Suture Zones through Earth History

缝合线带是一级构造线，它将大陆碎片分隔开来，这些大陆碎片在地质年代中融合形成了今天的大陆。它们通常含有外来的海洋岩石，表明缝合线是在从海洋俯冲到大陆碰撞的过渡过程中形成的。尽管缝合带作为古代板块边界的痕迹和海洋岩石圈的特殊暴露具有根本的重要性，但关于缝合带的意义仍有许多悬而未决的问题。特别是，被困海洋岩石圈碎片（蛇绿岩）的起源，以及导致它们在缝合带增生的过程仍然存在争议。同样不清楚的是，为什么许多缝合线，尤其是那些被严重侵蚀的缝合线，不含任何外来的海洋岩石。其他争议包括缝合线是否以及如何在早期地球发生，以及太古代绿岩带是否代表这种缝合线。此外，即使缝合带和经济上重要的矿床之间的空间联系很容易观察到，缝合在经济等级金属浓度中的作用仍存在争议。提出的研究的长期目标是通过集中研究海洋和变质岩来解决这些问题。这项研究将以地质测绘为基础，在可能的情况下与地质调查（QC、NU和加拿大）合作进行。利用地球化学的主要元素和微量元素对缝合岩的成因-蚀变进行了研究。重点将放在变质岩记录前，同步和/或缝合后的构造过程。埋藏深度(P)和平衡温度(T)将使用最先进的相平衡模型进行量化。埋藏-挖掘和加热-冷却速率和时间将使用一套地球时计(t)来计算，包括锆石和独居石中的U-Pb（原岩和峰值变质时代），角闪石和黑云母中的Ar（冷却时代），以及最有趣的是石榴石中最近的Lu-Hf和Sm-Nd（埋藏变质时代）。一旦与区域变形模式(D)结合起来，得到的P-T-t-D路径可以与热力学数值模型的预测相比较，热力学数值模型是一种了解构造过程的最新且非常强大的方法。在接下来的5年里，我们将研究三个具体的主题：主题1——变质底是在蛇绿岩底部发现的板块，根据氩定年，它们被认为是在与蛇绿岩形成同时的俯冲开始时期形成的。然而，我们最近首次将Lu-Hf石榴石应用于印度-亚洲缝合带的鞋底，并获得了明显比预期更早的年龄，从而对蛇绿岩成因、鞋底形成和俯冲开始之间的共时性提出了质疑。对印度-亚洲鞋底的研究将继续进行，而NL和QC的原型鞋底将被重新审视，并将设计数值模型来测试新的假设。主题2 -深度侵蚀缝合线。项目将集中在QC， NL和NU中记录不良的Torngat造山带。该研究将有助于定位缝合带，识别潜在的外来地体，约束不同变质期和覆印构造过程。主题3 -太古代缝合线和绿岩带。其中一个项目集中在QC的Pontiac沉积亚省，在那里金矿化和石榴石级变质作用之间存在潜在的联系，这在太古宙大陆缝合的背景下也是令人困惑的。第二个项目侧重于La Grande绿岩带，这是一个研究较少的新矿区，位于英国QC的詹姆斯湾地区。研究将首先集中在从带的核心到边缘观察到的无法解释的强烈变质梯度上。

Suture zones are first-order tectonic lineaments separating continental fragments that were amalgamated over geological time to form the present-day continents. They typically contain exotic oceanic rocks, indicating that sutures form during the transition from oceanic subduction to continental collision. Despite their fundamental importance as the trace of ancient plate boundaries and as exceptional exposures of oceanic lithosphere, there are many unanswered questions on the significance of suture zones. In particular, the origin of trapped oceanic lithosphere fragments (ophiolites) is still debated, as are the processes leading to their accretion in suture zones. It is also unclear why many sutures, especially deeply eroded ones, do not contain any exotic oceanic rocks. Other controversies include if and how suturing operated in the Early Earth, and if Archean greenstone belts represent such sutures. Additionally, even if the spatial association between suture zones and economically important mineral deposits is easily observed, the role of suturing in the concentration of metals at economic grades is debated. The long term goal of the proposed research is to address such problems by focusing on oceanic and metamorphic rocks.The research will be based on geological mapping conducted in collaboration, when possible, with geological surveys (QC, NU and Canada). The genesis-alteration of suture rocks will be investigated using major and trace element geochemistry. Emphasis will be put on metamorphic rocks that recorded pre-, syn- and/or post-suturing tectonic processes. Depth of burial (P) and temperature (T) of equilibration will be quantified using state-of-the-art phase equilibria modeling. Burial-exhumation and heating-cooling rates and timing will be derived using a suite of geochronometers (t) including U-Pb in zircon and monazite for protolith and peak metamorphic ages, Ar in hornblende and biotite for cooling ages, and most interestingly the recent Lu-Hf and Sm-Nd in garnet for burial metamorphism ages. Once integrated with the regional deformation patterns (D), the resulting P-T-t-D paths can be compared to predictions from thermal-mechanical numerical models, a recent and very powerful method for the understanding of tectonic processes.In the next 5 years, three specific themes will be addressed: Theme 1 – Metamorphic soles are slabs found at the base of ophiolites that, based on Ar dating, are thought to form during the inception of a subduction contemporaneously with ophiolite genesis. However, we recently applied, for the first time, Lu-Hf garnet dating to a sole from the India-Asia suture and obtained an age significantly older than expected, shedding doubt on the inferred synchronicity between ophiolite genesis, sole formation and inception of subduction. Research will continue on the India-Asia sole, while archetypal soles in NL and QC will be revisited and numerical models will be designed to test new hypotheses. Theme 2 – Deeply eroded sutures. Projects will focus on the poorly documented Torngat orogen in QC, NL and NU. The research will help localize the suture, identify potential exotic terranes and constrain the different metamorphic episodes and overprinting tectonic processes. Theme 3 – Archean sutures and greenstone belts. One project focuses on the Pontiac sedimentary subprovince, QC, where there is a potential link between gold mineralisations and garnet-grade metamorphism, which is also puzzling in the context of Archean continental suturing. A second project focuses on the La Grande greenstone belt, a poorly studied new mining district in the James Bay area, QC. The research will first focus on the strong unexplained metamorphic gradient that is observed from the core of the belt to its margins.