The long-term legacy of subvolcanic intrusions on fluid migration in sedimentary basins: The Cerro Alquitrán case study, northern Neuquén Basin, Argentina

Abstract

Cooling subvolcanic igneous intrusions are known to have a substantial impact on fluid flow in the shallow Earth´s crust, for example activation of geothermal systems, circulation of mineralized fluids in ore deposits, fast maturation of organic matter in sedimentary rocks and the potential release of large volumes of greenhouse gases, which have triggered mass extinctions during the Earth´s history. However, the long-term post-cooling legacy of subvolcanic intrusions on fluid flow received much less attention. Here we describe a demonstrative geological example in the Andean foothills, Argentina, showing that igneous intrusions have long-term effects on fluid flow after their emplacement and cooling. The case study is a ca. 11-million-year-old, eroded subvolcanic conduit, at the rims of which large volumes of bitumen are naturally seeping out on the Earth´s surface. This contribution highlights that intense syn-emplacement fracturing of the magma has created high-permeability pathways that affect the regional fluid circulations, even millions of years after cooling. Our observations reveal how extinct subvolcanic intrusions have long-term consequences on subsurface fluid circulations, which need to be accounted for in the exploration of geothermal energy, drinkable groundwater, hydrocarbons and CO2 sequestration in volcanic basins and regions hosting ancient shallow magma intrusions.