Low-temperature hydrothermal alteration of intra-caldera tuffs,Miocene Tejeda caldera,Gran Canaria,Canary Islands

The Miocene Tejeda caldera on Gran Canaria erupted ~ 20 rhyolite–trachyte ignimbrites (Mogán Group 14–13.3 Ma), followed by ~ 20 phonolitic lava flows and ignimbrites (Fataga Group 13–8.5 Ma). Upper-Mogán tuffs have been severely altered immediately within the caldera margin, whereas extra-caldera Mogán ignimbrites, and overlying Fataga units, are apparently unaltered. The altered intra-caldera samples contain minerals characteristic of secondary fluid–rock interaction (clays, zeolites, adularia), and relics of the primary mineral assemblage identified in unaltered ignimbrites (K-feldspar, plagioclase, pyroxene, amphibole, and groundmass quartz). Major and trace-element data indicate that Si, Na, K, Pb, Sr, and Rb, were strongly mobilized during fluid–rock interaction, whereas Ti, Zr, and Nb behaved in a more refractory manner, experiencing only minor mobilization. The δ¹⁸O values of the altered intra-caldera tuffs are significantly higher than in unaltered extra-caldera ignimbrites, consistent with an overall low-temperature alteration environment. Unaltered extra-caldera ignimbrites have δD values between − 110‰ and − 173‰, which may reflect Rayleigh-type magma degassing and/or post-depositional vapour release. The δD values of the altered intra-caldera tuffs range from − 52‰ to − 131‰, with ambient meteoric water at the alteration site estimated at ca. − 15‰. Interaction and equilibration of the intra-caldera tuffs with ambient meteoric water at low temperature can only account for whole-rock δD values of around − 45‰, given that ?D_clay–water is ca. − 30‰ at 100 °C, and decreases in magnitude at higher temperatures. All altered tuff samples have δD values that are substantially lower than − 45‰, indicating interaction with a meteoric water source with a δD value more negative than − 15‰, which may have been produced in low-temperature steam fumaroles. Supported by numerical modeling, our Gran Canaria data reflect the near-surface, epithermal part of a larger, fault-controlled hydrothermal system associated with the emplacement of the high-level Fataga magma chamber system. In this near-surface environment, fluid temperatures probably did not exceed 200–250 °C.     

Potentially active volcanoes of Peru-Observations using Landsat Thematic Mapper and Space Shuttle imagery

Landsat Thematic Mapper (TM) images and Space Shuttle color photograph have been used to make a synoptic study of the volcanoes of southern Peru (14°–17° S), the northernmost portin of the Central Volcanic Zone (CVZ 14°–28° S) of the Andes. Apart from providing consistent coverage, the chief merit of the TM for this study has been the spatial resolution provided by the 30-m pixel size. The optimal 20-m resolution, variable lighting and viewing geometry, and stereo capability of the Shuttle photography provided an invaluable ancilliary data set. At the resolution available, subtle glacial-morphological features such as valley and terminal moraines can be confidently identified, and these features have been used to determine the relative ages of volcanoes. Volcanoes have been classified as potentially active if they have; (i) a well-preserved summit crater, (ii) pristine lava flow texture and morphology, (iii) flank lava flows with low albedo, and (iv) evidence of postglacial (<10 000 years) activity. Eight major volcanoes are postulated to be potentially active. Most are large, dominantly andesitic, composite cones with edifice heights of up to 2500 m; some of which threaten nearby settlements. One of them, Sabancaya, was active as recently as July 1988. Other, little-known, postglacial volcanic features include Huaynaputina, site of a major explosive rhyolitic eruption in 1600 a.d., and several fields of monogenetic scoria cones and lava flows. The active volcanic front is some 200 km east of the Peru-Chile trench, and the volcanoes lie on a trenchparallel trend oblique to the EW subduction. This narrow volcanic zone is thought to reflect the steep dip of the Nazca plate through the zone of magma generation. The break in the trend of the volcanic front in the northern extremity of the volcanic zone is thought to reflect the complexity of the crustal stress field above a major segment boundary in the subducting plate. The fields of mafic monogenetic centers also occur in this region. In comparison with the southern part of the CVZ, the general paucity of older volcanic edifices north of 17° S suggests a more recent onset of volcanism north of this latitude probably resulting from the oblique subduction of the Nazca ridge and the consequent northward migration of its intersection with the Pere-Chile trench. This, coupled with the lack of any large silicic caldera systems and youthful dacite domes, like those found further south, suggest that there are real differences between the volcanic evolution of different parts of the CVZ.     

EC participation in protection of the marine environment : Legal and institutional aspects

Treaties are usually concluded among national governments, which are also the traditional members of international organizations. The emergence of the European Community — a regional economic integration organization (REIO) to which member States have ceded some authority — has led to tensions in international environmental meetings and negotiations, in part because of foreign partners' uncertainty about how responsibilities are allocated between the REIO and its member States. This paper discusses the issues that arise when an REIO becomes a party to an international agreement or participates in an International organization, with particular attention to agreements and institutions that address international environmental issues.     

西秦岭凤太矿集区丝毛岭金矿床地质地球化学特征

西秦岭凤太矿集区丝毛岭金矿床位于八卦庙造山型金矿床西侧5km左右,是一个新探明的剪切带型金矿。其成矿作用过程可分为早期石英-绢云母-硫化物阶段、中期多金属-硫化物阶段和晚期碳酸盐阶段。对早、中期的石英流体包裹体测试结果表明,丝毛岭金矿床成矿流体以富CO2、中温、低盐度为特征,总体上属于中温低盐度CO2-H2O体系,流体包裹体类型的多样性是流体不混溶性的产物。从早阶段到主成矿阶段成矿流体的温度、压力和盐度均有降低,硫逸度增高,有利于金的沉淀富集。H、O、S、C同位素研究结果,以及与八卦庙金矿床的对比分析表明,二者的成矿流体具有相似性和同源性,都是以深部来源为主的多源流体。由于丝毛岭金矿床产出的层位高于八卦庙金矿床,其成矿环境相对开放。     

HST/STIS observations of sdBV stars: testing diffusion and pulsation theory

We present the initial results of an abundance analysis of echelle UV spectra of five hot subdwarf B (sdB) stars. These stars have been identified as core helium burning objects on the extreme Horizontal Branch. Around 5% of sdBs show short-period acoustic-mode oscillations. Models predict that these oscillations are due to an opacity bump caused by the ionisation of iron group elements. The necessary metal abundance has to be maintained by diffusive equilibrium between gravitational settling and radiative levitation. However, analyses of high-resolution optical spectra has revealed that we cannot discriminate between pulsating and non-pulsating sdBs on the basis of the surface iron abundance. We have therefore obtained HST/STIS observations of three pulsators and two non-pulsators in the near- and far-UV to measure the surface abundance of elements that are unobservable from the ground. The overall aim of our study is to test diffusion and pulsation calculations by searching for significant differences between these surface abundances.     

Sea level history of the northern Gulf of Mexico coast and sea level rise scenarios for the near future

The sea level history of the northern Gulf of Mexico during recent geologic time has closely followed global eustatic sea level change. Regional effects due to tectonics and glacio-isostasy have been minimal. Over the past several million years the northern Gulf coast, like most stable coastal regions of the globe, has experienced major swings of sea level below and above present level, accompanied by major shifts in shoreline position. During advances of the northern hemisphere ice sheets, sea level dropped by more than 100 m, extending the shoreline in places more than 100 km onto the shelf. For much of the period since the last glacial maximum (LGM), 20,000 years ago, the region has seen rates of sea level rise far in excess of those experienced during the period represented by long-term tide gauges. The regional tide gauge record reveals that sea level has been rising at about 2 mm/year for the past century, while the average rate of rise since the LGM has been 6 mm/year, with some periods of abrupt rise exceeding 40 mm/year. During times of abrupt rise, Gulf of Mexico shorelines were drowned in place and overstepped. The relative stability of modern coastal systems is due primarily to stabilization of sea level approximately 6,000 years ago, resulting in the slow rates of rise experienced during historic time. Recent model projections of sea level rise over the next century and beyond may move northern Gulf coastal environments into a new equilibrium regime, more similar to that experienced during the deglaciation than that which has existed during historic time.     

The volcanic history of Ruapehu during the past 2 millennia based on the record of Tufa Trig tephras

 Tufa Trig Formation comprises a sequence of at least 19 andesitic tephras erupted from Mt. Ruapehu (Tongariro Volcanic Centre, New Zealand). Tephras of Tufa Trig Formation are the most recent eruptives from Ruapehu, dated between ca. 1850 years B.P. and the present. Members of the Formation show restricted dispersals, principally to the east of Mt. Ruapehu. Volumes calculated for the most widespread members are all less than 0.1 km³. Compared with other Mt. Ruapehu eruptives, Tufa Trig Formation tephras represent small eruptions that have contributed little tephra to the ring plain. They do, however, show a greater frequency of eruption with one event occurring on average every 100 years. Tufa Trig Formation members Tf3–Tf18 are black to dark grey, vitric, coarse-ash and lapilli-grade tephras which mantle the relief. They contain juvenile vitric particles which exhibit varying degrees of vesicularity, together with free crystals of pyroxene and feldspar, and few lithic fragments. Several morphological types of vitric pyroclasts are recognised in these tephras, the dominant type being of equant blocky morphology with fracture-bound surfaces (type-1 morphology). Field characteristics, tephra distributions, and the morphologies and textures of constituent pyroclasts suggest that these members (Tf3–Tf18) are the products of small-volume hydrovolcanic eruptions resulting from the interaction of fresh magma and meteoric water. We propose that a source of this water was an ancestral crater lake which formed within the late Holocene ca. 3000 years B.P. The morphological, compositional, and chemical (major-element) characteristics of three Tufa Trig Formation Tephras are compared with those of two new tephras erupted from Ruapehu Volcano during the October 1995 eruptions which comprise part of a newly defined member (Tf19) of Tufa Trig Formation. The comparisons support our interpretation that the majority of the Tufa Trig Formation tephras are primarily the products of hydrovolcanic eruptions. Other members of the Formation (Tf1 and Tf2) are coarse-grained scoriaceous tephras and are interpreted to be the products of strombolian events. Received: 14 September 1996 / Accepted: 6 June 1997     

Baseline Sediment Trace Metals Investigation: Steinhatchee River Estuary, Florida, Northeast Gulf of Mexico

This Florida Geological Survey U.S. Department of the Interior, Minerals Manage ment Service Cooperative Study provides baseline data for major and trace metal concentrations in the sediments of the Steinhatchee River estuary. These data are intended to provide a benchmark for comparison with future metal concentration data measurements. The Steinhatchee River estuary is a relatively pristine bay located within the Big Bend Wildlife Management Area on the North Central Florida Gulf of Mexico coastline. The river flows 55 km through woodlands and planted pines before emptying into the Gulf at Deadman Harbor. Water quality in the estuary is excellent at present. There is minimal development within the watershed. The estuary is part of an extensive system of marshes that formed along the Florida Gulf coast during the Holocene marine transgression. Sediment accretion rate measurements range from 1.4 to 4.1 mm yr on the basis of lead-210 measurements. Seventy-nine short cores were collected from 66 sample locations, representing four lithofacies: clay- and organic-rich sands, organic-rich sands, clean quartz sands, and oyster bioherms. Samples were analyzed for texture, total organic matter, total carbon, total nitrogen, clay mineralogy, and major and trace-metal content. Follow ing these analyses, metal concentrations were normalized against geochemical reference elements (aluminum and iron) and against total weight percent organic matter. Metals were also normalized granulometrically against total weight percent fines (0.062 mm). Concentrations were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) for all metals except mercury. Mercury concentrations were determined by cold-flameless atomic absorption spectrometry (AAS). Granulo metric measurements were made by sieve and pipette analyses. Organic matter was determined by two methods: weight loss upon ignition and elemental analysis (by Carlo-Erba Furnace) of carbon and nitrogen. X-ray diffraction was used to deter mine clay mineralogy. Trace-metal concentrations were best correlated when normalized with respect to sediment aluminum concentrations. Normalizations indicate that most major and trace-metal concentrations fall within 95 % prediction limits of the expected value. This finding suggests that little significant metal contamination occurred within this system prior to 1994 sediment sampling. Exceptions include lead, mercury, copper, zinc, potassium, and phosphorous. Lead and mercury are elements that generally enter this watershed through atmospheric deposition; thus, anomalous levels of these metals are not necessarily associated with activities within the watershed of the Steinhatchee River estuary. Anomalous concentrations of other metals such as zinc, copper, and phosphorous probably do originate within the Steinhatchee watershed. Copper failed to correlate well with any geochemical or granulometric normalizer, and this condition was not limited to a single facies or area within the estuary. This finding may indicate copper contamination in the system. Increased zinc and copper levels may be attributed to marine paints. Phosphorous levels also appeared to be elevated in a few locations in the two marsh facies sampled. This may be due to nutrient loading from two small communities, Jena and Steinhatchee, or from the application of this element in fertilizer to reduce moisture stress to young planted pines on tree farms within the watershed.     

Controls on accumulation of a volcaniclastic fan,Ruapehu composite volcano,New Zealand

The Whangaehu fan is the youngest sedimentary component on the eastern ring plain surrounding Ruapehu volcano. Fan history comprises constructional (830–200 years bp) and dissectional (<200 years bp) phases. The constructional phase includes four aggradational periods associated with both syneruptive and inter-eruptive behavior. All four aggradational periods began when deposition by large lahars changed flow conditions on the fan from channelized to unchannelized. Subsequent behavior was a function of the rate of sediment influx to the fan. The rate of sediment influx, in turn, was controlled by frequency and magnitude of volcanic eruptions, short-term climate change, and the amount of sediment stored on the volcano flanks. Fanwide aggradation occurred when rates of sediment influx and deposition on the fan were high enough to maintaìn unchannelized flow conditions on the fan surface. Maintenance of an undissected surface required sedimentation from frequent and large lahars that prevented major dissection between events. These conditions were best met during major eruptive episodes when high frequency and magnitude eruptions blanketed the volcano flanks with tephra and rates of lahar initiation were high. During major eruptive episodes, volcanism is the primary control on sedimentation. Climatic variations do not influence sediment accumulation. Local aggradation occurred when lahars were too small to maintain unchannelized flow across the entire fan. In this case, only the major channel system received much sediment following the deposition from the initial lahar. This localized aggradation occurred if (1) the sediment reservoir on the flank was large enough for floods to bulk into debris flows and (2) sedimentation events were frequent enough to maintain sediment supply to only some parts of the fan. These conditions were met during both minor eruptive and inter-eruptive episodes. In both cases, a large sediment reservoir remained on the volcano flanks from previous major eruptive intervals. Periods of increased storm activity produced floods that bulked to relatively small debris flows. When the sediment reservoir was depleted, the fan entered the present dissectional phase. Syneruptive and noneruptive lahars are mostly channelized and sediment bypasses the fan. Fan deposits are rapidly reworked. This is the present case at Ruapehu, even though the volcano is in a minor eruptive episode and the climate favors generation of intense storm floods.     

The Irish marine economy and regional development

The economic impact of the marine economy is poorly understood at both national and regional levels in Ireland. A recent paper estimated the national level economic value of the sector for Ireland. This paper presents a follow up analysis of the Irish marine sector at the regional level for 2007. The paper examines the impact of the marine sector in addressing regional disparities in Ireland, and the key marine sectors that drive regional economic performance within the marine sector. The analysis finds that in absolute values Dublin and the South West provide the highest levels of marine GVA; however, as a percentage of regional GVA, the marine sector is more important in the West and South West region. In terms of employment, the West and South-West provide the highest levels of marine employment, and this relationship is maintained when one examines marine employment as a percentage of regional employment. Finally, productivity rates for the sector were highest in the Dublin region. However, productivity in the marine-based sector was higher than the overall regional rate for five of the eight Irish regions.