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

地体观测 – 测试地球第一大洲演化模型

• 批准号: 404682919
• 负责人: Professorin Dr. Annika Dziggel
• 金额: --
• 依托单位: Institut für Geologie, Mineralogie und Geophysik
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/404682919?language=en
• 关键词: Terrane; spotting; Testing; models; evolution

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.

太古宙克拉通通常被陡倾的地壳尺度剪切带所分割。剪切带通常被解释为地体边界，分隔具有不同地质历史的地壳碎片。地体的增生需要水平缩短的主导作用，并且意味着某种形式的俯冲。然而，一些陡峭剪切带可能起源于沉入地壳深处的重力不稳定绿岩带的部分对流翻转。这个过程不需要俯冲。由于太古代地壳岩石的历史悠久而复杂，通常会因后来的构造事件而多次变形和叠印，因此区分形成太古宙大陆的一级地球动力学过程通常很困难。在这个项目中，我们的目标是结合相图模型和原位 U-Pb 来测试苏格兰大陆刘易斯杂岩的形成的两个对比假设（地体增生与太古代地壳曾经连续的部分的后期改造）。 、锆石的Lu-Hf、O同位素及微量元素分析。这项研究的主要目的是更好地了解地壳形成的时间和条件以及各个地体内部的改造，并澄清地壳块是否确实是地体，或者它们是否代表了曾经连续的太古宙大陆的不同地壳层次。