Mesozoic Limestones Research Articles

Provenance of the northern part of the Kahramanmaraş Peripheral Foreland Basin (Miocene, S Turkey)

The Miocene Kahramanmaraş Peripheral Foreland Basin (KPFB) resemble to classic foreland basin model, with small differences. In the classic model, both the accretionary wedge and foredeep extend lengthways parallel to the plate margin. In addition, accretionary wedge includes wedge top basin or piggy back basin that extends parallel to foredeep. However, the accretionary wedge of the KPFB contains small half-graben type basins that obliquely intersect the plate margin between the Arabian Plate and the Anatolide–Taurides Platform (due to the irregular shape of the plate boundary). Tectonic lineaments controlled the shape and orientation of these basins and larger main depocentre of the KFPB, which were predominantly filled with deep-sea sediments. This paper focuses on the provenance of features of the KFPB, predominantly was fed from the northern basin margin, while also aiming to resolve the complex basin evolution that occurred during the Miocene. Clasts of Palaeozoic and Mesozoic limestone and ophiolites are common components of the confined deep-water clastic systems, which evolved as elongated trenches in the north-western sector of the KPFB during the Early-Middle Miocene. During the Middle Miocene, continuous thrusting of the northern basin margin to south caused depocentre migration to south-east, through the basin interior. At that time, the north-east and central depocentres of the KPFB were filled primarily by clasts of ophiolite and metamorphic units. The tectonic control on basin fill architecture can be observed anywhere in the KFPB. The principal tectonic features controlled the geometry and orientation of the canyon, the channel geometry of the deep-water slope on the northern basin margin, the frequency and distribution of slump-slide-debris flows and the overall pattern of sedimentation cycles in the stratigraphy of the slope and the central basin floor. Some basin sectors have continuously reactivated and as a result, different sediment entry points with substantial local accumulation of sediment and deformation have evolved on the slope and basin floor. Three scales of provenance were used to investigate the source rock: (a) field-based observation and analysis of conglomerate clasts, (b) modal analysis of sandstone facies and (c) geochemical analysis, all of which were in agreement.

HYPOGENE Ba-RICH TODOROKITE AND ASSOCIATED NANOMETRIC NATIVE SILVER IN THE SAN MIGUEL TENANGO MINING AREA, ZACATLAN, PUEBLA, MEXICO

The San Miguel Tenango area, in the northern part of the State of Puebla, Mexico, is an old, now-abandoned silver mining district worked intermittently since Colonial times until the 1970s. Ores were high in grade, but had a low metallurgical recovery. We characterize the main ore mineral of this mining area, a Ba-rich manganese oxide with associated native silver, to investigate the cause of the low recovery. The ore deposits of this area consist of veins in Mesozoic limestone and shale, and hydrothermal breccias in early Pliocene dacitic volcanic rocks. Because of the present inaccessibility of the mine workings, only one vein was available for sampling. The ore mineral is Ba-rich todorokite with associated native silver, both occurring as cavity fillings. The vein-type ore deposits are related to adjacent early Pliocene dacitic volcanic rocks consisting of ash-fall tuffs, ash flows, volcanic necks, and a volcanic dome. Transmitted- and reflected-light petrography show that todorokite precipitated during the first stage of mineralization in a wide variety of habits. A second stage of mineralization consists of botryoidal to massive oxides and hydroxides of iron, ending with specular hematite. Filling open spaces in minerals of the second stage are minerals of a third stage consisting of irregular masses of pyrite, chalcopyrite, and pentlandite a few μm across. On the basis of this stage, a hypogene origin is assumed for the previous two stages. An XRD analysis of the vein material revealed the presence of todorokite and an amorphous phase, and probably also a hydrous manganese oxide. Semiquantitative analysis made with SEM–EDS and quantitative analysis with EPMA–SEM showed that the cations in both Mn oxide phases are Ag, Mn, Ba, Ca, Zn, K, Na, Mg, Fe, and Cu, with lesser amounts of Ni, Co, Sb, and Au, the absence of Pb being noteworthy. A TEM study corroborates the presence of todorokite and of an amorphous phase of hydrous manganese oxide, and shows a nanometric crystalline phase that corresponds to manganosite. Also, TEM analyses show that Ag occurs as nanometric particles of native silver adsorbed on the external surfaces of todorokite (not in the tunnels of its structure) and of the amorphous phase. In addition, IR analysis confirms the presence of todorokite. We attribute the low recovery of silver to scavenging of the dissolved silver by todorokite during the metallurgical process.

Basement configuration of on-land Kutch basin from seismic refraction studies and modeling of first arrival travel time skips

The Kutch basin is one of the three (Narmada, Cambay and Kutch) major marginal rift basins that are close to each other in mid-western part of the Indian subcontinent. The seismic refraction and wide-angle reflection data were acquired and a first order velocity structure of the Kutch sedimentary basin along Jakhau–Mandvi, Mandvi–Mundra, Mundra–Adesar and Hamirpur–Halvad profiles is derived. The travel time skip phenomenon has been noticed in the travel time plots and record sections indicating presence of low velocity sediments. Derived two-dimensional velocity–depth models revealed a Mesozoic sedimentary sequence sandwiched between Trap and Limestone layers, in some of the profiles. Two thick low velocity layers (that corresponds early to late Mesozoic era) have been identified. These are dipping towards Mandvi along Jakhau–Mandvi profile. The early Mesozoic layer that is thinning towards southeast is completely missing in Mandvi–Mundra profile. It is also noticed that the early Mesozoic Bhuj formation exists in the northern parts of the Mundra–Adesar and Hamirpur–Halvad profiles, where it directly overlies the granitic basement. The derived velocity–depth model suggests that the basement is about 3 km deep near Jakhau and reaches a depth of about 6 km near Mandvi. The layered structure may correspond to the Tertiary, Trap, Late Mesozoic sediments and Mesozoic limestone. The velocity–depth model obtained in Kutch is very similar to earlier derived model for Jamnagar and Dwarka sub-basins of northwestern Saurashtra peninsula suggesting probable continuity/linkage between southern on-land Kutch and, across the Gulf of Kutch to Saurashtra peninunsula. We also conclude that the evolution of Kutch basin, as a peri-cratonic rift basin, is essentially controlled by the four (F1–F4) faults inferred from obvious abrupt changes in layer thickness/velocity along the seismic refraction profiles.

The Vallo di Diano Fault System: New Evidence for an Active Range-Bounding Fault in Southern Italy Using Shallow, High-Resolution Seismic Profiling

Range-bounding normal faults can presentsignificant challenges for seis- mic exploration. This is the case of the fault system bounding the Vallo di Diano, the largest intermountain basin in the southern Apennines seismic belt. Industry reflection profiles define the large-scale structure of the basin but barely image the shallow fault system due to unfavorable topographic and near-surface conditions along the foothills of the eastern range. We present two high-resolution (HR) wide-aperture profiles recorded attheeastern marginof thebasin acrossunreported scarpsthat affect Middle- Late Pleistocene alluvial fans and slope debris. The survey is aimed at identifying possible recent faulting across these challenging terrains and at understanding the re- lationship between shallow structures and the master range-bounding fault at depth. Common depth point processing of wide-aperture reflection data and first-arrival tra- vel-time tomography provide detailed images of the upper 200-300 m and sounding evidence of recent activity along previously unknown splays of the fault system. These splays dissect the Mesozoic limestone bedrock and alluvial-fan sequences, affecting theirdepositionalpattern.VeryhighresolutionVPandreflectivityimagesalsogivehints ofpossiblecoseismicsurfacefaultinginHolocenecolluvia.Theseresultshaverelevant implicationsfortheevaluationoftheseismogenicpotentialoftherange-boundingfault systemandforseismichazardassessmentofthedenselyurbanizedVallodiDianobasin. Online Material: Table of acquisition and data processing parameters, and figures showing schematic stratigraphy of the Vallo di Diano basin, restoration of fault dis- placement along the HR profile, and resolution of the P-velocity tomographic images for the VHR profile.

Tectonically-related fluid circulation in the San Casciano dei Bagni-Sarteano area (M. Cetona ridge-Southern Tuscany): a coupled structural and geochemical investigation

The aim of this investigation is to examine the relationship between springs and structural setting in the Mt. Cetona Ridge. This area represents an important regional morpho-tectonic feature oriented NNW-SSE, separated from the geothermal area of Monte Amiata to the West by the Radicofani Neogene Basin, and bounded to the East by the Valdichiana Neogene-Quaternary Basin. This Ridge is constituted by the Tuscan Nappe and the overthrusted S. Fiora Unit. New detailed field mapping and a structural study allowed recognition of a polyphase structural setting defined by four folding phases followed by three extensional and transtensional phases.Coupled to the structural investigation, 13 spring water samples were collected in the area in May and in August 2005. Groundwater ranges from cold, low mineralized calcium-bicarbonate to warm, highly mineralised, calcium sulphate. Results are in general agreement with previous studies indicating the recharge area in the Cetona upland and a circulation in a highly fractured, quasi-continuous reservoir constituted by the Mesozoic limestone and the underlying Burano anhydrite formation. Geochemical modelling indicates that the high variability in the hydrochemical and isotopic composition cannot be explained by a simple binary mixing between two ground-water types, but rather reveals a geochemical evolution involving anhydrite and dolomite dissolution, and calcite precipitation. Outflows are closely related to the structural setting of the area and hydrochemistry allows discrimination of different fluids associated with specific hydrogeological circuits.The interpretation of the structural setting for Mt. Cetona Ridge was obtained by fieldwork studies integrating geochemical data of both thermal and cold springs. Results of this investigation allow us to propose a new tectonic evolution and fluid circulation model for this area.

Late Neogene rift-basin evolution and its relation to normal fault history and climate change along the southwestern margin of the Gerania Range, central Greece

ABSTRACTThe south- to southwest-dipping North and South Saros normal faults occupy the southeastern margin of the Gerania Range, a major massif of Mesozoic limestone and o phi-o lite in the eastern Gulf of Corinth Rift, cen-tral Greece. The history of the Saros faults is constrained by adjacent basin-fi ll sediments and modern drainage patterns. Older basin fi ll (Pliocene–lower Pleistocene?), which consists of terrestrial fi ne sands, carbona-ceous muds, marls, and micrite limestones, is uplifted on the South Saros fault block and onlaps the North Saros fault footwall block on its northern side to near its crest, suggest-ing that it predates major fault activity. In contrast, younger basin fi ll (middle Pleisto-cene?) was deposited and locally deformed during fault activity in a main basin south of the faults and in a perched basin on the South Saros fault block. Main-basin deposits consist of alluvial-fan, fan-delta, and shallow-marine sediments up to 50 m thick, whereas perched-basin fanglomerates are 5–15 m thick. Fault-scarp retreat and sediment onlap indicate that the faults became inactive late in the history of deposition of the younger basin fi ll. The perched and main basins are currently undergoing incision, allowing mod-ern sediment to bypass the basins and to be deposited on modern fan deltas and beaches along the Gulf of Megara coast. The absence of knickpoints and upstream deepening of the canyons suggest that a climatically driven increase in catchment runoff was responsible for basin incision, although uplift and sea-level change may have contributed as well.The North and South Saros faults each consist of three segments characterized by different strikes. The major drainages cross the Saros faults at or near segment boundar-ies, suggesting that the drainages may have initially fl owed between the tips of isolated fault segments. As the segments became linked, the antecedent drainages maintained their course and cut deep gorges. At the scale of the entire eastern Gulf of Corinth region, however, older unlinked faults were aban-doned, and new faults were created in a gen-eral northward and basinward direction; the origin of this process remains controversial.INTRODUCTION

The Itea–Amfissa detachment: a pre-Corinth rift Miocene extensional structure in central Greece

Abstract The Itea–Amfissa valley, separating Giona Mountain to the west from Parnassos Mountain to the east, is related to an extensional detachment observed along the eastern slopes of Giona. The detachment is traced for 30 km north of the Corinth Gulf and dips 25°–40° to the east, showing an east–west extension parallel to the Hellenic arc. The lower nappes of Pindos, Penteoria, Vardoussia and mainly the basal thrust of the Parnassos unit form part of the footwall, whereas the upper thrusts of the Parnassos unit and the Western Thessaly–Beotia nappe form part of the hanging wall. The eastern slopes of Giona are controlled by the detachment and several hundred metres of syn-tectonic breccia-conglomerates are observed at the top of the hanging wall rocks and are back-tilt towards the detachment plane. Two conglomeratic sequences are distinguished: the lower one consists of argillaceous matrix and abundant ophiolite detritus whereas the upper one bears carbonate matrix with carbonate detritus together with large olistholites of Mesozoic limestones. Based on calcareous nannofossils a middle Miocene age has been determined for the lower formation and a middle–upper Miocene age is probable for the upper. Planation surfaces cut on top of the sediments rise from south to north starting from sea level at Galaxidi to about 1400 m at Prosilio. The throw of the detachment is about 2.5–4.2 km measured mainly from the structural omission of the Alpine tectono-stratigraphic units. A contrast between the footwall and the hanging wall structure is described, with monoclinic sequence of the Parnassos nappe dipping to the west in the footwall but a complex synsedimentary horst and graben structure of sliding blocks of Alpine formations within the Miocene clastic sequences in the hanging wall. The detachment has been deformed by the east–west-trending steep normal faults that have created the Corinth rift during late Pliocene–Quaternary time showing a north–south extension. The Itea–Amfissa detachment forms the northern tip of the broader East Peloponnesus detachment, observed south of the Corinth rift structure from Feneos to Kyparissi. Similar geodynamic phenomena with large olistholites and breccia conglomerates are known from the Serravalian of Crete, related to the activity of the Cretan detachment.

Fluid flow and rock alteration along the Glarus thrust

Chemical alteration of rocks along the Glarus overthrust reflects different stages of fluid rock interaction associated with thrusting. At the base of the Verrucano in the hanging wall of the thrust, sodium was largely removed during an early stage of fluid-rock interaction, which is ascribed to thrust-parallel fluid flow in a damage zone immediately above the thrust. This alteration leads to the formation of white mica at the expense of albite-rich plagioclase and potassium feldspar. This probably enhanced mechanical weakening of the Verrucano base allowing for progressive strain localization. At a later stage of thrusting, fluid-mediated chemical exchange between the footwall and the hanging wall lithologies produced a second generation of alteration phenomena. Reduction of ferric iron oxides at the base of the Verrucano indicates fluid supply from the underlying flysch units in the northern section of the thrust. Fluid supply from the footwall may have kept pore fluid pressure close to lithostatic and enhanced cataclastic deformation. The chemical characteristics of the Lochseiten calc-tectonite suggest its derivation from Mesozoic limestone. In the southern sections of the thrust, the major element and stable isotope compositions show continuous trends from the Cretaceous limestone in the footwall of the thrust up to the contact with the Verrucano, indicating that the calc-tectonite developed due to progressive deformation from the footwall units. In the northern sections of the thrust, the Lochseiten calc-tectonite has a distinct chemical and stable isotope signature, which suggests that it is largely derived from Infrahelvetic slices, i.e. decapitated fragments of the footwall limestone from the southern sections of the thrust, which were tectonically emplaced along the thrust further north. Only at the Lochseiten type locality the original chemical and stable isotope signatures of the calc-tectonite were completely obliterated during intense reworking by dissolution and re-precipitation.

Depth and morphology of reflectors from the non‐linear inversion of arrival times and waveform semblance data. Part II: modelling and interpretation of real data acquired in Southern Apennines, Italy

ABSTRACTIn order to retrieve a 2D background velocity model and to retrieve the geometry and depth of shallow crustal reflectors in the Southern Apennines thrust belt a separate inversion of first arrival traveltimes and reflected waveforms was performed. Data were collected during an active seismic experiment in 1999 by Enterprise Oil Italiana and Eni‐Agip using a global offset acquisition geometry. A total of 284 on‐land shots were recorded by 201 receivers deployed on an 18 km line oriented SW–NE in the Val D'Agri region (Southern Apennines, Italy).The two‐step procedure allows for the retrieval of a reliable velocity model by using a non‐linear tomographic inversion and reflected waveform semblance data inversion. The tomographic model shows that the P wave velocity field varies vertically from approximately 3 km/s to 6 km/s within 4 km from the Earth's surface. Moreover, at a distance of approximately 11 km along the profile, there is an abrupt increase in the velocity field. In this zone indeed, an ascent from 2 km depth to 0 km above sea level of the 5.2 km/s iso‐velocity contour can be noted. The retrieved velocity can be associated with Plio‐Pleistocene clastic deposits outcropping in the basin zone and with Mesozoic limestone deposits. The inversion of waveform semblance data shows that a P‐to‐P reflector is retrieved at a depth of approximately 2 km. This interface is deeper in the north‐eastern part of the profile, where it reaches 3 km depth and can be associated with a limestone horizon.

Fold evolution and drainage development in the Zagros mountains of Fars province, SE Iran

ABSTRACTA central question in structural geology is whether, and by what mechanism, active faults (and the folds often associated with them) grow in length as they accumulate displacement. An obstacle in our understanding of these processes is the lack of examples in which the lateral growth of active structures can be demonstrated definitively, as geomorphic indicators of lateral propagation are often difficult, or even impossible to distinguish from the effects of varying lithology or non‐uniform displacement and slip histories. In this paper we examine, using the Zagros mountains of southern Iran as our example, the extent to which qualitative analysis of satellite imagery and digital topography can yield insight into the growth, lateral propagation, and interaction of individual fold segments in regions of active continental shortening. The Zagros fold‐and‐thrust belt contains spectacular whaleback anticlines that are well exposed in resistant Tertiary and Mesozoic limestone, are often >100 km in length, and which contain a large proportion of the global hydrocarbon reserves. In one example, Kuh‐e Handun, where an anticline is mantled by soft Miocene sediments, direct evidence of lateral fold propagation is recorded in remnants of consequent drainage patterns on the fold flanks that do not correspond to the present‐day topography. We suggest that in most other cases, the soft Miocene and Pliocene sediments that originally mantled the folds, and which would have recorded early stages in the growth histories, have been completely stripped away, thus removing any direct geomorphic evidence of lateral propagation. However, many of the long fold chains of the Zagros do appear to be formed from numerous segments that have coalesced. If our interpretations are correct, the merger of individual fold segments that have grown in length is a major control on the development of through‐going drainage and sedimentation patterns in the Zagros, and may be an important process in other regions of crustal shortening as well. Abundant earthquakes in the Zagros show that large seismogenic thrust faults must be present at depth, but these faults rarely reach the Earth's surface, and their relationship to the surface folding is not well constrained. The individual fold segments that we identify are typically 20–40 km in length, which correlates well with the maximum length of the seismogenic basement faults suggested from the largest observed thrusting earthquakes. This correlation between the lengths of individual fold segments and the lengths of seismogenic faults at depth suggest that it is possible, at least in some cases, that there may be a direct relationship between folding and faulting in the Zagros, with individual fold segments underlain by discrete thrusts.

Carbon dioxide degassing at Latera caldera (Italy): Evidence of geothermal reservoir and evaluation of its potential energy

In order to test the potentiality of soil CO2 diffuse degassing measurements for the study of underground mass and heat transfer in geothermal systems detailed surveys were performed at Latera caldera, which is an excellent test site, because of the abundant available subsurface data. Over 2500 measurements of soil CO2 flux revealed that endogenous CO2 at Latera caldera concentrates on a NE‐SW band coinciding with a structural high of fractured Mesozoic limestones hosting a water‐dominated high‐enthalpy geothermal reservoir. The total hydrothermal CO2 degassing from the structural high has been evaluated at 350 t d−1 from an area of 3.1 km2. It has been estimated that such a CO2 release would imply a geothermal liquid flux of 263 kg s−1, with a heat release of 239 MW. The chemical and isotopic composition of the gas indicates a provenance from the geothermal reservoir and that CO2 is partly originated by thermal metamorphic decarbonation in the hottest deepest parts of the system and partly has a likely mantle origin. The ratios of CO2, H2, CH4, and CO to Ar were used to estimate the T‐P conditions of the reservoir. Results cluster at T ∼ 200–300°C and PCO2 ∼ 100–200 bars, close to the actual well measurements. Finally, the approach proved to be an excellent tool to investigate the presence of an active geothermal reservoir at depth and that the H2‐CO2‐CH4‐CO‐Ar gas composition is a useful T‐P geochemical indicator for such CO2 rich geothermal systems.

Geophysical surveys of the Joya Honda maar (México) and surroundings; volcanic implications

Joya Honda (JH) is a Quaternary maar excavated in Mesozoic limestone. It is located in central Mexico and belongs to the Ventura volcanic field (VVF), which is composed by cinder cones and maars made of intraplate-type mafic alkalic rocks. Volcanoes in the region form ∼ N20W lineaments, roughly parallel to a regional set of normal faults, but there is no obvious relation between these faults and vent distribution in the exposed geology around the maar. The volcanic rock volume is small in the VVF, and most volcanoes and their products are scattered in a region where outcrops are dominated by limestone. The near-vent tephra associated to the JH maar lies north of the crater. This relation suggests that the crater was formed by directed hydromagmatic explosions and may indicate an inclined volcanic conduit near the surface. The tephra stratigraphy suggests that the initial explosions were relatively dry and the amount of water increased during the maar forming eruption. Therefore, the existing model of the maar–diatreme formation may not be applicable to Joya Honda as it requires the formation of a cone of depression in the aquifer and deepening of the focii of the explosions as the crater and underlying diatreme grew. Thus, it is unlikely that there is a diatreme below Joya Honda. Aeromagnetic data shows a boundary between two regional magnetic domains near the elongated volcanic cluster of the VVF. The boundary is straight, with a distinct kink, from NE- to NW-trend, near JH. The limit between the domains is interpreted as fault contacts between mid-Tertiary volcanic rocks and marine Mesozoic sedimentary rocks. Hence, magma ascent in the area may have been facilitated by fractures near the surface. Magnetic and gravimetric ground surveys show that the anomalies associated with the maar are not centered in the crater, which could be consistent with an inclined volcanic conduit. A magnetic profile measured on exposed limestone across the volcanic lineament failed to show an anomaly such as that caused by a connecting dike between the volcanoes. Therefore, either the dike does not exist or it is so deep or so thin that it is beyond the limit of detection of the method and/or equipment used. Thus, the volcanic conduit immediately below Joya Honda can be reasonably modeled in the shape of a plug. A 2-D model of the crater anomaly is consistent with a roughly tabular deposit formed by fall-back pyroclasts and slump deposits near the surface. Based on this result we propose an alternative model for the formation of maar-type volcanoes excavated in hard rock, where there is no evidence of a gradual decrease of the water/magma ratio as the eruption advanced.

Tectonic configuration of the Apuseni–Banat—Timok–Srednogorie belt, Balkans-South Carpathians, constrained by high precision Re–Os molybdenite ages

The Apuseni–Banat–Timok–Srednogorie magmatic–metallogenic belt (ABTS belt), forms a substantial metallogenic province in the Balkan-South Carpathian system in southeastern Europe. The belt hosts porphyry, skarn, and epithermal deposits mined since pre-Roman times. Generally, the deposits, prospects, and occurrences within the belt are linked to magmatic centers of calc-alkaline affinity. Fifty-one rhenium-osmium (Re–Os) ages and Re concentration data for molybdenites define systematic geochronologic trends and constrain the geochemical-metallogenic evolution of the belt in space and time. From these data and additional existing geologic-geochemical data, a general tectonic history for the belt is proposed. Mineralization ages in Apuseni-Banat, Timok, and Panagyurishte (the central district of the larger E–W Srednogorie Zone) range from 72–83, 81–88, and 87–92 Ma, respectively, and clearly document increasing age from the northwestern districts to the southeastern districts. Further, Re–Os ages suggest rapidly migrating pulses of Late Cretaceous magmatic–hydrothermal activity with construction of deposits in ~1 m.y., districts in ~10 m.y., and the entire 1,500 km belt in ~20 m.y. Ages in both Timok and Panagyurishte show systematic younging, while deposit ages in Banat and Apuseni are less systematic reflecting a restricted evolution of the tectonic system. Systematic differences are also observed for molybdenite Re concentrations on the belt scale. Re concentrations generally range from hundreds to thousands of parts per million, typical of subduction-related Cu–Au–Mo–(PGE) porphyry systems associated with the generation of juvenile crust. The geochronologic and geochemical trends are compatible with proposed steepening of subducting oceanic slab and relaxation of upper continental plate compression. Resulting influx of sub-continental mantle lithosphere (SCML) and asthenosphere provide a fertile metal source and heat, while the subducting slab contributes connate and mineral dehydration fluids, which facilitate partial melting and metal leaching of SCML and asthenosphere. Cu–Au–Mo–(PGE) porphyry deposits may develop where melts are trapped at shallow crustal levels, often with associated volcanism and epithermal-style deposits (South Banat, Timok, and Panagyurishte). Mo–Fe–Pb–Zn skarn deposits may develop where felsic melts are trapped adjacent to Mesozoic limestones at moderate crustal levels (North Banat and Apuseni). Systematic spatial variations in deposit style, commodity enrichment, Re–Os ages, and Re concentrations support specific tectonic processes that led to ore formation. In a post-collisional setting, subduction of Vardar oceanic crust may have stalled, causing slab steepening and rollback. The slab rollback relaxes compression, facilitating and enhancing orogenic collapse of previously thickened Balkan-South Carpathian crust. The progression of coupled rollback-orogenic collapse is evidenced by the width of Late Cretaceous extensional basins and northward younging of Re–Os ages, from Panagyurishte (~60 km; 92–87 Ma) to Timok (~20 km; 88–81 Ma) to Apuseni-Banat (~5 km; 83–72 Ma). Generation of a well-endowed mineral belt, such as the ABTS, requires a temporally and spatially restricted window of magmatic–hydrothermal activity. This window is quickly opened as upper plate compression relaxes, thereby inducing melt generation and ingress of melt to higher crustal levels. The window is just as quickly closed as upper plate compression is reinstated. The transient tectonic state responsible for economic mineralization in the ABTS belt may be a paleo-analogue to transient intervals in the present subduction tectonics of SE Asia where much mineral wealth has been created in the last few million years.

Deformation features within an active normal fault zone in carbonate rocks: The Gubbio fault (Central Apennines, Italy)

The Gubbio fault is an active normal fault defined by an important morphological scarp and normal fault focal mechanism solutions. This fault truncates the inherited Miocene Gubbio anticline and juxtaposes Mesozoic limestones in the footwall against Quaternary lacustrine deposits in the hanging wall. The offset is more than 2000 m of geological throw accumulated during a poly-phased history, as suggested by previous works, and has generated a complex zone of carbonate-rich fault-related structures. We report the results of a multidisciplinary study that integrates detailed outcrop and petrographic analysis of two well-exposed areas along the Gubbio fault zone, geochemical analysis (fluid inclusions, stable isotopes, and trace elements) of calcite-sealed fault-related structures and fault rocks, and biostratigraphic controls. Our aims are: (i) the characterization of the deformation features and their spatial–temporal relationships, and (ii) the determination of the P/ T conditions and the fluid behaviour during deformation to achieve a better understanding of fluid–rock interaction in fault zones. We show that few of the observed structures can be attributed to an inherited shortening phase while the most abundant structures and fault rocks are related to extensional tectonics. The outcropping extensional patterns formed at depths less than 2.5–3 km, in a confined fluid system isolated from meteoric water, and the fault structures are the response to a small amount of cumulated displacement, 12–19% of the total geological throw.

Geology, Geochemistry, Stable Isotope, and Fluid Inclusion Investigation of the Iron Oxide-Gold Mineralization in Bakir Tepe, Kangal-Sivas, East-Central Turkey

The Bakir Tepe area is characterized by four different lithologic units of Devonian-Carboniferous age. These units, from bottom to top, are metasiltstone, metacarbonate, metasandstone, and metaquartz sandstone. Metamorphic rocks in the study area are tectonically overlain by the recrystallized Mesozoic Munzur limestone. Iron oxide-gold mineralization in the Bakir Tepe area occurs in two different localities. The first is an alteration zone, which was formed at the thrust contact of metasiltstone with metacarbonate and metasandstone; the second locality is in metaquartz sandstone. The dominant minerals are quartz + hematite/magnetite ± pyrite ± gold in veins of various lengths and widths. Magnetite occurred after hematite, along fractures in hematite. Oxygen isotope data (δ18O = 6.2-13.3‰) from fluids in equilibrium with quartz, and hydrogen isotope data (δD = -55 to -75‰) from fluid inclusions trapped in quartz, indicate that the hydrothermal fluids responsible for formation of the gold mineralization were dominated by metamorphicderived waters. Hydrothermal solutions were of the NaCl-CO2-H2O type. Salinity values as NaCl equivalent wt% range between 34 and 39. Total homogenization temperatures range between 132 and 382°C in secondary L+V inclusions, and 237 to 324°C in primary L+V+H inclusions. Calculated temperatures of vein formation using oxygen isotopes in quartz-hematite mineral pairs yields formation temperatures between 200 and 330°C, consistent with the fluid inclusion measurements.

High-resolution seismic imaging of gas accumulations and seepage in the sediments of the Ria de Aveiro barrier lagoon (Portugal)

Methane is a powerful greenhouse gas and an important energy source. The global significance and impact in coastal zones of methane gas accumulation and seepage in sediments from coastal lagoon environments are still largely unknown. This paper presents results from four high-resolution seismic surveys carried out in the Ria de Aveiro barrier lagoon (Portugal) in 1999, 2002 and 2003. These comprise three chirp surveys (RIAV99, RIAV02, RIAV02A) and one boomer survey (RIAV03). Evidence of extensive gas accumulation and seepage in tidal channel sediments from the Ria de Aveiro barrier lagoon is presented here for the first time. This evidence includes: acoustic turbidity, enhanced reflections, acoustic blanking, domes, and acoustic plumes in the water column (flares). The stratigraphy and structural framework control the distribution and extent of gas accumulations and seepage in the study area. In these shallow systems, however, tidal altitude variations have a significant impact on gas detection using acoustic methods, by changing the raw amplitude of the enhanced seismic reflections, acoustic turbidity, and acoustic blanking in gas-prone areas. Direct evidence of gas escape from drill holes in the surrounding area has shown that the gas present in the Ria de Aveiro consists of biogenic methane. Most of the gas in the study area was probably generated mainly in Holocene lagoon sediments. Evidence of faults affecting the Mesozoic limestones and clays underlying some of the shallow gas occurrences, and the presence of high-amplitude reflections in these deeper units raise the possibility that some of this gas could have been generated in deeper sedimentary layers, and then migrated upward through the fractured Mesozoic strata.

Magmatic History of Somma–Vesuvius on the Basis of New Geochemical and Isotopic Data from a Deep Borehole (Camaldoli della Torre)

A continuous-coring borehole recently drilled at Camaldoli dellaTorre on the southern slopes of Somma^Vesuvius provides constraints on the volcanic and magmatic history of the Vesuvian volcanic area since c. 126 ka BP.The cored sequence includes volcanic units, defined on stratigraphical, sedimentological, petrological and geochemical grounds, emitted from both local and distal vents. Some of these units are of known age, such as one Phlegraean pre-Campanian Ignimbrite, Campanian Ignimbrite (39 ka), Neapolitan Yellow Tuff (14 9 ka) and Vesuvian Plinian deposits, which helps to constrain the relative age of the other units.The main rock types encountered are shoshonite, phonotephrite, latite, trachyte and phonolite. The sequence includes, from the base upwards: a thick succession of pyroclastic units emplaced between 126 and 39 ka, most of them attributed to eruptions that occurred in the Phlegraean area; the Campanian Ignimbrite; the products of a local tuff cone formed between 39 ka and the deposition of the products of the earliest activity of the Mt. Somma volcano; the products of the Somma^Vesuvius volcano, which include from the base upwards a thick sequence of lavas, pyroclastic rocks and the products of a local spatter cone dated between 3 7 ka and AD 79.The data obtained from the study of the borehole show that, before the Campanian Ignimbrite eruption, low-energy explosive volcanism took place in the Vesuvian area, whereas mostly high-energy explosive eruptions characterized the Campi Flegrei activity. In the Vesuvian area, Campanian Ignimbrite deposition was followed by the eruption of a local tuff cone and a long repose time, which predated the formation of the Mt. Somma edifice. Since 18 3 ka (Pomici di Base eruption) the activity of Somma^Vesuvius became mostly explosive with rare lava effusions.The shallowest cored deposits belong to the Camaldoli dellaTorre cone, formed between the Pomici di Avellino and Pomici di Pompei eruptions (3 7 ka^AD 79).Newgeochemical and Sr^Nd^Pb^ B-isotopic data on samples from the drilled core, together with those available from the literature, allow us to further distinguish the volcanic rocks as a function of both their provenance (i.e. Phlegraean or Vesuvian areas) and age, and to identify different magmatic processes acting through time in the Vesuvian mantle source(s) and during magma ascent towards the surface. Isotopically distinct magmas, rising from a mantle source variably contaminated by slabderived components, stagnated at mid-crustal depths (8^10 km below sea level) where magmas differentiated and were probably contaminated. Contamination occurred either with Hercynian continental crust, mostly during the oldest stages of Vesuvian activity (from 39 to 16 ka), or with Mesozoic limestone, mostly during recent Vesuvian activity. Energy constrained assimilation and fractional crystallization (EC-AFC) modelling results show that contamination with Hercynian crust probably occurred during differentiation from shoshonite to latite. Contamination with limestone, which is not well constrained with the available data, might have occurred only during the transition from shoshonite to tephrite. From the ‘deep’ reservoir, magmas rose towards a series of shallow reservoirs, in which they differentiated further, mixed, and fed volcanic activity.

Methane and hydrogen sulfide seepage in the northwest Peloponnesus petroliferous basin (Greece): Origin and geohazard

Gas seepages along the Ionian coast of the northwestern Peloponnesus (Greece), at Killini, Katakolo, and Kaiafas reflect deep hydrocarbon-generation processes and represent a real hazard for humans and buildings. Methane microseepage, gas concentration in offshore and onshore vents, and gas dissolved in water springs, including the isotopic analysis of methane, have shown that the seeps are caused by thermogenic methane that had accumulated in Mesozoic limestone and had migrated upward through faults, or zones of weakness, induced by salt diapirism. A link between local seismicity and salt tectonics is suggested by the analyses of hypocenter distribution. Methane acts as a carrier gas for hydrogen sulfide produced by thermal sulfate reduction and/or thermal decomposition of sulfur compounds in kerogen or oil. Methane seeps in potentially explosive amounts, and hydrogen sulfide is over the levels necessary to induce toxicological diseases and lethal effects.

Multiconfiguration GPR measurements for geometric fracture characterization in limestone cliffs (Alps)

Rock-mass fracturing is a key parameter in rock-fall hazard assessment. However, traditional geologic observations can provide information only about discontinuities at the surface. In this case study, detailed ground-penetrating-radar (GPR) measurements (with antennas of [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text]) were conducted on a test site, using different acquisition configurations deployed on vertical cliff faces. Conventional 2D profile data, common-midpoint (CMP) survey data, and transmission data were acquired to evaluate the potential use of radar waves to characterize the geometry and properties of the major discontinuities (fractures) within a Mesozoic limestone massif. Results showed that the continuity and geometry (orientation and dip) of the major observed fractures, which are crucial parameters for assessing rock stability, can be obtained by combining vertical and horizontal profiles measured along the cliff. We used [Formula: see text] antennae and reached a maximum penetration of [Formula: see text], which limits the technique to rock volumes of a few tens of thousands of cubic meters. We observed significant differences in reflectivity along the detected fractures, which suggests that the fractures’ characteristics vary in the rock mass. We used transmission data to obtain a radar velocity image. Although the results were consistent with radar profiles on the cliff, they showed that the technique has little utility, beyond that of more traditional GPR methods, for delineating fractures in a rock mass.

Characterization of Hungarian Red Soils

Some pedological and micromorphological investigations were carried out on representative red clay samples selected from a large number of profiles. On the basis of conclusions drawn from the analytical results, the red clays can be divided into the following groups: - The red clays of the foothills of the Tokaj Mountains were formed on rhyolite or rhyolite tuff, and are covered by loess in some areas. They are relic soils, older than loess, formed under the warm climate of the Tertiary Period. In addition to quartz they contain feldspars, illite, montmorillonite and a small amount of kaolinite. - The red clays of Aggtelek Karst are Tertiary relic soils formed on Mesozoic limestone. The dominant clay mineral is kaolinite, but they contain a siginificant amount of smectite as well. - The red clays of the Northern periphery of the Hungarian Plain are situated on clay, silt and sand layers of different origin or between loess depositions. They were formed in the Pliocene and at the turn of the Pliocene and Pleistocene. These soils have a medium clay content, with a large quantity of montmorillonite and a small amount of kaolinite. - Red clays formed on Permian sandstones . These rocks were formed in the Permian period, and were issued from a mixture of sediments under tropical climate, tropical weathering. They are the signs of the oldest soil formation in Hungary. They can be characterized by their kaolinite, illite, montmorillonite and hematite contents. - The red clays of the Transdanubian hilly region wereformed by the weathering of thePannonian surface between the end of the Miocene Period and the lower Pleistocene. Medium clay content is characteristic of these red clays. They contain kaolinite, montmorillonite, chlorite and a small amount of hematite. Concerning micromorphological features, speckled and granostriated b-fabrics of the groundmass, mainly due to swelling and shrinking, were observed in some samples. Clay coatings are mainly interpreted as micromorphological features of illuviation. The investigated red clays are similar to tropical and sub-tropical ferrallitic soils in respect of their formation and mineral characteristics.