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Wyszukujesz frazę "grabens" wg kryterium: Wszystkie pola


Wyświetlanie 1-2 z 2
Tytuł:
Phases of Palaeogene and Neogene tectonic evolution of selected grabens in the Wielkopolska area, central-western Poland
Autorzy:
Widera, M.
Powiązania:
https://bibliotekanauki.pl/articles/191603.pdf
Data publikacji:
2004
Wydawca:
Polskie Towarzystwo Geologiczne
Tematy:
tectonic phases
grabens
Palaeogene
Neogene
Wielkopolska area
central-western Poland
Opis:
In the Wielkopolska (Great Poland) area, there occur numerous tectonic grabens which were active in the Palaeogene and Neogene. The similarities and differences between their development are presented on the example of the Czempiń, Szamotuły, Lubstów, and Władysławów Grabens. Using various methods of palaeotec- tonic analysis, the stages of accelerated subsidence of the grabens, i.e. tectonic phases, were indicated. The extent of vertical movement in the studied grabens were compared and it was affirmed that there is a connection between the occurrence of older dislocations and salt structures in the deep basement. From among the examined grabens, the Lubstów Graben is the deepest one, and shows the most complex geological structure. The Czempiń and Szamotuły Grabens are characterized by relatively simple geological structure, where the stratigraphic complete- ness and tectonic style are very legible. These three grabens were active in different tectonic stages from the turn of the Eocene/Oligocene till the end of the Neogene, and perhaps also in the Prepleistocene. The Władysławów Graben is a very shallow tectonic structure and its evolution lasted for the shorter period of time. The time of its development extended from the Early through the Middle Miocene. These grabens provide a good example of the relationship between the fault throw and graben location. The Czempiń, Szamotuły, and Lubstów Grabens, connected with deeply-rooted dislocations, came to existence in the Pyrenean phase (latest Eocene - Early Oligocene). However, the Władysławów Graben was affected mainly by salt structure activity. Thus, its first stage of tectonic evolution took place in the Savian phase (Early Miocene).
Źródło:
Annales Societatis Geologorum Poloniae; 2004, 74, No 3; 295-310
0208-9068
Pojawia się w:
Annales Societatis Geologorum Poloniae
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Stephanian-Early Permian basaltic trachyandesites from the Sławków and Nieporaz-Brodła Grabens near Kraków, Southern Poland
Autorzy:
Lewandowska, A.
Rospondek, M. J.
Nawrocki, J.
Powiązania:
https://bibliotekanauki.pl/articles/191897.pdf
Data publikacji:
2010
Wydawca:
Polskie Towarzystwo Geologiczne
Tematy:
Upper Carboniferous/Permian volcanism
a-a lava flows
autoclastic breccias
basaltic trachyande-sites
transitional calc-alkaline to alkaline rocks
hydrous magma
Opis:
In the Kraków-Lubliniec section of the major Hamburg-Kraków-Dobrogea Fault Zone (HKDFZ), the Stephanian-Early Permian magmatic activity was simultaneous with subsidence/uplift of formed blocks. In the proximity of the uplifted areas the sedimentation started with fanglomerates, distally passing into playa siltstone and was accompanied by volcanism. In the Nieporaz-Brodła graben, basaltic trachyandesite a-a lava flows with autoclastic breccias reach ca. 150 m in thickness. The weathering recorded as adhesive rims around breccia clasts reflects palaeosoil formation during quiescence periods between the eruptions. The eruptions were effusive although scoriaceous lava indicates high volatile content of the magma. The water content before eruption had to be over 2 wt. percent. Only then the crystallisation model predicts accurately the type, composition and order of the crystallising phases. Thus, the basaltic trachyandesite magma originated from a source containing hydrous phase (i.e., amphibole or phlogopite). All the studied basaltic trachyandesites had fayalitic olivine on their liquidus reflecting the crystallisation stage in a magma chamber at crustal depths. During final decompression on the magma ascent due to water exsolution, the olivine was followed by plagioclase, spinel, augite, ilmenite, apatite, K-feldspar and residual high-K rhyolitic glass. The high potassium content of these volcanics was thus a primary feature reflecting the source geochemistry and differentiation trend, and its consequence was potassium metaso- matism. Due to water exsolution the glass was altered, however, homogenous interstitial glass survived in some rocks. The glass is strongly enriched in incompatible trace elements, showing that it is a highly fractionated residual melt fraction of the basaltic trachyandesite magma. Thus, the glass geochemistry reflects the trend of fractional crystallisation indicating that co-occurring K-rich felsic rocks were not derived from the same magma. All the basaltic trachyandesites studied have calc-alkaline to alkaline affinity. They contain fayalitic olivine and are low in MgO <5 wt. %, Cr and Ni, the features characteristic for evolved magmas. They show significant negative Sr/Sr*> 0.5-0.80 and small Eu/Eu* > 0.9-1.0 anomalies suggesting fractionation of plagioclase. The Eu/Eu* anomaly is probably compensated by amphibole retaining in the source. Negative Nb, Ti anomalies suggest Fe-Ti oxide fractionation characteristic for calc-alkaline evolution trend. A significant enrichment in LREE relatively to HREE (La/Yb > 10) indicates subduction-related metasomatism. However, the described tectonic context is inconsistent with subduction related characteristics. Concluding, the observed geochemical characteristics indicate remarkable role of water in magma evolution. The volcanism was related to strike-slip dextral movement along the Kraków-Lubliniec section of HKDFZ, transformed into crustal extension and subsidence, the features typical for the formation of pull-apart basins, in the late stages of the Variscan orogen evolution.
Źródło:
Annales Societatis Geologorum Poloniae; 2010, 80, No 3; 227-251
0208-9068
Pojawia się w:
Annales Societatis Geologorum Poloniae
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-2 z 2

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