Integrated Studies of Diamond Age and Composition: Constraints on Continental Lithospheric Evolution, Kaapvaal-Zimbabwe Craton, Southern Africa

钻石年龄和成分的综合研究：对南部非洲卡普瓦尔-津巴布韦克拉通大陆岩石圈演化的制约

• 批准号: 0310059
• 负责人: Steven Shirey
• 金额: --
• 依托单位: Carnegie Institution of Washington
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-07-01 至 2009-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0310059&HistoricalAwards=false
• 关键词: Integrated; Studies; Diamond; Age; Composition

EAR-0310059ShireyThe stable interiors of continents (cratons or shields) are composed of 35 to 40 km thick continental crust overlying up to 180 km of ancient lithospheric mantle root. In certain cratonic regions such as southern Africa, volcanic eruptions of kimberlite have sampled and brought to the surface, rocks (e.g. peridotites and eclogites) and minerals (e.g. diamonds) found in the man-tle root. These samples provide an important direct record of some of Earth's earliest continent-building. Diamonds and the silicate and sulfide minerals that they sometimes include are espe-cially unique as they are the most robust capsules of geochemical and geochronological informa-tion in the mantle.Seven mines in kimberlites (Bobbejaan/Bellsbank, Helam/Swartruggens, Palmietgat, Premier, Orapa, Star, and Venetia) from the Kaapvaal-Zimbabwe craton will provide sulfide-inclusion-bearing diamonds that will be used to expand our knowledge of the geological history of the mantle keel beneath this ancient southern African continent. The broad goals of the re-search are to determine the ages of diamonds at each kimberlite with the Re-Os method on sul-fide inclusions and to relate the ages and the compositions of both inclusions and their host dia-monds to the geologic setting of the diamond source region in the lithospheric mantle. More than three episodes of diamond formation are currently seen to match major episodes of creation (3.2-3.3 billion years ago), amalgamation (2.9-3.1 billion years ago) and magmatic modification of the craton (1-2 billion years ago). The new data will test the extent of these episodes, especially in areas like the eastern craton that have the oldest crustal history (3.3-3.5 billion years) or the Limpopo mobile belt that has been subject to craton collision. Supporting xenolith age and geo-chemistry studies will yield new information on the emplacement of diamondiferous protoliths or the source of the carbon-rich diamond fluids. The broader impacts of the research are in the training and scientific development of a postdoctoral associate and two students. The postdoctoral associate will join the academic teach-ing community and his training will contribute directly to his supervision of students. Both stu-dents reside in South Africa and would otherwise have little chance to train and learn at a high-level research facility in the United States. One student, a female African geochemist, is so un-der-represented as to be unique at the current time in southern Africa. The development of new analytical protocols is proposed; these will improve infrastructure for diamond research in gen-eral. The research will strengthen partnerships with the academic community (Universities of Glasgow, Cape Town, Witwatersrand) and the mining community (DTC - De Beers, Helam Mining). Dissemination of the research will enhance our background understanding of how dia-monds, economically important in stable countries and a problematic resource in areas of con-flict, were created. The project is partially supported by NSF's Office of International Science and Engineering.

大陆的稳定内部（板块或地盾）由35至40公里厚的大陆地壳组成，覆盖在长达180公里的古老岩石圈地幔根上。在某些南极地区，如南部非洲，金伯利岩的火山爆发取样并将地幔根中发现的岩石（如橄榄岩和榴辉岩）和矿物（如钻石）带到地表。这些样本为地球最早期的一些大陆形成过程提供了重要的直接记录。钻石和它们有时包含的硅酸盐和硫化物矿物是特别独特的，因为它们是地幔中地球化学和地质年代学信息的最可靠的胶囊。（Bobbejaan/Bellsbank，Helam/Swartruggens，Palmietgat，Premier，Orapa，星星，和韦内蒂亚）将提供硫化物包裹体，这些钻石将被用来扩大我们对这片古老的南部非洲大陆下地幔龙骨地质历史的了解。研究的主要目的是用硫化物包裹体的Re-Os法测定每一金伯利岩中金刚石的年龄，并将包裹体及其寄主金刚石的年龄和成分与岩石圈地幔中金刚石源区的地质背景联系起来。目前发现的三个以上的钻石形成期与克拉通的主要创造期（32 - 33亿年前）、合并期（29 - 31亿年前）和岩浆改造期（10 - 20亿年前）相匹配。新数据将测试这些事件的程度，特别是在具有最古老地壳历史（33 - 35亿年）的东部克拉通或遭受克拉通碰撞的林波波移动的带等地区。支持捕虏体年龄和地球化学研究将提供有关含金刚石原岩侵位或富碳金刚石流体来源的新信息。研究的更广泛的影响是在博士后助理和两名学生的培训和科学发展。博士后助理将加入学术教学社区，他的培训将直接有助于他对学生的监督。这两名学生都居住在南非，否则他们几乎没有机会在美国的高级研究机构接受培训和学习。有一位女学生是非洲的地球化学家，她是如此的不受欢迎，以至于在目前的南部非洲是独一无二的。提出了开发新的分析方案，这些方案将改善一般钻石研究的基础设施。这项研究将加强与学术界（格拉斯哥大学、开普敦大学、威特沃特斯兰德大学）和矿业界（DTC -戴比尔斯、Helam矿业）的伙伴关系。研究的传播将提高我们对钻石的背景了解，钻石在稳定国家具有重要的经济意义，在冲突地区是一种有问题的资源。该项目得到了NSF国际科学与工程办公室的部分支持。