Preferencje help
Widoczny [Schowaj] Abstrakt
Liczba wyników

Znaleziono wyników: 3

Liczba wyników na stronie
first rewind previous Strona / 1 next fast forward last
Wyniki wyszukiwania
w słowach kluczowych:  blueschists
help Sortuj według:

help Ogranicz wyniki do:
first rewind previous Strona / 1 next fast forward last
In the Klape Unit of the Pieniny Klippen Belt the Albian conglomerates with clasts of exotic carbonates, clastic sediments and also volcanic and plutonic rocks are relatively widespread. In the small area near the town Povażska Bystrica also scarce blueschist clasts of variegated petrographic types have been found. Three groups of starting rocks can be discerned for blueschists: pelagic sediments, metamorphic rocks (amphibolites, gneisses) and volcanic rocks. Based on immobile trace element (HFSE, REE) distribution two petrogenetic types of volcanic rocks have been identified: basalts with BABB signature and calc-alkaline basaltic andesites to rhyolites. Source of these rocks was probably a nappe stack located in the Carpathian interior and created in the Late Jurassic time as a result of subduction of the oceanic crust and adjacent volcanic arc and followed by collision during the Meliata Ocean closure
Albskie zlepieńce jednostki klapskiej pienińskiego pasa skałkowego zawierające egzotyki skał węglanowych, klastycznych, jak również wulkanicznych i plutonicznych są szeroko rozprzestrzenione. Na małym obszarze w okolicy Povażskiej Bystricy (Słowacja zachodnia) w kilku stanowiskach znaleziono rzadkie egzotyki zróżnicowanych petrograficznie łupków glaukofanowych. Wyróżniono trzy grupy pierwotnych utworów przekształconych w te łupki: osady pelagiczne, skały metamorficzne (amfibolity, gnejsy) i skały wulkaniczne. W oparciu o niestabilne pierwiastki śladowe (HFSE, REE) zidentyfikowano dwa typy petrogenetyczne skał wulkanicznych: bazalty o cechach bazaltów obszarów zaułkowych (BABB) oraz wapniowo-alkaliczne andezyty i ryolity bazaltowe. Obszarem źródłowym tych skał były prawdopodobnie spłaszczowinowane jednostki zlokalizowane w obrębie Karpat wewnętrznych, powstałe w późnej jurze jako rezultat subdukcji skorupy oceanicznej i utworzonego w związku z tym łuku wulkanicznego, w następstwie kolizji podczas zamykania się oceanu Meliaty
Content available remote The Sudetic geological mosaic : Insights into the root of the Variscan orogen
The Sudetes in the NE part of the Bohemian Massif stretch between the NW–SE-trending Odra Fault Zone and Elbe Fault Zone and represent a structural mosaic which was shaped, predominantly, during the Variscan orogeny. They are composed of various geological units, including basement units in which Neoproterozoic to Carboniferous rocks are exposed, and a post-orogenic cover of younger deposits. During the long history of geological research, the Sudetes have become a “type locality” for a range of important geological phenomena, such as granites and orthogneisses, ophiolites and (meta)volcanic sequences, granulites, eclogites and blueschists, nappe tectonics and terrane concepts. In spite of significant recent achievements, many key problems need further study, and a selection of them is proposed in this paper: (a) the presence of older, Neoproterozoic (Cadomian) rocks and their position within the Variscan collage, (b) the character and emplacement setting of Palaeozoic, pre-Variscan sedimentary successions and magmatic complexes (including ophiolites), (c) structural evolution, metamorphism (in particular HP/T grades) and exhumation of deeper crustal blocks during the Variscan orogeny, and (d) post-orogenic development. Future investigations would require an interdisciplinary approach, combining various geological disciplines: structural geology, petrology, geochemistry, geophysics and geochronology, and, also, multilateral interlaboratory cooperation.
Field and laboratory works realized in last years allowed us to redefine one of the lithotectonic units of the western Sudetes, till now considered to be composed of Cambrian to Lower Carboniferous, stratigraphically coherent, volcano-sedimentary succession, as the Lower Carboniferous, probably lower Visean, wildflysch-to- flysch succession. This unit forms the westernmost part of the Kaczawa Complex and is situated at the boundary zone between the Kaczawa Mts. (Polish Sudetes) and the Görlitzer Schiefergebirge (Germany) or - at a larger scale - between the Sudetes and Lugian tectonostratigraphic zones of the Variscan orogen. Petrographical studies of rocks sampled from the larger allochthonous bodies (olistolithes and slide-sheets) of the wildflysch sequence have revealed some peculiar features of the lithic composition of this succession. They consist in the presence of: (1) - unmetamorphosed and metamorphosed volcanites with a distinct HP-overprint, characteristic of supra- subduction zones, gabbro-type plutonites, and relatively numerous detrital chromite grains indicating the occur- rence of ophiolite ultramafics in the source area; and (2) - large block(s) of rock composed of quartz (almost 100% SiO 2 ), previously interpreted as Palaeozoic quartz vein, now documented by the authors to be totally silicified primary evaporites, composed of gypsum (selenite), anhydrite and salt. The last finding would be of special significance as the first strong evidence of evaporites within the Variscan orogenic complex in Europe, if further studies confirm proposed here tectonic position of the silicified evaporites. General lithic composition of the Jędrzychowice/Ludwigsdorf wildflysch detrital material is characterised by the presence of such litholog ies, as: black and gray-to-green cherts, black shale mudstones and cherts, (turbi- dite-)siliciclastics, carbonates (both bioclastic and diagenetic), basic and acid, unmetamorphosed and epi-to- HP-metamorphosed volcanites, and gabbros and ultrabasites (the latter noted only by detrital chromites). Moreover, the siliciclastic material of the olistosthrome matrix discloses the presence of acid magmatic (granites) and high-grade metamorphics of gneiss-to- mica-schist type in the source areas. Such a compositio n of detrital material clearly reflects a typical tectonic mélange as the source terrane for the wildflysch deposit. It would mean that the Jędrzychowice/Ludwigsdorf wildflysch should be considered as the next, strong and unequivocal signal of large-scale tectonic mélange stage in a tectonic/geodynamic evolution of the Central European Palaeozoic orogenic system.
first rewind previous Strona / 1 next fast forward last
JavaScript jest wyłączony w Twojej przeglądarce internetowej. Włącz go, a następnie odśwież stronę, aby móc w pełni z niej korzystać.