Piedmont, Rechnitz and Meliata zone a petrographic-geochemical comparison of metamorphic ophiolites of the Alpine-Carpathian /
In spite of the polyphase metamorphic history and intense deformation there are a lot of ultramafic, gabbro, and plagiogranite, mafic dykes, volcanic and deep-sea sediment occurrences of Mesozoic age in the Alp-Carpathian system. Our petrographic-geochemical comparison of these rock-types focuses on...
Elmentve itt :
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| Dokumentumtípus: | Cikk |
| Megjelent: |
University of Szeged, Department of Mineralogy, Geochemistry and Petrology
Szeged
1992
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| Sorozat: | Acta mineralogica-petrographica
33 |
| Kulcsszavak: | Kőzettan, Ásványtan, Földtan |
| Tárgyszavak: | |
| Online Access: | http://acta.bibl.u-szeged.hu/24801 |
| Tartalmi kivonat: | In spite of the polyphase metamorphic history and intense deformation there are a lot of ultramafic, gabbro, and plagiogranite, mafic dykes, volcanic and deep-sea sediment occurrences of Mesozoic age in the Alp-Carpathian system. Our petrographic-geochemical comparison of these rock-types focuses on two zones of the Alpine belt: the Western Alps (Piedmont) and the Eastern Penninic Alps (Rechnitz) and one zone of the Carpathians: the North Hungarian and South Slovakian Meliaticum. The first zone is characterized by the abundant relics of high pressure metamorphism of Cretaceous age which survived the greenschist facies metamorphism of Tertiary age, while the two latter show relatively limited relics of the (eoalpine) glaucophane schist facies conditions. The special interest of a comparison derives from the fact that the first two zones form a a typical Jurrasic-Cretaceous ophiolite nappe occurring in the west- and easternmost zones of the Alpine belt. These two zones display a genetic similarity. On the other hand, the third zone is considered as a Triassic-Jurassic incomplete ophiolite suite occurring in the present Innermost Carpathian belt. Based on detailed field and laboratory studies we compare the three zones in terms of their upper mantle rocks (serpentinite and pyroxene-rich chlorite schist), mafic plutonic suite (coarse grained eclogite, glaucophane schist- and greenschist-facies meta§abbro and plagio-granite), volcanic suite (fine grained eclogite, glaucophane schist- and greenschist-facies metavolcanic) and sedimentary cover (radiolarite, ophiolitic breccia, ophicarbonate, calcschist, micaschist and quartzite). The lithologies of the two zones of the Alps are relatively similar and comparable to the Western Alps metaophiolites (N- and T-type MORB volcanics, range of plutonic rocks from primitive Mg-Al rich gabbros to late fractionated plagiogranites, predominance of depleted lherzolites and/or harzburgites among the ultramafics). On the other hand, the lithology of the third zone (Meliaticum) of the Innermost Carpathians is relatively different from the ophiolite zones of Alpine belt (E- and T-type MORB, spilitic volcanics, albite-nch gabbros, dominant harzburgitic and minor lherzolitic ultramafics) whicn may exclude a close genetic connection between the two belts. Moreover, the volcanic (and probably the plutonic) rocks of the Alps show a much greater compositional variability, suggesting a relatively slow spreading rate. In contrast, the Meliata volcanics display almost a limited compositional variation and sometimes spilitic pillow lavas, suggesting a relatively fast spreading rate with occasional interaction with seawater. There are minor but interesting similarities among these ophiolites. All of them are high-Ti type, have tholeiitic affinitites with a tendency to "transitional" MORB character. All these ophiolite-sequences show a progressive enrichment of both rare earth and incompatible elements starting from ultramafics toward the effusive members as a result of magmatic differentiation. However, we found a Ba enrichment in all volcanic members, which can be derived from the deep-sea sediments covering the volcanics. All of these ophiolites have undergone some oceanic alterations and the complex Alpine regional metamorphic events, and mixed or covered by marine sediments. In conclusion, the comparison between the Alpine and Carpathian ophiolites lead to assign a peculiar significance among them (as previous) in relation to the various tectonic events dominating in the Jurassic-Cretaceous Piedmont-Ligurian basin and in the Triassic-Jurassic Vardar basin. |
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| Terjedelem/Fizikai jellemzők: | 37-55 |
| ISSN: | 0365-8066 |