The Assembly Of Pannotia: Implications for the Origin of Supercontinents

潘诺西亚大会：对超级大陆起源的影响

• 批准号: RGPIN-2020-03872
• 负责人: Murphy, JamesBrendan
• 金额: $ 3.72万
• 依托单位: St. Francis Xavier University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=751168
• 关键词: Assembly; Pannotia; Implications; Origin; Supercontinents

Pangea is only the most recent of a series of supercontinents that have punctuated Earth history for billions of years. Episodic recurrence of supercontinent amalgamation and breakup (the supercontinent cycle) has had a profound influence on the Earth's geology, climate, and life, but the processes responsible are poorly understood. For example, we know to a first order where and when Pangea formed, but not why. The most controversial of the hypothesized supercontinents is Pannotia, whose very existence is debated. Pannotia is thought to have formed ~ 600 million years ago, consisting of the ancient continents of Gondwana, Laurentia, Baltica and possibly Siberia. Available data are permissive but not conclusive, and if it existed, its tenure was fleeting. Irrespective of whether Pannotia qualifies for supercontinent status, an over-arching question is whether the thermal legacy of its amalgamation influenced early Paleozoic global-scale mantle convection patterns. If so, this thermal legacy would have first-order implications for models of Pangea assembly and should be recognizable in proxy signals of deep mantle convection patterns beneath Pannotia as it amalgamated. Over the next five years, I plan to investigate Pannotia's thermal legacy in the context of rival geodynamic models purported to explain the relationship between the amalgamation of supercontinents and deep mantle convection patterns. This research will involve detailed fieldwork by myself, my HQP and international colleagues that will focus on specific igneous complexes in selected areas (e.g. Mexico, Atlantic Canada, Iberia, Bohemia) along the Laurentian-western Gondwanan and northern Gondwanan margins. Field work will be complemented by a range of petrological, geochemical and isotopic (U-Th-Pb; Hf, Nd, Sr, Pb, Os and O) analyses of strategically collected samples. The geodynamic models under investigation provide contrasting predictions for the locations of zones of mantle upwelling (respectively beneath Laurentia and Gondwana) that can be tested against the geological record. Deep mantle plumes are preferentially produced along the edges of such upwellings and rise towards the surface carrying geochemical and isotopic fingerprints that reveal their deep mantle roots. Rival models predict their occurrence in mafic igneous complexes along the margins of Laurentia and Gondwana, respectively. As far as I am aware, this combined field and geochemical approach of investigating geodynamic models to determine the thermal legacy of a putative supercontinent has not been employed before. If dramatic changes in mantle convection patterns accompanying Pannotia amalgamation have a measurable effect on the lithosphere, they would provide new insights into the processes responsible for major tectonic events such as the opening of new oceans in the Early Paleozoic, dramatic changes in global sea-level, climate and seawater chemistry and profound evolutionary events in the biosphere.

盘古大陆只是数十亿年来贯穿地球历史的一系列超级大陆中最近的一个。超大陆合并和分裂（超大陆周期）的幕式重现对地球的地质，气候和生命产生了深远的影响，但对负责的过程知之甚少。例如，我们首先知道盘古大陆形成的时间和地点，但不知道为什么。最有争议的超级大陆是Pannotia，它的存在是有争议的。Pannotia被认为形成于约6亿年前，由古大陆冈瓦纳，劳伦蒂亚，波罗的海和西伯利亚组成。现有的数据是允许的，但不是决定性的，如果它存在，它的任期是短暂的。不管Pannotia是否符合超大陆的地位，一个过度争论的问题是它的合并的热遗产是否影响了早古生代全球尺度的地幔对流模式。如果是这样的话，这种热遗产将有一阶的泛古陆组装模型的影响，并应在Pannotia下，因为它合并深地幔对流模式的代理信号识别。 在接下来的五年里，我计划在竞争对手的地球动力学模型的背景下，研究Pannotia的热遗产，这些模型旨在解释超大陆合并与深部地幔对流模式之间的关系。这项研究将涉及详细的实地工作，由我自己，我的HQP和国际同事，将集中在特定的火成岩复杂的选定地区（如墨西哥，大西洋加拿大，伊比利亚，波希米亚）沿着劳伦特-西冈瓦纳和北方冈瓦纳边缘。对战略性采集的样品进行一系列岩石学、地球化学和同位素（U-Th-Pb; Hf、Nd、Sr、Pb、Os和O）分析，以补充现场工作。 正在调查中的地球动力学模型提供了地幔上涌区（分别在劳伦提斯和冈瓦纳之下）的位置的对比预测，可以根据地质记录进行测试。深地幔柱优先产生沿着这种隆起的边缘，并上升到表面携带地球化学和同位素指纹，揭示他们的深地幔根。竞争对手的模型预测，它们的出现在镁铁质火成岩复合体沿着边缘的劳伦和冈瓦纳，分别。据我所知，这种结合野外和地球化学的方法来研究地球动力学模型，以确定一个假定的超大陆的热遗产，以前还没有被采用过。 如果地幔对流模式的剧烈变化伴随Pannotia合并对岩石圈有可测量的影响，他们将提供新的见解负责重大构造事件的过程，如在早古生代新海洋的开放，全球海平面，气候和海水化学的剧烈变化和深刻的进化事件在生物圈。