The calc-alkaline association of the Hercynian Sardinia-Corsica Batholith consists of multiple coalescent granitoid plutons and minor gabbroic complexes. Isotopic and trace element data are presented for selected gabbros and I-type granitoids representative of the parental mantle- and crust-derived magmas, respectively. The gabbros belong to normal calc-alkaline suites and have marked relative enrichments in Rb, Ba, K and Pb in primitive mantle-normalized trace element diagrams. The granitoids belong to high-K calc-alkaline suites and have fairly uniform trace element compositions resembling volcanic arc granitoids (VAG). A significant overlap in Sr and Nd isotope compositions is observed between gabbros and granitoids. Geochemical and isotopic data provide evidence for the origin of the gabbros from mantle sources enriched in incompatible trace elements through recycling of sediments via subduction zones, whereas the granitoids were derived from crustal sources composed mainly of igneous protoliths with relatively homogeneous composition. Sr and Nd isotope compositions of gabbros and granitoids are consistent with both the mantle enrichment process and the formation of the igneous crustal sources occurring at ∼450 Ma, during the earlier calc-alkaline igneous activity. The connection between Hercynian and Ordovician igneous activity has important and new implications for the Palaeozoic evolution of the Sardinia and Corsica lithosphere, and permits the Hercynian orogeny to be placed in a wider geodynamic setting, consisting of three main phases. The Ordovician precollisional phase was characterized by a N-NE-dipping subduction of an oceanic plate under a continental plate with emplacement of acid and subordinate basic-intermediate volcanic and intrusive rocks. The subcontinental mantle underneath Sardinia and Corsica experienced enrichment in incompatible trace elements through recycling of sediments. Major crustal accretion also occurred with underplating of basaltic magmas. The Devonian collisional phase was characterized by the collision of two continental plates after the total consumption of the oceanic plate. Crustal thickening processes took place together with regional metamorphic events that recorded a clockwise P-T-t path. The Carboniferous post-collisional phase was characterized by isostatic and thermal readjustments following crustal thickening that caused extensive partial melting. Large quantities of I-type granitoids and subordinate gabbroic complexes were emplaced in the middle-upper crust and formed the mainframe of the Sardinia-Corsica Batholith. This geodynamic model is consistent with the Palaeozoic evolution of other sectors of Western Europe suggested on the basis of geological, geochronological and palaeomagnetic data. The palaeomagnetic restoration of the Late Palaeozoic position of Sardinia and Corsica close to Southern France suggests that Sardinia and Corsica could have been portions of the southern edge of the Armorican plate that, during Siluro-Devonian, collided with the Ibero-Aquitanian plate after the total consumption of the Late Cambro-Ordovician South Armorican and/or Massif Central Ocean.
The Role of Sediment Subduction and Crustal Growth in Hercynian Plutonism: Isotopic and Trace Element Evidence from the Sardinia-Corsica Batholith
POLI, Giampiero;
1995
Abstract
The calc-alkaline association of the Hercynian Sardinia-Corsica Batholith consists of multiple coalescent granitoid plutons and minor gabbroic complexes. Isotopic and trace element data are presented for selected gabbros and I-type granitoids representative of the parental mantle- and crust-derived magmas, respectively. The gabbros belong to normal calc-alkaline suites and have marked relative enrichments in Rb, Ba, K and Pb in primitive mantle-normalized trace element diagrams. The granitoids belong to high-K calc-alkaline suites and have fairly uniform trace element compositions resembling volcanic arc granitoids (VAG). A significant overlap in Sr and Nd isotope compositions is observed between gabbros and granitoids. Geochemical and isotopic data provide evidence for the origin of the gabbros from mantle sources enriched in incompatible trace elements through recycling of sediments via subduction zones, whereas the granitoids were derived from crustal sources composed mainly of igneous protoliths with relatively homogeneous composition. Sr and Nd isotope compositions of gabbros and granitoids are consistent with both the mantle enrichment process and the formation of the igneous crustal sources occurring at ∼450 Ma, during the earlier calc-alkaline igneous activity. The connection between Hercynian and Ordovician igneous activity has important and new implications for the Palaeozoic evolution of the Sardinia and Corsica lithosphere, and permits the Hercynian orogeny to be placed in a wider geodynamic setting, consisting of three main phases. The Ordovician precollisional phase was characterized by a N-NE-dipping subduction of an oceanic plate under a continental plate with emplacement of acid and subordinate basic-intermediate volcanic and intrusive rocks. The subcontinental mantle underneath Sardinia and Corsica experienced enrichment in incompatible trace elements through recycling of sediments. Major crustal accretion also occurred with underplating of basaltic magmas. The Devonian collisional phase was characterized by the collision of two continental plates after the total consumption of the oceanic plate. Crustal thickening processes took place together with regional metamorphic events that recorded a clockwise P-T-t path. The Carboniferous post-collisional phase was characterized by isostatic and thermal readjustments following crustal thickening that caused extensive partial melting. Large quantities of I-type granitoids and subordinate gabbroic complexes were emplaced in the middle-upper crust and formed the mainframe of the Sardinia-Corsica Batholith. This geodynamic model is consistent with the Palaeozoic evolution of other sectors of Western Europe suggested on the basis of geological, geochronological and palaeomagnetic data. The palaeomagnetic restoration of the Late Palaeozoic position of Sardinia and Corsica close to Southern France suggests that Sardinia and Corsica could have been portions of the southern edge of the Armorican plate that, during Siluro-Devonian, collided with the Ibero-Aquitanian plate after the total consumption of the Late Cambro-Ordovician South Armorican and/or Massif Central Ocean.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
