Studio mineralogico-petrografico dei litotipi dell'ofiolite di Serra del Zanchetto (Bologna)

Mineralogical and petrographic studies of gabbros, sediments and serpentinites from an ophiolitic body at Serra del Zanchetto, Italy, are reported. Three groups are studied: 1) a mylonitized gabbro, near a gabbro-serpentinite contact, which contains serpentinite fragments, newly-formed diopsidic clinopyroxene, augite and chlorite, and shows textural characteristics which suggest strong tectonic movements following the serpentinization process; 2) a transformed coarse-grained gabbro, included in the serpentinite, which contains prehnite, after plagioclase and chlorite, after clinopyroxene; the chemical formulae of both minerals and the optical, IR and thermal behaviour of prehnite are given; and 3) fragments of sediment outcropping close to both gabbros and serpentinites. One type seems to be either a diagenetic or weakly metamorphosed arkose; a second, shows similar textures but has chloritized biotite and feldspars replaced by a regularly interstratified chlorite-saponite. The significance of the metasomatic effects of the serpentinization on gabbro xenoliths and arkosic sediments are discussed.