Metamorphic record of accretionary processes in the Neoarchaean

该项目与丹麦和格陵兰地质调查局合作，旨在调查西格陵兰南部努克地区新太古代岩石增生过程的变质记录。该地区是了解西太平洋中下部大陆地壳的少数窗口之一，因此提供了研究早期大陆地壳形成过程的理想场所。努克地区的地体融合作用与Færingehavn顶部的Tre Brødre和Tasiusarsuaq断层的广泛高级变质作用和逆冲作用有关。该项目的初步工作表明，这些岩石构成了一个新太古代成对变质带，包括（1）含有相对高压低温变质组合的下部板块（Færingehavn e），和（2）上部板块（Tre Brødre和Tasiusarsuaq es），以麻粒岩相条件为主，沿着明显更热的表观地热梯度。因此，这些数据支持了新太古代陆壳的形成是沿着与会聚有关的岩浆弧发生的观点。此外，现有的地质年代学和地球化学数据表明，上板块保存了一个长期的和幕式的记录，俯冲有关的岩浆活动，持续约。2.5亿年，这表明，大洋俯冲是与重复的高温变质事件。尽管如此，地壳会聚显然并没有导致下板块的深俯冲，这意味着西太平洋的会聚速度比今天慢得多，或者俯冲是间歇性的，并与更频繁的板片断裂或回滚有关。本项目旨在进一步研究上板块的变质记录和热结构，重点是造山带腹地和造山带弧后地区。这将涉及通过假剖面建模和U-Pb测年重建不同地区的P-T-t-d记录。总体目标是更好地评估努克地区的会聚类型，并澄清上层板块的热结构是否与间歇性俯冲模型一致。

In collaboration with the Geological Survey of Denmark and Greenland, this project aims to investigate the metamorphic record of the processes of Neoarchaean terrane accretion in the Nuuk region of southern West Greenland. The region is one of a few windows into Archaean mid- to lower continental crust, and therefore provides an ideal site to study the processes that formed the early continental crust. Terrane amalgamation in the Nuuk region was associated with extensive high-grade metamorphism and thrusting of the Tre Brødre and Tasiusarsuaq terranes on top of the Færingehavn. Preliminary work to this project indicates that these terranes constitute a Neoarchaean paired metamorphic belt, including (1) a lower plate (Færingehavn terrane) containing relatively high pressure low temperature metamorphic assemblages, and (2) an upper plate (Tre Brødre and Tasiusarsuaq terranes), dominated by granulite facies conditions along a distinctly hotter apparent geothermal gradient. Thus, the data support the view that the formation of Neoarchaean continental crust occurred along convergence-related magmatic arcs. Moreover, the available geochronology and geochemical data indicate that the upper plate preserves a prolonged and episodic record of subduction-related igneous activity that lasted for ca. 250 million years, suggesting that Archaean subduction was associated with repeated high temperature metamorphic events. Despite this, crustal convergence apparently did not result in the deep subduction of the lower plate, implying that Archaean convergence rates were much slower than today, or that subduction was intermittent and associated with a more frequent slab breakoff or rollback. This project aims to further investigate the metamorphic record and thermal structure of the upper plate, focusing on the orogen hinterland and back-arc region of the orogen. This will involve the reconstruction of the P-T-t-d record of different areas by means of pseudosection modelling and U-Pb dating. The overall goal is to better assess the style of convergence in the Nuuk region, and to clarify whether the thermal structure of the upper plate is consistent with a model of intermittent subduction.