Search results for "GEOCHRONOLOGY"
showing 10 items of 60 documents
Geodynamic Setting of the Tertiary Hocheifel Volcanism (Germany), Part II: Geochemistry and Sr, Nd and Pb Isotopic Compositions.
2007
Major and trace element as well as isotopic compositions on 26 volcanic rocks from the Tertiary Hocheifel volcanic field and for comparison from Upper Rhine Graben occurrences (western Central European Volcanic Province) were measured in order to provide geochemical evidence for the geodynamic setting of the Tertiary Eifel volcanism. Except for a few differentiated lavas there are mainly basanitic compositions. These rocks were produced by low degree partial melting of a previously metasomatized garnet peridotite source at pressures and temperatures corresponding to depths of about 75 to 90 km. In contrast to the differentiated lavas, most of the basanites are not significantly affected by …
Crustal age domains in the Kibaran belt of SW-Uganda: Combined zircon geochronology and Sm–Nd isotopic investigation
2008
Abstract Combination of geochemistry, Nd mean crustal residence ages and single zircon ages reveal distinct provinces not recognized previously within the Kibaran belt of SW-Uganda. Geochemical analyses (HFSE and REE) of four granitoids, namely the Ntungamo, Chitwe, Rwentobo and Kamwezi from the Karagwe Tinfield have been interpreted to be mainly composed of melt components from subduction modified parts of the continental lithospheric mantle. In addition we can demonstrate, from these distinctive batholiths crystallization ages that lead to the result of three age groups, one at around 1566 Ma, the second at 1444 Ma to and the third clusters between 1329 Ma and 1363 Ma. The eNd(t) values f…
Zircon geochronology of anatectic melts and residues from a highgrade pelitic assemblage at Ihosy, southern Madagascar: evidence for Pan-African gran…
1996
AbstractWe report U—Pb and207Pb/206Pb zircon ages for a granulite facies gneiss assemblage exposed in a large quarry at Ihosy, southern Madagascar. The granulites are derived from pelitic to arkosic sediments and attained equilibrium conditions at 650–700°C and 4–5 kbar. HigherP—Tconditions of 750–800°C and 6 kbar in the presence of low water activities have led to dehydration melting processes. The formation of granitic melts, which (partly) moved away from their source region, intruded into upper parts of the metapelitic gneisses as small granitic veins and left behind granulitic garnet-cordierite-quartz bearing rocks. Detrital zircons in a sample of metapelite and a sample of quartzofeld…
Geochronology and palaeomagnetism of a late Proterozoic island arc terrane from the Red Sea Hills, northeast Sudan
1992
Abstract Size fractions and single grains of zircon, hornblende and biotite have been dated to define the formation age and thermal history of the northern Haya Terrane (NHT), a late Proterozoic island arc terrane of the Red Sea Hills (RSH), northeast Sudan. U Pb and 207 Pb/ 206 Pb zircon data for acidic volcanics and granitoid rocks bracket the time of formation of the NHT between 887 ± 20 and 854 ± 9 Ma. 40 Ar/ 39 Ar hornblende and biotite ages of a gabbro near Suakin suggest passage through the argon closing temperature for hornblende at about 841 ± 4 Ma and 782 ± 6 Ma for biotite. The hornblende age is considered to be representative of the age of magnetic blocking and, hence, the age o…
Geochronology of the medium to high-grade metamorphic units of the Peloritani Mts., Sicily
2003
The Peloritani Mountains are a fragment of an orogen variably attributed to the Alpine or Hercynian orogeny. On the basis of 39 Ar- 40 Ar, U-Pb and Rb-Sr dating, the main metamorphism of the two medium-high grade metamorphic units, the Mela and Aspromonte Units, and most of the thrusting responsible for stacking the orogenic edifice are seen to be Hercynian. The main thrusting of the Aspromonte Unit over the lower grade units took place at 301€2 Ma. Brittle deformation during Tertiary reactivation of Hercynian thrust planes did not generate any rejuvenation of white micas in the studied sector. Our dataset shows a great complexity and we propose to unravel it by considering different levels…
Rutile crystals as potential trace element and isotope mineral standards for microanalysis
2009
Abstract The present paper reports trace element concentrations of 15 elements (V, Cr, Fe, Zr, Nb, Mo, Sn, Sb, Hf, Ta, W, Lu, Pb, Th and U) as well as Pb and Hf isotope data for four relatively homogeneous and large (centimeter size) rutile grains. Methods employed are SIMS, EMP, LA-ICP-MS, ID-MC-ICP-MS and TIMS. For most elements homogeneity is usually within ± 10% and occasionally variations are even narrower (± 5%), particularly in the core of two of the studied grains. The trace element concentrations of the grains span a broad compositional range (e.g., Zr concentrations are ca. 4, 100, 300 and 800 ppm). Provisional concentration values, calculated based on the homogeneity of the eleme…
Sinistral transport along the Trans-European Suture Zone: detrital zircon–rutile geochronology and sandstone petrography from the Carboniferous flysc…
2010
AbstractThe Lower Carboniferous flysch of the Istanbul Zone in Turkey is an over 1500 m thick turbiditic sandstone–shale sequence marking the onset of the Variscan deformation in the Pontides. It overlies Lower Carboniferous black cherts and is unconformably overlain by Lower Triassic continental sandstones and conglomerates. The petrography of the Carboniferous sandstones and the geochronology and geochemistry of the detrital zircons and rutiles were studied to establish the provenance of the clastic rocks. The sandstones are feldspathic to lithic greywackes and subgreywackes with approximately equal amounts of quartz, feldspar and lithic clasts. The amount of quartz and lithic fragments d…
Provenance of sediments during subduction of Palaeotethys: Detrital zircon ages and olistolith analysis in Palaeozoic sediments from Chios Island, Gr…
2008
Abstract Detrital zircon geochronology and analysis of fossiliferous olistoliths from Chios Island, Greece, are used here to constrain terrane accretion processes and the provenance of crustal sources for sediments during the subduction of (a branch of) the Palaeotethys Ocean. U/Pb ages obtained by ion microprobe (SHRIMP-II) analyses of detrital zircons from a Carboniferous greywacke belonging to the tectonostratigraphic Lower Unit of Chios gave major age groups of 2150–1890 Ma, 640–540 Ma, 505–475 Ma and 365–322 Ma. Detrital zircons from a Permian–Triassic sandstone yielded prominent age clusters of 2200–1840 Ma, 1100–910 Ma, 625–560 Ma and 385–370 Ma. The lack of zircon ages between 1.8 a…
Environmental radioactivity at Stromboli (Aeolian Islands)
2002
HPGe gamma spectrometry, thermoluminescence dosimetry, X-ray diffractometry and fluorescence techniques have been used to analyze the natural radionuclides content of soil and rock samples, air kerma and geochemical features on the island of Stromboli, belonging to the Aeolian Islands, in the Mediterranean Sea. The 214Bi, 238Ac, and 40K contents obtained are in agreement with the magmatic evolution of the rock formation, as shown by the correlations between radionuclide and chemical elements abundacies, depending on the various magmatic differentiation mechanisms. Correlations between radiometric, lithological and geochemical data have been assessed in order to obtain some hints on the geoc…
Neoproterozoic ophiolite and related high-grade rocks of the Baikal–Muya belt, Siberia: Geochronology and geodynamic implications
2015
Abstract We report zircon for from ophiolitic and high-grade rocks of the Neoproterozoic Baikal–Muya belt of Siberia that occupies an arc-shaped area on the southeastern margin of the Siberian craton. It consists of arc-related plutonic, metavolcanic and metasedimentary rocks as well as fragmented ophiolites and high-grade metamorphic assemblages. Magmatic zircons from two plagiogranite dyke samples of the Mamakan ophiolite complex in the Sredne–Mamakan massif of the eastern Baikal–Muya belt yielded similar and concordant SHRIMP mean 206 Pb/ 238 U ages of 640.0 ± 4.1 and 650 ± 6 Ma, respectively, that reflect the time of dyke emplacement and from which we suggest an age of ca. 645 Ma as the…