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Rezumat articol ediţie STUDIA UNIVERSITATIS BABEÅž-BOLYAI
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Rezumat: Geographically, Băiţa Bihor is located in the southwestern area of Bihor Mts., a subdivision of Northern Apuseni Mountains. The geological setting is controlled by a very complicated tectonic situation, in which Bihor, Codru and Arieşeni structural units are involved; the lithology of these units consists of limestones (the Bihor unit), dolomites and limestones (the Codru unit), clays and sandstones (the Arieşeni unit). This structure is penetrated, during four magmatic stages (Berbeleac, 1988), by banatitic intrusives (Upper Cretaceous-Lower Paleogene); the largest of it being a batholith made up of granites, granodiorites and pegmatites. The batholith belongs to the third magmatic stage and exhumes in the Valea Seacă area.
The present paper deals with some basic dykes of the fourth magmatic stage, named previously “basalts” by Stoici (1983) and showing no relationship with the felsic batholith. Based on the chemical data published by the quoted author, the study focuses on a more detailed geochemical characterization of the basic dykes. The chemical data concern the major elements and were performed using the wet chemical technique.
The plot of 65 samples supposed to be basalts, shows a wide range of samples distribution in TAS diagram (SiO2 vs. Na2O+K2O). Thus, the samples plot in the fields of basalts, trachybasalts, tephrites, basaltic andesites, basaltic trachyandesites, trachyandesites and finally andesites. De La Roche-Leterier diagram, based on the standard formula parameters of Si, Na, K, Fe, Ti (R1) versus Ca, Mg, Al (R2) leads to similar results.
In order to find out whether this conclusion is confirmed, a statistical processing of all 65 analyses has been performed considering their major elements. This approach revealed two maximums in the distribution of SiO2 contents: at about 48.7 wt% and at 52.7 wt% (Fig. 1). Based on this fact and knowing that SiO2 has generally a strong bimodal character in magmatic rocks (it means two maximums - at about 52.2 wt% and at 73.0 wt% respectively) we assumed that in the case of samples from Băiţa Bihor there are two populations of data: a basaltic population (with SiO2 < 50.7 wt%) and an andesitic one (with SiO2 > 50.7 wt%). ... |
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