Spatial distribution of cones and satellite-detected lineaments in the Pali Aike Volcanic Field (southernmost Patagonia): insights into the tectonic setting of a Neogene rift system

The relationships between the distribution and morphometric features of eruptive structures (scoria and spatter cones, maar, tuff rings) and the fracture network were investigated in the Pliocene-Quaternary Pali Aike Volcanic Field (southernmost Patagonia, Argentina-Chile). The alkali basaltic/basanitic magmas which erupted in this area have nearly primary magma compositions and often bear mantle xenoliths; hence magma ascent from deep-seated reservoirs was probably very fast, with no significant stagnation at crustal levels. Field surveys and satellite image analysis led to the identification of up to 467 eruptive structures and four main NW-SE, NE SW, E-W and N-S fracture systems. The spatial distribution of eruptive cones and fractures was investigated through the computation of power-law exponents (DJ) for self-similar clustering. The self-similarity of cones and fractures was defined between lower and upper cut-offs which were in turn related to the thickness of the fractured mechanical layer. The fractal character of cones and fracture distribution (clustering) in the Pali Aike Volcanic Field area was thus correlated with crustal thickness. The self-similarity of fractures was used to establish the relative chronology of the detected fracture systems. The self-similar clustering exponent is highest in the E-W and NW-SE fracture systems (Df = 1.78 and 1.77, respectively), and lowest in the N-S system (Df = 1.65). The self-similar clustering of eruptive structures is well defined (Df = 1.45). The intense volcano-tectonic activity in the Pali Aike area marks a major Pliocene-Quaternary phase in the development of the Magellan Neogene Rift System. (C) 2003 Elsevier Science B.V. All rights reserved.