THERMODYNAMIC PROPERTIES OF ESR SIGNALS OF DEEP-SEA CARBONATE
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摘要:
ESR测年方法的年代范围可以从数百年到几百万年,但在较老的深海碳酸盐岩测年研究中,ESR测年信号的平均寿命较短,其年龄极限受到质疑。利用较老的深海碳酸盐岩进行了ESR测年信号的热力学特征研究,同时估算了深海碳酸盐岩的平均寿命。研究结果表明:单一级热动力学模式不适于深海碳酸盐岩样品的平均寿命估算,而双一级动力学模式是一种较好的估算方法。经估算,深海碳酸盐岩试样的平均寿命为5.14 Ma,年龄为320±50 ka,与铀系不平衡法测得的365±49 ka具有较好的一致性。
Abstract:The ESR dating method could date the samples within a time span from hundreds of years to millions of years. However, the average lifetime of ESR signals from deep-sea carbonate rocks are relatively shorter. In this regard, the age limit of the deep-sea carbonate rocks dating need to be further studied. In this paper, we studied the thermodynamic characteristics of ESR dating signals acquired from old deep-sea carbonate rocks and the average lifetime of those deep-sea carbonate rocks is estimated. The results of the thermodynamic properties of deep-sea carbonate suggests that the single first-order kinetic equation might not be suitable to calculate the average lifetime, and the double first-order kinetic equation is more effective. The average lifetime of the deep-sea samples we calculated is about 5.14×106 years by using the double first-order kinetic equation. Thus the estimated age is 320±50 ka, which is in good agreement with the unbalanced U system dating result of 365±49 ka.
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Key words:
- ESR dating /
- deep-sea carbonate /
- thermodynamic properties /
- average lifetime
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表 1 生物灰岩样品ESR测年信号的测量结果
Table 1. The measured ESR signal of the carbonate
次数 1 2 3 4 5 6 平均值 RSD/% ESR信号/(a.u.) 9 368 000 9 280 000 9 361 000 9 298 000 9 182 000 9 191 000 9 280 000 0.87 表 2 样品的等温退火实验结果
Table 2. The results of isothermal annealing experiments
时间/min ESR信号强度(a.u.) 100 ℃ 150 ℃ 200 ℃ 230 ℃ 250 ℃ 280 ℃ 0 9 280 000 9 280 000 9 280 000 920 000 9 280 000 9 280 000 5 9 468 000 9 556 000 9 476 000 8 312 000 7 512 000 4 936 000 10 9 186 000 9 208 000 9 092 000 6 806 000 5 616 000 1 207 000 20 8 765 000 8 615 000 8 217 000 5 726 000 4 006 000 320 100 30 8 809 000 8 567 000 7 962 000 4 969 000 2 696 000 188 000 40 8 762 000 8 631 000 7 832 000 4 306 000 1 987 000 99 750 60 8 786 000 8 536 000 7 712 000 90 8 709 010 8 503 000 表 3 样品各温度下平均寿命的回归计算结果
Table 3. The calculated average life of sample at different temperature
温度/ ℃ 回归公式 平均寿命/min 相关系数 200 N=9 248 670exp(-3.73×10-3t) 268 0.833 230 N=8 797 690exp(-1.90×10-2t) 52.5 0.970 250 N=8 797 690exp(-3.86×10-2t) 25.9 0.993 280 N=6 168 710exp(-1.15×10-1t) 8.73 0.929 表 5 各温度下平均寿命的回归计算结果
Table 5. The calculated average life at different temperature
温度/℃ 回归公式Ⅰ段 平均寿命/min 回归公式Ⅱ段 平均寿命/min 200 N=9 969 090exp(-9.59×10-3t) 104 N=8 186 520exp(-1.02×10-3t) 980 230 N=9 065 620exp(-2.38×10-2t) 42.0 N=11 270exp(-1.43×10-2t) 69.9 250 N=9 407 330exp(-5.03×10-2t) 19.9 N=9 590exp(-3.51×10-2t) 28.5 280 N=9 587 780exp(-1.75×10-1t) 5.70 N=10 100exp(-5.83×10-2t) 17.2 表 6 样品20 ℃时平均寿命的回归计算结果
Table 6. The calculated average life of sample at 20 ℃
ESR信号 回归方程 τ/a CO2- τ-1=4.45×1012exp(-1.95×104/T) 5.14×106 PO22- τ-1=2.60exp(-5.89×103/T) 3.86×10-1 表 7 230Th/234U/238U测年结果
Table 7. 230Th/234U/238U dating results
/Ka 样品 U/×10-6 234U/238U 230Th/234U 230Th 生物灰岩 10.599± 0.233 1.006± 0.017 0.967± 0.018 364.5± 49 测年结果由中科院地球与地质研究所提供 表 8 ESR测年结果
Table 8. 8 ESR dating results
样品编号 U /×10-6 Th /×10-6 K2O /% 累积剂量TD/Gy 平均年龄/ka 生物灰岩 10.5 0.219 0.209 1 899.0 320 -
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