Search results for "Surface Processes"
showing 10 items of 1294 documents
Evidence of deep magma degassing and ascent by geochemistry of peripheral gas emissions at Mount Etna (Italy): Assessment of the magmatic reservoir p…
2003
[1] Five gas discharges in the area of Mount Etna volcano (Italy) and in the near Hyblean plateau have been monitored since 1996. All the emissions displayed low contributions from crustal fluids, whereas magmatic gases were the main component. Selective dissolution of these gases into hydrothermal aquifers has been recognized and modeled, allowing us to calculate the original composition of the magma-released gases. The inferred composition of the magmatic gases exhibits synchronous variations of He/Ne and He/CO2 ratios, which are coherent with the magma degassing process. On the basis of numerical simulations of volatile degassing from Etnean basalts we have computed the initial and final…
Hydrothermal macroscopic Fe-sepiolite from Oujda Mounts (Middle Atlas, Eastern Morocco)
2008
The Triassic-Jurassic series in the Oujda Mounts (Middle Atlas, NE Morocco) includes two basaltic units. The whole sequence is crosscut by veins filled with Fe-sepiolite + chalcedony + calcite + smectite and mixed layer talc-saponite. Fe-sepiolite occurs as macroscopic fibres and is one of the latest mineral phases in the filling sequence of the veins. The compositional relationships and crystallographic parameters obtained on carefully selected samples of sepiolite are compared with previous data, and support the actual development of Mg-Fe substitution in this clay mineral, given the adequate hydrothermal conditions. Genesis of this uncommon variety of sepiolite in veins is interpreted as…
Geochemistry, petrogenesis and tectonic setting of the Samothraki mafic suite, NE Greece: Trace-element, isotopic and zircon age constraints
2009
Abstract The Samothraki mafic suite in the north-eastern Aegean Sea, Greece, is an ‘in situ’ magmatic complex comprising gabbros, sparse dykes and basalt flows and pillows cut by late dolerite dykes. We have determined the age of the complex by SHRIMP zircon geochronology of a gabbro as 159.9 ± 4.5 Ma (i.e. Oxfordian; early Late Jurassic), which precludes any correlation with the so-called Lesvos ophiolite further south (253.1 ± 5.6 Ma; Latest Permian). Six distinct, hitherto unrecognised, geochemical groups have been identified among the basalts and dolerites of the Samothraki mafic suite on the basis of trace-element and Nd–Sr isotopic characteristics. All groups show the presence of an e…
Volcanism on the Eggvin Bank (Central Norwegian-Greenland Sea, latitude ∼71°N): age, source, and relationship to the Iceland and putative Jan Mayen p…
2004
Abstract The Eggvin Bank (Central Norwegian-Greenland Sea, latitude ∼71°N) is a topographically anomalous shallow area with scattered volcanic peaks extending between the island of Jan Mayen and East Greenland and straddling the northern segment of the mid-Atlantic Kolbeinsey Ridge axis. Basalts dredged from the Eggvin Bank range from variably depleted, tholeiitic, near-axis lavas to enriched, transitional-to-alkaline, off-axis seamount lavas. In terms of normalised incompatible element patterns, the most depleted, near-axis tholeiite is similar to neighbouring Kolbeinsey Ridge basalts, whereas the off-axis, transitional-to-alkaline lavas are similar to other alkaline basalts occurring clos…
Visible and near-infrared multispectral analysis of geochemically measured rock fragments at the Opportunity landing site in Meridiani Planum
2010
[1] We have used visible and near-infrared Panoramic Camera (Pancam) spectral data acquired by the Opportunity rover to analyze 15 rock fragments at the Meridiani Planum landing site. These spectral results were then compared to geochemistry measurements made by the in situ instruments Mossbauer (MB) and Alpha Particle X-ray Spectrometer (APXS) to determine the feasibility of mineralogic characterization from Pancam data. Our results suggest that dust and alteration rinds coat many rock fragments, which limits our ability to adequately measure the mineralogy of some rocks from Pancam spectra relative to the different field of view and penetration depths of MB and APXS. Viewing and lighting …
Chemical composition of modern and fossil hippopotamid teeth and implications for paleoenvironmental reconstructions and enamel formation – Part 2: A…
2012
Abstract. For reconstructing environmental change in terrestrial realms the geochemistry of fossil bioapatite in bones and teeth is among the most promising applications. This study demonstrates that alkaline earth elements in enamel of Hippopotamids, in particular Ba and Sr are tracers for water provenance and hydrochemistry. The studied specimens are molar teeth from Hippopotamids found in modern and fossil lacustrine settings of the Western Branch of the East African Rift system (Lake Kikorongo, Lake Albert, and Lake Malawi) and from modern fluvial environments of the Nile River. Concentrations in enamel vary by ca. two orders of magnitude for Ba (120–9336 μg g−1) as well as for Sr (9–21…
Cambrian ophiolite complexes in the Beishan area, China, southern margin of the Central Asian Orogenic Belt
2018
Abstract We present zircon ages and geochemical data for Cambrian ophiolite complexes exposed in the Beishan area at the southern margin of the Central Asian Orogenic Belt (CAOB). The complexes consist of the Xichangjing-Xiaohuangshan and Hongliuhe-Yushishan ophiolites, which both exhibit complete ophiolite stratigraphy: chert, basalt, sheeted dikes, gabbro, mafic and ultramafic cumulates and serpentinized mantle peridotites. Zircon grains of gabbro samples yielded 206 Pb/ 238 U ages of 516 ± 8, 521 ± 4, 528 ± 3 and 535 ± 6 Ma that reflect the timing of gabbro emplacement. The geochemical data of the basaltic rocks show enrichment in large-ion lithophile elements and depletion in the high f…
40Ar-39Ar ages and petrogenesis of middle Eocene post-collisional volcanic rocks along the Izmir-Ankara-Erzincan suture zone, NE Turkey
2019
Abstract The central and northeastern of Turkey were shaped by the transition from collisional to post-collisional tectonics and coeval magmatism during Early Cenozoic. However, the temporal and spatial evolution of the magmatism during the middle Eocene remains elusive. In this paper, we provide petrological, isotopic and radiometric data from two middle Eocene volcano-sedimentary successions, from the northern (Almus) and southern (Yildizeli) parts of the Izmir–Ankara–Erzincan Suture Zone, and discuss their generation in the post-collisional setting. Our results indicate that the volcanic units from these regions display similar stratigraphic and petrological evolution during the narrow w…
First observational evidence for the CO<sub>2</sub>-driven origin of Stromboli's major explosions
2011
Abstract. We report on the first detection of CO2 flux precursors of the till now unforecastable "major" explosions that intermittently occur at Stromboli volcano (Italy). An automated survey of the crater plume emissions in the period 2006–2010, during which 12 such explosions happened, demonstrated that these events are systematically preceded by a brief phase of increasing CO2/SO2 weight ratio (up to >40) and CO2 flux (>1300 t d−1) with respect to the time-averaged values of 3.7 and ~500 t d−1 typical for standard Stromboli's activity. These signals are best explained by the accumulation of CO2-rich gas at a discontinuity of the plumbing system (decreasing CO2 emission at the surfa…
Geochemical data and zircon ages for rocks in a high-pressure belt of Chu-Yili Mountains, southern Kazakhstan: Implications for the earliest stages o…
2011
Abstract The mechanism and age of Palaeozoic accretion in the Central Asian Orogenic Belt remain poorly constrained. One of the most complex belts extends from the Kokchetav area in northern Kazakhstan to the Kyrgyz northern Tianshan. It represents an assemblage of small blocks with Palaeoproterozoic continental crust, intervening slivers containing early Palaeozoic ophiolites and/or deep-marine sediments, and a number of HP and UHP metamorphic complexes. The HP–LT metamorphic rocks provide important clues for reconstructions of the overall structure and evolution of the accretionary collage. This study is aimed to constrain the metamorphic age and tectonic implications of HP garnet pyroxen…