Argon diffusion in pyroxenes: Implications for thermochronometry and mantle degassing
Argon diffusion in pyroxenes: Implications for thermochronometry and mantle degassing
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DOI：
10.1016/j.epsl.2011.02.019
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发表时间：
2011-04-15
影响因子：
5.3
通讯作者：
Shuster, David L.
中科院分区：
文献类型：
--
作者：
Cassata, William S.;Renne, Paul R.;Shuster, David L.
氩在辉石中扩散的速率与地球和行星科学中的几个问题有关。辉石是地球上地幔中最丰富的矿物之一，是钾和放射成因Ar-40（Ar-40*）的重要寄主。此外，辉石通常含有陨石中总Ar-40* 的25%以上，因此在量化陨石及其母体经历的事件的时间，持续时间和热条件方面具有很大的潜力。我们进行了详细的，反馈控制的激光加热扩散实验，使用合成产生的Ar-37宝石级单斜辉石（CPX）和斜方辉石（OPX）晶体。在850和1350摄氏度之间的逐步加热产生线性阿耳忒弥斯阵列，其中活化能（E-a）为379.2 +/- 4.1和371.0 +/- 6.0 kJ/mol，指前因子（D-o）为（1.36 x 10（-4））+1.12 x 10（-4）-6.15 x 10（-5）和CPX和OPX的平均浓度分别为（5.73 × 10（-2））+3.72 × 10（-2）-2.25 × 10（-2）;这些E-a比以前报道的用不同实验方法获得的值高一个数量级（沃森等人，2007），并表明辉石中的Ar扩散是强烈的温度依赖性。在高温下，Ar在辉石中的扩散是迅速的，这表明在陨石辉石中观察到的扩散Ar-40分布可能提供有关简短的高温冲击加热事件的信息。相反，随后的低T条件应最小限度地影响这些浓度梯度。OPX和CPX中的实验Ar扩散动力学分别对应于600-700和700-800摄氏度的闭合温度（对于10摄氏度/Ma冷却）。这些结果表明，通过0.1-0.5毫米的辉石颗粒扩散平衡发生在几分钟到几个小时的玄武岩熔体生成温度（类似于1300摄氏度），因此不太可能抑制地幔脱气。(C)2011爱思唯尔有限公司版权所有。
The rate at which argon diffuses in pyroxenes is relevant to several problems in the Earth and planetary sciences. Pyroxenes are among the most abundant minerals in the Earth's upper mantle and are important hosts for potassium and radiogenic Ar-40 (Ar-40*). Additionally, pyroxenes commonly contain >25% of the total Ar-40* within meteorites, and therefore hold great potential for quantifying the timing, duration, and thermal conditions of events experienced by meteorites and their parent bodies. We conducted detailed, feedback-controlled laser heating diffusion experiments using synthetically produced Ar-37 in gem-quality clinopyroxene (CPX) and orthopyroxene (OPX) crystals. Stepwise heating between 850 and 1350 degrees C yielded linear Arrhenius arrays from which activation energies (E-a) of 379.2 +/- 4.1 and 371.0 +/- 6.0 kJ/mol and pre-exponential factors (D-o) of (1.36 x 10(-4))+1.12 x 10(-4) -6.15 x 10(-5) and (5.73 x 10(-2)) +3.72 x 10(-2) -2.25 x 10(-2) were determined for CPX and OPX, respectively; these E-a's are an order of magnitude higher than previously reported values obtained with a different experimental approach (Watson et al., 2007) and indicate that Ar diffusion within pyroxenes is strongly temperature dependent. At high temperatures Ar diffusion in pyroxenes is rapid, which indicates that diffusive Ar-40 distributions observed within meteoritic pyroxenes may provide information about brief, high-temperature shock heating events. In contrast, subsequent low-T conditions should minimally influence these concentration gradients. The experimental Ar diffusion kinetics in OPX and CPX correspond to closure temperatures of 600-700 and 700-800 degrees C, respectively (for 10 degrees C/Ma cooling). These results suggest that diffusive equilibration through 0.1-0.5 mm pyroxene grains occurs in minutes to hours at basaltic melt generation temperatures (similar to 1300 degrees C), and is therefore unlikely to inhibit mantle degassing. (C) 2011 Elsevier B.V. All rights reserved.