Petrological and geological data of porphyritic dikes from the Capo Arco area (Eastern Elba Island, northern Tyrrhenian Sea)

摘要: New geological surveying at a 1:10.000 scale (CARG Project) allowed to refine the stratigraphic, structural and magmatic setting of Elba Island. This paper aims characterizing two dikes likely Late Miocene age (Casa Carpini dikes), previously defined as lamprophyres (i.e. kersantite), outcropping in eastern Elba, on southern slopes Monte Arco, close Porto Azzurro. The grey light-grey Casa dikes, phyllites metasandstones Ligurian- Piedmontese Acquadolce Unit, are quartz-diorites composition with maximum 23% mafic minerals (biotite). They show microcrystalline porphyritic texture consisting plagioclase, biotite, quartz, K-feldspar, rare muscovite scattered xenocrysts plagioclase K-feldspar. Plagioclase phenocrysts display normal zoning An% = 9-23; variability An microcrysts is wider (5-34%). REE patterns characterised by fractionated LREE MREE negative anomaly Eu. mantle-normalized trace element high content most incompatible elements positive spike Th Pb, LILE/HFSE ratios. Negative spikes Nb, P Ti also observable. No anomalies Sr present, Ce/Sr ratios much lower than other rocks from Elba. A depletion K, Rb Cs observed studies rocks, possibly result secondary processes. Sr-Nd isotopic for outcrops studied significant differences, 87 Sr/ 86 0.711845 0.711769 143 Nd/ 144 Nd 0.512223 0.512246. petrographically different dike associated granitoid plutons laccoliths Instead, analogies can be found granodiorites quartz-monzodiorite Orano porphyries, last products western petrological geochemical characteristics typical intermediate- acidic As they petrographic evidence mixing between calcalkaline mafic- intermediate magma similar that Capraia crustal anatectic melt. signatures suggest more important role magmas respect bulk