Time-space distribution of magmatic activity in the western Mediterranean and peripheral orogens during the past 30 Ma ( a stimulus to geodynamic considerations)

.- Age and rock type, regional distribution and structural setting of volcanic and plutonic manifestations from the western Mediterranean basin and peripheral orogens during the past 30 Ma are examined. Distinct magmatic phases (ranging between 30 and 15, 15 and 9, 8 and 6, 5 and 2, 2 and 1.5, and finally between 1.5 and 0 Ma) exhibit a large variety of rock types which reflect complex processes of backarc and arc extension related with convergence between the European and the African-Ionian-Adriatic plates. The overall length of a complex plate boundary zone increased with time from ca. 1400 to 2500 km along-strike. Widespread, extension-related orogenic products were emplaced subsequent to distinct convergent processes which led to formation of the Hercynian, Alpine and Apenninic orogens. Attenuation of the ‘Alpine’ area was initiated with eruption of plutonic and volcanic rocks of acidic calcalkaline composition and of volcanics of tholeiitic (subalkaline) affinity. Tholeiites were probably linked to faster rates of intra-orogenic extension reaching the stage of oceanic opening in the south Tyrrhenian sea. In addition, localized small- volume eruptions of ultrapotassic rocks (lamproites) accompanied thinning and stretching of the Alpine orogenic wedge. Intraplate Na-alkaline manifestations are widespread in the passive margins and in foreland areas. Overall, the episodic progression of magmatic activity in the western Mediterranean reflects complex geodynamic processes of retreating subduction, spreading and crustal attenuation which were preceded in time by continent-continent collision in the entire area.