Search results for " Petr"
showing 10 items of 1574 documents
Mercury gas emissions from La Soufrière Volcano, Guadeloupe Island (Lesser Antilles)
2009
Abstract Quantifying mercury (Hg) emissions from active volcanoes is of particular interest for better constraining the global cycle and environmental impact of this highly toxic element. Here we report on the abundance of total gaseous (TGM = Hg 0 (g) + Hg II (g) ) and particulate (Hg (p) ) mercury in the summit gas emissions of La Soufriere andesitic volcano (Guadeloupe island, Lesser Antilles), where enhanced degassing of mixed hydrothermal-magmatic volatiles has been occurring since 1992 from the Southern summit crater. We demonstrate that Hg in volcanic plume occurs predominantly as gaseous mercury, with a mean TGM/Hg (p) mass ratio of ~ 63. Combining the mean TGM/H 2 S mass ratio of …
Influences of surface processes on fold growth during 3-D detachment folding
2014
In order to understand the interactions between surface processes and multilayer folding systems, we here present fully coupled three-dimensional numerical simulations. The mechanical model represents a sedimentary cover with internal weak layers, detached over a much weaker basal layer representing salt or evaporites. Applying compression in one direction results in a series of three-dimensional buckle folds, of which the topographic expression consists of anticlines and synclines. This topography is modified through time by mass redistribution, which is achieved by a combination of fluvial and hillslope erosion, as well as deposition, and which can in return influence the subsequent defor…
Moroccan speleothem and tree ring records suggest a variable positive state of the North Atlantic Oscillation during the Medieval Warm Period
2013
We present a magnesium (Mg) and strontium (Sr) record from an aragonitic speleothem (Grotte de Piste, Morocco, 34°N; 04°W) providing a reconstruction of effective rainfall from 619 to 1962 AD. The corresponding drip site was monitored over 2 yr for drip water Mg/Ca and Sr/Ca ratios. Results show evidence for prior aragonite precipitation, which can explain negative correlations between speleothem Mg and Sr concentrations. The data shown here have important climate implications concerning the evolution of the North Atlantic Oscillation (NAO). A comparison of the stalagmite data from Grotte de Piste with an updated tree ring based drought reconstruction from Morocco and other NAO related pro…
Archean-Paleoproterozoic crustal evolution of the Ordos Block in the North China Craton: Constraints from zircon U–Pb geochronology and Hf isotopes f…
2015
Abstract The Ordos Block has been considered as an Archean micro-block in North China Craton. However, its formation and evolution are poorly understood for a long time due to lack of available basement rocks. Our LA-ICPMS and SIMS zircon U–Pb dating of gneissic granitoids from the Ordos Block basement identified two distinct periods of granitic magmatism at ∼2.5 Ma and 2.2–2.0 Ga, and two phases of metamorphisms at ∼1.95 Ga and ∼1.85 Ga, respectively. Of which most zircons of ∼2.5 Ga granitoids show positive ɛ Hf ( t ) values ranging from +0.1 to +4.1 with a peak T DM of ∼2.7 Ga. Minor zircons have negative ɛ Hf ( t ) values from −3.8 to −0.02 and T Hf C of 2.8–3.1 Ga. Moreover, the 3.40 G…
Archaean to Neoproterozoic magmatic events in the Kaoko belt of NW Namibia and their geodynamic significance
1998
Abstract Age relationships in the N–S trending Neoproterozoic (Pan-African) Kaoko belt of northwestern Namibia are still poorly constrained. U–Pb and Pb–Pb zircon age determinations by single grain evaporation, conventional multigrain fraction analyses and ion microprobe (SHRIMP) from a profile along the E–W Hoanib River reveal various episodes of zircon growth, ranging from late Archaean to late Neoproterozoic. From the eastern part of the profile we report crystallization ages of gneiss protoliths from 2645 to 2585 Ma, the oldest ages so far found in Namibia. Sm–Nd isotope data suggest the involvement of still older crustal material in the generation of these gneisses. A thermal event at …
Zircon geochronology and metamorphic evolution of mafic dykes in the Hengshan Complex of northern China: Evidence for late Palaeoproterozoic extensio…
2006
Abstract Magmatic and metamorphic zircons have been dated from ductilely deformed gabbroic dykes defining a dyke swarm and signifying crustal extension in the northern part of the Hengshan Complex of the North China Craton. These dykes now occur as boudins and deformed sheets within migmatitic tonalitic, trondhjemitic, granodioritic and granitic gneisses and are conspicuous due to relics of high-pressure granulite or even former eclogite facies garnet + pyroxene-bearing assemblages. SHRIMP ages for magmatic zircons from two dykes reflect the time of dyke emplacement at ∼1915 Ma, whereas metamorphic zircons dated by both SHRIMP and evaporation techniques are consistently in the range 1848–18…
Palaeoproterozoic crustal accretion and collision in the southern Capricorn Orogen: the Glenburgh Orogeny
2004
Abstract The Capricorn Orogen in central Western Australia records the Palaeoproterozoic collision of the Archaean Pilbara and Yilgarn Cratons. Until recently only one orogenic event was thought to be the cause of this collision, the 1830–1780 Ma Capricorn Orogeny. However, recent work has uncovered an older event, the Glenburgh Orogeny that occurred between 2000 and 1960 Ma. The Glenburgh Orogeny reflects the collision of a late Archaean to Palaeoproterozoic microcontinent (the Glenburgh Terrane) with the Archaean Yilgarn Craton and is therefore tectonically distinct as well as significantly older than the widespread 1900–1800 Ma tectonothermal events recorded in northern Australia. The Gl…
New geochemical and combined zircon U–Pb and Lu–Hf isotopic data of orthogneisses in the northern Altyn Tagh, northern margin of the Tibetan plateau:…
2014
Abstract Dunhuang Block is previously considered to be an eastern part of the Tarim Craton, but now it is proposed to be the western extension of the Alxa Block of the NCC as a result of displacement along the Altyn Tagh fault. The oldest basement rocks of the Dunhuang Block, named Aketashitage Complex, were mainly exposed in the northern Altyn Tagh. Migmatites of the Aketashitage Complex are sodic and subalkaline in composition. Zircon U–Pb dating of the tonalitic and monzogranitic migmatites indicates that these rocks were produced by strong deformation of earlier formed tonalites with innumerous granitic veins. The tonalitic melanosome of the migmatites was generated approximately at 2.7…
Zircon REE patterns and geochemical characteristics of Paleoproterozoic anatectic granite in the northern Tarim Craton, NW China: Implications for th…
2012
Abstract Because Archean basement rocks are sparsely distributed around the Tarim Basin, little is known of the relationship between the Tarim Craton and the Paleo- to Mesoproterozoic Columbia supercontinent. Zircon U–Pb dating of a Paleoproterozoic gneissic granite in the northern Tarim Craton yielded a crystallization age of 1915 ± 13 Ma, consistent with global Paleoproterozoic collisional events (ca. 2.1–1.8 Ga) recorded in most cratons. Despite the fact that some zircons display discordant U–Pb ages with a distinct loss of radiogenetic Pb, all grains have similar 176Lu/177Hf and 176Hf/177Hf(t) values. Zircons from this granite have high Th/U ratios (0.15–0.95), but contrasting rare eart…
Relationships between diffuse CO 2 emissions and volcanic activity on the island of Vulcano (Aeolian Islands, Italy) during the period 1984-1994
2002
Measurements of CO2 flux from the ground were periodically carried out on the island of Vulcano (Aeolian Islands, Italy) between 1984 and 1994. Three high-flux areas were identified at the foot of the volcanic cone (La Fossa), either inside or very close to the main village. Effect of the choice of the sampling grid was evaluated. A different sampling grid resulted in similar distribution patterns, but with different CO2 fluxes. Therefore, the absolute estimate of the total flux from the investigated area includes a large degree of uncertainty, but repeated measurements with permanent sampling sites are accurate and can detect small changes. No correlation of the flux with atmospheric param…