Hafnium Isotopic Approaches to Precambrian Crust-Mantle Evolution

前寒武纪壳幔演化的铪同位素方法

• 批准号: 9526536
• 负责人: P. Jonathan Patchett
• 金额: $ 29.6万
• 依托单位: University of Arizona
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1996
• 资助国家: 美国
• 起止时间: 1996-01-01 至 1999-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9526536&HistoricalAwards=false
• 关键词: Hafnium; Isotopic; Approaches; Precambrian; Crust

9526536 Patchett The primary aim of this project is to evaluate the large variability in initial (Nd values that have been reported for several early Archean gneisses. It is essential for a serious and thorough discussion of models of early Earth evolution to determine whether these initial (Nd values are real or if they are produced by disturbances in the Sm-Nd system. Preliminary work on this project has been completed and has shown that the Hf isotopic compositions of zircons from these early gneisses are consistent with their whole-rock Nd isotopic compositions and as such verify the early incompatible-element depletion of the mantle. The P.I.s have not yet been able to analyze zircons from those gneisses with negative (as low as -4.0) and highly positive (up to +4.0) initial (Nd values. The P.I.'s groundwork on this project has demonstrated the complexity of these rocks, and that a solution to this problem can only be achieved by analysis of carefully selected samples. The P.I.s proposes three studies: (1) investigation of highly positive (Nd values reported for Greenland gneisses; (2) evaluation of disturbances in Lu-Hf and U-Pb in samples with known Sm-Nd disturbances; (3) evaluation of the range of Nd values (-4 to +4) in the Acasta gneisses.

9526536 Patchett本项目的主要目的是评估几个早期太古代片麻岩中已报道的初始Nd值的大变化。 对早期地球演化模型进行认真和彻底的讨论，必须确定这些初始Nd值是真实的，还是由Sm-Nd系统中的扰动产生的。 该项目的初步工作已经完成，并已表明，Hf同位素组成的锆石从这些早期片麻岩是一致的，其全岩Nd同位素组成，并因此验证了早期不相容元素的地幔亏损。 P.I.s尚未能够分析那些具有负（低至-4.0）和高正（高达+4.0）初始（Nd值）的片麻岩中的锆石。 私家侦探该项目的基础工作已经证明了这些岩石的复杂性，只有通过仔细选择样本进行分析才能解决这个问题。 研究人员提出了三项研究：（1）调查格陵兰片麻岩报告的高正Nd值;（2）评估已知Sm-Nd扰动的样品中Lu-Hf和U-Pb的扰动;（3）评估格陵兰片麻岩中Nd值的范围（-4至+4）。