Garnet lherzolites from the Hanaus-I and Louwrensia kimberlites of Namibia
Garnet lherzolites from the Hanaus-I and Louwrensia kimberlites of Namibia
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纳米比亚 Hanaus-I 和 Louwrensia 金伯利岩中的石榴石二辉橄榄岩
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发表时间：
1984
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通讯作者：
R. Mitchell
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作者：
R. Mitchell
纳米比亚金伯利岩的吉本群位于已被吸积到卡普瓦尔克拉通的奥兰治河带中。这些“外克拉通”金伯利岩缺乏钻石，比“外克拉通”金伯利岩更年轻。哈瑙斯- 1和洛伦西亚金伯利岩均含有一套双峰型上地幔源榴辉橄榄岩包体，其特征是粗粒状或镶嵌状斑状碎屑结构。此外，洛伦西亚烟斗还含有石榴石哈尔茨伯茨矿。与粗粒型相比，变形橄榄岩不富铁。通过Wells-Wood方法计算的平衡条件分别为：劳伦西亚和哈瑙斯粗粒伊尔热斑岩的841 ~ 1013℃（25.6 ~ 36.3 kbar）和869 ~ 1195℃（23.9 ~ 39.4 kbar）；劳伦西亚和哈瑙斯花叶状斑岩的1080 ~ 1112℃（31.6 ~ 34.5 kbar）和983 ~ 1228℃（24.7 ~ 35.2 kbar）。来自这两个地区的粗品种与来自“克拉通上”金伯利岩的粗热斑岩具有相似的平衡条件，并确定了扰动地热的下限。纳米比亚地热的上高温分支被认为是由上地幔由上升的底辟引起的变形和交代作用所产生的表观地热。这种地热是金伯利岩与捕虏体相互作用的结果，不能提供有关金伯利岩或钻石形成地点的地层或热资料。
The Gibeon cluster of Namibian kimberlites is emplaced into the Orange River Belt which has accreted to the Kaapvaal Craton. These “offcraton” kimberlites lack diamonds and are younger than the diamondiferous “on-craton” kimberlites. The Hanaus-I and Louwrensia kimberlites each contain a bimodal suite of upper-mantle-derived garnet lherzolite xenoliths characterized by a coarse granular or mosaic porphyroclastic texture. The Louwrensia pipe in addition contains garnet harzburgites. Deformed lherzolites are not iron-enriched relative to the coarse types. Conditions of equilibration calculated by the Wells-Wood method are 841–1,013° C at 25.6–36.3 kbars, and 869–1,195° C at 23.9–39.4 kbars, for coarse lherzolites from Louwrensia and Hanaus respectively, and from 1,080–1,112° C at 31.6–34.5 kbars, and 983–1,228° C at 24.7–35.2 kbars, for mosaic porphyroclastic types from Louwrensia and Hanaus respectively. The coarse varieties from both localities have similar equilibration conditions to coarse lherzolites from “on-craton” kimberlites and define the lower limb of a perturbed geotherm. The upper high temperature limb of the Namibian geotherm is considered to be an apparent geotherm generated by the deformation and metasomatism of the upper mantle by a rising diapir. Such geotherms, being the result of kimberlite-xenolith interactions, provide no stratigraphic or thermal information concerning the site of kimberlite or diamond formation.