硫同位素地球化学

1、硫同位素地球化学,张 同 钢 2011.11.3,纲 要,第一节 硫同位素的基本概念 第二节 硫同位素的分析方法 第三节 硫同位素的应用,一、硫同位素种类、丰度 二、硫同位素组成、标准 三、硫同位素分馏,第一节 基本概念,32S(95.02%), 33S (0.75%), 34S(4.21%), 36S(0.02%) (MacNamara and Thode, 1950),硫同位素丰度,硫元素和硫同位素,原子序数Z为16 四种同位素：32S， 33S ，34S， 36S,第一节 基本概念,一、硫同位素种类、丰度,硫同位素组成的表示方法 34S ()=(34S/32Ssample/(34S/32

2、S) standard -1 1000 33S ()=(33S/32Ssample/(33S/32S) standard -1 1000 36S ()=(36S/32Ssample/(36S/32S) standard -1 1000 硫同位素标准 国际标准：CDT (Canyon Diablo Troilite) V-CDT 34S/32S=(45004.5 9.3) 10-6 , 34SCDT 0 33S/32S=7877.2 10-6 ，33SCDT 0 36S/32S=153.3 10-6 , 36SCDT 0 参考标准： NBS-122 (34S =0.3) NBS-122(34S

3、=17.1) NBS-122 (34S =20.3) GBW04414 (34S =-0.07), GBW04415 (34S =22.15),天然物质的硫同位素组成,三、硫同位素分馏,1、热力学平衡分馏 2、动力学分馏 3. 非质量相关分馏,热力学平衡分馏,A-B=RA/RB A-B=(34S/32S) A/(34S/32S) B,动力学分馏,非质量相关分馏,33S ()=0.515 34S () 36S ()=1.90 34S (),The marine sulfur cycle,Volcanic degassing,Riverine SO4-,Sedimentary rock,SO2,.

4、 Sulfate,weathering,uplift,subduction,SO42- H2S,Sulfide,OCEAN,(from Strauss, 1993),Inputs of S: weathering of S minerals, volcanic degassing Ouputs of S: burials of sulfide and sulfate minerals Microbial sulfate reduction,Chapter II,Microbial sulfate reduction,34SO42- + CH2O H232S + HCO3-,32S-O bond

5、 is easier to break than 34S-O bond, hence, sulfides is enriched in 32S, depleted in 34S.,34SO42- + H2 H232S + H2O,Fractionation (SR) = d34SSO4 d34SH2S,Chapter II,Biological Pyrite formation,SO42- H2S FeS,Fe2+,H2S,S0,FeS2,little S-isotopic fractionation,(1),(0- 46 ),Large S-isotopic fractionation,1) BSR can produce Large S-isotopic fractionation. 2) Scope of fractionation is related with SO42- and redox conditions.,Chapter II,(Canfield, 2001, Lyons et al., 1