Features of gas released from heated igneous rock, Tarim Basin

The fluid entrapped in Permian igneous rocks collected from the north and the center of the Tarim Basin has been studied using heating method so as to analyze the features of fluid from deep strata.The total amounts of gas released from the 2 igneous rock samples collected in the central Tarim region are 1 902.7 μL/g and 1 517.7 μL/g,much higher than those of the 5 igneous rock samples collected in the northern Tarim region(515.2-691.5μL/g).In both the central and the northern Tarim regions,gas release amounts reach a peak during the medium temperature stage(700℃).CO₂ is the dominant compound in released gas from each sample during each temperature stage,and reaches as high as 91.47%.N2 and SO₂ are also important compounds in released gas,and have high contents in some samples.CO,H₂,hydrocarbon and noble gas are found in released gas more or less.The ⁴⁰Ar/³⁶Ar ratios of released gas are high,usually between 450.3 and 1 170.3,indicating deep source.However,the 3He/4He ratios of released gas are low(0.0091-0.091Ra) except for one diabase sample(0.35 Ra),indicating crust source.The reason is that He in igneous rocks mixes with that in crust due to diffusion effect.