The Genesis of Ultra-Depleted Mantle Peridotites in Continental Lithosphere

9814632克莱门了解大陆下地幔岩石圈的起源和地球化学特征，是破译地幔分异和大陆地壳形成过程的核心。本研究的主要目的是为各种地幔过程提供新的信息和见解；最重要的是低密度、高镁铁比橄榄岩的形成和演化，这些橄榄岩可能在大陆克拉通下形成均衡稳定的地幔岩石圈。这一目标将通过实验室和实地研究相结合来实现，包括：(1)对格陵兰东南部Weidemann峡湾地区和西格陵兰Ubekendt岛第三纪岩脉地幔捕虏体中的矿物质进行微量元素和同位素分析，(2)对世界各地（巴布亚新几内亚、怀俄明克拉通和Kapvaal克拉通）类似橄榄岩样本进行比较研究，以及(3)从格陵兰岛收集橄榄岩样本。新数据将用于评估先前基于同一样品主要元素组成的两种假设：(1)Weidemann Fjord和Ubekendt岛的捕虏体中含有低模态正辉石，是未变质的克拉通橄榄岩的例子，是约40%部分熔融残留物形成的；(2)Kapvaal和北美克拉通中富含正辉石的克拉通橄榄岩是由开放体系、高度贫化残留物的SiO2富集产生的。

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.