Phanerozoic Morphotectonic Evolution of the Zimbabwe Craton: Unexpected Outcomes From a Multiple Low‐Temperature Thermochronology Study
Phanerozoic Morphotectonic Evolution of the Zimbabwe Craton: Unexpected Outcomes From a Multiple Low‐Temperature Thermochronology Study
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DOI：
10.1002/2017tc004703
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发表时间：
2017-09
期刊：
影响因子：
4.2
通讯作者：
Vhairi Mackintosh;B. Kohn;A. Gleadow;Yuntao Tian
中科院分区：
文献类型：
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作者：
Vhairi Mackintosh;B. Kohn;A. Gleadow;Yuntao Tian
津巴布韦克拉通异常抬升，其显生宙地质记录不完整，这使得利用常规的野外方法重建其历史变得困难。在此，我们利用一个空间范围广泛的磷灰石（U - Th - Sm）/He（AHe）、磷灰石裂变径迹（AFT）和锆石（U - Th）/He（ZHe）数据集来限定津巴布韦克拉通隐秘的显生宙演化。联合热历史模拟显示，该地区经历了两次冷却事件，推断是对地表隆升的剥蚀响应。第一次也是最显著的长期剥蚀期是由冈瓦纳拼合期间相邻的约750 - 500 Ma泛非造山运动的应力传递所触发。这种复活迹象的空间范围涵盖了当前广阔的地形高地，可能表明一个古老地形特征可能长期存在。ZHe数据揭示了第二次较小的剥蚀阶段，始于古近纪，从克拉通剥蚀掉了千米级的卡鲁覆盖层。在我们的数据集中，大多数ZHe年龄比相应的AHe和AFT年龄年轻，即使在相对较低的eU情况下也是如此。这种出乎意料的反复出现的年龄“倒置”表明，在某些环境中，中度以及极度受损的锆石有可能作为超低温热年代计。热历史模拟结果显示，锆石辐射损伤积累和退火模型（ZRDAAM）经常高估ZHe年龄。然而，对于极度受损的锆石情况则相反，其中ZHe和AHe数据似乎也不兼容。这表明对于中度到极度损伤水平，可能需要对ZRDAAM进行修正。
The fragmentary Phanerozoic geological record of the anomalously elevated Zimbabwe Craton makes reconstructing its history difficult using conventional field methods. Here we constrain the cryptic Phanerozoic evolution of the Zimbabwe Craton using a spatially extensive apatite (U‐Th‐Sm)/He (AHe), apatite fission track (AFT), and zircon (U‐Th)/He (ZHe) data set. Joint thermal history modeling reveals that the region experienced two cooling episodes inferred to be the denudational response to surface uplift. The first and most significant protracted denudation period was triggered by stress transmission from the adjacent ~750–500 Ma Pan‐African orogenesis during the amalgamation of Gondwana. The spatial extent of this rejuvenation signature, encompassing the current broad topographic high, could indicate the possible longevity of an ancient topographic feature. The ZHe data reveal a second, minor denudation phase which began in the Paleogene and removed a kilometer‐scale Karoo cover from the craton. Within our data set, the majority of ZHe ages are younger than their corresponding AHe and AFT ages, even at relatively low eU. This unexpectedly recurrent age “inversion” suggests that in certain environments, moderately, as well as extremely, damaged zircons have the potential to act as ultra‐low‐temperature thermochronometers. Thermal history modeling results reveal that the zircon radiation damage accumulation and annealing model (ZRDAAM) frequently overpredicts the ZHe age. However, the opposite is true for extremely damaged zircons where the ZHe and AHe data are also seemingly incompatible. This suggests that modification of the ZRDAAM may be required for moderate to extreme damage levels.