Gianfranco Simboli, Giorgio Gasparotto
Dipartimento di Scienze della Terra e Geologico-Ambientali, Università di Bologna,. Piazza Porta S. Donato 1, 40126 Bologna, Italy

Jan Messinò
Via Cà d'Ambroso 63, 40038 Vergato (BO), Italy

The Serra del Zanchetto and La Prada ophiolites (Bologna Apennines) and the associated rodingites

Volume 3, 2004, pages 67-80

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Abstract

At Serra del Zanchetto and La Prada (Northern Apennines, Bologna) crop out ophiolites belonging to the External Ligurian units, represented by slide blocks embedded or marking the base of flysch-like sequences of Cretaceous-Eocene age. The rocks outcropping at Serra del Zanchetto are serpentinites derived from spinel lherzolites and gabbros. This igneous sequence is intruded by dolerites both massive and as dikes. At La Prada gabbros, basalts and hydrothermally altered rocks crop out. The volcanites point out a T-MORB affinity. At Serra del Zanchetto the serpentinites are cutted by rodingite dikes that developed as a consequence of the metasomatic processes active during serpentinization. The dominant paragenesis in the rodingite dikes and veins are grossular garnet, vesuvianite and diopside. The protoliths for rodingites are: i) gabbros in veins, dikes or lenses embedded or in contact with the serpentinites; ii) serpentinites themselves, in which veins of diopside or more rarely tremolite or the association andradite-diopside-tremolite developed. During the rise of the serpentinites towards the surface there was the formation of ophicalcites characterized by a dense network of veins of chrysotile, lizardite, calcite, quartz and late calcite and datolite. Datolite is also diffused in prehnitized gabbros. At La Prada small bodies of hydrothermally-altered rocks crop out, rich in calcite and quartz veins, and characterized by the presence of millerite and anatase.

Keywords: Ophiolites, Serpentinized peridotites, Rodingites, Ophicalcites, Boron distribution

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