Episodic diamond genesis at Jwaneng, Botswana, and implications for Kaapvaal craton evolution
Episodic diamond genesis at Jwaneng, Botswana, and implications for Kaapvaal craton evolution
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DOI：
10.1016/j.lithos.2004.04.027
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发表时间：
2004-09
期刊：
影响因子：
3.5
通讯作者：
S. H. Richardson;S. Shirey;J. Harris
中科院分区：
文献类型：
--
作者：
S. H. Richardson;S. Shirey;J. Harris
对240 Ma Jwaneng金伯利岩中金刚石中单个硫化物包裹体的主量元素和Re-Os同位素分析表明，该地区至少存在两代榴辉岩金刚石，一个是元古代（约100 Ma）榴辉岩金刚石。1.5而另一个则是晚太古代（ca。2.9 Ga）。前一世代的Sm-Nd等时线年龄为1.54Ga，与Jwaneng榴辉岩石榴子石和单斜辉石包裹体金刚石的时代相同。后者是同时代的2.89 Ga俯冲有关的代榴辉岩硫化物包裹体含金刚石从金伯利在合并的西部和东部卡普瓦尔克拉通附近的科莱斯贝格磁性线性构造。金伯利、Jwaneng和Premier金伯利岩是描述幕式金刚石成因与Kaapvaal克拉通演化之间关系的关键地点。金伯利有3.2 Ga方辉橄榄岩钻石与西部Kaapvaal岩浆核的形成有关，以及2.9 Ga榴辉岩钻石与东部Kaapvaal岩浆核的增生有关。Jwaneng有两个主要的榴辉岩金刚石代（2.9和1.5 Ga），反映了克拉通的稳定和随后的修改。总理有1.9 Ga的二辉橄榄岩钻石，晚于布什费尔德-莫洛波岩浆作用（但其前体有太古代Sm-Nd模型年龄），以及1.2 Ga的榴辉岩钻石。因此，Jwaneng提供了分别在金伯利和总理钻石套房中明显的太古代与元古代钻石地层之间的重叠。此外，1.5 Ga Jwaneng榴辉岩金刚石代代表硫化物和硅酸盐夹杂物，允许表征长期趋势的金刚石类型和成分。Jwaneng和金伯利榴辉岩硫化物的结果表明，富Ni和Os的端员是更常见的太古代金刚石相比，元古代金刚石。同样，已发表的金伯利和Premier橄榄岩硅酸盐的数据表明，富钙（二辉橄榄岩）端元更有可能在元古代钻石中发现，而不是太古代钻石。因此，现有的钻石分布，成分和年龄数据支持一个多阶段的过程，以创造，稳定和修改太古代克拉通龙骨在十亿年的时间尺度和全球的基础上。
Major element and Re–Os isotope analysis of single sulfide inclusions in diamonds from the 240 Ma Jwaneng kimberlite has revealed the presence of at least two generations of eclogitic diamonds at this locality, one Proterozoic (ca. 1.5 Ga) and the other late Archean (ca. 2.9 Ga). The former generation is considered to be the same as that of eclogitic garnet and clinopyroxene inclusion bearing diamonds from Jwaneng with a Sm–Nd isochron age of 1.54 Ga. The latter is coeval with the 2.89 Ga subduction-related generation of eclogitic sulfide inclusion bearing diamonds from Kimberley formed during amalgamation of the western and eastern Kaapvaal craton near the Colesberg magnetic lineament. The Kimberley, Jwaneng, and Premier kimberlites are key localities for characterizing the relationship between episodic diamond genesis and Kaapvaal craton evolution. Kimberley has 3.2 Ga harzburgitic diamonds associated with creation of the western Kaapvaal cratonic nucleus, and 2.9 Ga eclogitic diamonds resulting from its accretion to the eastern Kaapvaal. Jwaneng has two main eclogitic diamond generations (2.9 and 1.5 Ga) reflecting both stabilization and subsequent modification of the craton. Premier has 1.9 Ga lherzolitic diamonds that postdate Bushveld–Molopo magmatism (but whose precursors have Archean Sm–Nd model ages), as well as 1.2 Ga eclogitic diamonds. Thus, Jwaneng provides the overlap between the dominantly Archean vs. Proterozoic diamond formation evident in the Kimberley and Premier diamond suites, respectively. In addition, the 1.5 Ga Jwaneng eclogitic diamond generation is represented by both sulfide and silicate inclusions, allowing for characterization of secular trends in diamond type and composition. Results for Jwaneng and Kimberley eclogitic sulfides indicate that Ni- and Os-rich end members are more common in Archean diamonds compared to Proterozoic diamonds. Similarly, published data for Kimberley and Premier peridotitic silicates show that Ca-rich (lherzolitic) end members are more likely to be found in Proterozoic diamonds than Archean diamonds. Thus, the available diamond distribution, composition, and age data support a multistage process to create, stabilize, and modify Archean craton keels on a billion-year time scale and global basis.