Petrogenesis of calc-alkaline,shoshonitic and associated ultrapotassic Oligocene volcanic rocks from the Northwestern Alps,Italy |
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| Authors: | G Venturelli R S Thorpe G V Dal Piaz A Del Moro P J Potts |
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| Institution: | (1) Istituto di Mineralogia, Universita di Parma, Parma, Italy;(2) Department of Earth Sciences, The Open University, Milton Keynes, UK;(3) Istituto di Geologia, Universita di Padova, Padova, Italy;(4) Istituto di Geocronologia e Geochimica Isotopica CNR, Pisa, Italy |
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| Abstract: | Along the Western Alps there is geological evidence of late-Alpine (Oligocene) magmatic activity which clearly postdates the
Lepontine (Eocene-early Oligocene) metamorphism and related deformation of the Alpine nappe pile. This magmatic activity was
notably delayed in relation to the most important convergent processes and may be related to buoyancy of lithosphere, tensional
tectonics and thermal updoming subsequent to the collision between the Eurasian and African plates. The geochemical features
of the rocks and the geophysical characteristics of the Alpine chain, suggest that: (a) shoshonitic and calcalkaline melts
may have been generated by partial melting of metasomatized peridotitic material and subsequent fractional crystallization
and crustal contamination; silicic andesites and latites, however, could have been also derived from metasomatized eclogite
or deep continental crust material; (b) the ultrapotassic lamprophyres with high K, P, LREE, Th, Zr, U and high 87Sr/86Sr ratios were generated by partial melting of strongly metasomatized mantle; the varied Sr-isotopic ratios may partially
also reflect additional radiogenic component from the continental crust following magma segregation from the source. |
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