Suture Zones through Earth History

缝合带是一级构造线条，将大陆碎片分开，这些大陆碎片在地质时期合并形成今天的大陆。它们通常含有奇异的大洋岩石，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。尽管它们作为古代板块边界的遗迹和大洋岩石圈的特殊暴露具有重要的基础意义，但关于缝合带的意义仍有许多悬而未决的问题。特别是，被困的大洋岩石圈碎片(蛇绿岩)的起源仍然存在争议，导致它们在缝合带中积累的过程也是如此。目前也不清楚为什么许多缝合线，特别是被深度侵蚀的缝合线，没有任何外来的海洋岩石。其他争议包括缝合在地球早期是否以及如何运作，以及太古宙绿岩带是否代表这种缝合。此外，即使很容易观察到缝合带和重要的经济矿藏之间的空间联系，缝合在经济品位金属集中中的作用也是有争议的。拟议研究的长期目标是通过专注于海洋和变质岩来解决这些问题。 这项研究将基于在可能的情况下与地质调查(QC、NU和加拿大)合作进行的地质测绘。用常量元素和微量元素地球化学方法研究缝合岩的成因蚀变。重点将放在记录缝合前、同生和/或缝合后构造过程的变质岩上。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-折返和加热冷却速率和时间将由一套地质年代学(T)得出，包括原岩和峰期变质年龄的锆石和独居石中的U-Pb，冷却年龄的角闪石和黑云母中的Ar，以及最近埋藏变质年龄的石榴石中的Lu-Hf和Sm-Nd。一旦与区域形变模式(D)相结合，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-力学数值模型是理解构造过程的一种最新和非常强大的方法。 在接下来的5年里，将讨论三个具体的主题：主题1-变质底板是在蛇绿岩底部发现的板片，根据Ar测年，它们被认为是在俯冲开始时形成的，与蛇绿岩的形成同时发生。然而，我们最近首次对印度-亚洲缝合带的一个鞋底进行了Lu-Hf石榴石测年，获得了比预期明显更早的年龄，从而对蛇绿岩成因、鞋底形成和俯冲开始之间的推测同步性提出了怀疑。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研究，并将设计数值模型来测试新的假设。主题2-严重侵蚀的缝合线。项目将集中在QC、NL和NU的文件很少的Torngat造山带。这项研究将有助于确定缝合线的位置，识别潜在的外来地体，并约束不同的变质幕和叠置构造过程。主题3-太古宙缝合和绿岩带。其中一个项目集中在庞蒂亚克沉积亚省QC，那里的金矿化和石榴石级变质作用之间存在潜在的联系，这在太古代大陆缝合的背景下也令人费解。第二个项目的重点是La Grande绿岩带，这是一个研究较少的新矿区，位于堪萨斯州詹姆斯湾地区。这项研究首先将重点放在从岩带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.