Tonalite–trondhjemite–granodiorite (TTG) gneiss forms a major component of Archean continental crust. Resolving the origin of TTG gneisses and the secular change in their compositions is critical for better understanding how the continental crust has evolved and when a global plate tectonic regime began on Earth. Archean TTGs were generated by partial melting of hydrous basalts, although the geodynamic setting in which this occurred is still debated. In this study, an integrated modeling including thermodynamic modeling, accessory mineral solubility modeling, and trace element modeling is conducted on Coucal basalts from Pilbara craton and averaged Archean arc-like basalts along various thermal gradients for both closed and melt-drained systems. The results show the amount and composition of melts would be primarily controlled by source compositions, although geothermal gradient and the ability for melt to leave the system also contribute. Of both bulk compositions, averaged Archean arc-like basalts generate more melts with a medium- to low-pressure signature by fluid-absent melting during intracrustal loading. High-pressure TTGs may be generated by mixing residua and melts derived by fluid-absent melting or just fluid-present melting in a hot subduction zone. Most TTGs produced before the Neoarchean were likely generated at the lower levels of thickened basaltic crust; however, rare Eoarchean and Mesoarchean TTGs with high-pressure signatures suggest subduction occurred on the early Earth in isolated localities. We interpret a secular increase in the proportion of high-pressure TTGs at c. 3.0–2.5 Ga as recording a transition from localized subduction to a global plate tectonic regime.

中文翻译：

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太古宙玄武岩的开放系统分次熔融：对英长岩-长闪长岩-花岗闪长岩（TTG）岩浆成因的影响

闪长岩-长闪长岩-花岗闪长岩 (TTG) 片麻岩是太古代大陆地壳的主要成分。解决 TTG 片麻岩的起源及其成分的长期变化对于更好地了解大陆地壳如何演化以及全球板块构造制度何时在地球上开始至关重要。太古代 TTG 是由含水玄武岩的部分熔化产生的，尽管发生这种情况的地球动力学环境仍有争议。在这项研究中，对来自皮尔巴拉克拉通的 Coucal 玄武岩和沿各种热梯度的封闭和熔体排水系统的平均太古代弧状玄武岩进行了包括热力学建模、辅助矿物溶解度建模和微量元素建模在内的综合建模。结果表明熔体的数量和成分主要受源成分控制，尽管地温梯度和熔体离开系统的能力也有贡献。在这两种整体成分中，平均太古代弧状玄武岩在地壳内加载过程中通过无流体熔化产生更多具有中低压特征的熔体。高压 TTG 可以通过混合残余物和熔体产生，这些熔体是由热俯冲带中无流体熔融或仅存在流体熔融产生的。大多数在新太古代之前产生的 TTG 很可能产生于增厚玄武岩地壳的较低层；然而，具有高压特征的罕见的始太古代和中太古代 TTG 表明俯冲发生在早期地球的偏远地区。我们解释了 c 处高压 TTG 比例的长期增加。3.0-2.5 Ga 记录了从局部俯冲到全球板块构造体制的转变。