Collaborative Research: Growth and Modification of the Tanzanian Lithosphere

9600030切斯利为了研究构造作用对克拉通岩石圈的影响，计划对坦桑尼亚克拉通内外的捕虏体进行详细检查。对所选包体的岩石学、矿物化学、温压测量、常量元素和微量元素地球化学的研究，以及最重要的是Os同位素组成的研究，将有助于表征坦桑尼亚岩石圈地幔的组成和克拉通地幔的垂直和横向范围。对整个岩石和铬铁矿矿物分离的OS同位素测量将限制这些岩石中熔体提取的最小年龄，从而限制岩石圈的形成时间。此外，硅酸盐和碳酸盐岩交代作用对橄榄岩中Re-Os体系的影响将通过将铬铁矿结果(应得到初始Os同位素组成)与全岩数据进行比较来评价，全岩数据可能记录了交代重新引入Re/Os比值的提高。这些岩石学和地球化学数据将有助于约束坦桑尼亚目前正在进行的地震和重力调查得出的岩石圈结构模型。此外，将这些新的地球物理数据与这里的岩石学和地球化学研究大纲相结合，将能够描述岩石圈地幔生长和改造所涉及的重要过程。

9600030 Chesley To investigate the influence of tectonic processes on cratonic lithosphere, a detailed examination of xenoliths both on and off the Tanzanian craton is planned. Investigation of the petrography, mineral chemistry, thermobarometry, major and trace element geochemistry and, most importantly, Os isotopic compositions on selected xenoliths will serve to characterize the composition of the Tanzanian lithospheric mantle and the vertical and lateral extent of cratonic mantle. Os isotopic measurements on whole rock and chromite mineral separates will constrain the minimum age of melt extraction in these rocks, hence timing of lithosphere formation. In addition, the effects of silicate and carbonatite metasomatism on the Re-Os systematics in peridotites will be evaluated by comparison of the chromite results (which should yield the initial Os isotopic composition) with whole rock data, which may record enhancement of the Re/Os ratio due to metasomatic re-introduction of Re. These petrologic and geochemical data will help constrain models of lithosphere structure derived from seismic and gravity surveys that are currently underway in Tanzania. Furthermore, integration of these new geophysical data with the petrological and geochemical studies outline here will allow delineation of the important processes involved in lithospheric mantle growth and modification.