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  • Author or Editor: Orlando Vaselli x
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In Central Europe, Early Cretaceous alkaline igneous rocks (lamprophyres, basanites, phonolites) occur in the Moravian-Silesian Beskidy area (northern Czech Republic and southern Poland) and in the Mecsek-Alföld Zone (southern Hungary). Presently they are located at about 400 km distance of each other. These alkaline igneous rocks show close similarities in their mineral, chemical, and bulk rock compositional data, implying similar petrogenesis and suggesting that these two regions could have been much closer during the Early Cretaceous; they could belong to the same rift zone in the European continental margin. Their trace element distribution and Sr and Nd isotopic ratios suggest that the parental magmas derived from an enriched, HIMU OIB-like asthenospheric mantle by different degrees (3-6%) of partial melting at the depth of spinel-garnet transitional and garnet stabilization zone (about 60-80 km depth). This mantle source appears to be akin to that thought to have supplied the Tertiary to Quaternary alkaline mafic magmas in Europe (EAR=European Asthenospheric Reservoir). This may imply that this EAR-type mantle reservoir could have been present beneath Europe at least since the Early Cretaceous. It could reside at the base of the upper mantle (670 km discontinuity) supplying upwelling hot mantle fingers, or it may represent a long-lasting, polluted (HIMU+depleted MORB mantle) upper mantle at shallow depth beneath Europe.

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In the Buda Mts. (Hungary) several Pleistocene travertine outcrops are known. The subject of this paper is a stable isotope study on the Pleistocene travertine from Budakalász that was deposited on the slope of Monalovác Hill of the Buda Mts. The principal goal of this work is to define the depositional environment and related implications by studying the petrographical and microfacies features and C and O stable isotope compositions. The Budakalász travertine can be divided into two stratigraphic units. The lower part of the studied sections (approx. 15 m thick) consists of massive limestone, which represents a "smooth-slope" facies and has mean d13C and d18O values of 2.21‰ and -11.1‰ relative to V-PDB, respectively. Microbial shrub structures were also recognized in the lower part of the section, showing slightly higher d13C values (2.6-2.7‰) relative to the other samples.  The upper unit of the sections is composed of what was originally calcareous mud. The studied samples have low d13C values (~1.8‰) and notably higher d18O values (~-10.6‰) than the average d18O value of the lower part of the section. The samples from the upper part contain microsparitic cement as an indication of stagnant water environment with calm lacustrine sedimentation and pond facies. Based on our integrated petrographic and microfacies description and stable isotope study, the Budakalász travertine can be classified as an originally thermogene travertine.

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