Non-detrital Gallium and Aluminum in Early Precambrian Marine Chemical Sediments and the Potential Use of the Ga/Al Ratio as a Geochemical Proxy for Metal Sources and Relative Fluxes to the Early Ocean

在拟议的项目“早期前寒武纪海洋化学沉积物中的非碎屑镓和铝以及Ga/Al比率作为金属来源和早期海洋相对通量的地球化学代用指标的潜在用途”中，研究将侧重于微量元素镓（Ga）及其地球化学相似的“假同位素”铝（Al）。虽然这两种金属在火成岩和碎屑沉积岩中的结合相当紧密，但它们在天然沃茨中，如河水、海水和热液中可能会相互分离。因此，Ga/Al比值从大陆岩石通过河水到海水大幅增加。然而，最高的Ga/Al比值是海洋高温热液流体的特征。假设这种系统关系在早前寒武纪海洋中是相同的，那么地质档案中的Ga/Al比值，如前寒武纪海洋化学沉积岩（例如，带状铁地层，硅质岩，石灰岩和白云岩）应该是这些金属的来源和相对通量的环境前寒武纪海水的地球化学代用品。因此，Ga-Al系统学可以用来验证其他地球化学指标如稀土元素（REE）和Ge-Si关系的结果。在拟议的项目中，重点将是地质特征明确的海洋化学沉积物中超纯（即无碎屑）样品的镓铝分布，将与侧重于同位素替代物的研究小组密切合作进行研究。虽然样品集，来自沉积年龄从3.8到0.6 Ga的沉积岩将提供信息的海水的Ga-Al系统的演变，通过时间，同期沉积的样品，但在不同的位置确定的数据将提供信息的Ga/Al比在地球早期的海洋的空间异质性。这不仅将扩大我们对早期地球表面系统中金属来源和通量的了解，而且还将提高我们对其他地球化学代理的潜力和局限性的理解。

In the proposed project "Non-detrital Gallium and Aluminum in Early Precambrian Marine Chemical Sediments and the Potential Use of the Ga/Al Ratio as a Geochemical Proxy for Metal Sources and Relative Fluxes to the Early Ocean" research will focus on the trace element gallium (Ga) and its geochemically similar „pseudo-isotope“ aluminium (Al). While these two metals are rather closely coupled in igneous and clastic sedimentary rocks, they may be fractionated from each other in natural waters, such as river water, seawater and hydrothermal fluids. Hence, Ga/Al ratios increase substantially from continental rocks via river water to seawater. Highest Ga/Al ratios, however, characterize marine high-temperature hydrothermal fluids. Assuming this systematic relationship was the same in the Early Precambrian oceans, the Ga/Al ratio in geoarchives such as Precambrian marine chemical sedimentary rocks (e.g., banded iron formations, cherts, lime- and dolostones) should be a geochemical proxy for the sources and relative fluxes of these metals to ambient Precambrian seawater. Hence, Ga-Al systematics may be used to verify the results derived from other geochemical proxies such as rare earth elements (REE) and Ge-Si relationships. In the proposed project, the focus will be on the Ga-Al distribution in ultrapure (i.e. detritus-free) samples from geologically well-characterized marine chemical sediments which will be studied in close collaboration with research groups which focus on isotope proxies. While sample sets that originate from sedimentary rocks with depositional ages from 3.8 to 0.6 Ga will provide information on the evolution of the Ga-Al systematics of seawater through time, data determined for samples deposited contemporaneously but at different locations will provide information on the spatial heterogeneity of the Ga/Al ratios in the Early Earth’s oceans. This will not only expand our knowledge of metal sources and fluxes in the Early Earth’s surface system, but will also improve our understanding of the potential and the limits of other geochemical proxies.