NW-SE Trending Faults Research Articles

Mineralogy, geochemistry and genesis of the modern sediments of Seyfe Lake, Kırşehir, central Anatolia, Turkey

Seyfe Lake (Kırşehir, Turkey) is located within a depression zone extending along a NW–SE-trending fault in central Anatolia. Evaporite and carbonate sediments occur at the bottom of the lake which is fed by high-sulfate spring and well waters circulating N–S through salt domes. The recent sediments of Seyfe Lake are deposited in delta, backshore, beach, mud-flat and shallow lake environments. In the mud-flat environment, calcite, gypsum, halite, and thenardite are associated with fine-grained detrital sediments. Sediments from the margin to the lake center are distributed as calcite, gypsum and halite±thenardite, yielding an annular distribution pattern. An increase in Na2O, SO3, and S, and a decrease in CaO toward the lake center are due to sediment distribution. On the other hand, a positive correlation of SiO2 with MgO, K2O, Na2O, Al2O3, and Fe2O3+TiO2 is attributed to the presence of smectite, illite and feldspar. In addition, a positive correlation of Sr and Ba with CaO is related to the amount of gypsum in the sediments. Strontium is associated with in situ gypsum crystals; it increases in the intermediate and central zones of the lake as a result of a relative increase in salinity toward the lake center. The association of Sr with gypsum in the sediments suggests that Ca and Sr were derived from Sr-bearing evaporites and their carbonate host rocks, which were the likely aquifers for the brine. The S- and O-isotopic compositions of sulfate crystals range from +19.1‰ to +21.7‰ and from +16.9‰ to +20.9‰ SMOW, respectively, suggesting precipitation in a closed lake system. A relative increase of oxygen and sulfur isotope ratios toward the lake center suggests dissolution of gypsum in the host rock, with contributions from circulating groundwater and sulfate reduction (possibly by bacterial reduction). 87Sr/86Sr isotope ratios range from 0.707286 to 0.707879, suggesting a non-marine Oligo-Pliocene evaporitic host rock source for precipitation in Seyfe Lake. The concentration of Sr- and S-isotope ratios in the gypsum crystals indicates formation by precipitation/recrystallization from brine rather than from seawater.

3D coseismic deformations and source parameters of the 2010 Yushu earthquake (China) inferred from DInSAR and multiple-aperture InSAR measurements

The coseismic deformation field related to the 2010 Mw6.9 Yushu earthquake (Qinghai, China) has been investigated by previous studies using the satellite differential interferometric synthetic aperture radar (DInSAR) method. However, one of the limiting factors in the conventional DInSAR is that it can measure only one-dimensional (1D) ground motion along the radar line of sight (LOS) direction, thus resulting in anamorphic coseismic displacements and biased source parameters. In this paper, the three-dimensional (3D) deformation maps for this earthquake were reconstructed over an area of about 100×70km2 for the first time by a combined use of the DInSAR method for detecting LOS motion and the multiple-aperture interferometry (MAI) method for detecting along-track (AT) motion. The fault slip map for this earthquake was generated using the 3D deformation maps. Based on the fault traces on the fault slip map, we constructed a fault model with five segments and preformed a two-step inversion using the 3D deformation data as the constraint. Our results show that the maximum coseismic displacements in up–down, north–south and east–west directions are −40.4, 113.8, and −65.7cm, respectively, and the peak-to-peak slip offset between the southern and northern fault wall is 1.82m. Our model reveals a shallow dislocation on a NW–SE trending fault extending about 74km, along which the four fault segments are nearly vertical (84°–88°) and the one fault segment dips 66.2° to the southwest. The estimated seismic moment is 2.43×1019Nm (Mw6.92), which is close to the solution provided by the Global Centroid Moment Tensor (GCMT) Project. The slip distribution derived for each fault patch shows that the slip occurrence extends down to 12km beneath the ground surface, and a peak slip of 2.23m appears at the depth of about 5km right near the epicenter. Comparison with the results derived from the seismic waves, field investigation, GPS and conventional DInSAR observations indicates that the source parameters of the Yushu earthquake can be improved due to the combined use of DInSAR and MAI measurements.

Petroleum Prospects of Lamu Basin, South-Eastern Kenya

Abstract: The hydrocarbon potential of the sub-surface Lamu basin (SE Kenya) offshore sedimentary rock sequences of Mesozoic age formed the premise of this study. Major similarities and some differences in structural styles can be seen between the offshore Lamu and the Gondwana basins along the margins of Indian Ocean and Carnarvon basin along Australia’s North West Shelf, where oil pools have been discovered. The existing well results and recent 2-D seismic data have been interpreted to identify various structural styles and play fairway segments, which bolster the possibility that the Karroo to late Tertiary sedimentary mega-sequences (∼3000 – 13000 m thick), suitable for hydrocarbon exploration, could be visualized in both the onshore and offshore Lamu basin areas. Similarly, major reservoir-seal and potential source intervals have been identified in the present study. The hydrocarbon indicator from the well-log data shows that oil potential in complex multiple petroleum systems, ranging in age from Triassic to Tertiary, have tested gas deposits. Well control of only one exploratory well per 25,000 sq km in the offshore Lamu basin shows evidence of the existence of at least two active petroleum systems. The Lamu basin has evolved consequent to a complex tectonic activity related to continental rifting and block faulting of the Lamu-Anza and Central African rift systems. An attempt has been made to recommend the probable prognostic structural leads, which are controlled by NW-SE trending faults sympathetic to the Anza-Lamu rift systems, for future essential sub-surface features of source rocks, reservoir rocks and the cap rocks in the Lamu basin.

Late Pleistocene–Holocene evolution of the southern Marmara shelf and sub-basins: middle strand of the North Anatolian fault, southern Marmara Sea, Turkey

Although there are many research studies on the northern and southern branches of the North Anatolian fault, cutting through the deep basins of the Sea of Marmara in the north and creating a series of pull-apart basins on the southern mainland, little data is available about the geometrical and kinematical characteristics of the middle strand of the North Anatolian fault. The first detailed geometry of the middle strand of the North Anatolian fault along the southern Marmara shelf, including the Gemlik and Bandirma Bay, will be given in this study, by a combined interpretation of different seismic data sets. The characteristic features of its segments and their importance on the paleogeographic evolution of the southern shelf sub-basins were defined. The longest one of these faults, the Armutlu-Bandirma segment, is a 75-km long dextral strike-slip fault which connects the W–E trending Gencali segment in the east and NE–SW trending Kapidag-Edincik segment in the west. In this context, the Gemlik Bay opened as a pull-apart basin under the control of the middle strand whilst a new fault segment developed during the late Pleistocene, cutting through the eastern rim of the bay. In this region, a delta front forming the paleoshoreline of the Gemlik paleolake was cut and shifted approximately 60 ± 5 m by the new segment. The same offset on this fault was also measured on a natural scarp of acoustic basement to the west and integrated with this paleoshoreline forming the slightly descending topset–foreset reflections of the delta front. Therefore the new segment is believed to be active at least for the last 30,000 years. The annual lateral slip rate representing this period of time will be 2 mm, which is quite consistent with modern GPS measurements. Towards the west, the Bandirma Bay is a rectangular transpressional basin whilst the Erdek Bay is a passive basin under the control of NW–SE trending faults. When the water level of the paleo-Marmara lake dropped down to −90 m, the water levels of the suspended paleolakes of Bandirma and Gemlik on the southern shelf were −50.3 (−3.3 Global Isostatic Adjustment—GIA) and −60.5 (−3.3 GIA) m below the present mean sea level, respectively. As of today a similar example can be seen between the Sea of Marmara and the shallow freshwater lakes of Manyas and Uluabat. Similarly, the paleolakes of Gemlik and Bandirma were affected by the water level fluctuations at different time periods, even though both lakes were isolated from the Sea of Marmara during the glacial periods.

Geophysical Mapping, Geochemical Evidence and Mineralogy for Nuweibi Rare Metal Albite Granite, Eastern Desert, Egypt

The present study aims to shed light on the rare metals of Nuweibiareaalbite granite in the Eastern Desert through the chemical analyses of the two types of fine-grained albite granite (FAG) and medium-grained albite granite (MAG) in addition to mineralogical studies as well as ground spectrometric survey and aeromagnetic mapping. On the basis of ground spectrometric measurements K, eUand eTh distribution maps were obtained. The concentration of K, U and Th content shows maxima (4.5%, 13 ppm and 27 ppm on average, respectively) in the FAG, and (4.5%, 10 ppm and 35 ppm on average) in the MAG. The eU/eTh ratio significantly increases in FAG with higher magma differentiation than MAG reaching 0.63. This paper uses magnetic geophysical methods to investigate geometry and sense of motion across the Nuweibi area. The interpreted structures from the magnetic maps are characterized by two main intersecting sets of NW-SE and NE-SW trending faults in addition to other three minor faults that trend in N-S, NNW-SSE and ENE-WSW directions. The NW-SE trending faults represent the recent sets in the study area where they are dissected and displaced by the other old faults. The Werner depth map shows the interface depths of the granite and basement rocks that extend to great depths ranging from 10 to 380 m. FAG is extended underneath most of the surrounding schist rocks because of their attributed low magnetic intensity that confirmed also with drilling. Microscope and Microprobe analyses indicated that the most important radioactive minerals include uranothorite, thorite, zircon, and monazite. Columbite group minerals represent the most common Nb-Ta host in Nuweibi-albite granites that contain significant levels of Ta (up to 65.4 wt. % Ta2O5) and Nb (up to 60 wt. % Nb2O5), with Ta/(Ta+Nb) ratio ranging from 0.17 to 0.84. Columbite group minerals are represented mostly by columbite-(Mn) and tantalite-(Mn), with Mn/(Mn+Fe) ratio ranging from 0.42 to 0.89. Ixiolite, wodgnite and tapiolite-(Mn) were found only in the FAG indicating the final stages of the evolution of parental granitic magma. The U-Th and U-K variation diagrams suggested that magmatic processes controlled the distribution of these elements. The Scanning Electron-microprobe analyses reveal variable compositions and extents between the MAG and FAG in the Nb, Ta-Ti, Sn-Fe, Mn triangular plot. It is worthy to be noted that because of the higher Ta/Nb ratio in the tapiolite-Mn and ixiolite of FAG in comparison with the coexisting Mn-columbite in the MAG, levels of HfO2 greater than 15% and even attaining 23%, characterized the hafnium zircon in the Nwueibialbite-enriched facies. There is a close correlation between Hf/(Hf + Zr) and Ta/(Nb + Ta) which seems mainly associated with the FAG.

Neotectonic and climatic impressions in the zone of Trans Himadri Fault (THF), Kumaun Tethys Himalaya, India: A case study from palaeolake deposits

Late Quaternary tectonic activity on a NW-SE trending fault within the Trans Himadri Fault (THF) zone in lower reaches of the Milam glacier (Indian Tethys Himalaya) resulted in development of a lake around 23 ka BP. The remnants of the ancient lake are preserved in form of a 25.6 m thick lacustrine profile, consisting of muds and sands. The palaeolake seems to have breached around 11 ka BP possibly due to revival of a further event of neotectonic activity. The geomorphic consequences of the tectonic movements in the fault zone are manifest in form of palaeo-landslide cones, unpaired terraces, fault facets, soaring waterfalls, deep gorges and slope failures etc. The soft sedimentary structures, e. g., micro-faulting and flame structures in the exposed profile also point to a possible reactivation of the THF in the Late Pleistocene. We present the first palynological results from otherwise a totally unexplored area in the eastern part of the Indian Tethys Himalaya. The preliminary results indicate that the area experienced cold desertic climatic conditions from ca. 22.9 to 15.7 ka BP covering a period of Last Glacial Maximum (LGM) and during which the sediment accumulation rate was also extremely slow. This phase was followed by deglaciation together with amelioration of climate between ca. 15.7 and 14.5 ka BP. A dry period from ca. 14.5 to 13.8 ka BP can be associated with the Older Dryas. The area underwent wetter/moist conditions from ca. 13.8 to 12.8 ka BP, followed by a century scale dry event (ca. 12.8 to 12.7 ka BP) which may be linked to the Younger Dryas episode.

Applications of geomorphology, tectonics, geology and geophysical interpretation of, East Kom Ombo depression, Egypt, using Landsat images

In the Southern Eastern Desert of Egypt, A NW–SE oriented structural graben extends from the North of Aswan to the Red Sea coast with a length of about 400km and an average width of 30km. The area has significant potential for development as it may be provided with water from surface and subsurface sources and is the site of prospection for petroleum. The present paper is an attempt to understand the structural evolution and genetic development of the geomorphologic features of the area and constructing presently a new geomorphological map at a scale of 1:250,000 using Landsat ETM images and field checks. Available geological maps and the produced geomorphological map are digitized by using the ARC-GIS software. The same program is also used to produce a 3D DEM for surface and subsurface features. Based on new interpretations of aeromagnetic and radiometric data, the subsurface features of the basement cover were illustrated on a 3D map. Geological–geomorphological profiles have been constructed in different directions in the area to identify present and ancient geomorphologic features. The place and shape of subsurface deep seated NW–SE trending faults have been determined. The faults, which generated the graben have downthrows in the order of 900–5800m. The surface and subsurface observations delineate the dominant downthrow of about 3750m. Three E–W subsurface faults have been detected under Nubia sandstone, one of them, displaying a downthrow of about 845m, cuts through the basement rocks.

Incipient status of dyke intrusion in top crust – evidences from the Al-Ays 2009 earthquake swarm, Harrat Lunayyir, SW Saudi Arabia

The 2009 earthquake-swarm in the Al-Ays volcanic zone in Harrat-Lunayyir in NW Saudi-Arabia is unique because of its intense character and focal-depth distribution at two depth bands (5–10 and 15–20 km) in upper crust without volcanic eruption. We investigate an anatomy of the dyke-intrusion model that supports the mechanism for the swarm itself with seismotectonics, pore pressure diffusion process and inference model. Inferred dyke-intrusion initially started at depth had a five-day peak period (15–20 May 2009) since inception of event-recordings, following which the activity diminished. The process of pore pressure perturbation and resultant “r–t plot” with modelled diffusivity (D = 0.01) relates the diffusion of pore pressure to seismic sequence in a fractured poro-elastic fluid-saturated medium. The spatio-temporal b-values show high b-values (>1.3) along the zone of dyke intrusion (length 10 km and height 5 km) at ∼20km depth. The main-shock and other prominent earthquakes originated on a moderate b-value zone (∼1.0). Temporal b-value analysis indicates an exceptionally low b-value (∼0.4) during the main-shock occurrence. The Al-Ays lava-field is inferred to underlie a seismic volume trending NW-SE bounded on both sides by two NW-SE trending fault systems, dipping 40–50° opposite to each other within a proposed nascent rift setting.

Source characteristics and fluid evolution of the Beiyingxigou Pb–Zn–Ag deposit, central North China Craton: An integrated stable isotope investigation

The Beiyingxigou quartz vein and alteration type Pb–Zn–Ag deposit forms part of the metallogenic region southwest of the Mapeng batholith in the Central North China Craton. The quartz vein-type polymetallic deposit is associated with intermediate-felsic intrusives emplaced with Mesoarchean metamorphic basement. The mineralization is dominantly controlled by N–S and NW–SE trending faults. We identify four distinct stages of mineralization associated with the hydrothermal activity: pyrite phyllic stage, quartz–pyrite stage, quartz–polymetallic sulfide stage, and quartz–carbonate stage. Among these, the first two stages and the quartz–polymetallic sulfide stage represent the early and main metallogenic stages, respectively. Here we present results from integrated stable isotope studies (S, Pb, He–Ar and H–O) to deduce the possible sources of the mineralizing fluids and metals. The δ34S values recorded in the sulfide minerals of the early and main metallogenic stages show ranges of +0.4‰ to +2.2‰, and −11.4‰ to −6.8‰, respectively. The data illustrate two distinct pulses of hydrothermal fluids with δ34S mean values of 1.1‰ and −8.7‰. The S isotopes of pyrite and galena, sphalerite from the early and main metallogenic stages suggest a mixed source from the Mesozoic magmatism and the Precambrian basement. We infer that the slow cooling magma at the main metallogenic stage led to a larger interaction with the country rocks and resultant contamination, as compared to the early–middle metallogenic stage. The lead isotopic composition of pyrite, galena and sphalerite from the early to main stages shows restricted ranges with 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of 15.720–16.275, 15.068–15.140 and 38.688–41.316, respectively. The data are all characterized by lower crustal nature, suggesting the contribution of Pb from both the Mesozoic intrusions and the basement rocks in the region. The 3He/4He and 40Ar/36Ar ratios of fluid inclusions from the Beiyinxigou Pb–Zn–Ag deposit show a range of 0.01–0.23 Ra and 270.2–298.1, respectively. The 4He and 40Ar concentrations vary from 26.6 to 340.6 (10−7cm3STP/g) and 165.6 to 357.9 (10−7cm3STP/g), respectively, suggesting dominantly crustal contribution. The δ18OQ values of quartz and the δ18Dw values show ranges of 10.9‰ to 13.6‰ and −85.2‰ to −57.8‰, respectively. The calculated δ18OW values of the mineralizing fluids show a range of 3.7‰ to 7.5‰. Our data suggest that the hydrothermal fluids were a mixture of both magmatic and meteoric water. The results presented in this study link the Beiyinxigou Pb–Zn–Ag deposit to metallogeny associated with Mesozoic magmatism in the North China Craton.

Recent tectonic model for the Upper Tagus Basin (central Spain)

Active tectonics within the Upper Tagus Basin is related to the lithospheric flexure affecting the Palaeozoic basement of the basin. This flexure displays NE-SW trending. Besides, this structure is in agreement with the regional active stress field defined by the maximum horizontal stress with NW-SE trending. In this tectonic framework, irregular clusters of instrumental seismicity (Mw< 5.0) fade in the zone bounded by the Tagus River and the Jarama River valleys. These clusters are related to major NW-SE trending faults of suspected strike-slip kinematics. Moreover, reverse faults with NE-SW trending are affected by the strike-slip system as well. Despite the reverse faults are in agreement with the present SHMAX orientation, though, they apparently are blocked as seismogenic sources (scarce instrumental seismicity recorded today). In addition, we have determined the regional and local stress/ strain fields and two different fracture patterns were observed. Hence, we have divided the area in two zones: (1) the lateral bands of the basin, defined by reverse faulting (NE-SW trending) and strike-slip faulting (NW-SE trending) and (2) the central zone of the basin characterized by shallow normal faulting and NE-SW trending strike-slip faults. Furthermore, surface faulting and liquefaction structures are described affecting Middle to Late Pleistocene fluvial deposits, suggesting intrabasinal palaeoseismic activity (5.5 < M < 6.5) during the Late Quaternary. The obtained structural and tectonic information has been used to classify and characterize the Upper Tagus Basin as a semi-stable intraplate seismogenic zone, featured by Pleistocene slip-rates < 0.02 mm/yr. This value is low but it affords the occurrence of Pleistocene paleoearthquakes.

Structural and hydrogeological features of a Lias carbonate aquifer in the Triffa Plain, NE Morocco

The rising demand for water and the contamination of shallow water table aquifers has led authorities in NE Morocco to look for deeper groundwater resources in the Triffa Plain, namely in Lower Jurassic (Lias) dolomitic limestones. The liassic aquifer is of strategic importance for the development of the region, however, its hydrodynamic behaviour is poorly understood due to lack of hydrogeological data and block structure.This article presents a first effort towards understanding the structure and hydraulic behaviour of the aquifer. Exploration borehole data and results from geophysical campaigns were integrated into a GIS environment to build a preliminary model of the aquifer structure. The aquifer behaves as an unconfined aquifer in the northern part of the Béni Snassen Mountains (the recharge area), but as it dips to the north, it becomes confined by marls and shales of the Middle/Upper Jurassic. Even though piezometric level data are scarce, a tentative piezometric map was produced. Three blocks separated by NW–SE trending faults in a horst and graben structure, with distinct flow behaviours were identified: Berkane, Fezouane and Sidi Rahmoun blocks. Those blocks also show differences in hydraulic conductivity distribution. As a result of the reaction with the dolomitic limestones, the groundwater is of calcium-magnesium bicarbonate type. Groundwater temperature as measured in springs ranges from 29°C to 37°C in springs and constitutes a potential low enthalpy geothermal resource.

Possible evidence of remotely triggered and delayed seismicity due to the 2001 Bhuj earthquake (Mw = 7.6) in western India

Remote triggering by large earthquakes at regional distances is a globally observed phenomenon. However, there are no reports of observations of dynamic triggering at regional distances of several source lengths associated with the large Mw = 7.6 Bhuj earthquake of January 26, 2001, in western India. In the present study, a swarm of over 140 microearthquakes that occurred about 500 km southeast of Bhuj, in the geothermal province of the Western Ghats in the Deccan volcanic province (DVP) of India, immediately after the occurrence of the Bhuj earthquake in 2001 is investigated. The post-Bhuj seismicity (M < 2.0) occurred in three bursts spread over 2 months with each burst of intense activity lasting for 2–3 days. All the three bursts of seismicity occurred in the same volume along a 5-km-long NW–SE trending fault. The temporal coincidence and the sudden rise in seismicity that interrupts the characteristically low background seismicity strongly suggest that the Bhuj earthquake may have remotely triggered this activity. The triggered seismicity began approximately 2.5 h after the onset of the Bhuj mainshock and continued well after the passage of the surface waves, suggesting that the dynamic stresses possibly gave rise to secondary time-dependent mechanisms leading to the triggering. It is proposed that the triggered and delayed seismicity is possibly a consequence of the redistribution in pore fluid pressure due to the Bhuj earthquake. This is the first documented observation of remotely triggered seismicity at regional distances due to the Bhuj earthquake.

Potassium-rich magmatism in the Western Outer Carpathians: Magmagenesis in the transitional zone between the European Plate and Carpathian–Pannonian region

Miocene igneous rocks of the Western Outer Carpathians in Poland and Moravia, Czech Republic, were emplaced in a tectonic setting transitional between the European foreland and the Carpathian–Pannonian arc system. They form medium- to high-K calc-alkaline suites which are compositionally different to each other and to other calc-alkaline sequences in the region. Geographically and compositionally the Moravia rocks can be seen as transitional between the rift-related alkaline magmatism of the foreland and the dominantly calc-alkaline magmatism of the Carpathian–Pannonian region. Certain Moravia rocks are unusually enriched in incompatible trace elements, e.g. Nb≤122ppm and Th≤31ppm. The primary magmas of both suites were formed in metasomatised lithosphere mantle of the European plate but the enrichment mechanism differed: in Poland, it was by ancient subduction-related events whereas in Moravia metasomatism was mainly by melts and/or fluids from deeper mantle sources. Partial melting was promoted by impingement of rising asthenosphere on the base of the lithosphere, possibly related to reactivation of trans-lithospheric, NW–SE-trending fault zones.

Spatial distribution of sea-level markers on Lesvos Island (NE Aegean Sea): Evidence of differential relative sea-level changes and the neotectonic implications

The aim of this study is to provide new data on relative sea-level changes and neotectonics of the northeastern Aegean Sea region (Eastern Mediterranean) through the analysis of the coastal geomorphology of Lesvos, the third largest Greek island. There is a paucity of presently available data in this sector of the Aegean Sea, which is a tectonically active area strongly controlled by the North Anatolian Fault. In this paper, morphological, biological and sedimentary records of paleo-sea levels have been used to reconstruct relative sea-level changes, to identify variations in the tectonic regimes as well as to assess the paleoseismicity in the studied areas. According to the results, late Quaternary relative sea-level changes at Lesvos were not homogenous and variations in the tectonic setting played a crucial role in the coastal evolution. The NW-SE trending faults on the southern shore of the island control a significant uplift affecting about 30km of coastline. This uplift trend is controlled by the footwall of the Lesvos Fault, a major offshore normal fault that has been subject to relatively little quantitative investigation. Radiocarbon dating indicated that the last co-seismic uplift took place at 3365–3963calyr BP and resulted in about 0.75m of vertical displacement. In contrast, all the paleo-sea-level markers mapped in the northeastern sector were presently underwater and, despite the high seismicity of the area, no evidence of coastal uplift was observed in this part of the island. Thus, the paper provides the first field evidence of a differential late Quaternary evolution of Lesvos Island. In addition, results represent the first quantitative information on the activity of the Lesvos Fault, suggesting a reconsideration of its importance in the neotectonics of the area.

新潟県中越地域の新第三系-第四系におけるNW-SE走向横断断層の特徴

新潟県中越地域の新第三系-第四系におけるNW-SE走向横断断層の特徴

Structurally controlled fluid flow: High-grade silver ore-shoots at Martha epithermal mine, Deseado Massif, Argentina

The role of structurally controlled fluid flow during epithermal ore-shoot formation is addressed through a structural study of the high grade Martha Mine epithermal deposit (Deseado Massif, Patagonia, Argentina). Martha is a silver-rich deposit, characterised by a complex mineralogy dominated by Ag–As–Sb sulphosalts and Cu–Pb–Zn sulphides. Mineralised veins can be subdivided into two groups: master structures that trend approximately NW–SE, and second-order structures that trend E–W and coalesce into the master structures. The Martha vein system is interpreted as a hard-linked step-over zone between two NW–SE trending fault segments. Furthermore, the geometry of ore-shoots at Martha Mine suggests a first-order structural control on their location and orientation. At the deposit scale, mineralisation is concentrated in the step-over zone. Mineralisation, and presumably hydrothermal fluid flow, was concentrated at the intersection between the two main vein groups. Finally, at the scale of single veins, jogs and subordinate step-overs were important channels for hydrothermal fluids and the formation of high-grade ore-shoots.

Strymon and Strymonikos Gulf basins (Northern Greece): Implications on their formation and evolution from faulting

In Central and Eastern Macedonia of Northern Greece large NW–SE trending basins filled up mainly with terrestrial sediments developed during the Neogene over the Alpine basement rocks. Among them, the Strymon basin was established along the NNW–SSE trending Strouma/Strymon Lineament which formed over the tectonic boundary of the Serbomacedonian and Rhodope massifs, both representing the hinterland of the Hellenic orogen. The present study suggests that the Strymon basin was not formed as a syn-detachment basin over the Strymon Valley Detachment Fault, considered to have caused exhumation of the Rhodope massif metamorphic complex. Instead, transpressional s.l. tectonics dominated the region in the Late Oligocene-Early Miocene and it progressively changed into a wrench tectonics under which the Strymon basin has been initiated in the Middle Miocene. The basin continued to develop further under a short-lived NW–SE extension in the Middle-Late Miocene. The whole deformation is attributed to the late-stage collisional processes between the Apulia and Eurasia plates. The prevalent NE–SW extension has been constrained later on in the Late Miocene and Pliocene times activating both low-angle and high-angle NW–SE trending faults and causing the regional tilting towards the SW of the mountain fault blocks (i.e., mountain chains). From Quaternary onwards, the Strymon basin has been separated from the Strymonikos Gulf basin due to an N–S extension that mainly activates E–W striking normal faults.

Active normal faulting along the Mt. Morrone south-western slopes (central Apennines, Italy)

In the present work we analyse one of the active normal faults affecting the central Apennines, i.e. the Mt. Morrone normal fault system. This tectonic structure, which comprises two parallel, NW-SE trending fault segments, is considered as potentially responsible for earthquakes of magnitude ≥ 6.5 and its last activation probably occurred during the second century AD. Structural observations performed along the fault planes have allowed to define the mainly normal kinematics of the tectonic structure, fitting an approximately N 20° trending extensional deformation. Geological and geomorphological investigations performed along the whole Mt. Morrone south-western slopes permitted us to identify the displacement of alluvial fans, attributed to Middle and Late Pleistocene by means of tephro-stratigraphic analyses and geomorphological correlations with dated lacustrine sequences, along the western fault branch. This allowed to evaluate in 0.4 ± 0.07 mm/year the slip rate of this segment. On the other hand, the lack of synchronous landforms and/or deposits that can be correlated across the eastern fault segment prevented the definition of the slip rate related to this fault branch. Nevertheless, basing on a critical review of the available literature dealing with normal fault systems evolution, we hypothesised a total slip rate of the fault system in the range of 0.4 ± 0.07 to 0.8 ± 0.09 mm/year. Moreover, basing on the length at surface of the Mt. Morrone fault system (i.e. 22–23 km) we estimated the maximum expected magnitude of an earthquake that might originate along this tectonic structure in the order of 6.6–6.7.

The Southern Tyrrhenian subduction system: recent evolution and neotectonic implications

Geological and geophysical data have been integrated with the aim of presenting a new evolutionary model for the Southern Tyrrhenian and adjacent regions. The Southern Tyrrhenian backarc basin opened within a plate convergence regime because of sinking and rollback of the oceanic Ionian lithosphere. On the basis of seismological observations, I infer that the sinking slab was torn apart on either side in the last 2 Ma and this process controlled the neotectonics of the Southern Apennines - Tyrrhenian region. On the north-eastern side the slab broke off from NW to SE and this process triggered volcanism and NW-SE extension along the Eastern Tyrrhenian margin, and strike-slip tectonics along NW-SE trending faults in Northern Calabria. On the south-western side the slab broke off from W to E along the Aeolian Island alignment, although the tear has currently been reoriented along the NNW-SSE Malta escarpment. During its sinking the subducted slab also detached from the overriding plate, favouring the wedging of the asthenosphere between the two plates and the regional uplift of the Calabrian arc and surroundings. This regional uplift promoted gravitational instability within the orogenic wedge, particularly towards low topography areas; the large-scale sliding of the Calabrian arc towards the Ionian basin can be the cause of CW rotation and graben formation in Calabria. Also the E-dipping extensional faults of the Southern Apennines can be related to accommodation of vertical motions within the fold-and-thrust belt. The pattern of recent seismicity reflects this neotectonics where crustal-scale gravity deformation within the orogenic wedge is responsible for extensional earthquakes in Calabria and the Southern Apennines, whereas Africa plate convergence can account for compressional earthquakes in Sicily.

Late Quaternary deformation on the island on Pantelleria: New constraints for the recent tectonic evolution of the Sicily Channel Rift (southern Italy)

Abstract Structural observations carried out on the volcanic Island of Pantelleria show that the tectonic setting is dominated by NNE trending normal faults and by NW-striking right-lateral strike-slip faults with normal component of motion controlled by a ≈N 100°E oriented extension. This mode of deformation also controls the development of the eruptive fissures, dykes and eruptive centres along NNE–SSW belts that may thus represent the surface response to crustal cracking with associated magma intrusions. Magmatic intrusions are also responsible for the impressive vertical deformations that affect during the Late Quaternary the south-eastern segment of the island and producing a large dome within the Pantelleria caldera complex. The results of the structural analysis carried out on the Island of Pantelleria also improves the general knowledge on the Late Quaternary tectonics of the entire Sicily Channel. ESE–WNW directed extension, responsible for both the tectonic and volcano-tectonic features of the Pantelleria Island, also characterizes, at a greater scale, the entire channel as shown by available geodetic and seismological data. This mode of extension reactivates the older NW–SE trending fault segments bounding the tectonic troughs of the Channel as right-lateral strike-slip faults and produces new NNE trending pure extensional features (normal faulting and cracking) that preferentially develop at the tip of the major strike-slip fault zones. We thus relate the Late Quaternary volcanism of the Pelagian Block magmatism to dilatational strain on the NNE-striking extensional features that develop on the pre-existing stretched area and propagate throughout the entire continental crust linking the already up-welled mantle with the surface.