Weak compositional zonation in a silicic magmatic system: Incesu ignimbrite,Central Anatolian Volcanic Province (Kayseri – Turkey)

The Central Anatolian Volcanic Province (CAVP), one of four major volcanic provinces in Turkey, plays a significant role in the interpretation of the tectonic evolution of Central Anatolia. The CAVP developed within a complex collisional system involving the African, Arabian and Eurasian plates during the Miocene. The volcanism exhibits complicated variations in mineralogical, petrological and geochemical compositions resulting from post-collisional lithospheric dynamics. The Incesu ignimbrite has 5–20 m thick and covers an area of ～7800 km². It is composed of three stratigraphic levels. The lower level (LL) shows blackish brown and glassy welded structure. The middle level (ML) is a well-welded, reddish pink in color and has large amounts of fiamme. The upper level (UL) is grayish pink, weakly welded and has rock fragments of different compositions. The Incesu ignimbrite is composed of plagioclase (oligoclase, andesine) + pyroxene (augite, clinoenstatite) + opaque minerals and low amount of amphibole, biotite and quartz. Eutaxitic texture is dominant in ML and LL samples; these levels are more strongly and contain more flattened pumice fragments and volcanic glass shards than in the UL. A sharp color contrast defines the contact between LL and ML.Major, trace and rare earth element of the Incesu ignimbrite, characterized by their rhyolite, rhyodacite–dacite composition, medium–high K, calcalkaline and peraluminous nature, show fractional crystallization primarily controlled by plagioclase, clinopyroxene, magnetite, ilmenite and titanomagnetite. Sr and Nd isotopic ratios of Incesu ignimbrite display isotopic variations between the ignimbrite levels; they exhibit a limited range in ⁸⁷Sr/⁸⁶Sr (0.7043–0.7049) and ¹⁴³Nd/¹⁴⁴Nd (0.512716–0.512760). The Sr–Nd isotopic ratio of Incesu ignimbrite reveals an age of 3 Ma. The ignimbrite evolved through fractional crystallization and crystal contamination of the parent magma derived from Ocean Island Basalt (OIB) like magma. This suggestion is supported by the AFC modeling based on the trace elements and Sr isotope data.Variation of several major oxide concentrations (Fe₂O₃, TiO₂, CaO and K₂O), trace element concetrations (V, Sr, Cs and Rb) and trace element ratios (Ba/Rb, Sr/, K/Sr, K/Nb, Rb/Sr, Rb/Y and Rb/Nb) versus SiO₂ concentration show the magma chamber that generated the Incesu ignimbrite was compositionally zoned. All geochemical and Sr–Nd isotpic datas can be interepreted to be the result of a subduction related source.     

Cement stratigraphy: image probes of cathodoluminescent facies

Cement stratigraphy of carbonates aims to establish the chronology of processes involved in the rock diagenesis. Regional cement stratigraphy allows correlations and understanding of the petrological heterogeneities in reservoirs and aquifers, but is a long and rigorous approach. This article exposes a methodology of image analysis that facilitates the spatial correlation of diagenetic events in carbonate rocks. Based on the statistical comparison of signals extracted from the red spectrum emission of cathodoluminescence digital images, it gives via crosscorrelation a measure of similarity (values scaled from minimum −1 to maximum 1) between two cathodoluminescence facies. Cementation events and diagenetic chronologies can thus be quickly correlated without the support of a full chronology, the model normally established on cement morphologies, petrological analyses and cathodoluminescence zonation sequences. A case study from two Upper Kimmeridgian Mount Salève outcrops (France) illustrates this methodology. Their diagenetic sequences recorded in cathodoluminescent cements are presented and being compared. The final statistical similarity between the two outcrops reaches an index of R = 0.78. This result is sustained by petrological and geochemical analyses such as alizarine–ferricyanure stained thin sections, X microfluorescence mapping of elements, and microthermometry of fluid inclusions.     

The effect of welding degree on geotechnical properties of an ignimbrite flow unit: the Bitlis castle case (eastern Turkey)

Ignimbrites are associated with nearly most of the world’s volcanoes and are defined as a deposit from pyroclastic density currents. They consist predominantly of pumiceous lapilli and blocks, and glass shards, which shows evidence of having been emplaced as a concentrated hot and dry particulate flow. These rocks are widely used as building stone especially in ancient buildings. Bitlis valley is covered by ignimbritic products, derived from Nemrut stratovolcano, one of the significant volcanic centers in Eastern Anatolia. The Bitlis ignimbrite is separated into lower level (LL), middle level (ML) and upper level (UL) according to color, welding degree and structural features. All three levels were used extensively in many parts of the Bitlis castle as masonry materials. Studies were carried out on mineralogical and geochemical composition and on physical and mechanical properties of the ignimbrites. In addition, a freeze–thaw cycle test was executed. There are no considerable differences in mineralogical composition among the levels of ignimbrite. All levels contain plagioclase, sanidine, pyroxene, and opaque mineral. In addition, anorthoclase and quartz are seen. In general, the LL of ignimbrite shows relic perlitic and eutaxitic texture, whereas eutaxitic and vesicular texture are commonly developed in the ML and UL, respectively. Lower, middle, and upper level ignimbrite samples display similar and limited compositional spread in terms of major oxide elements. They have trachyte composition. Building stones can be classified according to mineralogy, mechanical and physical properties and processing types. Mechanical and physical properties are very important with respect to stone quality/durability. The mechanical and physical properties of the ignimbrites are controlled by the welding degree. It was found that increasing welding degree from UL to LL correlates with increasing density, compressive strength and slake durability index and with decreasing porosity. The Bitlis ignimbrites have turned out as susceptible to freeze–thaw cycles.     

Magma Mixing and Crustal Recycling Recorded in Ternary Feldspar from Compositionally Zoned Peralkaline Ignimbrite A', Gran Canaria, Canary Islands

Miocene Ignimbrite ‘A’ on Gran Canaria containsthree compositional endmember fiamme types(two rhyolites andone trachyte) each of which crystallized distinct feldspar.Various textural and compositional criteria are interpretedas reflecting a complex scenario within the magma chamber inwhich the crystals formed. About 25–30% of the feldsparphenocrysts contain evidence for magma mixing in the form of(1) partial to severe dissolution–resorption rims, (2)distinct zones of drastically different compositions and (3)overgrowth textures on formerly resorbed crystals. Four majortypes of zoning in the oligoclase to anorthoclase feldsparsof ignimbrite ‘A’ include a normal and a reverselyzoned type and two complexly zoned types. The feldspars withnormal and reverse zonation show only minor compositional amplitudesbetween individual zones (     

Topographical controls on small‐volume pyroclastic flows

Emplacement of small‐volume (<0·1 km³) pyroclastic flows is significantly influenced by topography. The Arico ignimbrite on Tenerife (Canary Islands) is a characteristic small‐volume pyroclastic flow deposit emplaced on high relief topography. The pyroclastic flow flowed down pre‐existing valleys on the southern slopes of the island. In proximal areas deep (up to 100 m) valleys acted as efficient conduits for the pyroclastic flow, which was mostly channelled; in this particular area the ignimbrite corresponds to a homogeneous, moderately welded deposit, consisting of flattened pumices in an abundant ashy matrix with a relatively low lithic fragment content. In intermediate zones significant changes occur in the steepness of the slope and, although still channelled, here the pyroclastic flow was influenced by hydraulic jumps. In this area, two different units can be clearly distinguished in the ignimbrite: the lower unit is composed of a lithic‐rich ground‐layer deposit that formed at the turbulent, highly concentrated head of the flow; the upper unit consists of a well welded pumice‐rich deposit that occasionally reveals a basal layer formed by shearing with the lower part. This division into two units is maintained as far as distal areas near the present‐day coastline, where the slope is very gentle or null and the ignimbrite is not channelled. The ground layer is not found in distal areas. The ignimbrite here only consists of the upper unit, which is occasionally repeated due to a surging process provoked by the lower flow speed, as the pyroclastic flow spread out of the channelled zone. A theoretical model on how topography controlled the deposition of the Arico ignimbrite is derived by interpreting the observed lithological and sedimentological variations in terms of changes in topography and bedrock morphology. This new model is of general applicability and will help to explain other deposits of similar characteristics.     

Probabilistic seismic hazard map of NW Himalaya and its adjoining area,India

The seismically active Northwest (NW) Himalaya falls within Seismic Zone IV and V of the hazard zonation map of India. The region has suffered several moderate (~25), large-to-great earthquakes (~4) since Assam earthquake of 1897. In view of the major advancement made in understanding the seismicity and seismotectonics of this region during the last two decades, an updated probabilistic seismic hazard map of NW Himalaya and its adjoining areas covering 28–34°N and 74–82°E is prepared. The northwest Himalaya and its adjoining area is divided into nineteen different seismogenic source zones; and two different region-specific attenuation relationships have been used for seismic hazard assessment. The peak ground acceleration (PGA) estimated for 10% probability of exceedance in 50 and 10 years at locations defined in the grid of 0.25 × 0.25°. The computed seismic hazard map reveals longitudinal variation in hazard level along the NW Himalayan arc. The high hazard potential zones are centred around Kashmir region (0.70 g/0.35 g), Kangra region (0.50 g/0.020 g), Kaurik-Spitti region (0.45 g/0.20 g), Garhwal region (0.50 g/0.20 g) and Darchula region (0.50 g/0.20 g) with intervening low hazard area of the order of 0.25 g/0.02 g for 10% probability in 50 and 10 years in each region respectively.     

The source of fluoride toxicity in Muteh area,Isfahan, Iran

Endemic dental fluorosis has been observed in most inhabitants of three villages of Muteh area, located in northwest of Isfahan province, with mottled enamel related to high levels of fluoride in drinking water (1.8–2.2 ppm). Forty-seven groundwater samples from six villages were collected and fluoride concentrations along with physico-chemical parameters were analyzed. Fluoride concentration in this area varies from 0.2 to 9.2 mg/l with highest fluoride level at Muteh gold mine (Chahkhatun mine). Fluoride concentration positively correlates with pH and HCO₃ ⁻ indicating that alkaline pH provides a suitable condition for leaching of fluoride from surrounding rocks. The district is mainly covered by three lithological units, namely, metamorphic and granite rocks, alluvial sediments, and carbonate rocks. Factor analysis shows that parameters can be classified into four components: electrical conductivity (EC), total dissolved solids (TDS), Cl⁻, Na⁺ and K⁺, pH and F⁻, SO₄ ²⁻and Mg²⁺, HCO₃ ⁻ and Ca₂ ⁺. The groundwaters from the three geological units were compared using Mann–Whitney U test. The order of median fluoride concentration is: metamorphic and granite rocks > alluvial sediments > carbonate rocks. Hence, the fluoride content is most probably related to fluoride-bearing minerals such as amphibole and mica group minerals in metamorphic and granitic rocks. The concentration of fluoride in drinking water wells located near the metamorphic complex in Muteh area is above 2 ppm.     

Generation of voluminous silicic magmas and formation of mid-Cenozoic crust beneath north-central Mexico: evidence from ignimbrites,associated lavas,deep crustal granulites,and mantle pyroxenites

 Isotopic and trace element data from mantle and granulite xenoliths are used to estimate the relative contributions of mantle and crustal components to a large ignimbrite, referred to as the upper ignimbrite, that is representative of the voluminous mid-Cenozoic rhyolites of northwestern Mexico. The study also uses data from the volcanic rocks to identify deep crustal xenoliths that are samples of new crust created by the Tertiary magmatism. The isotopic composition of the mantle component is defined by mantle-derived pyroxenites that are interpreted to have precipitated from mid-Cenozoic basaltic magmas. This component has ɛ_Nd≈+1.5, ⁸⁷Sr/⁸⁶Sr≈0.7043 and ²⁰⁶Pb/²⁰⁴Pb≈18.6. Within the upper ignimbrite and associated andesitic and dacitic lavas, initial ⁸⁷Sr/⁸⁶Sr is positively correlated with SiO₂, reaching 0.7164 in the ignimbrite. Initial ²⁰⁶Pb/²⁰⁴Pb ratios also show a positive correlation with silica, whereas ɛ_Nd values have a crude negative correlation, reaching values as low as −2. Of the four isotopically distinct crustal components identified from studies of granulite xenoliths, only the sedimentary protolith of the paragneiss xenoliths can be responsible for the high initial ⁸⁷Sr/⁸⁶Sr of the upper ignimbrite. The Nd, Sr, and Pb isotopic compositions of the upper ignimbrite can be modeled with relatively modest assimilation (≤20%) of the sedimentary component ± Proterozoic granulite. Gabbroic composition granulite xenoliths have distinctive Nd, Sr, and Pb isotope ratios that cluster closely within the range of compositions found in the andesitic and dacitic lavas. These mafic granulites are cumulates, and their protoliths are interpreted to have precipitated from the intermediate to silicic magmas at 32–31 Ma. These mafic cumulate rocks are probably representative of much of the deep crust that formed during mid-Cenozoic magmatism in Mexico. Worldwide xenolith studies suggest that the relatively great depth (≤20 km) at which assimilation-fractional crystallization took place in the intermediate to silicic magma systems of the La Olivina region is the rule rather than the exception. Oligocene ignimbrites of the southwestern United States (SWUS) have substantially lower ɛ_Nd values (e.g. <−6) than the upper ignimbrite and other rhyolites from Mexico. This difference appears to reflect a greater crustal contribution to ignimbrites of the SWUS, perhaps due to a higher temperature of the lower crust prior to the emplacement of the Oligocene basaltic magmas. Received: 16 December 1994 / Accepted: 13 September 1995     

Magma plumbing beneath Anak Krakatau volcano, Indonesia: evidence for multiple magma storage regions

Understanding magma plumbing is essential for predicting the behaviour of explosive volcanoes. We investigate magma plumbing at the highly active Anak Krakatau volcano (Indonesia), situated on the rim of the 1883 Krakatau caldera by employing a suite of thermobarometric models. These include clinopyroxene-melt thermobarometry, plagioclase-melt thermobarometry, clinopyroxene composition barometry and olivine-melt thermometry. Petrological studies have previously identified shallow magma storage in the region of 2–8 km beneath Krakatau, while existing seismic evidence points towards mid- to deep-crustal storage zone(s), at 9 and 22 km, respectively. Our results show that clinopyroxene in Anak Krakatau lavas crystallized at a depth of 7–12 km, while plagioclase records both shallow crustal (3–7 km) and sub-Moho (23–28 km) levels of crystallization. These magma storage regions coincide with well-constrained major lithological boundaries in the crust, implying that magma ascent and storage at Anak Krakatau is strongly controlled by crustal properties. A tandem seismic tomography survey independently identified a separate upper crustal (<7 km) and a lower to mid-crustal magma storage region (>7 km). Both petrological and seismic methods are sensitive in detecting magma bodies in the crust, but suffer from various limitations. Combined geophysical and petrological surveys, in turn, offer increased potential for a comprehensive characterization of magma plumbing at active volcanic complexes.     

Quartz zoning and the pre-eruptive evolution of the ~340-ka Whakamaru magma systems,New Zealand

Cathodoluminescence (CL) zoning in quartz crystals from rhyolitic pumices in two ignimbrite members of the ~340-ka Whakamaru super-eruption deposits, Taupo Volcanic Zone, New Zealand, is investigated in conjunction with the analysis of Ti concentration in quartz to reconstruct the history of changing magma chamber conditions and to elucidate the eruption-triggering processes. CL intensity images are taken as a proxy for Ti concentration and thus temperature and/or pressure and/or compositional variations during crystal growth history. Estimates of the maximum temperature changes (i.e., assuming other factors influencing Ti uptake remain constant) are made using the TitaniQ geothermometer based on the Ti concentration in quartz. These results are reviewed in comparison with Fe–Ti oxide, feldspar-melt and amphibole geothermometry. Core-to-rim quartz Ti profiles record a marked change in conditions (temperature increase and/or pressure decrease and/or change in melt composition) causing and then following a significant resorption horizon in the outer parts of the crystals. Two alternative models that could explain the quartz Ti zonation invoke a temperature increase caused by mafic recharge and/or a pressure decrease due to magma ponding and re-equilibration at shallow crustal levels. Concomitant changes in melt composition and Ti activity may, however, also have strongly influenced Ti uptake into the quartz. Some crystals also show other marked increases in CL brightness internally, but any accompanying magmatic changes did not result in eruption. Diffusion modelling indicates that this significant change in conditions occurred over ~10–85 years prior to caldera-forming eruption. This rapid thermal pulse or pressure change is interpreted as evidence for open-system processes, and appears to record a magma chamber recharge event that rejuvenated the Whakamaru magma system (melt-dominant magma plus crystal mush), and potentially acted as a trigger for processes that led to eruption.     

Stratigraphy and evolution of the trachy-rhyolitic volcanism of the Senafe area (Eastern Eritrean Plateau)

The Senafe area reveals a pile of stratoid volcanic rocks (“Senafe” ignimbrite), of considerable extent and thickness, which are the products of the first volcanic event which took place in this sector, close to the upper margin of the Afar escarpment.The Senafe ignimbrite is composed prevalently of trachyte with differing degrees of alkalinity: trachy-dacite of transitional series, and trachyte s.s. of mildly alkaline series. K/Ar radiometric measurements carried out on three samples give ages ranging between 21 and 23 Ma (Lower Miocene) and show that the Senafe ignimbrite with transitional character is an extension of the Serae rhyolite of the Central Eritrean Plateau, and may also be correlated with the Miocene Alaji rhyolite of the Central Ethiopian Plateau. In contrast, the more alkaline ignimbrite shows good correlations with the trachyte emitted by the Miocene Termaber alkaline central volcanoes of Ethiopia.It is noted that, in the course of the Miocene volcanism in Eritrea, the volumetric ratio between associated basalt and ignimbrite diminishes from west to east, i.e., approaching the Afar escarpment.The stratoid volcanic rocks are injected by thick trachytic and rhyolitic dykes. As radiometric measurements on them could not be performed, their age is unknown, but it is probably more recent than that of the injected ignimbrite, according to Merla and Minucci [Merla, G., Minucci, E., 1938. Missione geologica nel Tigrai. In: La serie dei terreni, vol. 1. Regia Accademia d’Italia, Centro Studi per l’Africa Orientale Italiana, Rome, Italy, pp. 1–362] for similar dykes and domes occurring in the Adwa-Axum area (Tigrai, Ethiopia), not far from Senafe.A section is devoted to the dyke feeders of the Eritrean and Adwa-Axum volcanism.     

The Granada ignimbrite: A compound pyroclastic unit and its relationship with Upper Miocene caldera volcanism in the northern Puna

The Granada ignimbrite, an Upper Miocene volcanic unit from the northern Puna, previously has been interpreted as an extensive ignimbrite (>2300 km²) associated with eruptions from the Vilama caldera (trap-door event). On the basis of new data, we revise its correlation and redefine the unit as a compound, high aspect ratio ignimbrite, erupted at approximately 9.8 Ma. Calculated volumes (100 km³) are only moderate in comparison with other large volume (>1000 km³) ignimbrites that erupted approximately 2–6 m.y. later in the region (e.g. Vilama, Panizos, Atana). Six new volcanic units are recognized from sequences previously correlated with Granada (only one sourced from the same center). Consequently, the area ascribed to the Granada ignimbrite is substantially reduced (630 km²), and links to the Vilama caldera are not supported. Transport directions suggest the volcanic source for the Granada ignimbrite corresponds to vents buried under younger (7.9–5 Ma) volcanic rocks of the Abra Granada volcanic complex. Episodes of caldera collapse at some stage of eruption are likely, though their nature and timing cannot be defined from available data. The eruption of the Granada ignimbrite marks the onset of a phase of large volume (caldera-sourced) volcanism in the northern Puna.     

Human-induced sedimentological changes in Manzala Lagoon, Nile Delta, Egypt

 The Manzala Lagoon in Egypt's Nile Delta has become a sediment sink of reduced area and depth, with increased contaminant levels. Loss of much-needed fresh to brackish water reserves and decreased fish catches have serious ramifications. Herein, maps of temporal and regional sediment distributions in Manzala incorporate petrological and statistical analyses of 200 surficial and short core samples. These provide baseline information needed to help implement protection measures for this vital wetland. Four periods are considered: 1920s, 1940s, ∼1965, and 1990. Important depositional changes between 1940s and ∼1965 resulted from anthropogenic effects on this quasi-closed lagoon system, including industrial buildup, wetland conversion to agricultural land, and irrigation waterway development. Further modification from ∼1965 to 1990 is associated with closure of the Aswan High Dam, continued construction of waterways that discharge waste water into lagoon margins, and marine incursion into the northern lagoon. If current practices continue, the lagoon could be reduced to about one-third of its present area by 2050 AD. Received: 2 October 1997 · Accepted: 13 January 1998     

福安地区碎斑熔岩的基本特征及成因

福安地区碎斑熔岩的形成受北东向火山基底断裂控制，具有明显的分带现象，由中心到边缘可划分出酸性粒状碎斑熔岩、中酸性粒状碎斑熔岩、中酸性霏细状碎斑熔岩、酸性霏细状碎斑熔岩、酸性隐晶状碎斑熔岩等岩石类型，是晚侏罗世火山活动衰亡时期岩浆以侵出一溢流形式活动的产物。碎斑熔岩与同期潜火山岩、流纹质晶屑熔结凝灰岩(熔离型)是同源岩浆分异及演化的结果，在空间上构成三相一体的共生组合地质体。     

Structural and magnetic fabric study of the Marimanha granite (Axial Zone of the Pyrenees)

The structural and magnetic fabric study of the Marimanha granite, Axial Zone of the Pyrenees, provides new data to characterize the zonation and the internal structure of the pluton. The Marimanha granite intrudes Cambro–Ordovician clastic rocks and Silurian–Devonian limestones and slates. The zonation of the low field magnetic susceptibility, consistent with the petrological zonation of the igneous body, indicates a concentric arrangement of rock types, with more basic compositions at the external areas. This pluton is characterized by a low susceptibility, and rock–magnetic studies indicate a majority of “paramagnetic” samples. Magnetic foliations strike parallel to petrographic contacts and to contours of zonation of magnetic susceptibility, and show a dominant NE–SW strike, steeply dipping towards the North. Locally, in the northern border of the pluton foliation directions become perpendicular to petrographic contacts and depict sigmoidal trajectories. Magnetic lineations are characterized by the predominance of NE–SW trends with shallow plunges to the NE and SW. These foliations and lineations are parallel to the slight elongation of internal petrographic zonation. Magnetic fabric within the granitoid body and internal elliptical shape of petrographic zonation, suggest an intrusion contemporary with a transpressional regime and NNW–SSE shortening, syntectonic with the late stages of the Variscan orogeny. These results are in accordance with anisotropy of magnetic susceptibility studies of others plutons in the Pyrenees. To explain the origin of the Marimanha granite we propose magma ascent through faults at depth and emplacement by ballooning in situ at the rheological boundary between Cambro–Ordovician and Siluro–Devonian metasediments.     

Impacts of at-site wastewater disposal systems on the groundwater aquifer in arid regions: case of Sfax City, Southern Tunisia

Groundwater in Sfax City (Tunisia) has been known since the beginning of the century for its deterioration in quality, as a result of wastewater recharge into the aquifer. An average value of 12 × 10⁶ m³ of untreated wastewater reaches the groundwater aquifer each year. This would result not only in a chemical and biological contamination of the groundwater, but also in an increase of the aquifer piezometric level. Quantitative impacts were evaluated by examining the groundwater piezometric level at 57 surface wells and piezometers. The survey showed that, during the last two decades, the groundwater level was ever increasing in the urban area with values reaching 7 m in part; and decreasing in Sidi Abid (agricultural area) with values exceeding −3 m. Groundwater samples for chemical and microbial analysis were collected from 41 wells spread throughout the study area. Results showed significantly elevated levels of sodium, chlorides, nitrates and coliform bacteria all over the urban area. High levels (NO₃: 56–254 mg/l; Na >1,500 mg/l; Coliforms >30/100 ml) can be related to more densely populated areas with a higher density of pit latrine and recharge wells. Alternatively results showed a very variable chemical composition of groundwater, e.g. electrical conductivity ranges from 4,040 to19,620 μs/cm and the dry residual varies between 1.4 and 14 g/l with concentrations increasing downstream. Furthermore a softening of groundwater in Set Ezzit (highly populated sector) was observed.     

Analysis of fibrous zeolites in the volcanic deposits of the Viterbo Province,Italy

Since Etrurian age, the Viterbo Province (Central Italy) is famous for its ancient towns carved out of local ignimbrite deposits which geologically represent the sedimentation of pumice-rich, volcano-related pyroclastic flows. Almost the entire study area is geologically characterized by a thick succession of ignimbrites, tephra fallouts and lava flow deposits locally subjected to zeolitization. Among zeolites, fibrous erionite represents a well-known health hazard and so this work aims at locating and quantifying the presence of fibrous zeolites in volcanic deposits of the Viterbo area, suggesting at the same time a standard operational procedure useful in other areas showing the same possible hazard. 41 samples collected in the Viterbo area were analyzed by X-ray powder diffraction, optical and electron microscopy. Fibrous zeolites were detected in five samples and quantified in amounts ranging from 0.35 to 1.66% vol. They generally occur in tetragonal or orthorhombic prismatic habit and showed chemical composition mainly consistent with K-phillipsite. Fibrous zeolites occurred with aspect ratios (mean = 6.3), comparable or lower than those of erionite fibers reported in previous studies and mean diameters >3 μm.     

Epithermal mineralization controlled by synextensional magmatism in the Guazapares Mining District of the Sierra Madre Occidental silicic large igneous province,Mexico

We show here that epithermal mineralization in the Guazapares Mining District is closely related to extensional deformation and magmatism during the mid-Cenozoic ignimbrite flare-up of the Sierra Madre Occidental silicic large igneous province, Mexico. Three Late Oligocene–Early Miocene synextensional formations are identified by detailed volcanic lithofacies mapping in the study area: (1) ca. 27.5 Ma Parajes formation, composed of silicic outflow ignimbrite sheets; (2) ca. 27–24.5 Ma Témoris formation, consisting primarily of locally erupted mafic-intermediate composition lavas and interbedded fluvial and debris flow deposits; (3) ca. 24.5–23 Ma Sierra Guazapares formation, composed of silicic vent to proximal ignimbrites, lavas, subvolcanic intrusions, and volcaniclastic deposits. Epithermal low-to intermediate-sulfidation, gold–silver–lead–zinc vein and breccia mineralization appears to be associated with emplacement of Sierra Guazapares formation rhyolite plugs and is favored where pre-to-synvolcanic extensional structures are in close association with these hypabyssal intrusions.Several resource areas in the Guazapares Mining District are located along the easternmost strands of the Guazapares Fault Zone, a NNW-trending normal fault system that hosts most of the epithermal mineralization in the mining district. This study describes the geology that underlies three of these areas, which are, from north to south: (1) The Monte Cristo resource area, which is underlain primarily by Sierra Guazapares formation rhyolite dome collapse breccia, lapilli-tuffs, and fluvially reworked tuffs that interfinger with lacustrine sedimentary rocks in a synvolcanic half-graben bounded by the Sangre de Cristo Fault. Deposition in the hanging wall of this half-graben was concurrent with the development of a rhyolite lava dome-hypabyssal intrusion complex in the footwall; mineralization is concentrated in the high-silica rhyolite intrusions in the footwall and along the syndepositional fault and adjacent hanging wall graben fill. (2) The San Antonio resource area, underlain by interstratified mafic-intermediate lavas and fluvial sandstone of the Témoris formation, faulted and tilted by two en echelon NW-trending normal faults with opposing dip-directions. Mineralization occurs along subvertical structures in the accommodation zone between these faults. There are no silicic intrusions at the surface within the San Antonio resource area, but they outcrop ∼0.5 km to the east, where they are intruded along the La Palmera Fault, and are located ∼120 m-depth in the subsurface. (3) The La Unión resource area, which is underlain by mineralized andesite lavas and lapilli-tuffs of the Témoris Formation. Adjacent to the La Unión resource area is Cerro Salitrera, one of the largest silicic intrusions in the area. The plug that forms Cerro Salitrera was intruded along the La Palmera Fault, and was not recognized as an intrusion prior to our work.We show here that epithermal mineralization is Late Oligocene to Miocene-age and hosted in extensional structures, younger than Laramide (Cretaceous-Eocene) ages of mineralization inferred from unpublished mining reports for the region. We further infer that mineralization was directly related to the emplacement of silicic intrusions of the Sierra Guazapares formation, when the mid-Cenozoic ignimbrite flare-up of the Sierra Madre Occidental swept westward into the study area about 24.5–23 Ma ago.     

Report on the 5th International Meeting of the IUGS Lower Cretaceous Ammonite Working Group,the Kilian Group (Ankara,Turkey, 31st August 2013)

The 5th meeting of the IUGS Lower Cretaceous Ammonite Working Group (the Kilian Group) held in Ankara, Turkey, 31st August 2013, discussed the Mediterranean ammonite zonation, and its calibration with different ammonite zonal schemes of the Boreal, Austral and Central Atlantic realms. Concerning the standard zonation, that corresponds to the zonal scheme of the West Mediterranean province, some changes have been made on two stages. For the Valanginian, the Busnardoites campylotoxus Zone was abandoned; the upper part of the lower Valanginian is now characterised by the Neocomites neocomiensiformis and Karakaschiceras inostranzewi zones. For the upper Barremian, the former Imerites giraudi Zone is here subdivided into two zones, a lower I. giraudi Zone and an upper Martellites sarasini Zone. The I. giraudi Zone is now subdivided into the I. giraudi and Heteroceras emerici subzones, previously considered as horizons. The current M. sarasini and Pseudocrioceras waagenoides subzones correspond to the lower and upper parts of the M. sarasini Zone, respectively. The Anglesites puzosianum Horizon is kept. The Berriasian, Hauterivian, Aptian and Albian zonal schemes have been discussed but no change was made. The upper Hauterivian zonal scheme of the Georgian (Caucasus) region (East Mediterranean province) has been compared with the standard zonation. Discussions and some attempts at correlations are presented here between the standard zonation and the zonal schemes of different palaeobiogeographical provinces: the North-West European area for the Valanginian and Hauterivian, the Argentinean region for the Berriasian, Valanginian and Hauterivian, and the Mexican area for the Valanginian–Hauterivian and Aptian–lower Albian. The report concludes with some proposals for future work.     

江西相山铀矿田如意亭剖面火山岩的年代学格架及其地质意义

江西相山铀矿田如意亭剖面最底部的熔结凝灰岩代表了相山火山-侵入活动的开始时间,本文首次报导了该熔结凝灰岩的LA-ICP-MS锆石U-Pb定年结果,得出其形成年龄为137.3±0.9Ma,表明相山火山-侵入活动开始于早白垩世。此外,对如意亭剖面的两个流纹英安岩样品的锆石U-Pb定年结果分别是136.8±2.5Ma和136.4±1.5Ma,对采自如意亭剖面的流纹英安斑岩的锆石U-Pb定年结果是135.0±2.0Ma,对采自如意亭剖面的碎斑熔岩的定年结果是134.1±1.6Ma,这些定年结果结合前人已有的研究,得出相山火山-侵入杂岩的形成时代集中在135Ma左右（137~132Ma）,再次证实了相山火山-侵入活动始于早白垩世,是一次集中且短暂的火山-侵入活动。本文对如意亭剖面的定年结果证实相山地区打鼓顶组和鹅湖岭组的火山岩地层应属于早白垩世。然而赣杭构造带上原先所划分的打鼓顶组与鹅湖岭组火山岩形成的时间与武夷山北坡冷水坑盆地中火山岩系并不相同,因此,打鼓顶组与鹅湖岭组地层在区域上应予重新厘定。