Terrane spotting – Testing models for the evolution of Earth’s first continents

太古代的岩石通常被陡倾的地壳规模剪切带切割。剪切带通常被解释为地壳边界，将具有不同地质历史的地壳碎片分开。碎屑岩的增生要求水平缩短占优势，并暗示着某种形式的俯冲。然而，这是合理的，一些陡峭的剪切带可能起源于部分对流翻转的重力不稳定的绿岩带，沉入地壳深部。这个过程不需要俯冲。由于太古代地壳岩石的历史漫长而复杂，通常会受到后来构造事件的多次变形和叠加，因此区分形成太古代大陆的一级地球动力学过程往往很困难。在这个项目中，我们的目标是测试两个对比的假设（加积与后来改造的一次连续的太古代地壳段）的形成大陆刘易斯复杂，苏格兰，使用相结合的相图建模和原位U-Pb，Lu-Hf，O同位素和微量元素分析的锆石。本研究的主要目的是提供一个更好的了解的时间和条件的地壳形成和改造的个别岩石圈，并澄清是否地壳块体确实是岩石圈或如果他们代表不同的地壳水平的一次连续的太古代大陆。

Archean cratons are generally dissected by steeply-dipping crustal-scale shear zones. The shear zones are commonly interpreted as terrane boundaries, separating fragments of crust with different geological histories. The accretion of terranes requires a dominance of horizontal shortening and implies some form of subduction. However, it is plausible that some of the steep shear zones may have originated from partial convective overturn of gravitationally unstable greenstone belts that sank into the deep crust. This process does not require subduction. Distinguishing between the first order geodynamic processes that formed the Archean continents is often difficult due to the long and complex history of Archean crustal rocks, which are commonly multiply deformed and overprinted by later tectonic events. In this project, we aim to test two contrasting hypotheses (terrane accretion versus later reworking of a once continuous segment of Archean crust) for the formation of the mainland Lewisian Complex, Scotland, using a combination of phase diagram modelling and in situ U-Pb, Lu-Hf, O isotope and trace element analysis of zircon. The main aim of this study is to provide a better understanding of the timing and conditions of crust formation and reworking within individual terranes, and to clarify if the crustal blocks are indeed terranes or if they represent different crustal levels of a once continuous Archean continent.