Petrogenesis of Archean Granitoids and Implications for the Chemical Evolution of Cratonic/Lithosphere

太古代花岗岩类岩石成因及其对克拉通/岩石圈化学演化的意义

• 批准号: 0003638
• 负责人: Robert Rapp
• 金额: $ 12.29万
• 依托单位: SUNY at Stony Brook
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-12-01 至 2002-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0003638&HistoricalAwards=false
• 关键词: Petrogenesis; Archean; Granitoids; Implications; Chemical

RappEAR-0003638Despite comprehensive field, petrologic, isotopic, geochemical, and structural studies in a number of well-exposed early- to late-Archean terrains (2.7-3.8 Ga old), some relatively basic issues regarding the origin and early growth of the continental crust remain unresolved. These include the tectonic setting in which early continental growth took place, the ultimate source of the granitoid magmas that helped stabilize continental masses in the Archean, and the nature of the relationship between granitoid magmatism within the evolving Archean continents and the stabilization of deep cratonic roots (keels) in the underlying mantle. The proposal seeks funding to conduct high-pressure experiments in the multi-anvil apparatus aimed at constraining the origin of Archean granitoids, and designed to provide insight into the extent to which the mantle was involved in their origin. Previous experimental studies have shown that low degrees of melting of hydrous basalt at 1-3 GPa produces liquids with the general chemical composition of Archean tonalite-trondhjemite-granodiorite suites (TTG), the dominant granitoid rock in Archean high- and low-grade terrains, but with some minor but perhaps significant discrepancies. Late-Archean (2.6-2.9 Ga old) granite-greenstone terrains in the Superior and Slave Provinces of the Canadian Shield (members of the so-called "sanukitoid suite"), possess chemical characteristics (such as high Cr and Ni contents) that are inconsistent with a simple origin by partial melting of metabasalt, and that suggest a mantle lineage. Yet in terms of most geochemical parameters, TTG granitoids, derived from partial melting of mafic crust, appear to be compositionally continuous with presumably mantle-derived granitoids of the sanukitoid suite. A number of explanations, which will be tested experimentally, could account for these observations: (1) assimilation of mantle peridotite by TTG melts, (2) the basaltic source for Archean TTG was more magnesian than the starting materials used in the basalt melting experiments at1-3 GPa, or (3) sanukitoids result from partial melting of mantle that had been previously modified by TTG melts. Possibilities (1) and (3), of course, involve intimate chemical interaction between TTG melts and peridotitic mantle, with potentially profound implications for the chemical evolution of the sub-continental mantle.

RappEAR-0003638尽管对许多暴露良好的早太古代至晚太古代地形（2.7-3.8 Ga）进行了全面的野外、岩石学、同位素、地球化学和结构研究，但有关大陆起源和早期生长的一些相对基本的问题仍然没有得到解决。地壳。 这些包括早期大陆生长发生的构造背景，帮助稳定太古代大陆块的花岗岩岩浆的最终来源，以及太古代大陆演化中花岗岩岩浆活动与底层地幔中深层地幔根（龙骨）稳定之间关系的性质。该提案寻求资金，以便在多砧装置中进行高压实验，旨在限制太古代花岗岩类的起源，并旨在深入了解地幔在其起源中的参与程度。 以往的实验研究表明，在1-3 GPa下，含水玄武岩的低程度熔融产生的液体具有太古代英云闪长岩-奥长花岗岩-花岗闪长岩套组（TTG）的一般化学成分，这是太古代高级和低级地形中的主要花岗岩类岩石，但有一些微小但可能是显著的差异。加拿大地盾上级省和奴隶省的晚太古代（2.6-2.9 Ga）花岗岩-绿岩地体（所谓的“sanukitoid套件”的成员）具有的化学特征（如高Cr和Ni含量）与变玄武岩部分熔融的简单起源不一致，并建议地幔血统。 然而，在大多数的地球化学参数，TTG花岗岩类，来自镁铁质地壳的部分熔融，似乎是成分连续的推测幔源花岗岩sanukitoid套件。 这些观测结果可以解释为：（1）地幔橄榄岩被TTG熔体同化，（2）太古代TTG的玄武岩源比1 - 3GPa玄武岩熔融实验中使用的起始材料更含镁，（3）sanukitoids是由先前被TTG熔体改性的地幔部分熔融产生的。假设（1）和假设（3）涉及TTG熔体与橄榄岩地幔之间的密切化学作用，对陆下地幔的化学演化具有潜在的深远意义。