Rare Earth Element and Isotopic Studies of Precambrian Chemical Sediments

本文研究了元古代和太古代化学沉积物中Nd、Sr同位素组成的变化及稀土元素丰度模式。其目的是追踪元古宙外生地球化学旋回中的主要物质通量，并了解这一时期沉积储层、海洋和大气的演化关系。我们将重点研究元古代海洋沉积物样品的Nd和Sr同位素变化和REE丰度模式。提出了以下具体项目：1)确定元古代碳酸盐岩和页岩中143Nd/144Nd的变化；2)确定- 0.8 ~ 3.5 Ga年龄的条带状铁地层的稀土元素模式；3) 3.5 Ga外生地球化学旋回的Sr和Nd同位素记录模拟，强调元古代；4)利用加拿大维多利亚岛（nw.t）和澳大利亚各沉积盆地的样品，扩展了中寒武纪至- 2.0 Ga前碳酸盐的高精度Sr同位素数据记录。我们建议建立一个详细的、精确的记录在0.5 - 2.0 Ga之间的化学沉积物的Sr和Nd同位素变化。在元古代，海水Nd和Sr的收支似乎从主要的热液输入（如太古宙）转变为主要的大陆（河流）输入。该研究获得的数据将用于约束热液环流速率、大陆侵蚀速率和元古代大陆侵蚀产物平均年龄的变化。

This research is on variations in the Nd and Sr isotopic composition and REE abundance patterns in Proterozoic and Archean chemical sediments. It's purpose is to trace the major mass fluxes in the exogenic geochemical cycle through the Proterozoic and to understand the relationship between the evolution of the sedimentary reservoir, the oceans and the atmosphere during this time period. We will concentrate on measurements of Nd and Sr isotope variations and REE abundance patterns on samples of Proterozoic marine sediments. The following specific projects are proposed: 1) Determine 143Nd/144Nd variations in Proterozoic carbonates and shales.; 2) Determine REE patterns of banded iron formations ranging in age from - 0.8 Ga to 3.5 Ga.; 3) Modeling of the Sr and Nd isotope records of the exogenic geochemical cycle through the past 3.5 Ga, emphasizing the Proterozoic.; and 4) Extend the record of high precision Sr isotopic data of carbonates from the mid-Cambrian to - 2.0 Ga ago, using well dated and documented samples from Victoria Island (N.W.T., Canada), and various sedimentary basins in Australia. We propose to establish a detailed, precise record of Sr and Nd isotopic variations of chemical sediments for the time between 0.5 and 2.0 Ga ago. During the Proterozoic, seawater Nd and Sr budgets appear to have changed from dominantly hydrothermal inputs (as in the Archean) to dominantly continental (river) inputs. Data obtained from this research will be used to constrain the changes in rates of hydrothermal circulation, continental erosion rates and variations in the mean age of continental erosion products through the Proterozoic.