摘要
虽然富有机质沉积岩中的Re和Os主要都富集在有机质中,但其中碎屑部分中的Re和Os也会影响其Re-Os等时线的准确度和精度。目前最常用的Cr O3-H2SO4溶样法虽然能尽量避免碎屑物质中Re和Os的溶出,但该方法具有Re流程空白高和环境污染严重等问题。因此,本研究尝试在富有机质沉积岩Re-Os同位素分析中使用H2O2-HNO3溶样来代替Cr O3-H2SO4溶样。本研究利用国际油页岩标样SGR-1b(USGS)为实验研究对象,分别对HCl-HNO3溶样、Cr O3-H2SO4溶样和H2O2-HNO3溶样3种溶样方法进行了对比研究。研究表明,H2O2与HNO3的体积比约为5﹕1的H2O2-HNO3溶液,不仅能保证样品和稀释剂的Re、Os同位素达到同位素交换平衡而且尽可能地避免碎屑物质中Re和Os的溶出。本方法相比于HCl-HNO3溶样,能尽量避免碎屑物质中Re和Os的溶出;而相比于Cr O3-H2SO4溶样,该方法具有本底低、无污染的优点。最后利用H2O2-HNO3溶样方法对广西金秀地区的泥岩样品和广东大宝山地区的碳质页岩样品进行了Re-Os同位素定年分析,分别得到了(404±5)Ma(IOs=1.57±0.13,n=8,MSWD=50)和(211±11)Ma(IOs=0.67±0.09,n=5,MSWD=11.1)的等时线年龄,这一结果与HCl-HNO3溶样得到的结果((412±11)Ma,IOs=1.18±0.38,n=8,MSWD=311;(223±18)Ma,IOs=0.59±0.14,n=5,MSWD=63)在误差范围内一致,但更为精确。
Rhenium and osmium in organic-rich sedimentary rocks are dominantly enriched in organics, but Re-Os components left in clasts of these rocks will certainly influence the accuracy and precision of the Re-Os isochron generally obtained. The commonly used CrOa-H2SO4 digestion method can minimize the influence of any clast-originated Re and Os, but this medium is restricted by high reagent blank and environmental pollution issues. Therefore, we employ H2O2-HNO3 digestion medium instead of CrO3-H2SO4. We evaluate bulk rock analysis using H2OE-HNO3 digestion medium together with HCl-HNO3 and CrO3-H2SO4, for international standard sample SGR-1b. The results of Re-Os dating indicate that the HEOE-HNO3 medium with a volume ratio of H2O2 to HNO3 being 5 ： 1 can allow tracer-sample equilibration via complete oxidation of all Os species, and can also minimize the influence of any non-organic derived Re and Os. Meanwhile, the HEOE-HNO3 medium shows a lower reagent blank and proves to be environmentally friendly. The HEO2-HNO3 digestion technique was used for Re-Os dating of mudstone from Jinxiu, Guangxi Province and carbonaceous shale from Dabao Mountain in Guangdong Province. Compared with the dating results of aqua regia digestion technique, more precise isochron ages of （404±5） Ma with initial ^187Os/^188Os ratio of 1.57±0.13 （n=8, MSWD=50） and of （211±11） Ma with initial ^187Os/^188Os ratio of 0.67±0.09 （n=5, MSWD=11.1） were obtained by H2O2-HNO3 digestion technique.
出处
《地球化学》
CAS
CSCD
北大核心
2015年第3期225-237,共13页
Geochimica
基金
同位素地球化学国家重点实验室技术研发基金(SKLIG-JY-14-01)
国家自然科学基金(41173038)
作者简介
尹露（1989-），男，硕士研究生，地球化学专业。E—mail：13450482245@163，com
通讯作者（Corresponding author）： LI Jie, E-mail： jieli@gig.ac.cn; Tel： ＋86-20-85290119
