Carbon isotope ratios, nitrogen content and aggregation state, and inclusion chemistry of diamonds from Jwaneng, Botswana

被引:48
作者
Deines, P
Harris, JW
Gurney, JJ
机构
[1] UNIV GLASGOW,DEPT GEOL & APPL GEOL,GLASGOW G12 8QQ,LANARK,SCOTLAND
[2] UNIV CAPE TOWN,DEPT GEOCHEM,ZA-7700 RONDEBOSCH,SOUTH AFRICA
基金
美国国家科学基金会;
关键词
D O I
10.1016/S0016-7037(97)00199-3
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
A detailed study of diamonds from the Jwaneng kimberlite leads to the conclusion that diamonds formed in at least seven physically or chemically distinct environments and over an extended time interval which may have lasted as long as 3 Ga. The work revealed a delta(13)C range for P-Type (peridotitic) diamonds from -3 to -14 parts per thousand; E-Type (eclogitic) diamonds have a delta(13)C range from -4 to -19 parts per thousand and more delta(13)C values lower than -10 parts per thousand. The nitrogen content of P-Type diamonds tends to be lower than that of the E-Type, but the degree of nitrogen aggregation of the two types is indistinguishable. Among those E-Type diamonds for which a nitrogen aggregation age could be computed, low delta(13)C diamonds tend to show older ages. P-Type diamonds are more often octahedral and green coated or brown and deformed than E-Type diamonds. The latter are more often colorless, partially resorbed, and of irregular shape. It is postulated that diamonds containing olivines formed in at least three different environments based on their nitrogen content, delta(13)C value, and the chemical composition of the inclusions. The Jwaneng peridotitic minerals inclusion suite (ol, gt, chr) is enriched in Fe compared to similar suites from other southern African kimberlites. Considering these suits together one observes that the Fe content of olivine inclusions is negatively correlated with the delta(13)C Of their hosts. In the suite of E-Type diamonds no compositional subgroups could be identified, but, the Mg content of the E-Type mineral suite tends to be lower than that of E-Type inclusions in diamonds from other southern African kimberlites. It is suggested that as many as four distinct time/temperature histories for E-Type diamonds can be discerned based on coexisting garnet/clinopyroxene equilibration temperatures, the nitrogen content, and the state of nitrogen aggregation in the host diamonds. Copyright (C) 1997 Elsevier Science Ltd.
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页码:3993 / 4005
页数:13
相关论文
共 42 条
[41]   A STUDY OF DIAMONDS OF CUBE AND CUBE-RELATED SHAPE FROM THE JWANENG MINE [J].
WELBOURN, CM ;
ROONEY, MLT ;
EVANS, DJF .
JOURNAL OF CRYSTAL GROWTH, 1989, 94 (01) :229-252
[42]  
WILDING MC, 1994, CPRM SPEC PUBL B, V1, P116