Search results for "CRA"
showing 10 items of 4890 documents
First-time lidar measurement of water vapor flux in a volcanic plume
2011
Abstract The CO 2 laser-based lidar ATLAS has been used to study the Stromboli volcano plume. ATLAS measured water vapor concentration in cross-sections of the plume and wind speed at the crater. Water vapor concentration and wind speed were retrieved by differential absorption lidar and correlation technique, respectively. Lidar returns were obtained up to a range of 3 km. The spatial resolution was 15 m and the temporal resolution was 20 s. By combining these measurements, the water vapor flux in the Stromboli volcano plume was found. To our knowledge, it is the first time that lidar retrieves water vapor concentrations in a volcanic plume.
Isotope composition of rain water, well water and fumarole steam on the island of Vulcano, and their implications for volcanic surveillance
1992
Abstract Water samples from eight wells in the Vulcano Porto area and fumarole steam from the crater of Vulcano (Southern Italy) were collected at monthly intervals over a two-year period from February 1987 to January 1989. Samples of bulk precipitation were also collected in three points at Vulcano Porto and Vulcano Piano (island of Vulcano) and Castroreale (Tyrrhenian coast of Sicily), again at monthly intervals. The weighted mean isotopic composition of rain water on Vulcano is δ D =−32‰ , and δ D 18 O =−6.4‰ . Results for well waters tend to support the existence of at least two water bodies: one of purely meteoric water and the other of brackish thermal water. An intermediate water bod…
A ∼700 Ma Sm–Nd garnet–whole rock age from the granulite facies Central Kaoko Zone (Namibia): Evidence for a cryptic high-grade polymetamorphic histo…
2007
Continental collision of the Kalahari and the Congo craton in Africa and the Rio de la Plata Craton in South America resulted in a structurally complex Neoproterozoic belt system, the Kaoko–Dom Feliciano–Ribeira belt. It is uncertain whether these three cratons collided more or less simultaneously during one single orogenic event at ∼580–550 Ma or whether the belt owe its structural and metamorphic features to several so far poorly constrained events. The Kaoko Belt (NW Nambia), representing the belt system between the southern Congo Craton and the Rio de la Plata Craton, is an ideal object to study these complexities. Within this belt, high-grade meta-igneous and metasedimentary rocks of t…
Single zircon ages from high-grade rocks of the Jianping Complex, Liaoning Province, NE China
1998
Abstract The high-grade rocks of the Jianping Complex in Liaoning Provi nce, NE China, belong to the late Archaean to earliest Proterozoic granulite belt of the North China craton. Single zircon ages obtained by the Pb–Pb evaporation method and SHRIMP analyses document an evolutionary history that began with deposition of a cratonic supracrustal sequence some 2522–2551 Ma ago, followed by intrusion of granitoid rocks beginning at 2522 Ma and reaching a peak at about 2500 Ma. This was followed by high-grade metamorphism, transforming the existing rocks into granulites, charnockites and enderbites some 2485–2490 Ma ago. The intrusion of post-tectonic granites at 2472 Ma is associated with wid…
Ca. 1318 Ma A-type granite on the northern margin of the North China Craton: Implications for intraplate extension of the Columbia supercontinent
2012
Abstract Identification of the Mesoproterozoic A-type Jining granite and granite porphyry, which with abundant coeval mafic dike sills and volcanic rocks on the northern margin of the Precambrian North China Craton (NCC), may suggest intraplate extension of Columbia supercontinent. Major and trace elements of the Jining granite show an affinity to A-type granites, and may reflect an intraplate rift setting (A 1 ‐type granite). High Rb, Y, Yb, and Ta contents also show features of within-plate granites. SHRIMP zircon dating yielded concordant weighted mean 207 Pb/ 206 Pb ages of 1318 ± 7 Ma and 1321 ± 15 Ma, which define a Mesoproterozoic magmatic event. The zircons have negative e Hf(t) of …
Mesoproterozoic (Grenville-age) terranes in the Kyrgyz North Tianshan: Zircon ages and Nd–Hf isotopic constraints on the origin and evolution of base…
2013
Abstract The North Tianshan orogenic belt in Kyrgyzstan consists predominantly of Neoproterozoic to early Paleozoic assemblages and tectonically interlayered older Precambrian crystalline complexes and formed during early Paleozoic accretionary and collisional events. One of the oldest continental fragments of late Mesoproterozoic (Grenvillian) age occurs within the southern part of the Kyrgyz North Tianshan. Using SHRIMP zircon ages, we document two magmatic events at ~ 1.1 and ~ 1.3 Ga. The younger event is characterized by voluminous granitoid magmatism between 1150 and 1050 Ma and is associated with deformation and metamorphism. The older event is documented by ~ 1.3 Ga felsic volcanism…
The Pan-African continental margin in northeastern Africa: evidence from a geochronological study of granulites at Sabaloka, Sudan
1987
Ion microprobe zircon ages, a Nd model age and RbSr whole-rock dates are reported from the high-grade gneiss terrain at Sabaloka on the River Nile north of Khartoum, formally considered to be part of the Archaean/early Proterozoic Nile craton. The granulites, which are of both sedimentary and igneous derivation, occur as remnants in migmatites. Detrital zircon ages range from ≈ 1000 to ≈ 2650 Ma and prove the existence of Archaean to late Proterozoic continental crust in the sedimentary source region. The Nd model age for one sedimentary granulite is between 1.26 (TCHUR) and 1.70 (TDM) Ga and provides a mean crustal residence age for the sedimentary precursor. Igneous zircons in enderbitic …
Exhumation of high-pressure granulites and the role of lower crustal advection in the North China Craton near Datong
1997
Granulites in the Datong-Huai'an area of North China are characterized by high P-T assemblages (14 16 kbar, -9OOY) that underwent decompression cooling to -7 kbar and -800°C during a 250&2400 Ma tectonic event. Nearly all structures in the grantilites developed during the retrograde exhumation history, and can be subdivided into: (1) the stratigraphically lower, 'lower structural domain' that is characterized by complex folding with 55-10 km wide domes surrounded by concentric troughs, preserving concentric lineation patterns; and (2) the stratigraphically higher 'upper structural domain' that is characterized by a planar gneissic foliation, upright folds and a constant, shallowly SW-plungi…
A New Web-Based Catalog of Earth Degassing Sites in Italy
2008
Italy is a region characterized by intense and widespread processes of Earth degassing. High-temperature gases are released by crater plumes and fumaroles in volcanic environments throughout Italy. Also prevalent are numerous low-temperature gas emissions rich in carbon dioxide (CO2). These low-temperature emissions are located in a large area, mainly in the western sector of central and southern Italy (Figure 1).
Genesis and evolution of the fumaroles of vulcano (Aeolian Islands, Italy): a geochemical model
1981
A geochemical model explaining the presence of fumaroles having different gas composition and temperature at the top of the crater and along the northeastern coast of Vulcano island is proposed. A pressurized biphase (liquid-vapor) reservoir at the depth of about 2 km is hypothesized. Energy and mass balance sheets controlP-T conditions in the system.P-T must vary along a boiling curve of brine as liquid is present. The CO2 content in the steam is governed by the thermodynamic properties of the fluids in the H2-NaCl-CO2 system. On the assumption that oxygen fugacity in the system is between the HM-FMQ oxygen buffers, observed SO2/H2S, CO2/CO, CO/CH4 ratios in the fumarolic gases at the Foss…