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中文期刊篇目索引

摘要

本篇出處 中國地質學會會刊 41:2 民87.05 頁185-197
篇名 The Ages from Rb-Sr Mineral Isochrons in the Slow Cooling Rocks
作者 陳中華 ; 藍晶瑩 ; 沈君山
中文摘要        在緩慢冷卻的岩石中,礦物的冷卻封存年齡可以應用銣-鍶同位素定年系統來求得 。理論上在定年系統中連接任兩個不同銣╱鍶比例的礦物等時線,就可求得一種年齡,然而 這些年齡並非所有都有其地質意義,其原因為在冷卻過程中,礦物間並非達到完全平衡。因 此本文建立一模式來探討這些礦物等時線所代表的意義。 1. 從第一個達到封存溫度的礦物與全岩間的等時線,可以得到此礦物的正確封存年齡。 如 果此封存溫度與岩石形成溫度接近時,此礦物封存年齡與岩石形成年齡將十分接近。 2. 無法求得正確封存年齡時,由礦物與全岩間的等時線,所求得的年齡, 將是該礦物最接 近的封存年齡。當(銣╱鍶)礦物>(銣╱鍶)全岩,所求得的年齡為該礦物封存年齡的上 限。反之當(銣╱鍶)礦物<(銣╱鍶)全岩,則求得年齡為該礦物封存年齡的下限。 3. 任何一個後來達到封存溫度礦物與第一個達到封存溫度礦物所連成的等時線, 而求得的 年齡,與該礦物封存年齡,可能會有明顯誤差。
英文摘要        In the Rb-Sr dating system, ages are calculated from tie lines connecting two minerals with different Rb/Sr ratios in slow cooling rocks. However, not all of these ages have geological significance since complete isotopic equilibrium is often not achieved in the cooling history. It may be asked how we can obtain the exact or approximate closure ages for minerals in the Rb-Sr dating system. Based on discussions from both graphical and mathematical models, some criteria are suggested: 1. The exact closure temperature age is obtained from the slope of the tie line between whole rock and the first mineral to close. Moreover, if the closure temperature of the first mineral to close is very near the emplacement temperature of rock, the closure temperature age of the first mineral to close should be close to the emplacement age of the plutonic rock. 2.The ages obtained connecting the minerals and the whole rock should be regarded as the best estimations for the closure temperature ages of these minerals. Moreover, the estimated ages shall be considered as the upper limit of the age of closure temperature for that mineral when (Rb/Sr) >(Rb/Sr) and the lower limit of the age for that mineral when (Rb/Sr) < (Rb/Sr). 3. Some errors in the closure temperature age may possibly occur if the age is from the tie line connecting the mineral and the first mineral to close, especially, when the mineral of late closure has a much higher Rb/Sr ratio than that of the first mineral to close.