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: 2021
• 资助国家: 加拿大
• 起止时间: 2021-01-01 至 2022-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=739525
• 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.

盘古大陆只是一系列超级大陆中最近的一个，这些超级大陆贯穿了地球几十亿年的历史。间断性的超大陆合并和分裂（超大陆旋回）对地球的地质、气候和生命产生了深远的影响，但人们对其过程知之甚少。例如，我们只知道盘古大陆形成的时间和地点，却不知道原因。超级大陆假说中最具争议的是潘诺提亚，它的存在与否一直存在争议。Pannotia被认为形成于6亿年前，由古冈瓦纳大陆、劳伦西亚大陆、波罗的海大陆和可能的西伯利亚大陆组成。现有的数据是允许的，但不是决定性的，即使它存在，它的任期也很短暂。不管Pannotia是否符合超大陆的地位，一个首要的问题是，它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，这种热遗产将对泛大陆组合模式具有一级意义，并且应该在Pannotia合并时的深部地幔对流模式的替代信号中被识别出来。在接下来的五年里，我计划在不同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。这项研究将包括我自己、我的HQP和国际同事详细的实地调查，重点关注沿着劳伦蒂亚-冈瓦南西部和冈瓦南北部边缘的选定地区（如墨西哥、加拿大大西洋、伊比利亚、波西米亚）的特定火成岩复合体。实地工作将辅以一系列岩石学、地球化学和同位素（U-Th-Pb、Hf、Nd、Sr、Pb、Os和O）分析战略收集的样品。正在研究的地球动力学模型提供了对地幔上升流带位置的对比预测（分别在劳伦西亚和冈瓦纳之下），这些预测可以根据地质记录进行测试。深地幔柱优先沿着这些上升流的边缘产生，并向地表上升，携带地球化学和同位素指纹，揭示它们的深地幔根源。相对应的模型预测它们分别出现在劳伦西亚和冈瓦纳边缘的基性火成岩复合体中。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。如果伴随Pannotia合并的地幔对流模式的剧烈变化对岩石圈具有可测量的影响，那么它们将为研究早期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以及生物圈的深刻进化事件等重大构造事件的过程提供新的见解。