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首页> 外文期刊>Contributions to Mineralogy and Petrology >Interpreting high-pressure phengite 40Ar/39Ar laserprobe ages: an example from Saih Hatat, NE Oman
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Interpreting high-pressure phengite 40Ar/39Ar laserprobe ages: an example from Saih Hatat, NE Oman

机译：解释高压锂镁铝石 40 Ar / 39 Ar激光探针年龄：来自阿曼东北部Saih Hatat的一个例子

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New single grain fusion and core-rim 40Ar/39Ar laserprobe phengite data from the Saih Hatat high-pressure terrane in NE Oman show that individual samples yield a range of apparent ages which is similar to that previously reported from across the entire terrane. The majority of the determined ages are older than the previously reported U-Pb zircon peak metamorphic age. Core to rim age variations within individual grains range from no discernible difference across the grain to grains with older cores, or, rarely, older rims; some samples manifest all three patterns. Numerical diffusion modelling shows that due to the peak temperature of ca. 550°C, the measured apparent ages cannot be explained by simple cooling or by partial retention of crystallisation or detrital ages in an open system. The age variability is better explained by spatially and temporally variable open or closed system behaviour at the mm-cm scale coupled with pervasive and heterogeneously distributed excess argon. Anomalously old eclogite phengite 40Ar/39Ar ages are due either to internally derived 40Ar inherited from a K-bearing precursor, or externally derived 40Ar distributed by grain boundary fluids. Mica-rich schists within the eclogite boudins yield younger phengite ages, suggesting excess argon was absent or diluted. Pelites hosting the eclogite appear to have been affected by later fluid ingress during deformation and greenschist-facies overprint and yield very variable ages commonly with apparently older rims on younger cores. The grain- and sample-scale age variations measured in Saih Hatat indicate that the grain boundary network in eclogite pods was not an efficient transfer pathway for argon transport, whereas the grain boundary network in the surrounding pelites acted as a more efficient pathway on the timescale of the metamorphic cycle.
机译：来自阿曼东北部Saih Hatat高压地层的新单晶熔合和芯-边缘 40 Ar / 39 Ar激光探针的锂蒙脱石数据显示，单个样品产生了一系列明显的的年龄与先前从整个地层报告的相似。确定的大多数年龄都比以前报道的U-Pb锆石峰变质年龄大。单个谷物中核心到轮辋的年龄变化范围从谷物之间没有明显差异，到核心较旧的轮辋，或者很少有较旧的轮辋。一些样本体现了这三种模式。数值扩散模型表明，由于约有峰值温度。在550°C下，无法通过简单的冷却或在开放系统中部分保留结晶或碎屑年龄来解释测得的表观年龄。年龄可变性可以通过在毫米-厘米尺度上随空间和时间变化的开放或封闭系统行为以及无处不在的和不均匀分布的过量氩来更好地解释。异常古老的榴辉岩辉绿岩 40 Ar / 39 Ar年龄是由于内部含钾的前体继承自内部的 40 Ar或来自外部 40 Ar由晶界流体分布。榴辉岩布丁中富含云母的片岩可产生较年轻的辉石岩年龄，表明缺少或稀释了过量的氩气。主持榴辉岩的岩屑似乎在变形和绿片岩相叠印期间受到后期流体进入的影响，并且产生的年龄变化很大，通常在较年轻的岩心上具有较旧的轮辋。在Saih Hatat中测得的晶粒度和样本尺度年龄变化表明，榴辉岩豆荚中的晶界网络不是氩气传输的有效传递途径，而周围白云母中的晶界网络在时间尺度上却是更有效的途径。变质周期。

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