首页 | 本学科首页   官方微博 | 高级检索  
     检索      


Garnet lherzolites from the Hanaus-I and Louwrensia kimberlites of Namibia
Authors:Roger H Mitchell
Institution:(1) Department of Geology, Lakehead University, P7B 5E1 Thunder Bay, Ontario, Canada
Abstract:The Gibeon cluster of Namibian kimberlites is emplaced into the Orange River Belt which has accreted to the Kaapvaal Craton. These ldquooffcratonrdquo kimberlites lack diamonds and are younger than the diamondiferous ldquoon-cratonrdquo 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 ldquoon-cratonrdquo 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.
Keywords:
本文献已被 SpringerLink 等数据库收录!
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号