Metamorphic record of accretionary processes in the Neoarchaean

该项目与丹麦和格陵兰岛地质调查局合作，旨在调查西格陵兰岛南部努克地区新太古代地体吸积过程的变质记录。该地区是进入太古宙中、下大陆地壳的少数窗口之一，因此为研究形成早期大陆地壳的过程提供了理想的场所。努克地区的地体融合与广泛的高级变质作用和在Færingehavn顶部的Tre Brødre和Tasiusarsuaq地体的推覆有关。该项目的初步工作表明，这些地体构成了一个新太古代成对变质带，包括(1)下板块(Færingehavn地体)，包含相对高压的低温变质组合；(2)上板块(tre Brdre和Tasiusarsuaq地体)，以麻粒岩相条件为主，沿明显较热的表观地温梯度。因此，这些数据支持了新太古代陆壳的形成是沿着与汇聚相关的岩浆弧进行的这一观点。此外，现有的年代学和地球化学数据表明，上板块保存了长达2.5亿年的与俯冲有关的火成岩活动的长期和幕式记录，表明太古代俯冲与反复的高温变质事件有关。尽管如此，地壳会聚显然没有导致下部板块的深度俯冲，这意味着太古代的会聚速度比今天慢得多，或者俯冲是间歇性的，与更频繁的板片断裂或回滚有关。该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的弧后区。这将涉及到不同地区的P-T-t-d记录的重建，通过假断面模拟和U-Pb测年。总体目标是更好地评估努克地区的会聚风格，并澄清上板块的热结构是否与间歇俯冲模式一致。

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.