摘要
根据开放体系条件下的瑞利分馏原理，并考虑岩浆中可能溶解的合碳和含硫组分，从理论上定量模式了岩浆去气作用对火成岩碳、硫同位素组成的影响。结果表明，岩浆ＣＯ２去气作用能够导致岩石中碳酸盐显著亏损１３Ｃ，其δ１３Ｃ值能够从原始－５‰变化到－２０‰（ＰＤＢ）；岩浆ＣＨ４去气作用则导致岩石中碳酸盐相对富集１３Ｃ，其δ１３Ｃ值能够从原始－５‰变化到＋４‰。岩浆ＳＯ２去气作用可以导致岩石中硫化物显著亏损３４Ｓ，其δ３４Ｓ值能够从０‰变化到－８‰（ＣＤＴ）；岩浆Ｈ２Ｓ去气作用则导致岩石中的硫化物相对富集４Ｓ，其δ３４Ｓ值能够从０‰变化到＋６‰。因此，除源岩原始同位素不均一性和地壳物质混染能引起火成岩的碳、硫同位素组成发生较大变化外，岩浆去气作用也是重要原因之一。
The effect of magma degassing on the carbon and sulfur isotopic compositionsof igneous rocks has been modelled theoretically. All possible dissolved carbon andsulfur species in magmas have been taken into account. The carbon isotopic variations of carbonate and graphite in melts are treated, respectively. So do for the sulfur isotopic variations of sulfate and sulfide. The modelling is based on the principles of Rayleigh distillation in an open system. Assuming the b13C value of- 5 ‰ for the initial magma, the outgassing of CO_2 can result in the large negative δ￣(13) C values of melt, whereas the outgassing of CH. can drive the 613C valuesof melt in the positive direction. The theoretical predictions can be used to explainthe fall range of b13C values from - 30 ‰, to + 3 ‰, observed for natural basalts.Likewise, assuming the δ￣(34)S value of 0 ‰ for the initial magma, the outgassingof SO_2 or H_2S can cause the sulfide sulfur in melts to be significantly depleted orenriched in (34)￣S. Therefore, the carbon and sulfur isotopic variations in igneousrocks can be caused by magma degassing instead of the isotopic heterogeneities inprovenace or the contamination of crustal sediments.
出处
《地质科学》
CAS
CSCD
北大核心
1996年第1期43-53,共11页
Chinese Journal of Geology(Scientia Geologica Sinica)
基金
中国科学院专项基金
国家自然科学基金
关键词
岩浆
去气作用
碳同位素
硫同位素
火成岩
Magma degassing Geochemistry Reservoir effect Carbon isotopes Sulfur isotopes Theoretical modeling
