Worldwide Distribution of Major Carbon Dioxide Deposits, Geologic Setting and Gas Isotopic Evidence of Mantle Sources in Areas of Crustal Extension and Transtension

Cassidy, Martin M.¹, Kevin Burke¹ (1) University of Houston, Houston, TX

CO₂-rich (>50%) gas deposits are present worldwide but in limited areas. To find or avoid them we need to know the origin of the gas.

Compilation of data from 120+ deposits about their geologic settings finds they are preferentially located in areas where the crust is fractured and in regional extension, and often in areas of recent basaltic volcanism.

In the plate tectonic model CO₂ deposits are usually found in cratonic basins with basic igneous intrusions, continental rifts, back arc basins, area of tectonic escape, along plate bounding strike slip faults, and in foreland basins associated with major cross trends. World plate tectonic maps showing the locations of CO₂ deposits illustrate these facts. The percentage distribution of deposits among tectonic settings is also shown.

A spreadsheet of data about worldwide CO₂ deposits has been compiled. Where isotope data about the gases in the deposits is available, carbon isotope ratios in CO₂ of about d¹³C –5 0/00 PDB, ³He/⁴He ratios of 0.5 or above (compared to the ratio in air) and a ratio of CO₂/³He between 1 x 10⁹ and 10 x 10⁹ are evidences that the mantle is the source of the CO₂. Gas composition, reservoir types and stratigraphic facts about the deposits are tabulated. Graphical displays relating properties are shown.

Regularities found in this compilation are useful in assessing the risk of encountering CO₂ and for predicting where economic deposits of the CO₂ gas may be found.