Dependence of Fission Track Annealing Kinetics on Crystallographic Orientation and Crystal Chemistry

PI开发并测试了一种方法， 可蚀刻裂变径迹（FT）长度平行和垂直于 磷灰石中晶体学c轴可以精确地 测定 如此确定的长度对于单个 FT（平行轨道垂直）的人口，但是，因为 在它们的等效热历史中，它们定义为 “等效长度”。 PI计划使用此新方法来 确定磷灰石中FT退火的物理过程是否 随晶体学取向而变化， 观察由于各向异性蚀刻而产生的实验性伪影。 同样，他们将确定FT退火过程是否 随晶体化学性质而变化（例如，富Cl径迹长度F- 丰富）或者这是否也是蚀刻现象。 述的方法 为了解决这些问题，并更好地 校准这个重要的热时计，是一系列的 等时实验室退火实验（范围从0.3- 10000小时和23- 400 oC）。 具体而言，他们将调查： 1)观察到的FT长度各向异性与蚀刻的相关性 磷灰石的各向异性，2）平均可蚀刻FT的变化 长度随时间、温度和晶体学取向的变化 适用于一系列磷灰石成分;（富F-、Cl-、OH-和Mn） 在低温（23 oC）和高温下，3）如何 FT退火的激活能随平均FT长度而变化 在固定方向，B）在相等长度之间，和c）具有 基质晶体化学; 4）上述结果之间的关系 与目前发表的结果（Galbraith和Laslett，1988年） 将FT密度（轨道/单位面积）的依赖性与 平均可蚀刻FT长度。 这些新的数据将被用来推导出一个数学模型。 关于“相等长度”与时间的表述- 磷灰石的温度（t-T）历史。 这个新的表达 应该会导致t-T估计值的显著改善 地质样品所经历的路径。

The PIs have developed and tested a method whereby the mean etchable fission track (FT) lengths parallel and perpendicular to the crystallographic c-axis in apatite may be precisely determined. The lengths so determined differ for a single population of FTs (parallel tracks perpendicular) but, because of their equivalent thermal histories, they are defined as "equivalent lengths". The PIs plane to use this new method to determine whether the physical process of FT annealing in apatite varies with crystallographic orientation or whether we are observing experimental artifacts due to anisotropic etching. Similarly, they will determine whether the FT annealing process varies with crystal chemistry (e.g. Cl-rich track lengths F- rich) or whether this is also an etching phenomenon. The method proposed, in order to address these questions and to better calibrate this important thermochronometer, is a series of isochronal laboratory annealing experiments (ranging from O.3- 1OOOO hours and 23-400oC). Specifically, they will investigate: 1) the correlation of observed FT length anisotropy with etching anisotropy in apatite, 2) the variation of mean etchable FT length with time, temperature and crystallographic orientation for a range of apatite compositions ;(F-, Cl-, OH-, and Mn-rich) at low temperature (23oC) and elevated temperatures, 3) how activation energy for FT annealing varies a) with mean FT length at fixed orientation, b) between equivalent lengths, and c) with host crystal chemistry, 4) the relationship of the above results with currently published results (Galbraith and Laslett, 1988) relating the dependence of FT density (tracks/unit area) to the mean etchable FT length. These new data will then be used to derive a mathematical expression relating the "equivalent length" to the time- temperature (t-T) history of the apatite. This new expression should result in a significant improvement in estimates of t-T paths experienced by geologic samples.