction with previous information on sedimentary basins in eastern Australia, indicate that Cenozoic contractional deformation is stronger at the continental margins, possibly due to the presence of pre-existing rift-related structures.