We report recent progress in determination of geothermal gradients and heat flow in the State of Tocantins, Central Brazil. This region lying between the Amazonas and Sao Francisco cratons has been affected by metamorphic folding events (Brasilia and Araguaia) during Proterozoic times. This area is also characterized by moderate micro-seismic seismic activity. Results of recent investigations have revealed the presence of several areas where geothermal gradients and heat flow have values higher than normal, which is considered atypical of stable tectonic settings. In southern parts of the State of Tocantins heat flow values are higher than 80 mW/m2. Extrapolations based on near surface heat flow data point to crustal temperatures in excess of 200°C at depths less than 5 km. However, there are no evidences of magmatic intrusions at shallow intra-crustal depths. In the absence of other geologic source mechanisms and tectonic events the process responsible for high heat flow has been postulated to be enhanced heat transport by carbonic gas flow in the upper crust. This possible alternative is supported by observations of carbonic gas flow at sites of thermal springs within the study area and also in geothermal areas in the neighboring state of Goiás. Model simulations of deep crustal geotherms indicate that temperatures may approach levels of partial fusion at the crust mantle boundary.

Within the oil and gas industry, igneous rocks are still seen as exploration and production challenges, due to their diverse petrogenesis and the wide range of values of some important petrophysical properties. This petrophysical variability depends on both primary and secondary processes. These facts made these rocks unattractive for decades. This condition is still observed in many fields around the world. This article has as main objective to make a historical review of studies developed globally with a focus on igneous rocks that act as a reservoir in petroleum systems. The review covered in this article was developed from a compilation of global data, thus allowing an overview of the countries that produce hydrocarbons in volcanic rocks, what types of rocks, geological age, and size of the reserve. Countries such as China and Indonesia stand out with higher daily production, exceeding orders of quantities of 108 cubic meters of gas and 104 tons of barrels of oil. In these countries, geological patterns are already being noticed in volcanic reservoirs, such as more recent geological ages and typical lithologies. Also, this work seeks to emphasize the importance of studying this type of reservoir, as its knowledge can lead to the solution of real problems within the world oil and gas industry.