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

尽管在许多早太古代至晚太古代(2.7-3.8Ga)暴露良好的地形中进行了综合的野外、岩石学、同位素、地球化学和构造研究，但关于大陆地壳起源和早期生长的一些相对基本的问题仍未得到解决。这些问题包括发生早期大陆生长的构造环境、帮助稳定太古代大陆质量的花岗岩类岩浆的最终来源，以及太古代大陆演化中的花岗岩类岩浆活动与下地幔深克拉通根(龙骨)稳定之间的关系的性质。该提案寻求资金，以在多砧板装置中进行高压实验，旨在限制太古宙花岗岩的起源，并旨在深入了解地幔参与其起源的程度。以往的实验研究表明，含水玄武岩在1-3 Gpa的低熔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(TTG)的一般化学成分，TTG是太古宙高、低等级地体中的主要花岗岩类岩石，但有一些微小但可能显著的差异。加拿大地盾上位省和奴隶省晚太古代(2.6-2.9Ga)花岗岩-绿岩地体(即所谓的“山玄岩套”的成员)，具有与变质玄武岩部分熔融的简单成因不符的化学特征(如高铬和镍含量)，表明了地幔的谱系。然而，就大多数地球化学参数而言，来自镁铁质地壳部分熔融的TTG花岗岩类似乎在成分上与萨努基特岩套中推测的地幔起源花岗岩类是连续的。有几种解释可以解释这些观察结果，这些解释将得到实验验证：(1)TTG熔体对地幔橄榄岩的同化作用，(2)太古代TTG的玄武岩来源比1-3 GPa玄武岩熔融实验中使用的原始物质更具镁质，或(3)Sanukite是先前被TTG熔体变质的地幔部分熔融的结果。当然，可能性(1)和(3)涉及TTG熔体和橄榄岩地幔之间的密切化学作用，对次大陆地幔的化学演化具有潜在的深远影响。

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.