During Early Mesozoic, a diffuse magmatic activity developed in western-central Sicily in relation to the extensional tectonics associated with the opening of the Neotethys Ocean. In this work, we report and discuss geochemical and Sr-Nd isotopic data for Sicilian Triassic tholeiitic and alkaline volcanic rocks. Tholeiitic basalts from western Sicily are characterized by relative HFSE enrichment, high HFSE/LILE ratios, flat REE patterns (LaN/YbN = 2.27-2.48), Ti, Sr and K negative anomalies and Pb peaks in primitive mantle-normalized diagrams. The Sr (87Sr/86Sri = 0.707-0.708) and Nd isotopic compositions (εNdi = from -1.7 to -2.2) are compatible with an origin from enriched mantle sources. Additionally, the relatively high Sr isotopic ratios and diagnostic trace elements ratios, such as La/Nb (~ 17), LaN/SmN (~ 1.20), Nb/U (~ 20) and Pb/Nd (~ 0.3), could reflect involvement of the lower crust in the magmatic evolution of the tholeiitic rocks. Alkali basalts from central Sicily preserve a clear geochemical signature despite the intense alteration. The behaviour of immobile elements such as the low Y/Nb and Zr/Nb and high Th/Yb and Ta/Yb ratios, positive Nb-Ta-Ti anomalies, and the radiogenic Nd isotope ratio (εNdi = +3.4 to +3.7) suggests an OIB-like source. The LREE/HREE ratio (LaN/YbN = 7.43-8.76) is higher than in the tholeiitic samples, suggesting a possible role of residual garnet in the magma source, or a lower degree of partial melting, or both. The behaviour of mobile elements, such as the Sr isotopic composition (87Sr/86Sri = 0.706-0.707) and the K depletion, does not contradict this. On the basis of trace elements and Sr-Nd isotopic composition, the Sicilian Triassic dykes could reflect the early stages of rifting in a continental setting, including initial lithospheric thinning, passive upwelling of hot asthenosphere, and related processes of partial melting involving differently enriched mantle reservoirs.

Triassic Tholeiitic and alkaline basaltic magmatism in western central Sicily (southern Italy): geochemical and isotopic clues to mantle sources involved during early continental rifting.

CIRRINCIONE, ROSOLINO;FIANNACCA, PATRIZIA;Tranchina A;
2011

Abstract

During Early Mesozoic, a diffuse magmatic activity developed in western-central Sicily in relation to the extensional tectonics associated with the opening of the Neotethys Ocean. In this work, we report and discuss geochemical and Sr-Nd isotopic data for Sicilian Triassic tholeiitic and alkaline volcanic rocks. Tholeiitic basalts from western Sicily are characterized by relative HFSE enrichment, high HFSE/LILE ratios, flat REE patterns (LaN/YbN = 2.27-2.48), Ti, Sr and K negative anomalies and Pb peaks in primitive mantle-normalized diagrams. The Sr (87Sr/86Sri = 0.707-0.708) and Nd isotopic compositions (εNdi = from -1.7 to -2.2) are compatible with an origin from enriched mantle sources. Additionally, the relatively high Sr isotopic ratios and diagnostic trace elements ratios, such as La/Nb (~ 17), LaN/SmN (~ 1.20), Nb/U (~ 20) and Pb/Nd (~ 0.3), could reflect involvement of the lower crust in the magmatic evolution of the tholeiitic rocks. Alkali basalts from central Sicily preserve a clear geochemical signature despite the intense alteration. The behaviour of immobile elements such as the low Y/Nb and Zr/Nb and high Th/Yb and Ta/Yb ratios, positive Nb-Ta-Ti anomalies, and the radiogenic Nd isotope ratio (εNdi = +3.4 to +3.7) suggests an OIB-like source. The LREE/HREE ratio (LaN/YbN = 7.43-8.76) is higher than in the tholeiitic samples, suggesting a possible role of residual garnet in the magma source, or a lower degree of partial melting, or both. The behaviour of mobile elements, such as the Sr isotopic composition (87Sr/86Sri = 0.706-0.707) and the K depletion, does not contradict this. On the basis of trace elements and Sr-Nd isotopic composition, the Sicilian Triassic dykes could reflect the early stages of rifting in a continental setting, including initial lithospheric thinning, passive upwelling of hot asthenosphere, and related processes of partial melting involving differently enriched mantle reservoirs.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.11769/109009
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