Inference from basalt-rhyolite dyke swarms on the petrogeneis of a granodiorite to leucorgranite suite from Patagonian Batholith (42.40°-42.50°Lat. S)

The main petrogenetic processes relative to basic-intermediate dyke swarms of the Cordillera Patagonica have been investigated. Dyke swarms intrude Early Cretaceous 'granitic' plutons between Futalauquen and Rivadavia lakes (42.40°-42.50° Lat.S). A whole rock Rb/Sr isochron for the granitic rocks yielded an age of 130 ± 7 Ma, consistently with literature data and stratigraphical constraints on the Patagonian Batholith. Dykes, on the basis of geological setting and field evidences, are considered close in the time to 'granitoid' pluton. On the basis of mineralogy and chemistry the 'granitoid' plutons are represented by rock-types ranging from granodiorite through monozongranite to leucogranite. The investigated aphyric-subaphyric dykes range in composition from basalt to rhyolite. The 'granitoids' and dykes show, beginning from intermediate rocks, comparable and overlapped geochemical patterns, so that similar evolutive-petrogenetic models may be proposed. Mineralogical and geochemical data suggest that inter-dyke differentiation is compatible with crystal fractionation processes, associated with minor contamination by crustal components represented by meta sediments of Patagonian crystalline basement. Sr and Nd isotope data suggest that parental basalt melts generated from an isotopically depleted mantle source contaminated by slab-derived sediments.