The KTB apatite fission-track profiles: Building on a firm foundation?
The KTB apatite fission-track profiles: Building on a firm foundation?
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DOI：
10.1016/j.gca.2015.06.015
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发表时间：
2015-10
影响因子：
5
通讯作者：
B. Wauschkuhn;R. Jonckheere;L. Ratschbacher
中科院分区：
文献类型：
--
作者：
B. Wauschkuhn;R. Jonckheere;L. Ratschbacher
深井是在地质条件下测试热时计的天然实验室。TheKontinentale Tiefbohrung（KTB）是一个有趣的候选人，因为地质证据表明，近似等温举行，因为最后记录的折返在晚白垩世至古新世是一个合理的假设的热历史的KTB样品。我们报告了30个新的磷灰石裂变径迹年龄和50个新的平均约束径迹长度确定的核心从4公里深的先导孔。外部探测器和外部探测器的年龄与早期研究的人群年龄一致，共同定义了明确的年龄特征。本研究和早期研究的平均径迹长度揭示了实验因素的影响。测得的年龄和长度的配置文件进行了比较与24个退火模型的等温保持的预测。测量的和计算的轮廓之间存在明显的差异。下至1.5公里深度，测得的平均径迹长度比预测的要短。方法学证据的平衡表明，这是由于老化，即，化石局限足迹的缩短而没有伴随年龄的减少。从2.5到4.0公里的深度，平均轨道长度比预测的要长。这表明，偏置模型的权重观察轨道的不同长度的概率，这是基于表面轨道密度的平均轨道长度的实验是不合适的限制轨道。实验和方法因素有时很难理清，但提供了足够的余地，没有必要去反对独立的地质证据。不能排除未知的地质事件，但不能仅从裂变轨迹数据推断其存在，更不能具体说明这些事件的性质或规模。
Deep boreholes serve as natural laboratories for testing thermochronometers under geological conditions. TheKontinentale Tiefbohrung(KTB) is an interesting candidate because the geological evidence suggests that approximate isothermal holding since the last documented exhumation in the Late Cretaceous to Palaeocene is a reasonable assumption for the thermal histories of the KTB samples. We report 30 new apatite fission-track ages and 50 new mean confined track lengths determined on cores from the 4 km deep pilot hole. The ϕ- and ζ-external detector ages are consistent with the population ages from earlier studies and together define a clear age profile. The mean track lengths from this and earlier studies reveal the effects of experimental factors. The measured age and length profiles are compared with the predictions of 24 annealing models for isothermal holding. There are clear discrepancies between the measured and calculated profiles. Down to 1.5 km depth, the measured mean track lengths are shorter than the predicted. The balance of methodological evidence indicates that this is due to seasoning, i.e., a shortening of the fossil confined tracks without attendant age reduction. From 2.5 to 4.0 km depth, the mean track lengths are longer than the predictions. This suggests that the bias model that weights the probabilities of observing tracks of different length and which is based on experiments relating surface track densities to mean track lengths is not appropriate for confined tracks. Experimental and methodological factors are sometimes difficult to disentangle, but present a sufficient margin for there to be no need to go against the independent geological evidence. Unknown geological events cannot be ruled out but their existence cannot be inferred from the fission-track data alone, much less can the nature or magnitude of such events be specified.