The interplay between NE striking transverse faults and Pleistocene-Holocene dike systems in the Southern Volcanic Zone

Abstract

Dikes are thought to be the most efficient way of transporting magma through the upper crust andare the prevailing feeding mechanism of volcanic systems. As they propagate, dikes may eitheroccupy existing fractures or create their own (as in Andersonian dikes), and so, can be foundrandomly or systematically oriented. Whereas Andersonian dikes are expected to propagate parallelto the direction of the maximum compressive stress (σ1), the propagation of dikes along existingcracks depends on their orientation with respect to σ1. If optimally oriented,these faults andfractures may reactivate in extension, allowing melt flow through this conduit. Therefore, it isimportant to analyze the spatial and genetic relation between faults and dykes, to better understandthe kinematic constraints and interplay of faulting and transport of magma.The Tatara-San Pedro-Pellado (TSPP) is a NE-aligned volcanic complex found in the SouthernVolcanic Zone. NE striking transverse faults close to the TSPP are kinematically consistent with theprevailing Quaternary orogen-scale and spatially associated to parallel NE mafic dike swarms. Tounderstand the role of inherited structures in magma transport, we performed detailed structuralmapping and fault slip analysis. Preliminary results show a regional NE-striking steeply dipping rightlateral transtensional fault system parallel to the TSPP alignment, that cuts Oligo-Miocenevolcanoclastic rocks of the Cura Mallín Formation and Mid Pleistocene volcanic rocks. Near SanPedro Volcano, transtensional faults with a right lateral displacement have orientations ranging fromN40E/74W to EW/58N. The western termination of this NE transtensional system consists of EWstriking steeply dipping normal faults and NS striking Melado Valley fault, which is kinematicallyconsistent with a crustal 6.0Mw right lateral earthquake (2012). Second order NW to WNW strikingsteeply dipping left lateral faults are observed in structural sites in the east end of the study area,where structures cut a Late Cretaceous granodiorite intrusion. Age of deformation of one of thesefaults will be obtained with Ar-Ar dating on clays in fault gouge.