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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Extending the time range of apatite (U-Th)/He thermochronometry in slowly cooled terranes: Palaeozoic to Cenozoic exhumation history of southeast Sweden
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Extending the time range of apatite (U-Th)/He thermochronometry in slowly cooled terranes: Palaeozoic to Cenozoic exhumation history of southeast Sweden

机译：在缓慢冷却的地层中扩展磷灰石（U-Th）/ He热计时的时间范围：瑞典东南部的古生代至新生代掘出历史

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摘要

The use of (U-Th)/He thermochronometry in old slowly cooled terranes has long been debated. Hence, studies of natural setting are needed to verify the expected diffusivity behaviour of helium. Our results demonstrate that the (U-Th)/He method can be applicable to samples older than 200 Ma, and that available helium diffusion models can reproduce the results obtained from the age-vs.-depth trends. In addition, the results shed some light on the cross-validation with the apatite fission-track thermochronometer. (U-Th)/He thermochronometry on apatites has been applied to samples taken from drill cores in the Precambrian basement in southeast Sweden to unravel the time of exhumation of the uppermost 1-3 km of the crust. Much of the Phanerozoic exhumation history in Sweden is poorly constrained due to a large hiatus in the sediment record. Results from the drill cores yield He ages decreasing with increasing depth from similar to 270 Ma at the surface down to similar to 120 Ma at 1700 in depth. The age-vs.-depth trend shows an inflection point at similar to 1400 in depth, which coincides with the upper boundary of the present Helium Partial Retention Zone. A period of slow exhumation (similar to 17 m/my), probably linked to the isostatic uplift of the Caledonian foreland basin, is revealed by the upper section of the trend in the data. The results demonstrate that the area has not been reheated since the mid-Permian. This argues against the existence of a thick Mesozoic sedimentary cover in this region, which, if present at all, cannot have exceeded 100 in in thickness. Furthermore, the age-vs.-depth trend below the inflection point allows dating the cessation of exhumation at approximately 100 Ma. The area has had no significant amount of sedimentation, erosion or uplift since this time.
机译：在古老的缓慢冷却的地层中使用（U-Th）/ He温度计时法一直存在争议。因此，需要进行自然环境研究以验证氦的预期扩散行为。我们的结果表明（U-Th）/ He方法可以适用于200 Ma以上的样品，并且可用的氦扩散模型可以重现从年龄与深度趋势得出的结果。此外，该结果为与磷灰石裂变径迹热时计的交叉验证提供了一些启示。磷灰石的（U-Th）/ He热时计已应用于瑞典东南部前寒武纪地下室钻芯中采集的样品，以揭示出最上层1-3 km地壳的挖掘时间。由于沉积物记录中存在大量的裂隙，因此瑞典的多生代发掘史受到很大限制。钻芯的结果表明，He的年龄随着深度的增加而减小，从地表的270 Ma下降到深度1700的120 Ma。年龄与深度的趋势显示出一个拐点，深度接近1400，与当前的氦气部分滞留区的上边界重合。趋势的上部显示了缓慢发掘的时期（类似于17 m / my），这可能与喀里多尼亚前陆盆地的等静压上升有关。结果表明，该地区自二叠纪中期以来尚未再加热。这与该地区厚厚的中生代沉积覆盖层相抵触，如果存在的话，其厚度不能超过100。此外，拐点以下的年龄与深度的趋势允许在大约100 Ma处停止挖掘尸体。自该时间以来，该地区没有大量的沉积，侵蚀或隆升。

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