Suture Zones through Earth History

地球历史上的缝合带

• 批准号: RGPIN-2014-05681
• 负责人: Guilmette, Carl
• 金额: $ 1.89万
• 依托单位: Université Laval
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2015
• 资助国家: 加拿大
• 起止时间: 2015-01-01 至 2016-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=588557
• 关键词: Suture; Zones; through; Earth; History

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.

缝合带是一级构造线性构造，将地质时期合并形成今天大陆的大陆碎片分开。它们通常含有外来的大洋岩石，表明缝合线形成于从大洋俯冲到大陆碰撞的过渡时期。尽管它们作为古板块边界的痕迹和大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还有许多未解之谜。特别是，被困的海洋岩石圈碎片（蛇绿岩）的起源仍有争议，因为是导致其在缝合带的增生过程。也不清楚为什么许多缝合线，特别是深度侵蚀的缝合线，不包含任何外来的海洋岩石。其他的争议包括是否以及如何在早期地球上运作，如果太古代绿岩带代表这样的缝合。此外，即使缝合带和经济上重要的矿床之间的空间关联很容易观察到，在经济品位的金属浓度的作用，是有争议的。拟议研究的长期目标是通过关注大洋和变质岩来解决这些问题。 研究将以地质测绘为基础，在可能的情况下，与地质调查机构（QC、NU和加拿大）合作进行。利用常量和微量元素地球化学研究缝合带岩石的成因-蚀变。重点将放在记录前，同和/或后变质构造过程的变质岩。将使用最先进的相平衡建模对平衡的埋藏深度（P）和温度（T）进行定量。埋藏-折返和加热-冷却速率和时间将使用一套地质年代计（t）得出，包括锆石和独居石中的U-Pb用于原岩和峰变质年龄，角闪岩和黑云母中的Ar用于冷却年龄，最有趣的是石榴石中的最近Lu-Hf和Sm-Nd用于埋藏变质年龄。一旦与区域变形模式（D）整合，所产生的P-T-t-D路径就可以与热-力学数值模型的预测进行比较，这是一种最近的非常强大的理解构造过程的方法。 在接下来的5年里，将讨论三个具体的主题：主题1 -变质鞋底是在蛇绿岩底部发现的板，根据Ar测年，被认为是在俯冲开始时与蛇绿岩成因同时形成的。然而，我们最近应用，第一次，Lu-Hf石榴石测年的唯一从印度-亚洲缝合线，并获得了年龄显着大于预期，脱落的推断蛇绿岩成因，唯一的形成和俯冲开始之间的同步性的怀疑。研究将继续对印度-亚洲鞋底，而原型鞋底在荷兰和QC将被重新审视和数值模型将被设计来测试新的假设。主题2 -缝线深度腐蚀。项目将侧重于QC、NL和NU记录不全的Torngat造山带。这一研究将有助于确定缝合线的位置，识别潜在的外来变质作用，并限制不同的变质幕和叠加构造过程。专题3 -太古宙缝合带和绿岩带。一个项目的重点是庞蒂亚克沉积亚省，QC，那里有一个潜在的金矿化和石榴石级变质作用之间的联系，这也是令人费解的太古代大陆变质的背景下。第二个项目的重点是拉格兰德绿岩带，一个研究不足的新矿区在詹姆斯湾地区，QC。研究将首先集中在从带的核心到其边缘观察到的强烈的无法解释的变质梯度上。