Growth of Early Continental Crust and Chemical Evolution of Cratonic Lithosphere

地球上最古老的岩石出现在太古宙时期（~3.0-4.0 Ga），由花岗岩（“TTG”）岩石组成，这些岩石形成了这些大陆的物理核或克拉通。克拉通位于大陆岩石圈的地幔橄榄岩之下，具有独特的化学和物理性质，这是它们自太古宙以来长期稳定的原因。在我们太阳系的类地行星中，地球似乎是独一无二的，它拥有广泛的、高度分化的大陆地壳（或克拉通）。本研究考虑了最古老大陆地壳的起源，并探讨了太古宙地壳生长与克拉通岩石圈化学演化的关系。实验室实验将在与次克拉通岩石圈相关的压力和温度下进行，将考虑太古代花岗岩（TTG）岩浆在演化中的克拉通根中与橄榄岩相互作用的程度和化学机制。这些实验将产生不同比例的熔体（“岩浆”）和结晶（矿物）相，作为压力、温度和其他变量的函数，实验熔体和矿物的详细化学特征将与适当的自然样品（分别是太古宙花岗岩类和亚克拉通岩石圈样品）进行比较，这些样品在金伯利岩喷发中被带到地表，以橄榄岩“包体”的形式，或作为钻石中的微小矿物“包裹体”)。从几何上说，现代俯冲带是由地幔岩石圈（橄榄岩）的“楔子”覆盖在俯冲的海洋岩石圈的“板”上组成的。这个项目将解决太古宙地壳演化的问题，包括传统的地幔楔形俯冲板块几何形状是否适合早期地球，或者是否有某种独特的构造运动在起作用，以及现代风格的板块构造过程在什么时间点起作用？更好地了解地球早期花岗岩类岩浆活动与地幔下克拉通深根或“龙骨”发育之间的成因关系，是对其他类地行星（如火星和金星）地壳进行现场研究以及寻找太阳系外类地行星的重要前提。

The oldest rocks on Earth occur within the continents are of Archean age (~3.0-4.0 Ga), and are comprised of granitoid ("TTG") rocks that form the physical nucleus, or craton, of these continents. The cratons are underlain by mantle peridotites of the continental lithosphere, which possess unique chemical and physical properties that are responsible for their long-term stability since the Archean. Amongst the terrestrial planets of our solar system, the Earth appears to be unique in possessing extensive, highly-differentiated continental crust (or cratons). This study considers the origins of the oldest continental crust, and addresses how crustal growth in the Archean was related to the chemical evolution of the cratonic lithosphere. Laboratory experiments, to be performed at pressures and temperatures relevant to those of the subcratonic lithosphere, will consider to what extent and by what chemical mechanisms Archean granitoid (TTG) magmas interacted with peridotite rocks in evolving cratonic roots. These experiments will produce variable proportions of melt ("magma") and crystalline (mineral) phases as a function of pressure, temperature and other variables, and the detailed chemical features of the experimental melts and minerals will be compared with appropriate natural samples (respectively, Archean granitoids, and samples of the subcratonic lithosphere brought to the surface in kimberlite eruptions, in the form of peridotite "xenoliths, or as minute mineral "inclusions" in diamonds). Geometrically, modern subduction zones consist of a "wedge" of mantle lithosphere (peridotite) overlying a "slab" of subducting oceanic lithosphere. Questions for Archean crustal evolution, which this project will address, include whether or not a conventional mantle wedge-subducting slab geometry is appropriate for the early Earth, or if some unique style of tectonism was operative, and at what point in time did modern-style, plate tectonic processes take over? A better understanding of the genetic relationship between granitoid magmatism on the early Earth and the development of deep roots or "keels" for the cratons in the underlying mantle is an important prerequisite for on-site studies of crusts on the other terrestrial planets (e.g., Mars and Venus), and for the search for Earth-like planets beyond our solar system.