Geological, geochemical and isotope diversity of ~Â 134Â Ma dykes from the Florianópolis Dyke Swarm, Paraná Magmatic Province: Geodynamic controls on petrogenesis

The Florianópolis Dyke Swarm (FDS), one of the major dyke swarms belonging to the Early cretaceous (135-131 Ma) Paraná Magmatic Province, is largely dominated by high Sr-Ti-P basalts that are confirmed here as feeders of the unique Urubici (= Khumib) lavas of the Paraná and Edendeka lava piles on the basis of their age and geochemistry. Our study integrates field, petrographic, whole-rock geochemistry, and Sr-Nd-Pb isotope geochemistry of representative samples from three main areas of exposition (Santa Catarina Island, Garopaba and Pinheira beaches), thus encompassing the whole extension of the FDS. Compared to the Urubici lavas, the dykes have usually higher contents of LILE and LREE, more radiogenic Sr and Pb, and more unradiogenic Nd, features attributed to a more pronounced interaction with melts derived from the country rocks registered in the basic magmas that remained in the conduits. Some of these dykes show strongly interactive contacts that must be part of a wider zone of crustal melting, probably more developed at greater depths. Small volumes of intermediate to acidic rocks form the cores of some composite dykes, and correspond to products of fractional crystallization from Urubici basalts contaminated with high Rb/Sr, and U/Th crustal melts (probably derived from Neoproterozoic granites), as indicated by geochemical and Sr-Nd-Pb isotope data. The chemical and isotope signatures of the less contaminated FDS basalts and related Urubici lavas do not show clear evidence of inputs from primitive mantle, and seem heavily influenced by enriched mantle. This suggests that the mantle wedge that was affected by subduction during the Neoproterozoic may have been frozen and coupled to the base of the lithospheric plate where the Early cretaceous magmatism occurred. A control of previous tectonic limits on the sources of the Urubici basalts seems evident, since they seem to be related to the younger lithosphere from the South Domain, related to the Florianópolis Batholith, and no influence from the older “cratonic” lithosphere of the Central Domain can be identified in their feeders.