基础地球科学专家谘询纪录表.doc

基礎地球科學專家諮詢紀錄表 諮詢主題：基礎地球科學相關專業問題 二 諮詢時間：95.9.25、95.9.26、95.9.30、95.10.12 方式：電子郵件 專 家 學 者 姓名 林慧玲 服務單位 國立中山大學 主要內容 主要問題 補充說明層狀鐵礦相關形成因子 具體建議與意見 經過四次諮詢討論，具體內容整理如下： few things need to be clarified first.? 1 the dissolubility of iron is controlled by the pH and Eh of ocean water, but not oxygen concentrations.? of course, Eh is related to O2 conc.lower pH and Eh - higher solubility of iron in form of Fe +2 higher pH and Eh - lower solubility of iron in form of Fe +3 ? 2 the pH and Eh value was mainly controlled by the degassing of the Earth in early time. and it varied and not always kept a constant value. 首先，必須先澄清幾件事情： 1. 鐵的溶解度是受海水的pH值及氧化還原電位控制，而不是氧的濃度。 雖然氧化還原電位也是和氧的濃度有關。較低的pH值和氧化還原電位 會使鐵有較高的溶解度，而以Fe+2存在，而較高的pH值和氧化還原電位則會使鐵有較低的溶解度，而以Fe+3形式存在。 2. pH值和氧化還原電位在早期主要是受地球的除氣作用控制，而且是一直 變動的狀態，而不是固定的值。 ok, here is the story.in late Archean time, the degassing volcanic activity was still severe.so, the atmosphere was dominated with CO2 and H2O , and pH and Eh were very low, ie. ocean was very acidic and reducing. iron metal become soluble and can migrate from onland into ocean.? somehow the volcanic activity became relative quiet, the pH and Eh varied and may become higher. so, some oversaturated dissolved Fe +2 in seawater could become Fe +3 oxidized and precipitate as iron deposits. 以下是故事的開始： 在太古代晚期，除氣作用 火山活動 是很劇烈的。因此，大氣中的組成是以二氧化碳和水氣為主，而pH值和氧化還原電位是低的，也就是說當時的海水是非常酸且還原的環境。金屬鐵變得可溶解，並可從陸地搬運到海洋中。而當火山活動轉為寂靜時，pH值和氧化還原電位一直變動而且可能變的更高，而使海水中的過飽和的溶解態鐵離子變成三價鐵 氧化作用 ，並形成鐵沉澱。 so, why BIF occurred only in Archean and early Proterozoic? 為何BIF只在太古代及原生代發生？ first all, we need a very acidic environment to dissolve the iron from silicates and make it able to migrate into ocean and enrich the iron conc somehow.then, need to change the environments of pH and Eh values to precipitate oxidize the iron become a deposit. and repeat it again, then can deposit thick BIF layersuntil the ocean no more acid and reducing enough to dissolve iron in Proterozoic.?so, actually BI