The search for the terrestrial protocrust

月球和火星上保存着大量的原始（原始）地壳，与之不同的是，地球上显然完全没有超过40.5亿年的岩石。然而，已经发现了43.5亿年前的矿物，证明了陆地原地壳的存在。地壳的形成和破坏是地球分化过程中最神秘的步骤。然而，在已知最古老的岩石中保存着放射性同位素的线索，这些岩石要么是通过地幔枯竭，要么是通过地壳再循环，从古老但已经消失的地壳中继承而来。学会阅读这些线索将会破译原始地壳的历史。在这里，我建议对其中一个特征的意义进行第一次系统的研究，即所谓的高mu （U/Pb）特征，该特征在包括加拿大在内的几个盾区前寒武纪岩石的铅同位素系统中得到表达。值得注意的是，高原省份（奴隶，伊尔加恩，津巴布韦，格陵兰岛西南部，怀俄明州，温尼伯河地）是地球上研究人员发现最古老的已知矿物的地方，这些矿物在所有情况下都明显超过了岩石的年龄。提议的方法背后的基本原理有两个方面。首先，我建议测试岩石的高穆特征强度与携带该特征的岩石中古锆石的数量之间是否存在关系。这意味着两者都继承自不再保存的原地壳。该研究将采用快速的原位U/Pb锆石定年技术，在cfi资助的最先进的设施中，从最高的晚太古宙片岩和变质沉积层中选择矿物。其次，不考虑锆石产量，该提案还旨在研究是否有任何化学变化伴随着铅同位素指纹，就像在月球上一样（也有高地壳）。这将沿着跨同位素梯度的系统样带进行研究，例如在温尼伯河地体中暴露。该项目将培养一名初级博士后研究员和研究生，旨在加强加拿大在早期地球研究方面的地位。

Unlike the Moon and Mars, where heavily cratered original (primordial) crust is preserved, there is an apparent complete absence of rocks older than 4.05 billion years on Earth. Yet minerals as old as 4.35 billion years have been discovered, testifying to the former existence of a terrestrial protocrust. The formation and destruction of this crust are the most cryptic steps of the Earth's differentiation. There are, however, radiogenic isotope clues preserved in the oldest known rocks that were inherited, either via mantle depletion or crustal recycling, from the ancient but lost crust. Learning to read these clues will decipher the history of the primordial crust. Here I propose the first systematic study of the significance of one of these, the so called high mu (U/Pb) signature, which is expressed in the lead isotope systematics of Precambrian rocks in several shields, including Canada. Significantly, the high mu provinces (Slave, Yilgarn, Zimbabwe, SW Greenland, Wyoming, Winnipeg River Terrane) are those places on Earth where researchers also find the oldest known minerals, which in all cases significantly exceed the ages of the rocks. The rationale behind the proposed approach is two-fold. First, I propose to test whether there exists a relationship between the strength of the high mu character of a rock and the amount of ancient zircon in the rocks that carry the signature. The implication being that both were inherited from the no longer preserved protocrust. The research will employ rapid, in situ U/Pb zircon dating in a CFI-funded state-of-the-art facility on minerals selected from the highest mu late Archean gneisses and metasediments. Second, regardless of the zircon yield, the proposal also aims at studying whether there are any chemical variations that accompany the lead isotopic fingerprint, like on the Moon (also with a high mu crust). This will be studied along systematic transects across isotopic gradients, exposed e.g. in the Winnipeg River Terrane. A junior postdoctoral researcher and graduate students will be trained in this program aimed at strengthening Canada's position in early Earth research.