He, Ar and C isotopes in coated and polycrystalline diamonds
He, Ar and C isotopes in coated and polycrystalline diamonds
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DOI：
10.1016/s0009-2541(98)00011-4
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发表时间：
1998-05-05
期刊：
影响因子：
3.9
通讯作者：
Turner, G
中科院分区：
文献类型：
--
作者：
Burgess, R;Johnson, LH;Turner, G
对来自非洲和巴西的不同质量的工业级多晶金刚石进行了氦、氩和碳同位素测量。这些包括含有丰富的富含挥发物的微包裹体和framesites的涂层和多云金刚石以及由散布有矿物包裹体的微米级金刚石晶体聚集体组成的碳酸盐。在尝试从钻石中选择性地释放初级捕获的He时，使用真空破碎技术对它们进行分析。He数据与Ar，K和U数据相结合，从40Ar-39Ar步进加热研究的辐射馏分的金刚石和散装碳同位素数据从粉碎的残余物。结果表明，涂层和云状金刚石最好地保留了地幔特征，其中He-3/He-4值为1 - 7 Ra，δ（13）C为-5至6 ‰。涂层金刚石具有10（-6）-10（-5）cm（3）g（-1）的均匀高的He和Ar浓度。框架具有较低的He-3/He-4值0.1 - 3 Ra和双峰δ（13）C值，模式为-6和-20 ppm。碳酸盐显示出小于或等于千分之-25的最低δ（13）C值和<0.1 Ra的He-3/He-4。U和K的浓度从涂层<框架<碳酸盐岩逐渐增加。虽然人们倾向于将低δ（13）C、低He-3/He-4和高U归因于俯冲地壳物质的影响，但靠近微金刚石的富含U、Th的矿物注入4He也可能是低He同位素比值的原因。(C)1998 Elsevier Science B.V.保留所有权利。
Helium, Ar and C isotopic measurements have been undertaken on different qualities of industrial grade and polycrystalline diamond from localities in Africa and Brazil. These include coated and cloudy diamonds which contain abundant volatile-rich micro-inclusions and framesites and carbonados which consist of aggregates of micron-sized diamond crystals interspersed with mineral inclusions. In an attempt to release selectively the primary trapped He from the diamonds, they were analysed using an in vacuo crushing technique. The He data are combined with Ar, K and U data obtained from 40Ar-39Ar stepped-heating studies of irradiated fractions of the diamonds and bulk carbon isotope data obtained from the crushed residues. Results indicate that coated and cloudy diamonds best preserve a mantle signature with He-3/He-4 values of 1-7 Ra and delta(13)C of -5 to -6 parts per thousand. Coated diamonds have uniformly high He and Ar concentrations of 10(-6)-10(-5) cm(3) g(-1). Framesites have lower He-3/He-4 values 0.1-3 Ra and bimodal delta(13)C values with modes at -6 and -20 parts per thousand. Carbonados show both the lowest delta(13)C values less than or equal to -25 parts per thousand and He-3/He-4 of < 0.1 Ra. U and K concentrations show a progressive increase from coats < framesites < carbonados. While it is tempting to attribute low delta(13)C, low He-3/He-4 and high U to the influence of subducted crustal material, it is likely that implantation of 4He by U, Th-rich minerals adjacent to the micro-diamonds is also a possible cause of the low He isotope ratios. (C) 1998 Elsevier Science B.V. All rights reserved.