The chemical compositions and abundances of volatiles in the Siberian large igneous province: Constraints on magmatic CO2 and SO2 emissions into the atmosphere

Abstract

The Siberian large igneous province (SLIP) is known to be synchronous with the most severe mass extinction on the Earth at the end of Permian. The viability of the SLIP as a trigger for the mass extinction depends crucially on the total amounts of important volatiles such as CO2 and SO2 emitted from the SLIP into the atmosphere. The chemical compositions and abundances of volatiles in picrite and gabbroic rocks of the SLIP have been determined by a vacuum stepwise heating mass spectrometer system. The volatiles released at temperatures <400°C from mineral separates are interpreted to derive from secondary fluid inclusions and are therefore not included in the summation of primary volatiles which had been primarily entrapped in the minerals from magma. The primary volatiles released from different types of samples from the SLIP are characterized by dominant H2O with high contents of CO2, SO2 and H2, plus detectable He. The total amounts of primary volatiles in the picrite are 19,991mm3.STP/g (STP-standard temperature and pressure) H2O, 331 CO2, 202 H2, 28 CO, 13 SO2 and 2 H2S. The total amounts of primary volatiles in the gabbroic rocks are 2869mm3.STP/g H2O, 131 SO2, 120 H2, 85 CO2, 79 H2S and 16 CO. These data, together with other important constraints from literatures, are used to calculate the total amounts of volatiles emitted from the SLIP into the atmosphere. In our mass balance calculations we used the abundances of CO2 and SO2 in melt inclusions in olivine phenocrysts from the SLIP determined previously by other researchers to represent their initial concentrations in magma before degassing, and our new data for the SLIP picrite to represent the volatile compositions of magma (basalt) after eruption. Our results for the gabbroic rocks are used to estimate the proportions of volatiles that are still retained in the subvolcanic intrusions of the SLIP. The results reveal that the total amounts of important volatiles emitted from the SLIP are 8.5×107 Tg CO2, 4.4×106 Tg CO, 7.0×106 Tg H2S and 6.8×107 Tg SO2 (Tg, Trillion grams). These values are similar to the previous estimates using different methods by other researchers. Our data support a popular notion that the end-Permian mass extinction on the Earth was caused by the emission of enormous amounts of volatiles from the SLIP into the atmosphere.