Tracing the emergence and evolution of Continental Crust in the Archean–Proterozoic using in-situ B isotopic analysis of Oceanic deposits

利用大洋矿床原位 B 同位素分析追踪太古代元古代大陆地壳的出现和演化

• 批准号: 539548092
• 负责人: Dr. Avishai Abbo
• 金额: --
• 依托单位: Abteilung Petrologie und Geochemie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/539548092?language=en
• 关键词: Tracing; emergence; evolution; Continental; Crust

The growth and accumulation of continental crust on Earth through time is a contested topic in Earth Science research, with implications on the onset of modern-style plate tectonics and its operation over different periods of the geologic record. Tracing crustal growth in the Early Earth from the fragments of preserved Archean-Proterozoic crust may carry biases related to preservation and difficulty in establishing a global regime from local or regional datasets, while in large global datasets it is nearly impossible to account for the equal validity and/or significance of every single point. Here I propose to trace the accumulation of continental crust on Earth, and specifically its exposure and emergence above sea-level, by monitoring boron isotopes in Archean-Proterozoic oceanic deposits – cherts and Iron Formations (IFs). Boron in the oceanic system is sourced mostly from continental erosion and consumed mainly through alteration of oceanic crust. Processes of continental crustal buildup and exposure will bear impact on the oceanic composition, which will in turn be preserved in the marine sediments I will analyze. As boron behaves conservatively and is completely mixed in seawater over ca. 10^3 years, the boron signal recorded in chemical oceanic deposits is a good indication of the global regime. Cherts and IFs are chemical marine deposits, precipitated directly from seawater, thus serving as an archive of oceanic chemistry. In the absence of exposed continental crust above sea-level, the ocean is expected to have a very low boron concentration in equilibrium with the oceanic crust or mantle. With increasing exposure and continental emergence, boron concentrations and isotopic composition of the ocean are expected to slowly approach modern values. Accounting for the different fractionation factors between seawater and silica/Fe-oxide, my new data will enable to establish oceanic boron elemental and isotopic evolution curves for the Archean-Proterozoic. Time dependent modelling accounting for the different boron inputs and outputs to and from the ocean should allow me to quantify the best fitting set of conditions, rising from obtained data, as for the extent of continental emergence, its timing, and the interplay between continental buildup and oceanic crust production through time. The proposed study will therefore tackle the question of crustal growth through time in a novel, revolutionary and underexplored fashion, and will provide a significant contribution to the study of crustal evolution, the onset of plate tectonics, and boron isotopes in the oceanic environment.

大陆地壳随时间的增长和积累是地球科学研究中一个有争议的话题，它对现代板块构造的开始及其在地质记录的不同时期的运作有影响。从保存的太古代-元古代地壳碎片中追踪早期地球的地壳生长可能会带来与保存有关的偏见，并且难以从局部或区域数据集建立全球制度，而在大型全球数据集中，几乎不可能解释每个点的同等有效性和/或重要性。在这里，我建议跟踪地球上的大陆地壳的积累，特别是其暴露和海平面以上的出现，通过监测硼同位素在太古代元古代海洋矿床-硅质岩和铁的形成（IF）。大洋系统中的硼主要来源于大陆侵蚀，而主要通过洋壳蚀变作用消耗。大陆地壳的形成和暴露过程将对海洋成分产生影响，而海洋成分又将保存在我将要分析的海洋沉积物中。由于硼的行为是保守的，在大约1000年以上的海水中是完全混合的。10^3年，化学海洋沉积物中记录的硼信号是全球机制的良好指示。燧石和IFs是海洋化学沉积物，直接从海水中沉淀出来，因此可以作为海洋化学的档案。在海平面以上没有暴露的大陆地壳的情况下，预计海洋中与海洋地壳或地幔平衡的硼浓度很低。随着暴露的增加和大陆的出现，预计海洋的硼浓度和同位素组成将慢慢接近现代值。考虑到海水和二氧化硅/铁氧化物之间的不同分馏因子，我的新数据将能够建立太古代-元古代的海洋硼元素和同位素演化曲线。考虑到不同的硼输入和输出的时间依赖性模型，从海洋应该让我量化的最佳拟合的条件，从获得的数据上升，大陆出现的程度，它的时间，以及大陆建设和海洋地壳生产之间的相互作用，通过时间。因此，拟议的研究将以一种新颖的、革命性的和探索不足的方式解决地壳随时间增长的问题，并将为研究地壳演化、板块构造的开始和海洋环境中的硼同位素作出重大贡献。