Several occurrences of metamorphosed pre-Hercynian volcanic rocks crop out in the Paleozoic basement of Southern Sulcis (SW Sardinia), hosted in Cambrian-Early Carboniferous sedimentary sequences belonging to two different structural units (Suicis-Iglesiente and Arburese tectonic units). Basic lava flows and intermediate to acid sub-volcanic bodies may be related to different Paleozoic volcanic events. Geological, petrographical, chemical and U-Pb geochronological data suggest three distinct volcanic episodes: (1) an Early Ordovician episode, (475,00 Ma; U-Pb standard determinations on zircons), consisting of intermediate to acid calcalkaline volcanics, presumably related to an ancient active continental margin/volcanic arc setting; (2) a Middle Devonian episode (387+/-2 Ma; U-Pb standard determinations on zircons), with calcalkaline acid products of orogenic affinity; (3) a Devonian(?)-Early Carboniferous (?) episode, consisting of within-plate alkaline basalts (WPB), derived from a depleted upper mantle source. Early Ordovician calcalkaline metavolcanics and Devonian(?)-Early Carboniferous (?) metabasites may be correlated to similar magmatic products typical of the External Nappe Zone of SE Sardinia. Regional-scale correlations for the Middle Devonian acid metavolcnics, here defined for the first time in Sardinia, are still problematic; age determinations suggest to date back the lower part of the hosting lithostratigraphic unit, interpreted as Hercynian flysch of SW Sardinia.
New evidence of pre-hercynian volcanics from Southern Sulcis (Southwestern Sardinia)
NAITZA, STEFANO;
2005-01-01
Abstract
Several occurrences of metamorphosed pre-Hercynian volcanic rocks crop out in the Paleozoic basement of Southern Sulcis (SW Sardinia), hosted in Cambrian-Early Carboniferous sedimentary sequences belonging to two different structural units (Suicis-Iglesiente and Arburese tectonic units). Basic lava flows and intermediate to acid sub-volcanic bodies may be related to different Paleozoic volcanic events. Geological, petrographical, chemical and U-Pb geochronological data suggest three distinct volcanic episodes: (1) an Early Ordovician episode, (475,00 Ma; U-Pb standard determinations on zircons), consisting of intermediate to acid calcalkaline volcanics, presumably related to an ancient active continental margin/volcanic arc setting; (2) a Middle Devonian episode (387+/-2 Ma; U-Pb standard determinations on zircons), with calcalkaline acid products of orogenic affinity; (3) a Devonian(?)-Early Carboniferous (?) episode, consisting of within-plate alkaline basalts (WPB), derived from a depleted upper mantle source. Early Ordovician calcalkaline metavolcanics and Devonian(?)-Early Carboniferous (?) metabasites may be correlated to similar magmatic products typical of the External Nappe Zone of SE Sardinia. Regional-scale correlations for the Middle Devonian acid metavolcnics, here defined for the first time in Sardinia, are still problematic; age determinations suggest to date back the lower part of the hosting lithostratigraphic unit, interpreted as Hercynian flysch of SW Sardinia.
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