Oxygen and strontium diffusion kinetics in apatite and potential applications to thermal history determinations
Oxygen and strontium diffusion kinetics in apatite and potential applications to thermal history determinations
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DOI：
10.1016/0016-7037(89)90243-3
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发表时间：
1989-07
影响因子：
5
通讯作者：
J. Farver;B. Giletti
中科院分区：
文献类型：
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作者：
J. Farver;B. Giletti
在水热条件下，用离子探针测量了天然氟磷灰石（杜兰戈，墨西哥）中氧和锶的扩散动力学。氧的扩散系数在550至1200° C的温度下获得，锶的扩散系数在650至1200° C的温度下获得。所有实验都在1000巴（100 MPa）水压下进行，除了那些设计用于测量水压依赖性的实验，其在200至2000巴下进行。在1000巴的水压下，平行于c轴的扩散得到的阿耳忒弥斯关系式为：元素D 0（cm 2/sec）Q（kcal/mol）T（° C）氧9· 10− 5 49±3 550-1200锶2· 10− 11 25±4 650-1000锶1· 10 5 120±22 1100-1200。在实验的温度范围内，平行于c轴的氧传输的扩散系数比垂直于c轴的氧传输的扩散系数大约大三个数量级。锶在磷灰石中的扩散没有观察到各向异性。对于800° C下平行于c轴的氧扩散，水压从200巴增加到2000巴，导致D增加约三倍。在1100 ~ 1200° C温度范围内锶扩散的Arrhenius关系与沃森等人的结果一致。（1985）在1050至1250° C下干燥1个大气压实验的数据。在650至1000° C温度范围内获得的锶扩散系数产生的D值明显大于通过高温Arrhenius关系外推预测的D值。新的数据表明，磷灰石中锶扩散计算的闭合温度明显低于高温研究预测的温度。因此，磷灰石晶体在远低于大多数火成岩的固相线温度时，仍然对锶扩散交换开放。这可能会导致更高的87 Sr-86 Sr值的磷灰石比整个岩石的初始值。磷灰石中87 Sr-86 Sr值的可测量富集也可以由后来的热扰动在中等地质温度和持续时间。
The kinetics of oxygen and strontium diffusion in natural fluorapatite (Durango, Mexico) have been measured under hydrothermal conditions using an ion microprobe. Diffusion coefficients were obtained at temperatures from 550 to 1200° C for oxygen, and 650 to 1200° C for strontium. All experiments were run at 1000 bars (100 MPa) water pressure except those designed to measure the water pressure dependence, which were at 200 to 2000 bars. The Arrhenius relations obtained for diffusion parallel to the c axis at 1000 bars water pressure are: Element D 0 (cm 2/sec) Q (kcal/mol) T (° C) Oxygen 9· 10− 5 49±3 550–1200 Strontium 2· 10− 11 25±4 650–1000 Strontium 1· 10 5 120±22 1100–1200. The diffusion coefficient for oxygen transport parallel to the c axis is approximately three orders of magnitude greater than that perpendicular to the c axis over the temperature range of the experiments. No anisotropy was observed for strontium diffusion in apatite. An increase in water pressure from 200 to 2000 bars yields an increase in D of approximately a factor of three for oxygen diffusion parallel to the c axis at 800° C. The Arrhenius relation for strontium diffusion in the temperature range 1100 to 1200° C is in good agreement with the Watson et al.(1985) data for dry 1 atm experiments at 1050 to 1250° C. Strontium diffusion coefficients obtained in the temperature range 650 to 1000° C yield significantly greater D values than predicted by extrapolation of the high-temperature Arrhenius relation. The new data show that closure temperatures calculated for strontium diffusion in apatite are significantly lower than the hightemperature studies would predict. Thus, apatite crystals would remain open to strontium diffusional exchange well below the solidus temperature of most igneous rocks. This could result in higher 87 Sr 86 Sr values in the apatite than the whole-rock initial value. Measurable enrichment in 87 Sr 86 Sr values in apatite could also be produced by a later thermal disturbance at moderate geologic temperatures and durations.