The Assembly Of Pannotia: Implications for the Origin of Supercontinents

盘古大陆只是数十亿年来打断地球历史的一系列超级大陆中最新的一个。超大陆合并和解体(超大陆旋回)的间歇性重复已经对地球的地质、气候和生命产生了深远的影响，但人们对其产生的过程知之甚少。例如，我们第一次知道了盘古大陆形成的地点和时间，但不知道为什么。在假想的超级大陆中，最具争议的是潘诺尼娜，她的存在本身也受到了争议。潘诺塔岛被认为形成于约6亿年前，由冈瓦那大陆、劳伦西亚大陆、波罗的海大陆和可能的西伯利亚大陆组成。可获得的数据是允许的，但不是决定性的，如果它存在的话，它的任期是短暂的。不管潘诺塔岛是否有资格成为超大陆，一个最重要的问题是，它合并的热遗产是否影响了早古生代全球范围的地幔对流模式。如果是这样的话，这一热遗迹将对盘古大陆组装模型产生一级影响，并应可在潘诺塔岛下深部地幔对流模式的代理信号中识别出来。 在接下来的五年里，我计划在与之竞争的地球动力学模型的背景下，研究潘诺塔的热遗产，这些模型旨在解释超级大陆的融合和深部地幔对流模式之间的关系。这项研究将涉及我、我的总部律师和国际同事的详细实地工作，重点是沿劳伦西亚-西冈德瓦南和北冈德瓦南边缘选定地区(如墨西哥、大西洋加拿大、伊比利亚、波希米亚)的特定火成岩杂岩。除了实地工作外，还将对战略收集的样品进行一系列岩石学、地球化学性质和同位素(U-Th-Pb；Hf、Nd、Sr、Pb、Os和O)分析。 正在调查的地球动力学模型对地幔上升区(分别位于劳伦蒂亚区和冈瓦纳区下方)的位置提供了对比的预测，可以根据地质记录进行检验。深部地幔热柱优先沿着这种上升流的边缘产生，并向地表上升，携带着揭示其深部地幔根的地球化学和同位素指纹。相互竞争的模型预测，它们分别出现在劳伦蒂亚和冈瓦那边缘的镁铁质火成岩中。据我所知，这种研究地球动力学模型以确定假定的超大陆的热遗留问题的现场和地球化学相结合的方法以前从未被采用过。 如果伴随着潘诺塔合并而来的地幔对流模式的戏剧性变化对岩石圈产生了可测量的影响，它们将为导致重大构造事件的过程提供新的见解，例如早古生代新海洋的开放，全球海平面、气候和海水化学的戏剧性变化，以及生物圈深刻的演化事件。

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.