Search results for "petrology"
showing 10 items of 1516 documents
Soil CO2 degassing along tectonic structures of Mount Etna (Sicily): the Pernicana fault
1997
Abstract Carbon dioxide emissions from the soil have been investigated along lines of equally spaced sampling points perpendicular to the Pernicana fault on Mt Etna. Anomalous values of soil CO2 have been found not only along the fault plane, but also along directions parallel to it, both to the N and to the S of the main fault. The acquired data seem to reveal a shallow step-like geometry of the Pernicana fault system with parallel faults being generally not deeper than the interface between Etna's volcanic cover and its sedimentary basement (a few hundred meters). The distribution of the anomalous CO2 emissions has also revealed that the Pernicana fault continues at least as far as the Io…
Crustal xenoliths from Cenozoic volcanic fields of West Germany: Implications for structure and composition of the continental crust
1991
Crustal xenoliths in three Cenozoic volcanic fields of West Germany, the Northern Hessian Depression (NHD), the Eifel and the Urach/Hegau, include medium to high-grade meta sedimentary and felsic to mafic meta-igneous rocks. Also present in all three suites are pyroxenites and hornblendites. For each volcanic field, a model crustal profile is proposed based on calculated or measured P-wave velocities of xenoliths and depth-Vp relationships (EGT Central Segment and Rhenish Massif traverses). The xenolith lithologies from the NHD and the Eifel show some similarities. The middle crust between the depths of about 10 and 25 km consists mainly of meta-sediments, felsic gneisses and granulites. Me…
Mesoproterozoic (Grenville-age) granitoids and supracrustal rocks in Kaokoland, northwestern Namibia
2017
Abstract We identified and describe rocks of a late Mesoproterozoic Grenville-age igneous province and associated supracrustal sequence in northwestern Kaokoland, Namibia. These rocks are ca. 1176–1534 Ma in age and mostly consist of pinkish granitic and trondhjemitic plutons that are unfoliated within the Palaeoproterozoic Epupa Metamorphic Complex but become progressively deformed farther west together with late Neoproterozoic rocks of the Pan-African Kaoko orogen. Furthermore, a supracrustal assemblage of clastic sedimentary rocks and felsic volcanic rocks, known as Okapuka Formation, unconformably overlies the Epupa gneisses and also became deformed in the west during the Kaoko orogeny.…
Zircon evaporation ages and geochemistry of metamorphosed volcanic rocks from the Vinjamuru domain, Krishna Province: evidence for 1.78 Ga convergent…
2012
Palaeoproterozoic intermediate to potassic felsic volcanism in volcano-sedimentary sequences could either have occurred in continental rift or at convergent magmatic arc tectonic settings. The Vinjamuru domain of the Krishna Province in Andhra Pradesh, SE India, contains such felsic and intermediate metavolcanic rocks, whose geochemistry constrains their probable tectonic setting and which were dated by the zircon Pb evaporation method in order to constrain their time of formation. These rocks consist of interlayered quartz–garnet–biotite schist, quartz–hematite–baryte–sericite schist as well as cherty quartzite, and represent a calc-alkaline volcanic sequence of andesitic to rhyolitic rock…
UV camera measurements of fumarole field degassing (La Fossa crater, Vulcano Island)
2011
Abstract The UV camera is becoming an important new tool in the armory of volcano geochemists to derive high time resolution SO2 flux measurements. Furthermore, the high camera spatial resolution is particularly useful for exploring multiple-source SO2 gas emissions, for instance the composite fumarolic systems topping most quiescent volcanoes. Here, we report on the first SO2 flux measurements from individual fumaroles of the fumarolic field of La Fossa crater (Vulcano Island, Aeolian Island), which we performed using a UV camera in two field campaigns: in November 12, 2009 and February 4, 2010. We derived ~ 0.5 Hz SO2 flux time-series finding fluxes from individual fumaroles, ranging from…
Fluid-pressure controlled soft-bed deformation sequence beneath the surging Breiðamerkurjökull (Iceland, Little Ice Age).
2009
16 pages; International audience; The general subject of this paper is subglacial deformation beneath Breiðamerkurjökull, a surging Icelandic glacier. More specifically it discusses the evolution and the role of fluid pressure on the behaviour of subglacial sediments during deformation. During Little Ice Age maximum, the two outcrops studied, North Jökulsarlon (N-Jk) and Brennhola-Alda (BA), were located at 2550 m and 550 m respectively from the front of the Breiðamerkurjökull. Sedimentological analysis at the forefield of the glacier shows thick, coarse glaciofluvial deposits interbedded with thin, fine-grained shallow lacustrine/swamp deposits, overlain by a deformed till unit at N-Jk. BA…
Thermal anomalies in fumaroles at Vulcano island (Italy) and their relationship with seismic activity
2013
Abstract Fumarole thermal monitoring is a useful tool in the evaluation of volcanic activity, since temperatures strongly relate to the upward flux of magmatic volatiles. Once depurated from meteorological noise, their variations can reflect permeability changes due to crustal stress dynamics eventually associated to seismic activity. In this work, we discuss a fumarole temperature record acquired in the period September 2009–May 2012 at Vulcano island (Italy), during which changes of volcanic state, local seismic activity and teleseisms occurred. Apart from positive thermal anomalies driven by increments in volcanic activity, we observed 3 episodes at least of concurrence between tectonic …
Dating of late Proterozoic ophiolites in Egypt and the Sudan using the single grain zircon evaporation technique
1992
Abstract Zircons from gabbro and plagiogranite in late Proterozoic ophiolites of the Arabian-Nubian Shield (ANS) in Egypt and the Sudan, as well as post-ophiolite granites have been dated using the stepwise evaporation method. Zircons from a plagiogranite in the Wadi Ghadir ophiolite, Eastern Desert of Egypt, yielded a mean 207Pb/206Pb age of 746±19 Ma, while a gabbro and diorite associated with the Abu Swayel ophiolite nappe ∼ 250 km southwest of Wadi Ghadir provided zircon 207Pb/206Pb ages of 729±17 and 736±11 Ma, respectively. Zircons from layered gabbro along the western margin of the Jabal Gerf ophiolite just north of 22°N were dated at 741±21 Ma, indistinguishable from the Wadi Ghadir…
Carboniferous and Cretaceous mafic–ultramafic massifs in Inner Mongolia (China): A SHRIMP zircon and geochemical study of the previously presumed int…
2012
Abstract We present SHRIMP zircon ages and whole-rock geochemical data to identify mafic–ultramafic massifs of early Carboniferous and early Cretaceous ages from northern Inner Mongolia, China. The early Carboniferous massifs (Chongenshan–Xiaobaliang–Wusnihei) comprise predominantly lherzolite and minor gabbroic rocks. Zircons from a microgabbro (e Nd (t) = 9.8) and a plagiogranite (e Nd (t) = 9) yielded weighted mean 206 Pb/ 238 U ages of 354 ± 7 Ma and 333 ± 4 Ma, that we interpret as reflecting the time of zircon (and magma) crystallization. A volcanic breccia resting unconformably on the ultramafic rocks (serpentinites) has an eruption age of 300 ± 2 Ma and provides a younger minimum …
Devonian to Permian plate tectonic cycle of the Paleo-Tethys Orogen in southwest China (I): Geochemistry of ophiolites, arc/back-arc assemblages and …
2009
Abstract The Paleo-Tethys Orogen in southwest China is an amalgamation of continental terranes (Sibumasu, Simao and Yangtze), which are bounded by ophiolite belts (Ailaoshan, Jinshajiang and Changning–Menglian) that represent former ocean basins. This study concentrates on ophiolites, arc/back-arc assemblages, and within-plate igneous rocks that occur in this complex orogen. Mainly based on geochemical fingerprinting of basalts, the Paleo-Tethys ophiolites are here classified as MORB and SSZ types. The Ailaoshan ophiolite (NMORB-type; ca. 387–374 Ma) is associated with a non-volcanic segment of the rifted western Yangtze margin. The Jinshajiang ophiolite (EMORB-type; 346–341 Ma), which has …