Mafic dike swarms in the South Shetland Islands volcanic arc: Unravelling multiepisodic magmatism related to subduction and continental rifting

摘要: Eight groups of mafic dikes and related high-level stocks cut Triassic accretionary complex Mesozoic magmatic arc formations on Livingston Island. Some are affected by silicic/sericitic alteration, to Cretaceous hydrothermal activity, propylitic/epidosite analogous that in ocean floor sheeted dikes. Alteration was accompanied major trace element metasomatism. Ar-Ar analysis the freshest rocks indicates five intrusive events, some which unexpectedly young. Groups 1–3 were intruded mid late (∼108–74 Ma) coeval with calc-alkaline arc. Between 70 50 Ma, relatively rapid oblique plate convergence led strike-slip tectonism a pause magmatism. At ∼52 orthogonal, slow resulted extensional faulting emplacement (group 2) primitive tholeiitic (groups 4–6) between 51 45 Ma. Extension Antarctic Peninsula-southern South American crust culminated intermediate, medium-grained plutons group C porphyries 44 36 Localized flow along fault zones partial complete argon loss from nearby lavas reset ages ∼40 Ma mid-Cretaceous K-feldspar. Primitive olivine basalts D) epithermal carbonate veins (31–29 emplaced during along-arc extension accompanying opening Drake Passage Powell Basin. Excess occurs two forms: strongly held melt? inclusions tholeiites weakly secondary alteration. There is no radiometric evidence, area studied, for magmatism Cenozoic subduction, nor Pleistocene-Recent back Bransfield rift.