Search results for "petrology"
showing 10 items of 1516 documents
U–Pb zircon geochronology and Hf–Nd isotopic systematics of Wadi Beitan granitoid gneisses, South Eastern Desert, Egypt
2015
Abstract Migmatitic granitoid gneisses are widespread in the southern Eastern Desert of Egypt, but their formation ages are poorly understood. They consist of granitoid gneiss ranging in composition from tonalite to granodiorite, with a distinct calc-alkaline chemical character. Zircons from three migmatitic gneiss samples from Wadi Beitan were dated on SHRIMP II and yielded magmatic emplacement ages of 719 ± 10, 725 ± 9 and 744 ± 10 Ma, respectively, indicating that the gneiss protoliths are Neoproterozoic. The zircons yielded eHf(t) values of − 4.8 to + 12.5 and corresponding Hf crustal model ages ranging from 824 to 1753 Ma. These data indicate the involvement of both juvenile and older …
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 …
Fluid escape structures in the north Sicily continental margin
2014
Abstract High resolution and multichannel seismic profiles coupled with multibeam echosounder (seafloor relief) data, acquired along the northern Sicily continental margin (southern Tyrrhenian Sea), document the occurrence of mound and pockmark features, revealing fluid escape processes. Along this margin, morphology of the high-gradient continental slope is irregular due to the presence of structural highs, slope failures and canyons, and is interrupted by flat areas at a mean depth of 1500 m. Seismostratigraphic analysis tools and methods were used to identify fluid escape structures and to work out a classification on the basis of their morpho-acoustic characteristics. The detailed 3D ba…
Soil CO2 degassing on Mt Etna (Sicily) during the period 1989?1993: discrimination between climatic and volcanic influences
1995
Wide variations were measured in the diffuse CO2 flux through the soils in three selected areas of Mt Etna between August 1989 and March 1993. Degassing of CO2 from the area of Zafferana Etnea-S. Venerina, on the eastern slope of the volcano, has been determined to be more strongly influenced by meteorological parameters than the other areas. The seasonal component found in the data from this area has been excluded using a filtering algorithm based on the best fitting equation calculated from the correlation between CO2 flux values and those of air temperature. The filtered data appear to have variations temporally coincident with those from the other areas, thus suggesting a common and pro…
Interference between shallow and deep-seated structures in the Sicilian fold and thrust belt.
2010
Abstract: The fold and thrust belt in western Sicily is characterized by the presence and interference of shallow and deep-seated compressional structures, which were generated and developed at different structural levels. The shallow structures consist of imbricated thrusts and asymmetric folds, with a typical wavelength of 2 km, involving relatively thin deep-water units. These units are superimposed on thick platform carbonate units, along a wide and originally almost flat floor thrust. The axial trend of the folds is variable, as multi-phase folding often occurred, producing a characteristic interference pattern, reflecting continuous variations of the apparent transport direction durin…
Clastic injection dynamics during ice front oscillations: A case example from Sólheimajökull (Iceland).
2015
18 pages; International audience; Soft-sediment deformation structures are being increasingly used as a tool for reconstructing palaeoenvironments and porewater pressure conditions in glacial settings. However, the potential of hydrofractures and clastic injections in the reconstruction of ice dynamics remains poorly constrained. This paper presents the results of a detailed study of a clastic injection network outcropping in the Sólheimajökull forefield (South Iceland). Sedimentological descriptions are combined with microscopic to macroscopic analyses of clastic injection geometries, sediment-fills, and cross-cutting relationships. The 250 m long and 20 m high exposure observed along the …
230Th/U dating of Last Interglacial brain corals from Bonaire (southern Caribbean) using bulk and theca wall material
2016
Abstract We compared the suitability of two skeletal materials of the Atlantic brain coral Diploria strigosa for 230Th/U-dating: the commonly used bulk material comprising all skeletal elements and the denser theca wall material. Eight fossil corals of presumably Last Interglacial age from Bonaire, southern Caribbean Sea, were investigated, and several sub-samples were dated from each coral. For four corals, both the ages and the activity ratios of the bulk material and theca wall agree within uncertainty. Three corals show significantly older ages for their bulk material than for their theca wall material as well as substantially elevated 232Th content and (230Th/238U) ratios. The bulk mat…
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…
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…