The Chemical Compositions Of Volatiles In Siberian Large Igneous Province And Its Geological Implications

Siberian large igneous province (LIP) was the largest volume Phanerozoic LIP in the world. It contained the world-class Noril'sk-Talnakh Cu-Ni-PGE sulfide deposits, and coincided with the Permian-Triassic mass extinction. The chemical compositions of volatiles in Siberian LIP will provide the important clue to the Cu-Ni-PGE mineralization and environmental impact on mass extinction. The chemical compositions of volatiles from rocks in Siberian LIP were determined by stepwise heating mass spectrometer. The main results were as follows:1. The chemical compositions of volatiles in constituent minerals and matrix of intrusive and extrusive rocks from Siberian LIP were characterized by stage release during stepwise heating. The volatiles were released at low temperature interval (LT,200-400℃), mid-temperature interval (MT, 400-1000℃) and high temperature interval (HT,1000-1200℃). The volatiles released at LT were mainly composed of N2+CO (av.56.41%) and CO2 (24.60%). The volatiles at MT showed largest volatile amount, and were mainly composed of H2 (30.12%) and CO2 (23.30%), and those at HT were mainly composed of SO2 (38.24%) and CO2 (34.08%). The chemical compositions of volatiles varied between extrusive rocks and intrusive rocks.2. The chemical compositions of volatiles in constituent minerals and matrix of extrusive rocks released at LT were mainly composed of N2+CO (av.58.29%). The volatiles at MT were mainly composed of CO2 (40.67%), H2(37.18%) and N2+CO (15.94%), and those at HT were mainly composed of CO2 (83.56%).3. The chemical compositions of volatiles in constituent minerals and matrix of intrusive rocks released at LT were mainly composed of N2+CO (av.55.83%) and CO2 (26.36%). The volatiles at MT were mainly composed of H2 (27.95%), SO2 (27.22%) and CO2 (17.96%), and those at HT were mainly composed of SO2 (48.78%).4. The chemical compositions of volatiles from ore-forming magma in sulfide deposits of Siberian LIP were characterized by high contents of CO2 and minor contens of N2+CO, implying a oxidized condition. Volatiles at early stage of ore-forming magmatism were dominated by N2+CO and CO2, and the contents of H2 and CH4 were relatively high. Those volatiles captured in the process of consolidation of magma were mainly composed of H2, and the contents of CO2, H2S and SO2 were relatively high, implying a reduced condition. Volatiles of metasomatism and secondary alteration were characterized by high contents of N2+CO and CO2.5. The released amount of volatiles of CO2, SO2, H2S and CH4 were 0.82-4.61×1015kg, 0.04-2.15x1016kg,0.72-3.92x1015kg and 1.62-2.57×1014kg respectively during Siberian volcanic eruptions. We argued that Siberian volcanic eruption had a rather great influence on environment, and it was a major factor to late Permian mass extinction.