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首页> 外文期刊>Contributions to Mineralogy and Petrology >Dating fault-generated pseudotachylytes: comparison of ~(40)Ar/~(39)Ar stepwise-heating, laser-ablation and Rb-Sr microsampling analyses
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Dating fault-generated pseudotachylytes: comparison of ~(40)Ar/~(39)Ar stepwise-heating, laser-ablation and Rb-Sr microsampling analyses

机译：约会故障产生的假速溶电解质：〜（40）Ar /〜（39）Ar逐步加热，激光烧蚀和Rb-Sr微采样分析的比较

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摘要

Three different geochronological techniques (stepwise-heating, laser-ablation ~(40)Ar/~(39)Ar, Rb-Sr microsampling) have been evaluated for dating fault-generated pseudotachylytes sampled along the Periadriatic Fault System (PAF) of the Alps. Because pseudotachylytes are whole-rock systems composed of melt, clast and alteration phases, chemical control from both Ar isotopes (Cl/K, Ca/K ratios) and EMPA analyses is crucial for their discrimination. When applied to stepwise-heating ~(40)Ar/~(39)Ar analyses, this approach yields accurate melt-related ages, even for complex age spectra. The spatial resolution of laser-ablation ~(40)Ar/~(39)Ar analyses is capable of contrasting melt, clast and alteration phases in situ, provided the clasts are not too fine grained, the latter of which results in integrated "mixed" ages without geological information. Elevated Cl/K and Ca/K ratios were found to be an invaluable indicator for the presence of clast admixture or inherited ~(40)Ar. Due to incomplete isotopic resetting during frictional melting, Rb-Sr microsampling dating did not furnish geologically meaningful ages. On the basis of isotopic disequilibria among pseudotachylyte matrix phases, and independent Rb-Sr microsampling dating of cogenetic (ultra)mylonites, the concordant ~(40)Ar/~(39)Ar pseudotachylyte ages are interpreted as formation ages. The investigated pseudotachylytes altogether reveal a Cretaceous to Miocene history for the entire PAF, consistent with independent geological evidence. Individual faults, however, consistently reveal narrower intervals of enhanced activity lasting a few million years. Electronic supplementary material to this paper can be obtained by using the Springer LINK server at http://dx.doi.org/10.1007/s00410-002-0381-6.
机译：已评估了三种不同的地质年代学技术（逐步加热，激光烧蚀〜（40）Ar /〜（39）Ar，Rb-Sr微量采样）来确定沿阿尔卑斯山古生断裂系统（PAF）采样的断层产生的假速溶质的年代。 。由于假速溶质是由熔体，碎屑和蚀变相组成的全岩石系统，因此从Ar同位素（Cl / K，Ca / K比）和EMPA分析中进行化学控制对于区分它们至关重要。当应用于逐步加热〜（40）Ar /〜（39）Ar分析时，即使对于复杂的年龄谱，该方法也可以得出与熔体相关的准确年龄。激光烧蚀〜（40）Ar /〜（39）Ar分析的空间分辨率能够在原位对比熔解，碎屑和蚀变相，但前提是碎屑的晶粒不太细，后者导致整体“混合”。没有地质信息的时代。发现Cl / K和Ca / K比率升高是存在碎片混合物或遗传〜（40）Ar的宝贵指标。由于在摩擦熔化过程中同位素重置不完全，Rb-Sr微量采样年代无法提供具有地质意义的年龄。根据假速溶质基质相之间的同位素失衡，以及共生（超）淀粉状岩的独立的Rb-Sr微量采样年代，将〜（40）Ar /〜（39）Ar假速溶液年龄解释为形成年龄。所研究的假速溶电解质总共揭示了整个PAF的白垩纪至中新世历史，与独立的地质证据一致。但是，个别断层始终显示出持续活动持续几百万年的狭窄间隔。可以使用http://dx.doi.org/10.1007/s00410-002-0381-6上的Springer LINK服务器获得本文的电子补充材料。

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