摘要：

Alpine - Apennine ophiolites derive from the Jurassic Ligurian Tethys oceanic basin formed by lithosphere extension and failure in the pre-Triassic Europe-Adria system. The basin was floored by mantle peridotites and was characterized by along-axis alternation of avolcanic and volcanic segments. Lithosphere extension and thinning caused asthenosphere adiabatic upwelling and decompressional melting. Mid-ocean ridge basalt (MORB)-type melts diffusely percolated through and reacted with the overlying lithospheric peridotites, which were strongly modified, both depleted (harzburgites and dunites) and enriched (plagioclase peridotites), by melt-peridotite interaction and melt refertilization. The stratigraphic - structural features (mantle at the sea floor and alternation of avolcanic and volcanic segments) coupled with petrological features (presence of alkaline melts and strongly heterogeneous, melt-modified peridotites) allow us to interpret the Ligurian Tethys as a Jurassic analogue of modern ultraslow-spreading oceans. The Liguria Mode for the inception of an oceanic basin consists of: (1) the rifting (continental) stage, dominated by extension of continental lithosphere and tectonic exhumation of lithospheric mantle; (2) the drifting (transition) stage, characterized by melt-related processes (i.e. inception of asthenosphere partial melting and MORB melt percolation through the overlying mantle lithosphere); (3) the spreading (oceanic) stage, characterized by failure of the continental crust, sea-floor exposure of mantle peridotites and discontinuous MORB extrusion.

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