Apatite fission track and (U-Th)/He thermochronology from the Archean Tanzania Craton: Contributions to cooling histories of Tanzanian basement rocks
Apatite fission track and (U-Th)/He thermochronology from the Archean Tanzania Craton: Contributions to cooling histories of Tanzanian basement rocks
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DOI：
10.1016/j.gsf.2016.09.007
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发表时间：
2017-09
影响因子：
8.9
通讯作者：
C. H. Kasanzu
中科院分区：
文献类型：
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作者：
C. H. Kasanzu
钻孔和表面样品从太古代坦桑尼亚岩磷灰石裂变径迹（AFT）和（U-Th）/He数据进行了分析，目的是破译冷却历史的基底岩石。钻孔和露头样品的裂变径迹年龄为石炭纪-二叠纪（345 ± 33.3 Ma ~ 271 ± 31.7 Ma），而露头颗粒的（U-Th）/He年龄为石炭纪-三叠纪（336 ± 45.8 Ma ~ 213 ± 29 Ma），一致地比相应的AFT年龄年轻。钻孔中的单颗粒（U-Th）/He测年由于其有效铀含量低、辐射损伤和颗粒大小等原因，很可能会因过量氦注入而出现缺陷。所有的AFT和（U-Th）/He的年龄显着年轻比他们的寄主岩石的地层年龄，这意味着样品经历了中生代升高的古温度。对数据的考虑表明，自古生代以来，覆盖层的移除高达9公里。350 Ma），速率为46 m/Ma，结束于三叠纪（约350 Ma）。220 Ma）。该模型还表明，在白垩纪的样品表面温度轻微冷却。建议的后期降温事件仍有待测试。在石炭纪的主要冷却阶段被解释为与压缩构造在华力西Orogenysensufar场诱导应力。该地区卡鲁盆地的同时代沉积作用表明，石炭纪期间大部分岩石的冷却与剥蚀有关。
Borehole and surface samples from the Archean Tanzania Craton were analysed for apatite fission track (AFT) and (U-Th)/He data with the aim of deciphering cooling histories of the basement rocks. Fission track dates from borehole and outcrop samples are Carboniferous–Permian (345 ± 33.3 Ma to 271 ± 31.7 Ma) whereas (U-Th)/He dates are Carboniferous–Triassic (336 ± 45.8 Ma to 213 ± 29 Ma) for outcrop grains and are consistently younger than corresponding AFT dates. Single grain (U-Th)/He dates from the borehole are likely to be flawed by excessive helium implantation due to their very low effective uranium contents, radiation damage and grain sizes. All AFT and (U-Th)/He dates are significantly younger than the stratigraphic ages of their host rocks, implying that the samples have experienced Phanerozoic elevated paleo-temperatures. Considerations of the data indicate removal of up to 9 km overburden since the Palaeozoic.Thermal modelling reveals a protracted rapid cooling event commencing during the early Carboniferous (ca. 350 Ma) at rates of 46 m/Ma ending in the Triassic (ca. 220 Ma). The model also suggests minor cooling during the Cretaceous of the samples to surface temperatures. The suggested later cooling event remains to be tested. The major cooling phase during the Carboniferous is interpreted to be associated with compressional tectonics during the Variscan Orogenysensufar field induced stresses. Coeval sedimentation in the Karoo basins in the region suggests that most of the cooling of cratonic rocks during the Carboniferous was associated with denudation.