Deep-reaching Faults Research Articles

Deep structure of the Pieniny Klippen Belt in Poland

An interpretation of the deep structure of the Pieniny Klippen Belt in Poland is presented, utilizing a high-resolution deep seismic reflection survey. The studied profiles reach a depth of around 23 km. The seismic lines depict the structure and mutual relationships between the main domains analyzed—the Central Carpathians (CC), the Pieniny Klippen Belt (PKB) and the Outer Carpathians. The seismic lines show the Central Carpathian Paleogene (CCP) sediments covering the Tatric units and overlying Krížna and Choč nappes of the CC south of the PKB. The entire nappe pile comprising the CC units is thrust over sedimentary rocks that probably derived from the European Plate, representing a mixture of autochthonous platform Paleozoic to Neogene sediments and slices of Outer Carpathian and PKB rocks. The older crystalline basement of the European Plate is suspected to be below these sedimentary rocks. The reflections below 20 km depth show a possible boundary between different crustal elements within this plate. The PKB is part a of 3–5 km wide flower structure, limited by fault zones that include faults cutting across sediments of the CCP and the Magura Nappe. The fault marking the southern limit of the PKB is particularly well visible in the seismic sections. The Albian–Lower Miocene flysch sequences, constituting the main components of the PKB, form north-vergent thrust-sheets. During the Albian to Miocene the PKB originated as an accretionary prism in front of the moving CC Plate, followed by plate rotation and strike-slip processes. The entire CC nappe pile is thrust over the Precambrian and Lower Paleozoic crystalline basement of the European Plate and probably slices of the PKP. The Outer Carpathians display an allochthonous character above the European Plate and comprise several north-verging imbricated nappes (thrust-sheets). The European plate dips gently southwards below the PKB and the CC Plate, cut by several deep-reaching faults.

Penetration depth of meteoric water in orogenic geothermal systems

Warm springs emanating from deep-reaching faults in orogenic belts with high topography and orographic precipitation attest to circulation of meteoric water through crystalline bedrock. The depth to which this circulation occurs is unclear, yet it is important for the cooling history of exhuming orogens, for the exploitation potential of orogenic geothermal systems, and for the seismicity of regional faults. The orogenic geothermal system at Grimsel Pass, Swiss Alps, is manifested by warm springs with a clear isotopic fingerprint of high-altitude meteoric recharge. Their water composition and their occurrence within a 3 Ma fossil upflow zone render them particularly favorable for estimating the temperature along the deep flow path via geochemical modeling. Because the background geotherm has remained stable at 25 °C/km and other heat sources are unavailable, the penetration depth can be derived from the deep-water temperature. We thus estimated the base of the Grimsel system to be at 230–250 °C and 9–10 km depth. We propose that deep temperatures in such systems, particularly those with normal background geotherms (<30 °C/km), have been systematically underestimated. Consequently, far more enthalpy may be accessible for geothermal energy exploitation around the upflow zones than previously thought. Further, the prevalence of recent earthquake foci at ≤10 km beneath Grimsel suggests that meteoric water is involved in the seismicity of the host faults. Our results therefore call for reappraisal of the heat budget and the role of meteoric water in seismogenesis in uplifting orogens.

The Starzach site in Southern Germany: a site with naturally occurring CO2 emissions recovering from century-long gas mining as a natural analog for a leaking CCS reservoir

In this paper, we present the Starzach site, a region featuring numerous natural CO2 emission spots, such as mofettes, that reappeared after a longer period of extensive industrial CO2 mining. We discuss the results of a detailed literature study on the geological setting and the activities related to the gas mining in combination with own measurements to introduce the site as an example on how gas leakage from an insecure CCS reservoir could manifest at the surface. The site is in particular interesting for such investigations as the CO2 emissions started to replenish after the end of the CO2 mining and offers the unique possibility to investigate an increase in degassing activity as it might be expected for an active CCS site where leakage is suspected. Based on the geological setting and soil, gas emission, and isotope investigations, we further discuss the source of the CO2 emission and the gas ascent to the ground surface via deep-reaching faults, latter being so far excluded by previous work. The combination of our extensive literature review and recent field investigations allowed us to draw new geological conclusions for the site that were under discussion for a long time and to give insight into the site’s potential for CCS-related analog studies in the future.

Regional two-dimensional magnetotelluric profile in West Bohemia/Vogtland reveals deep conductive channel into the earthquake swarm region

The West Bohemia/Vogtland region, characterized by the intersection of the Eger (Ohře) Rift and the Mariánské Lázně fault, is a geodynamically active area exhibiting repeated occurrence of earthquake swarms, massive CO2 emanations and mid Pleistocene volcanism. The Eger Rift is the only known intra-continental region in Europe where such deep seated, active lithospheric processes currently take place. We present an image of electrical resistivity obtained from two-dimensional inversion of magnetotelluric (MT) data acquired along a regional profile crossing the Eger Rift. At the near surface, the Cheb basin and the aquifer feeding the mofette fields of Bublák and Hartoušov have been imaged as part of a region of very low resistivity. The most striking resistivity feature, however, is a deep reaching conductive channel which extends from the surface into the lower crust spatially correlated with the hypocentres of the seismic events of the Nový Kostel Focal Zone. This channel has been interpreted as imaging a pathway from a possible mid-crustal fluid reservoir to the surface. The resistivity model reinforces the relation between the fluid circulation along deep-reaching faults and the generation of the earthquakes. Additionally, a further conductive channel has been revealed to the south of the profile. This other feature could be associated to fossil hydrothermal alteration related to Mýtina and/or Neualbenreuth Maar structures or alternatively could be the signature of a structure associated to the suture between the Saxo-Thuringian and Teplá-Barrandian zones, whose surface expression is located only a few kilometres away.

Hydrothermal dolomitization in a complex geodynamic setting (Lower Palaeozoic, northern Spain)

AbstractBurial hydrothermal dolomitization is a common diagenetic modification in sedimentary basins with implications for oil and gas reservoir performance. Outcrop analogues represent an easily accessible source of data to refine the genetic models and assess risk in hydrocarbon exploration and production. The Palaeozoic succession of northern Spain contains numerous excellent exposures of epigenetically dolomitized limestones, particularly in the Carboniferous and Cambrian. The epigenetic dolomites in the Cambrian carbonates of the Láncara Formation are volumetrically small, but have a large aerial distribution across different tectonic units of the Variscan fold and thrust belt. Coarse crystals, abundant saddle dolomite cement, negative δ18O and fluid inclusion homogenization temperatures between 80°C and 120°C characterize these dolomites, which are petrographically and geochemically similar to the tens of kilometre‐sized hydrothermal dolomites replacing the Upper Carboniferous succession in the same area. In both cases, the dolomitizing fluids are derived from highly evaporated sea water, modified to a limited degree through fluid‐rock interaction. The dolomitization events affecting both Cambrian and Carboniferous strata are probably related to the same post‐orogenic hydrothermal fluid flow. The formation of the post‐collisional (latest Carboniferous) Cantabrian arc fostered dolomitization: the extension related to bending of the arc generated deep‐reaching faults and strike‐slip movements, which favoured the circulation of hot dolomitizing fluids in the outer parts of this orocline. A similar dolomitization process affected other areas of Europe after the main stages of the Variscan orogeny. Dolomitization was a continuous, uninterrupted, isochemical process. Limestone replacement resulted in a major porosity redistribution and focused the fluid flow into the newly created porous zones. Replacement was followed immediately by partial to complete cementation of the pores (including zebra fabrics and vugs) with saddle dolomite. The amount of porosity left depends on the volume of cement and therefore on the volume of fluids available.

Insights into the emplacement dynamics of volcanic landslides from high-resolution 3D seismic data acquired offshore Montserrat, Lesser Antilles

We present results from the first three-dimensional (3D) marine seismic dataset ever collected over volcanic landslide deposits, acquired offshore of the Soufriere Hills volcano on the island of Montserrat in the Lesser Antilles. The 3D data enable detailed analysis of various features in and around these mass wasting deposits, such as surface deformation fabrics, the distribution and size of transported blocks, change of emplacement direction and erosion into seafloor strata. Deformational features preserved on the surface of the most recent debris avalanche deposit (Deposit 1) reveal evidence for spatially-variant deceleration as the mass failure came to rest on the seafloor. Block distributions suggest that the failure spread out very rapidly, with no tendency to develop longitudinal ridges. An older volcanic flank collapse deposit (Deposit 2) appears to be intrinsically related to large-scale secondary failure of seafloor sediments. We observe pronounced erosion directly down-slope of a prominent headwall, where translational sliding of well-stratified sediments was initiated. Deep-reaching faults controlled the form and location of the headwall, and stratigraphic relationships suggest that sliding was concurrent with volcanic flank collapse emplacement. We also identified a very different mass wasting unit between Deposit 1 and Deposit 2 that was likely emplaced as a series of particle-laden mass flows derived from pyroclastic flows, much like the recent (since 1995) phase of deposition offshore Montserrat but at a much larger scale. This study highlights the power of 3D seismic data in understanding landslide emplacement processes offshore of volcanic islands. Highlights: ► 3D seismic data show new detail of volcanic landslide deposits offshore Montserrat. ► Volcanic flank collapse material has been diverted around seafloor topographic highs. ► This bending during emplacement has caused pronounced erosion into seafloor strata. ► Erosion can destabilize seafloor slopes, which then fail as translational slides. ► Block distributions and surface deformation give insight into debris avalanche style.

Hydrocarbon occurrences in the western Anatolian (Aegean) grabens, Turkey: Is there a working petroleum system?

Western Anatolian graben basins are filled with continental sediments and minor carbonates deposited in lacustrine, alluvial, and fluvial environments. Individual grabens are composite basins and comprise multiple depocenters or subbasins, with sediment thickness rarely exceeding 3000 m (9843 ft). A number of hydrocarbon occurrences are reported from the basins. Regional geologic framework justifies these occurrences by providing a generous heat budget, good quality source rock, fair reservoir seal sequences, and suitable traps, although no economically producible reserves have been discovered to date. The rich source rock with an average total organic carbon of 2.34% and hydrogen index up to 800 mg/g is oil and gas generative at maturation. However, the composite nature of the grabens controlled the stratigraphic variability and led to sporadic distribution of the lacustrine deposits hosting the source rock facies in the basins. The depth of burial is generally insufficient (2000 m [6562 ft]) for the source rock to effectively generate and expel hydrocarbons. This limitation was locally overcome by additional heat input into the system through deep-reaching faults, volcanism, and/or after volcanic hydrothermal circulation. Thermal maturity of organic matter effectively increases in the vicinity of the major border structures, volcanic rocks, and zones of polymetallic mineralization, yet this effect is typically constrained within a narrow zone adjacent to heat source and diminishes within short distances. Thus, the hydrocarbon system remains regionally inefficient. Exploration success in the region depends on the discovery of deeper Neogene depocenters that could provide sufficient source rock burial depths.

The contribution of fluid geochemistry to the volcano monitoring of Stromboli

The persistent open-vent mild explosive activity of Stromboli volcano is episodically interrupted by more violent and dangerous explosive events (major explosions and paroxysms). According to the nature of erupted products, paroxysms can be related either to the explosion of overpressured gas pockets located in the proximity of the magma column or to the sudden uprise of hot, gas-rich magma from a deep part of the plumbing system. In both cases, these more energetic explosive events should be preceded by an escape or a preferential uprise of the highly mobile volatiles which, in turn, should produce gas leakage anomalies at the surface in sites of high vertical permeability, such as deep-reaching faults. In order to identify such gas leaking sites, a systematic CO 2 soil flux survey has been carried out on the island using an accumulation chamber. Four hundred sixty-one points have been measured with a high density in the summit crater area, where high flux values have been found (10 −3–10 −2 cm/s). Anomalous points are concentrated along the main NE–SW axial feeding system of the volcano. CO 2 soil flux decreases from the crater zone to the base of the volcanic cone, where, however, an interesting gas leakage anomaly occurs (Pizzillo mofette). In the Pizzillo area thermal water wells also occur, whose chemistry indicates an origin by sea water heated by hot gas. Soil gases have been sampled in the sites with the highest CO 2 flux in the crater area and at the base of the cone. Chemical and isotopic analyses indicate the presence of a deep gas component especially in the crater zone samples (high CO 2, appreciable contents of He and H 2, 3He/ 4He values up to 3.55, δ 13C of CO 2=−2 ‰). The SC5 low-flux fumarole on the crater rim has shown, during six years, a remarkable persistence of temperature (93–95°C), with only minor fluctuations of chemistry. Appearance of anomalous peaks of H 2 in correspondence with strombolian explosions was observed during a 2-h 30-min experiment of continuous recording of hydrogen content of the fumarole. Together with previous data on H 2O, CO 2 and He, this experiment confirms that strombolian blasts produce rapid fluctuations in the fumarolic gas composition. In the light of this study, SC5 fumarole and Pizzillo mofette look promising sites for the testing of a continuous geochemical monitoring system of Stromboli volcano.

Isotopic characteristics of geothermal waters and fossil spring deposits in Mygdonia Basin, Northern Greece

Mygdonia Basin is an active seismotectonic zone. Its regional geology is characterized by step-faulted metamorphosed Paleozoic and Mesozoic sediments partly intruded by igneous rocks. Two geothermal anomalies, heating groundwater to more than 40°C at 100 m below the surface, are tied to horst-like basement uplifts along deep-reaching faults. Inorganic carbon dissolved in thermal waters of the region is isotopically rather heavy, indicating an endogenic origin. In spite of the considerable variation, δ 18 does not allow differentiation of thermal and non-thermal waters. It does not agree with the isotopic pattern of recently recharged groundwaters. δ 13C in fossil spring deposits of tufa towers and bedded travertines indicates a derivation from endogenic CO 2 similar to that dissolved in present thermal waters. In contrast, their δ 18O is remarkably high, suggesting evaporated basin waters as a possible source.

Helium and CO2 soil gas emission from Santorini (Greece)

Soil gas investigation is a useful tool to detect active faults. The sudden appearance of soil gas anomalies in zones of deep-reaching faults represents a promising potential precursor of earthquakes and volcanic eruptions. In volcanic areas the development of soil gas monitoring techniques is particularly important, as they can represent, together with remote sensing techniques, the only geochemical methods that can be safely applied during volcanic unrest, when it becomes impossible or too dangerous to sample crater fumaroles. A soil gas survey was carried out in June 1993 at the main island of Thera, in the Santorini volcanic complex. CO2 flux and CO2 and helium concentrations were measured at 50 cm depth for 76 points covering the entire island, with a spacing of 500 m or less. Several anomalous soil degassing sites have been detected. The main anomalies correspond to the Kolumbos line and to the Kameni line, two volcano-tectonic fault systems that controlled all the historic volcanic activity of Santorini. A third anomaly is related to a gas-leaking fault cutting the geothermal field of southern Thera. Soil gas data, together with geovolcanological and seismological evidence, indicate that the Kolumbos and Kameni lines are the most probable sites for future volcanic or seismic reactivation, and provide the basis for the establishment of a new geochemical monitoring technique at Thera.

NIZUSE: a deep seismic reflection line in north-eastern Germany

Out of a dense network of seismic reflection lines for hydrocarbon exploration in the North-east German Basin, several lines were recorded to 12 s TWT to obtain information about the structure of the crust and the crust-mantle transition. One of these profiles is presented here. This stretches for 110 km in a NNE direction between Neustrelitz and the island of Usedom. It reaches from the External Variscides in the south across the North German Massif into the Rugen-Pomorze Terrane in the Baltic Sea. Below Cenozoic-Mesozoic-Paleozoic cover with clear reflections down to base Zechstein, the reflectivity varies considerably with depth and also laterally. The Paleozoic and Precambrian sediments and basement are generally void of reflections, but the lower crust and the Moho show strong reflections. To the north the reflectivity decreases, and the Moho depth increases to beyond the bottom of the record section at 12 s. There are no direct indications for deep-reaching faults such as the Trans-European Fault in the north. The North German Massif acted as a ramp towards the Variscan Orogeny, similar to the London-Brabant Massif further west.

A genetic model for the Woodcutters PbZnAg orebodies, Northern Territory, Australia

The Woodcutters PbZnAg base-metal deposit is hosted by an inverted intracontinental-basin sequence of Early Proterozoic age, near Darwin, Australia. The 1800 Ma inversion event (D 1) resulted in horizontal upright folds (F 1), axial plane cleavage (S 1) and extension lineation (L e), and lowermost greenschist facies metamorphism. Northwest-trending left-lateral faults of Late Proterozoic to Cambrian age offset the folds. A mine sequence of five dolomitic carbonate units in dominant slate defines the “3” and “5” anticlines, with the “3” and “5” faults on their eastern limbs. A lamprophyre dyke within the “5” fault is pre-S 1; a second is oblique and post-dates S 1. The deposit has two main distributions of sulphide: banded PbZnFe massive sulphides which have saddle, inverted wishbone and poddy-shaped forms in the hinge zones of the “3” and “5” anticlines; and laminated (crack-seal) pyrite-rich, vein-type mineralization which partly occupies the “3” and “5” faults. The banded (layered) ore is mainly stratiform and stratigraphically controlled, having mimetically replaced bedding in carbonate-rich units. The fault-hosted mineralization comprises the “3” and “5” “feeder” channels, vertically linking the banded sulphide orebodies. Mine-, meso-, and micro-scale relationships between the sulphides and the dykes, faults and D 1 structures, such as folds (F 1), S 1 L e and boudinage, strongly suggest that the ore was emplaced pre- to early syn-D 1. There is a compelling case for the ore having been folded, overprinted by cleavage, and locally remobilized. Post-D 1 emplacement of ore is disproved, but the possibility of syn-deformational genesis (that is, progressive emplacement of ore during folding and cleavage development) remains. Substantially after syn-S 1 remobilization, the ore underwent left-lateral faulting and fault-related remobilization, followed by intrusion of lamprophyre and intrusion-related remobilization. The genetic model involves basin dewatering and channelled flow up deep-reaching faults reactivated by the onset of basin inversion. The ore formed by volume-for-volume replacement of carbonate-rich units and was progressively folded and remobilized during overprinting by cleavage. Woodcutters is a deformed epidiagenetic deposit comprising replacement-ore and attendant “feeder” mineralization.

Lower Palaeozoic volcanism of the Eastern Alps and its geodynamic implications

A geodynamic model for the lower Palaeozoic evolution of the Eastern Alps (upper Ordovician to middle Devonian; Gurktal Nappe, Styrian Greywacke Zone, Palaeozoic of Graz) is discussed, based on new field work and numerous geochemical analyses of volcanic rocks. It is suggested that in the upper Ordovician there existed on the one hand a passive continental margin or continental rift flooded by the sea, where mildly-alkaline basalts erupted (Magdalensberg-Series/Carinthia; Kaser-Series/Gurktaler Alpen). On the other hand, a convergent plate boundary in the form of an active continental margin or island arc or in the form of an orogen formed by continent-continent collision which can be recognized by the eruption of calc-alkaline volcanic rocks, probably also existed in the upper Ordovician (Blasseneck »Porphyroid«/Styrian Greywacke Zone; NockSeries/Gurktaler Alpen). In the lower Silurian a reorganization of the plate boundaries took place, resulting in the disintegration of the upper Ordovician collision zone along deep-reaching faults. Further extensional movements during the Silurian and Devonian led to the disintegration of a broad shelf platform and to the eruption of alkaline within-plate basalts. The extensional movements were responsible for the thinning of the continental crust and a general subsidence, which probably lasted until Lower Carboniferous time.

Seismic investigations in the Skagerrak and Kattegat

During the Meteor 66 cruise in the offshore areas surrounding Jutland in November 1983, seismic reflection and refraction measurements were made. A streamer, Ocean Bottom Seismographs, and land stations were deployed, which enabled both vertical-incidence and wide-angle reflections to be recorded. Seismic energy was provided by an airgun array fired at two-minute intervals. For the reflection seismic observations, this resulted in onefold coverage only, but it was established that airguns are a suitable energy source for crustal refraction seismic measurements out to distances of more than 100 km, and in areas with considerable sedimentary cover. This observation was an important contribution to the planning of the EUGENO-S project. Simultaneous application of reflection and refraction seismic methods at sea permits the observation of both the sedimentary horizons and the lower crust. This provided insight into the deeper sedimentary layers to the north of Jutland. No evidence for deep-reaching faults below the Norwegian Channel is indicated. We are thus able to reinforce the theory of glacial erosion. The seismic survey failed to confirm any seismic evidence for the gravity and magnetic anomaly near Kristiansand. A seismic section obtained by a land station in Sweden clearly delineates the upper-lower crust and the crust-mantle transitions. Strong S-waves, converted at the sea floor, were also observed.

Neue Beobachtungen �ber die Tektonik und die Antimonlagerst�tten Boliviens

New publications and geochronological data allow revisions concerning the Hercynian and Andinian orogeneses, their associated magmatic rocks and mineralizations to be made. Four metallogenic epochs may be distinguished: 1. Syntektonic, permian batholiths with goldquartz veins, and rutile and spodumene bearing Pegmatites; 2. Post-tectonic Triassic batholiths with W, Sn, Bi, Pb and Zn mineralization; 3. Early Miocene batholiths with rich Sn-W-Bi-Pb-Zn mineralization; 4. Pliocene volcanites with rich Sn, Pb, Zn, Ag and Bi mineralization. The large monomineralic antimony deposits do not occur around the batholiths or volcanites, but are bound to deep-reaching faults, connected to a deep-seated magma reservoir. A late Sb-mineralization phase is associated with recent thermal springs having a low Sb content.