Magmatic underplating, plumbing system, and carbon-enhanced electrical conductivity in the Paraná Magmatic Province

Abstract

The origin of large igneous provinces (LIPs) is still an enigma but likely involves magma storage and pathways spread throughout the crust, requiring indirect methods for its study. Here, we present 3-D resistivity models derived from the inversion of broadband (∼0.0001–3000 s) magnetotelluric data with 9–13 km lateral spacing in the central Paraná Magmatic Province, an expressive Early Cretaceous LIP in South America. Our results map in greater detail the previously interpreted LIP magma conduit and support, in contrast with seismological models, significant magmatic underplating to explain the observed conductivity near the LIP central axis. The potential axial lava feeder appears as a pair of crustal conductors (5–15 km; >0.1 S/m) parallel to the region of maximum thickness of both pre-volcanic sedimentary rocks and erupted tholeiitic basalts along an extension of at least 800 km. We propose the high conductivity is due to graphite films of precipitated carbon during the ascension of carbon-bearing fluids released by crystallizing magmas underplated at the base of the crust. The association of high conductivity with underplating is supported by high Vp/Vs ratios close to the conductive lineament, by a lower-crustal zone of high P-wave velocities at the basin axis attributed to mafic intrusions, and by a residual gravity high interpreted as gabbros underplated/intruded in the lower crust. Moreover, the conductive lineament is spatially associated with intracrustal high densities inferred from geoid inversion and upper-crustal high P-wave velocities. Early CO2 release during crystallization of underplated magma before eruption could explain the time gap between the Weissert ocean anoxic event and the volcanism. Our study advances in the controversial topic of magmatic intrusive components in the Paraná LIP with implications for LIP generation and paleo-climate studies.