Seawater 187Os/186Os Variation Over Time

187 Re是一种放射性同位素，衰变速度为半- 寿命约4.6x1010年至187 Os。 第187章A 这取决于该系统的年龄， 187 Os/186 Os比率和187 Re/186 Os（使用186 Os时 作为非放射性锇示踪剂）。 大陆 地壳的~（187）Re/~（186）Os比地幔高100倍左右 所以平均大陆地壳的187 Os/186 Os 平均年龄约200亿年， 而直接来自地幔的锇 值约为1。 海水~（187）Os/~（186）Os为8.5， 现在流入大海的锇有80%来自 20%来自大陆，20%来自海洋地幔。 预计这一来源比例将随着时间的推移而变化， 海洋87 Sr/86 Sr记录。 含氢部分 氧化深海沉积物和富含有机物的还原 地层年代系统的沉积物可以提供 过去海水187 Os/186 Os的记录。 巨型活塞 来自北太平洋中部的“岩心”（LL GPC-3）和材料 从DSDP和ODP核心是现成的来源的研究。 涉及氢的浸出的程序 使用稀过氧化氢的氧化核的部分 已经被开发出来了。 初步结果显示， 与海洋97 Sr/86 Sr记录的有序相关 这表明，大陆和 洋幔源影响这两种元素。 强加于此 影响是87 Sr/86 Sr和 晚更新世的~（187）Os/~（186）Os指示不同的 这两种元素的来源。 我们将全面探索 187 Os/186 Os海水记录在过去1亿年中， 将其与已知的87 Sr/86 Sr记录进行比较，从而 增加了我们对两个人之间关系的理解 不同的同位素标记， 蚀变和风化作用。

187Re is a radioactive isotope that decays with a half- life of about 4.6x1010 years to 187Os. The 187Os of a system depends on the age of that system, the initial 187Os/186Os ratio and the 187Re/186Os (where 186Os is used as the non-radiogenic osmium tracer). The continental crust has 187Re/186Os about 100 times higher than the mantle so that the 187Os/186Os of the average continental crust with a mean age of about 20 billion years is about 10.5 whereas osmium immediately derived from the mantle has a value of about 1. The seawater 187Os/186Os of 8.5 implies that 80% of the present-day osmium supplied to the sea comes from the continents and 20% from oceanic mantle sources. This ratio of sources is expected to vary over time based on the marine 87Sr/86Sr record. The hydrogenous fraction of oxidized deep-sea sediments and organic-rich reduced deposits from stratigraphically dated systems can provide records of past seawater 187Os/186Os. The "giant piston core" from the central North pacific (LL GPC-3) and material from DSDP and ODP cores are ready sources for the study. The procedures involving leaching of the hydrogenous fraction of oxidized cores using dilute hydrogen peroxide have been developed. Preliminary results shows a first order correlation with the marine 97Sr/86Sr record indicating that the relative roles of continental and oceanic mantle source affect both elements. Imposed on this effect is the inverse relationship between 87Sr/86Sr and 187Os/186Os in the latest Pleistocene indicating different sources for the two elements. We will explore the full 187Os/186Os seawater record over the past 100 million years, compare it with the known 87Sr/86Sr record and thereby to add to our understanding of the relationship of two different isotopic signatures to the geologic record of alteration and weathering.