Magmatismo acido e basico dei Colli Euganei e Berici

During Paleogene time in the Veneto region developed a magmatic province that involved four main areas: Lessini hills, Marostican hills, Euganean hills and Berici hills. This work is focused on Euganean and Berici areas. Euganean hills started their activity around 40 Gy ago (upper Eocene), and it’s possible to divide their activity in two stages: the first shows basic magmatism, the second (during lower Oligocene) both basic and acidic activity. Berici hills started their eruption around 50 Gy ago (middle Eocene) and during all the period the eruption belonged to basic magmatism. Acidic rocks from Euganean hills show very similar concentration in major elements, but the abundance of Rare Earth Elements is different. The gap between the two samples regards mainly the Light REE, and this is probably due to subaerial and subaqueous alteration. Subaqueous alteration is confirmed by the gap in Ce: the Ce loss is typical of sea sediments. The two samples belonged to very similar magmas, and their flows have been erupted at the same period. Euganean basic rocks show different degree of magmatic differentiation (from basalt to trachy-andesite basalt), and consequently different concentrations in major and minor elements. Studying the REE concentration normalized to chondrite values it emerges that all the samples could be genetically related by partial melting process. In particular it’s possible to divide the samples in two groups: EU 50 and EU 52 belong to alkaline series, EU 53 belongs to sub alkaline series. Sub alkaline rock has been developed from an high-degree partial melting process, meanwhile alkaline rocks developed from a low-degree partial melting process. Alkaline rocks, moreover, shows high concentrations in LREE due to residual garnet during the melting event. Stratigraphic relations show that alkaline rocks are younger than sub alkaline sample. Berici rocks belong all to basic and ultrabasic composition. They show differences in major and minor elements due to their evolution, but generally they have a low concentration in alkalis, and an abundance in SiO2 lower than 53%. The chondrite normalized values show that basanites have very similar concentration in REE, and the trend from basanites to andesite basalts is compatible with partial melting process. Like euganean samples, also berici rocks can be divide in alkaline (BE1, BE2, BE6) and sub alkaline series (BE4, BE5), that belong to two different partial melting degree processes. From isotopic evidences it’s possible to affirm that all the samples belong to the same mantle rock. The comparison between Berici and Euganean rocks shows that there are three groups of samples having the same concentration in REE. Those samples are: BE 1-BE 6 (basanites), EU 50-BE 2 (basalts), EU 53-BE5 (andesite-basalts). This relation suggest that all the basic rocks from both areas belong to the same mantle rock which has been depleted by several partial melting event. The analysis show that the peridotite has been involved in two main melting event. The first produced sub alkaline rocks by an high-degree melting, the second produced alkaline rocks by a low-degree melting process that also involved residual garnet which enriched the melt in LREE components. Finally, looking for a relationship between Berici-Euganean rocks with magmatic events of VVP, it has been made a comparison between Berici and Marostican basanites. From the concentration of Ce and Ce/Pb it emerges that Berici and Marostican flows have very similar compositions (also in major and minor elements), and both belong to an HIMU mantle. Since Marostican flows developed only during Oligocene time, it’s possible to affirm that also the samples of this work have been erupted at the same time. Concluding, all the samples has been erupted during the final period of activity of the Veneto Vulcanic Province. Basic samples belong to an HIMU mantle which has been depleted by several partial melting. Rhyolites have been erupted in a second time.