PALEOATMOSPHERIC CONSEQUENCES OF CO2 RELEASED DURING EARLY CENOZOIC REGIONAL METAMORPHISM IN THE TETHYAN OROGEN

The Eocene was the warmest epoch of the Cenozoic, with published estim ates of Eocene atmospheric CO2 content ranging from two to six times t he current value. Calculations of CO2 consumption by silicate weatheri ng show that CO2 fluxes to the atmosphere of ca. 10(18)/Myr could acco unt for inferred Paleocene/Eocene atmospheric CO2 contents, and the re sulting greenhouse effect would have contributed to Eocene warmth. Ext ensive portions of the Tethyan orogen underwent regional metamorphism culminating in the Eocene. Prograde metamorphism may have been contemp oraneous with the Late Paleocene global warming. We calculated the amo unt of metamorphic CO2 produced at depth in the Himalayan orogen with data on the timing of the India/Asia collision, duration of prograde r egional metamorphism, and proportions and bulk compositions of metamor phic CO2 source rocks. If CO2 was generated at a constant rate over a 10 Myr period of prograde metamorphism in the Himalayan orogen, we est imate that ca. 10(18)-10(19) moles/Myr of metamorphic CO2 were produce d al depth. Significant expulsion of metamorphic CO2 to the atmosphere may have occurred by focused fluid flow along shear zones such as the extensive Main Central Thrust in the Himalayan orogen. An additional ca. 10(18)/Myr could have been contributed by Eocene regional metamorp hism in the Mediterranean Tethys (i.e., from the Alps to Turkey). The extensive metamorphism associated with the India/Asia collision, and t he closing of Tethys, may have contributed to CO2-greenhouse warming i n the early to mid Cenozoic.