Search results for " petrology"
showing 10 items of 1353 documents
Mobility and fluxes of major, minor and trace metals during basalt weathering and groundwater transport at Mt. Etna volcano (Sicily)
2000
Abstract The concentrations and fluxes of major, minor and trace metals were determined in 53 samples of groundwaters from around Mt Etna, in order to evaluate the conditions and extent of alkali basalt weathering by waters enriched in magma-derived CO 2 and the contribution of aqueous transport to the overall metal discharge of the volcano. We show that gaseous input of magmatic volatile metals into the Etnean aquifer is small or negligible, being limited by cooling of the rising fluids. Basalt leaching by weakly acidic, CO 2 -charged water is the overwhelming source of metals and appears to be more extensive in two sectors of the S-SW (Paterno) and E (Zafferana) volcano flanks, where out …
Geochemical mapping of magmatic gas–water–rock interactions in the aquifer of Mount Etna volcano
2001
Abstract Systematic analysis of major and minor elements in groundwaters from springs and wells on the slopes of Mt. Etna in 1995–1998 provides a detailed geochemical mapping of the aquifer of the volcano and of the interactions between magmatic gas, water bodies and their host rocks. Strong spatial correlations between the largest anomalies in pCO2 (pH and alkalinity) K, Rb, Mg, Ca and Sr suggest a dominating control by magmatic gas (CO2) and consequent basalt leaching by acidified waters of the shallow (meteoric) Etnean aquifer. Most groundwaters displaying this magmatic-type interaction discharge within active faulted zones on the S–SW and E lower flanks of the volcanic pile, but also in…
Petrography, mineralogy and geochemistry of a primitive pumice from Stromboli: implications for the deep feeding system
2011
We describe the field relations, petrographic, mineralogical and geochemical characteristics of an exceptional “ golden ” pumice belonging to a tephra layer exposed on the summit area of Stromboli volcano, Italy. Pumice sample PST-9 comes from a fallout deposit older than a spatter agglutinate sequence emplaced during the twentieth century. The eruption that produced it had a size exceeding that of intermediate paroxysms but was smaller than large-scale, spatter-forming, paroxysms from the sixteenth century and 1930 A.D. Lapilli are strongly vesicular and crystal-poor, similar to other “ golden ” pumices. Modal proportions include 89 vol% glass, 8 vol% clinopyroxene, 1–2 vol% olivine and 1–…
Evidence of magmatic activity related to Middle Jurassic and Lower Cretaceous rifting from northeastern Brazil (Ceará-Mirim): K/Ar age, palaeomagneti…
1992
The Mesozoic magmatic activity in the easternmost part of NE Brazil (Ceara-Mirim) is mainly represented by two-pyroxene tholeiitic dykes; only few dykes have alkaline character. K/Ar ages and palaeomagnetism data indicate that Ceara-Mirim dykes are of Middle Jurassic (175-160 Ma) and Early Cretaceous (140-130 Ma) age. Both Middle Jurassic and Lower Cretaceous dykes have high incompatible-element concentrations and TiO2 with the lower contents generally confined to the Middle Jurassic dykes; rare tholeiitic dykes low in TiO2 and incompatible elements are present. Sr/1bNd isotopic and other chemical data do not support appreciable crustal contamination and in a 87Sr86Sr vs. 143Nd144Nd diagram…
First gas and thermal measurements at the frequently erupting Gamalama volcano (Indonesia) reveal a hydrothermally dominated magmatic system
2020
Abstract The first gas and thermal measurements at the summit of the Gamalama volcano indicate that the system is dominated by hydrothermal processes. This is highlighted by the prevalence of H2S over SO2 (H2S/SO2 = 2–8), a high CO2/SO2 ratio (76–201), and a low heat transfer (3.0 MW) to the surface. A relative variation in gas composition is observed along the degassing fracture zone, possibly due to partial S scrubbing. Despite this surface hydrothermal signature, the system exhibits high gas equilibrium temperatures (425–480 °C), indicating that fluids are not exclusively derived from a boiling hydrothermal aquifer, but also sourced by cooling and crystallizing basaltic magma at deep tha…
Chemo-probe into the mantle origin of the NW Anatolia Eocene to Miocene volcanic rocks: Implications for the role of, crustal accretion, subduction, …
2017
Post-collisional Cenozoic magmatic activity in NW Anatolia produced widespread volcanism across the region. In the Biga Peninsula, in the west, medium-K calc-alkaline to ultra-K rocks with orogenic geochemical signature were emplaced at similar to 43-15 Ma (Biga orogenic volcanic rocks; BOVR). Volcanic activity in the Central Sakarya region, to the east, is mainly restricted to-53-38 Ma, but also continued during the Early Miocene with small basaltic extrusives (Sakarya orogenic volcanic rocks; SOVR). This study presents a new set of geochemical data (whole rock major and trace elements and Sr-Nd-Pb isotopic compositions), obtained from the Cenozoic calc-alkaline volcanic rocks from these t…
Amygdaloidal basalts: Isotopic and petrographic evidence for non-diagenetic crustal source of carbonate inclusions
1980
Even though carbonate amygdules in volcanics are generally assumed to be diagenetic in origin, the authors are of the opinion that almost all carbonate inclusions in the investigated amygdaloidal volcanic rocks from Sicily (Italy), Pindos (Greece) and Bohemia (Czechoslovakia), have a different origin. On the basis of a mineralogical, petrological and geochemical study these “amygdules” are interpreted as being remains ofmagmatic incorporation of carbonate. Therefore, the identification of carbonate globules in volcanics purely on field observations, is inadequate to distinguish true amygdules from carbonate assimilation remnants. A nomenclature of the various types of inclusions is proposed…
Crystal size distribution in Jurassic Ferrar flows and sills (Victoria Land, Antarctica): evidence for processes of cooling, nucleation, and crystall…
1996
Jurassic Ferrar rocks in Victoria Land (Antarctica) occur predominantly as basaltic or andesitic flows and sills. Both show characteristic petrographical and chemical variations, which can be related to in-situ differentiation processes. Such characteristics have been investigated at one flow (“Colonnade flow”) and one sill (“Thumb Point sill”) in the Prince Albert Mountains (Central Victoria Land) based on a statistical grain size analysis and the application of the crystal size distribution theory. A third magma body (“HiTi-unit”), which in previous literature was described as a flow, does not show clear similarities to either the flow or sill. Sill and flow are in-situ differentiated wit…
Hafnium-Neodymium isotope, trace element and U-Pb zircon age constraints on the petrogenesis of the 3.44–3.46 Ga Dwalile greenstone remnant, Ancient …
2020
Abstract The geodynamic setting of the 3.44–3.46 Ga Dwalile greenstone remnant (DGR) of the Ancient Gneiss Complex (Swaziland) and its relationship to other Greenstone belts of similar age is investigated in this contribution. We present Hf-Nd isotope, major and trace element data for komatiites, komatiitic basalts, basalts, basaltic andesites as well as felsic volcanic and sedimentary rocks, all metamorphosed at amphibolite-facies grade. Major and trace element compositions of metabasalts and metakomatiites indicate crustal contamination. The best-preserved samples yield 176Lu-176Hf and 147Sm-143Nd isochron ages of ca. 3500 and 3460 Ma, respectively, in line with U-Pb zircon ages of interl…
Generation of early Archaean felsic greenstone volcanic rocks through crustal melting in the Kaapvaal, craton, southern Africa
2013
Abstract High-potassium felsic volcanic rocks interlayered with basalt and komatiite in early Archaean greenstone sequences in the Barberton Greenstone Belt of South Africa and Swaziland, previously considered to be derived from melting of mafic precursors, are shown to be the result of melting of significantly older felsic crust. This is documented by a combination of SHRIMP zircon dating with Hf-in-zircon and whole-rock Lu–Hf and Sm–Nd isotopic data. Zircons from felsic rocks of the oldest Barberton unit, the 3.53 Ga Theespruit Formation, yielded predominantly negative e Hf ( t ) -values, whereas whole-rock e Hf ( t ) - and e Nd ( t ) -data are slightly negative to slightly positive. Simi…