Obsidian Diffusion Dating by Secondary Ion Mass Spectrometry: A Test using Results from Mound 65, Chalco, Mexico
Obsidian Diffusion Dating by Secondary Ion Mass Spectrometry: A Test using Results from Mound 65, Chalco, Mexico
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通过二次离子质谱法进行黑曜石扩散测年：使用墨西哥 Chalco 65 号土墩结果进行的测试
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发表时间：
2002
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通讯作者：
D. Cole
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作者：
L. Riciputi;J. Elam;L. Anovitz;D. Cole
二次离子质谱法（西姆斯）被用来测量氢和其他元素的浓度作为深度的函数在10个黑曜石文物（帕丘卡源），每个有一个很好的约束14 C日期，从土墩65，中铝，墨西哥。氢的深度分布的不同文物都显示出一个特征的S形，并增加最大氢含量在每个配置文件和配置文件的深度与时间有很好的相关性。这些数据被用来调查黑曜石扩散测年的西姆斯（ODDSIMS）的黑曜石文物的外在和内在的约会的潜在用途。使用氢剖面上的“特征点”（半落深度，拐点深度），简单的水化速率方程进行了评估，对相关的14 C日期提供的时间限制。我们证明，无论是传统的OHD方程的深度（x）作为时间（t1/2）的平方根的函数，也不是一个线性函数（t1）适合的数据。求解更广义的tn函数提供了特征点深度和14 C日期之间的良好拟合（对于n = 0·75），并且满足了在时间等于零时，水合剖面的深度也必须为零的约束。然而，这可能是可用年龄范围内的平均系数，可能无法准确反映较短或较长时间的比率。仅使用两个黑曜石样品及其相关的14 C日期，校准曲线可以得出，提供ODDSIMS日期的其他件是在极好的协议与associated 14 C日期，表明经验应用的技术是潜在的可行性，至少在个别网站。
氢运输到黑曜石的基本过程也进行了研究，通过使用有限差分模拟再现的氢深度剖面的形状。通过假设浓度依赖性扩散获得了极好的拟合，并且也可以从有限差分曲线中提取与相关14 C日期一致的日期。虽然相当多的额外工作需要做，有限差分建模的成功表明，一个独立的，内在的ODDSIMS模型的发展是可能的。
Secondary ion mass spectrometry (SIMS) was used to measure hydrogen and other elemental concentrations as a function of depth in ten obsidian artifacts (Pachuca Source), each with a well-constrained 14C date, from Mound 65, Chalco, Mexico. Hydrogen depth profiles for the different artifacts all display a characteristic S-shape, and increasing maximum hydrogen content in each profile and profile depths are well correlated with time. These data are used to investigate the potential use of Obsidian Diffusion Dating by SIMS (ODDSIMS) for both extrinsic and intrinsic dating of obsidian artifacts. Using “characteristic points” on the hydrogen profile (half-fall depth, inflection point depth), simple hydration rate equations were evaluated against time constraints provided by associated 14C dates. We demonstrate that neither the traditional OHD equation for depth (x) as a function of the square root of time (t1/2) nor a linear function (t1) fit the data. Solving the more generalized tn function provides an excellent fit between characteristic point depths and 14C dates (for n≈0·75), and meets the constraint that at time equal to zero, the depth of the hydration profile must also be zero. However, this may be an average coefficient over the range of ages available, and may not accurately reflect rates at shorter or longer times. Using only two obsidian samples and their associated 14C dates, a calibration curve can be derived that provides ODDSIMS dates for the other pieces that are in excellent agreement with associated14 C dates, indicating that empirical application of the technique is potentially feasible, at least at individual sites.
The underlying processes governing hydrogen transport into the obsidian were also investigated by using finite difference modelling to reproduce the shape of the hydrogen depth profile. Excellent fits were obtained by assuming concentration-dependent diffusion, and dates that agree well with associated 14C dates can also be extracted from the finite difference profiles. Although considerable additional work needs to be done, the success of the finite difference modelling suggests that development of an independent, intrinsic ODDSIMS model may be possible.