Flat plateau and impossible isochrons: apparent 40Ar-39Ar geochronology in a high-pressure terrain
Flat plateau and impossible isochrons: apparent 40Ar-39Ar geochronology in a high-pressure terrain
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平坦的高原和不可能的等时线：高压地形中明显的 40Ar-39Ar 地质年代学
DOI：
10.1016/s0016-7037(99)00116-7
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发表时间：
1999
影响因子：
5
通讯作者：
N. Arnaud
中科院分区：
文献类型：
--
作者：
S. Sherlock;N. Arnaud
直到最近，由40Ar-39Ar技术确定的大多数年龄都是由年龄谱和等时线表示的。在这项技术的早期历史中，人们概述了一系列标准，以便区分被认为反映受干扰的同位素系统的光谱和被认为反映岩石或矿物的准确年龄的光谱。随着40Ar-39Ar仪器的进步和激光烧蚀技术的引入，现在可以从单颗粒和亚颗粒尺度上获得年龄。在这种情况下，没有年龄谱的产生或平台年龄的确定；然而，等时线仍然很容易产生并用于讨论Ar同位素比率，特别是过剩的Ar。在这里，新的数据首先说明了在高压地体中没有独立的地质年代学约束的情况下年龄谱和高原年龄的可能缺陷，其次是伴随的等时线的缺陷，我们证明这可能是不正确的，并且在地质上没有意义。
Until recently most ages determined by the40Ar-39Ar technique have been represented by the age spectrum and isochron. Early in the history of the technique a series of criteria were outlined in order to discriminate between spectra which were considered to reflect disturbed isotopic systems and spectra which were considered to reflect the accurate age of the rock or mineral. With the advancement of40Ar-39Ar instrumentation and the introduction of laser-ablation techniques, it is now possible to obtain an age from single grains and on a sub-grain scale. In this case there is no production of an age spectra or determination of a plateau age; however, isochrons are still readily produced and used in the discussion of Ar isotope ratios, and specifically excess argon. Here, new data illustrate the possible drawback first of the age spectrum and plateau age in the absence of an independent geochronological constraint in high-pressure terranes, and second, of the accompanying isochron, which we demonstrate can be both incorrect and geologically meaningless.