The Genesis of Ultra-Depleted Mantle Peridotites in Continental Lithosphere

了解大陆下地幔岩石圈的起源和地球化学特征是解释地幔分异和大陆地壳形成过程的核心。这项研究的主要目标是提供新的信息和见解的各种地幔过程，最重要的是低密度，高镁/铁橄榄岩，可能形成一个均衡稳定的地幔岩石圈大陆地幔岩下的形成和演化。这一目标将通过实验室和野外研究相结合来实现，包括（1）格陵兰东南部Weidemann峡湾地区和格陵兰西部Ubekendt岛第三纪岩脉地幔捕虏体矿物的微量元素和同位素分析，（2）全球类似橄榄岩样品的比较研究（巴布亚新几内亚、怀俄明州克拉通和卡普瓦尔克拉通），以及（3）从格陵兰岛额外收集橄榄岩样本。新数据将用于评估先前基于相同样品的主要元素组成的两个假设：（1）来自Weidemann峡湾和Ubekendt岛的捕虏体，含有低模态斜方辉石，是未交代的橄榄岩的例子，形成为约40%部分熔融的残余物;（2）富含斜方辉石的橄榄岩，如Kapvaal和北美的橄榄岩，通过开放系统，SiO2富集高度贫化的残留物产生。

9814632KelemenUnderstanding the origin and geochemical characteristics of the mantle lithosphere beneath the continents is central to deciphering the processes responsible for mantle differentiation and continental crust formation. The primary goal of this research is to provide new information and insights on a variety of mantle processes; most importantly the formation and evolution of low density, high Mg/Fe peridotites that may form an isostatically stable mantle lithosphere beneath continental cratons. This goal will be achieved by a combination of laboratory and field studies including (1) trace element and isotopic analysis of minerals in mantle xenoliths from Tertiary dikes in the Weidemann Fjord area in Southeast Greenland and Ubekendt Island in West Greenland, (2) comparative studies of samples of similar peridotites worldwide (Papua New Guinea, Wyoming craton, and the Kapvaal craton), and (3) additional collection of peridotite samples from Greenland. The new data will be used to evaluate two hypotheses previously based on major element compositions of the same samples: (1) xenoliths from Weidemann Fjord and Ubekendt Island, with low modal orthopyroxene, are examples of unmetasomatized cratonic peridotite, formed as the residues of about 40% partial melting, and (2) orthopyroxene-rich cratonic peridotites, such as those in the Kapvaal and North American cratons, were produced by open-system, SiO2 enrichment of highly depleted residues.