Show description

38 Fig. 3. (Continued) S. ISHIMARU & S. ARAI Ca-AMPHIBOLES IN AVACHA PERIDOTITES Fig. 3. (Continued) 39 40 S. ISHIMARU & S. ARAI In Zone 2, minerals are almost the same as in Zone 1 except for the absence of calcic amphiboles in the former. Minerals are coarser in Zone 2 than in Zone 1, and there are some metasomatic veins, composed of metasomatic orthopyroxenes replacing olivine with or without clinopyroxenes (Fig. 2a and b). The metasomatic orthopyroxenes sometimes show radial aggregation replacing olivine, and are the same as those typically observed in the metasomatized C-type peridotites (Arai et al.

The thermo-mechanical erosion of the mantle lithosphere facilitates the transition from distributed lithosphere deformation to localized oceanic spreading. Conclusion The following steps have been envisaged during the progressive exhumation of Ligurian peridotites from the sub-continental mantle lithosphere to the sea floor. (1) Mantle protoliths of the Ligurian ophiolitic peridotites were accreted to the thermal lithosphere and underwent complete equilibrium recrystallization at sub-continental lithospheric conditions after isolation from the convecting asthenosphere.

H OFFMANN , A. W. 2004. Triassic emplacement of the external Gabbro Unit of the Finero mafic complex: U– Pb SHRIMP zircon age and their implication for the Ivrea–Verbano zone, Western Italian Alps. Geophysical Research Abstracts, 6, abstract number 05072. P ICCARDO , G. B. 1976. Petrologia del massiccio lherzolitico di Suvero (La Spezia). Ofioliti, 1, 279–317. ULTRASLOW LIGURIAN TETHYS: MANTLE VIEW P ICCARDO , G. B. 1984. Le ofioliti metamorfiche del Gruppo di Voltri, Alpi Liguri: caratteri primari ed interpretazione geodinamica.