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: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=611782
• 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.

缝合带是分隔大陆碎片的一级构造线，这些碎片在地质时期合并形成了今天的大陆，它们通常含有奇异的海洋岩石，这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，尽管它们具有重要意义。作为古代板块边界的痕迹和海洋岩石圈的特殊暴露，关于缝合带的重要性，特别是被困海洋岩石圈的起源，还有许多悬而未决的问题。碎片（蛇绿岩）以及导致其在缝合带中增生的过程仍然存在争议。还不清楚为什么许多缝合带，尤其是深度侵蚀的缝合带，不包含任何奇异的海洋岩石，其他争议包括缝合带是否以及如何起作用。早期地球，如果太古宙绿岩带代表了这种缝合线，即使缝合带和具有重要经济意义的矿床之间的空间联系很容易观察到，缝合线在矿藏集中的作用也很明显。拟议研究的长期目标是通过关注海洋和变质岩来解决这些问题。 该研究将基于与地质调查（QC、NU 和加拿大）合作进行的地质测绘，将利用主量和微量元素地球化学研究缝合岩的成因变化，重点将放在变质岩上。记录缝合前、同步和/或缝合后构造过程的埋藏深度 (P) 和平衡温度 (T) 将使用最先进的阶段进行量化。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，包括用于原岩和峰值变质年龄的锆石和独居石中的 U-Pb、用于冷却年龄的角闪石和黑云母中的 Ar 等。有趣的是，最近石榴石中的 Lu-Hf 和 Sm-Nd 的埋藏变质作用年龄一旦与区域变形模式 (D) 结合起来，就得到了结果。 P-T-t-D 路径可以与热力数值模型的预测进行比较，这是一种了解构造过程的最新且非常强大的方法。 未来 5 年，将讨论三个具体主题： 主题 1 – 变质底是在蛇绿岩底部发现的板片，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。我们最近首次应用了 Lu-Hf 石榴石年代测定法，对来自印度-亚洲缝合线的鳎鱼进行了年代测定，并获得了比预期年龄要大得多的年龄，这使人们对推断产生了怀疑蛇绿岩成因、底部形成和俯冲开始之间的同步性将继续对印度-亚洲底部进行研究，同时将重新审视 NL 和 QC 的原型底部，并设计数值模型来测试新的假设 2 – 深度侵蚀缝合线。项目将重点关注 QC、NL 和 NU 的托恩加特造山带，该研究将有助于定位缝合线、识别潜在的外来地体并限制不同的地体。主题 3 – 太古宙缝合线和绿岩带。一个项目重点关注 QC 的庞蒂亚克沉积亚省，该地区的金矿化和石榴石级变质作用之间存在潜在联系，这在背景下也令人费解。第二个项目的重点是拉格兰德绿岩带，这是位于魁北克省詹姆斯湾地区的一个研究很少的新矿区。首先关注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。