Mantle Evolution from Continental Rifting to Ocean Birth: The Record of Alpine-Apennine Ophiolitic Peridotites

• Main Authors: MONTANINI, Alessandra, PICCARDO G. B, TRIBUZIO R.
• Other Authors: Montanini, Alessandra, Piccardo, G. B., Tribuzio, R.
• Format: Conference Object
• Language: English
• Published: 2008
• Subjects: Newfoundland; North Atlantic
• Online Access: http://hdl.handle.net/11381/1896384; http://a-c-s.confex.com/crops/2008am/webprogram/Paper48177.html

Western Alps - Northern Apennines (AA) ophiolites are lithosphere remnants of the Ligurian Tethys oceanic basin (the Ligurian-Piemontese basin) that separated the Europe and Adria continental blocks during Middle Jurassic – Cretaceous times. AA ophiolites stratigraphy evidences that the Ligurian Tethys was floored by a gabbro-peridotite basement discontinuously covered by basaltic lava flows, underlying the oceanic sediments. Present-day oceanic analogues are: (i) the ocean-continent transition zones (e.g. the paired Galicia-Newfoundland margins of North Atlantic); (ii) the slow - ultra-slow spreading ridges (e.g. the Polar Ridges and SWIR), (iii) the oceanic core complexes along MAR. AA ophiolitic peridotites derive from the sub-continental Europe-Adria lithospheric mantle that was exhumed during passive lithosphere extension and was exposed at the sea-floor of the Ligurian Tethys after Middle Jurassic continental break-up. Mantle peridotites show different structural/compositional characteristics depending on their palaeogeographic settings within the ancient basin. Peridotites from more marginal, peri-continental settings consist of pristine fertile spinel lherzolites, showing spinel (garnet) pyroxenite layers, that underwent extensional shearing and metamorphic evolution from spinel- to plagioclase- to amphibole-chlorite-peridotite facies conditions to near sea-floor serpentinization. Peridotites from more internal, oceanic settings show highly variable compositions, ranging from depleted spinel harzburgites and dunites to plagioclase-enriched peridotites. This extreme heterogeneity was formed by porous flow melt percolation, melt-rock interaction and refertilization of the pristine sub-continental lithospheric mantle by MORB-type asthenospheric melts, that occurred during exhumation and preceding shallow level emplacement or sea-floor exposure. Present knowledge evidences that pre-oceanic rifting in the Ligurian-Piemontese domain was accomplished by: 1) tectonic-metamorphic stages, active during Triassic ...