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Chemical and oxygen isotope behavior of deep sea sediments during diageneti clay mineral formation

成岩粘土矿物形成过程中深海沉积物的化学和氧同位素行为

基本信息

批准号：
07640660
负责人：
NAKAYA Harue
金额：
$ 1.41万
依托单位：
OSAKA CITY UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

项目摘要

The project was planned to estimate the diagenetic temperature of sediments, because we have not had good geothermometers at low temperatures to interpret the thermal history in the shallow crust.First, authigenic mineral formation mechanism and its related chemical behavior during early stage of diagenesis was precisely studied. The natural authigenic minerals (clay minerals and zeolites), obtained from the 1300 m sediment column in the Nankai trough, were mineralogically and chemically studied mainly by a transmission electron microscope and analytical electron microscope. The mechamism of clay mineral formation was mainly dissolution-precipitation even at the diagenetic condition. The authigenic mineral assemblages were different from the volcanic ash layrs (zeolites were formed) and shales (illite and illite/smectite mixed layred clay minerals were formed) in the same sediment column. Chemical composition of the authigenic smectite would be useful for the geothermometer, however, the mineral assemblage is not useful for estimation of diagenetic temperature.The fractionation factors of oxygen isotope ratios were tried to determine by the two different approaches ; one was the measurement of oxygen isotope ratios of authigenic clay mineral, same as used for the study of formation mechanism. The oxygen isotope ratios of separated authigenic clay minerals vary with increasing depths (equal to the temperature), and it is useful for low temperature geothermometer. The other was laboratory experiment of oxygen isotope exchange of water-clay minerals at hydrothermal condition. Two sets of hydrothermal reaction bombs were designed, and used to determine the oxygen isotope fractionation factors between illite-water at the temperature lower than 200ﾟC.The bombs were worked well at the temperature lower tham 300ﾟC under the hydrostatic conditions. Artificial and natural illite samples were selected for the exchange experiments of oxygen isotopes between illite and water.

本项目的目的是估算沉积物的成岩温度，因为我们还没有很好的低温地质温度计来解释地壳浅部的热历史。首先，精确地研究了成岩作用早期自生矿物的形成机制及其相关的化学行为。利用透射电子显微镜和分析电子显微镜对南海海槽1300 m沉积柱中的天然自生矿物（粘土矿物和沸石）进行了矿物学和化学研究。即使在成岩条件下，粘土矿物的形成机制仍以溶解-沉淀为主。自生矿物组合不同于同一沉积柱中的火山灰层（形成沸石）和页岩（形成伊利石和伊蒙混合层状粘土矿物）。自生蒙皂石的化学成分可用于地质温度计，但矿物组合不能用于成岩温度的估算。本文尝试用两种不同的方法确定氧同位素比值的分馏因子，一种是测定自生粘土矿物的氧同位素比值，这与研究形成机制的方法相同。分离的自生粘土矿物的氧同位素比值随深度（等于温度）的增加而变化，这对低温地质温度计是有用的。另一个是室内热液条件下水-粘土矿物氧同位素交换实验。设计了两套水热反应弹，用于测定温度低于200 ℃的伊利石-水之间的氧同位素分馏因子，在静水条件下，反应弹在温度低于300 ℃时工作良好。选取人工和天然伊利石样品进行了伊利石与水的氧同位素交换实验。