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首页> 外文期刊>South African journal of geology >New Rb-Sr ages for igneous rocks from the area of the Pretoria Saltpan impact crater
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New Rb-Sr ages for igneous rocks from the area of the Pretoria Saltpan impact crater

机译：比勒陀利亚Saltpan撞击坑地区火成岩的新Rb-Sr年龄

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摘要

An age for the Pretoria Saltpan (Tswaing) impact crater of about 200 ka has recently been obtained by ~(14)C dating of algal debris in a drillcore and in a fission-track study of impact glass fragments from suevitic breccia of the lower crater fill. These relatively young ages for the cratering event are in excellent agreement with the preserved state of the crater. However, sceptics of the impact origin of the Tswaing crater have continued to quote alkaline and mafic intrusions in the crater rim as prime evidence for an internal origin for this crater. In order to establish whether these intrusions are related to the cratering event, or perhaps belong to the late-Proterozoic Pienaars River Alkaline Complex (PRAC), which is of regional significance, selected samples of intrusive rocks from the crater area and from the crater environs were dated with the Rb-Sr isotope method. These results prove unequivocally that the intrusions in the crater rim are part of a regional magmatic event which appears to have occurred around 1.3 Ga ago, and includes all intrusions of the PRAC. Thus, there remains no reason to relate intrusive magmatism to the formation of the much more recent crater structure.
机译：最近通过在钻芯中对藻类碎片进行〜（14）C测年以及在下火山口的角砾岩角砾岩对撞击玻璃碎片的裂变径迹研究中，获得了比勒陀利亚萨尔特潘（Tswaing）撞击坑的年龄约为200 ka。填。这些相对较小的火山口活动年龄与火山口的保存状态极为吻合。然而，人们对茨瓦宁火山口撞击起源的怀疑论者继续将火山口边缘的碱性和铁镁质侵入物作为该火山口内部起源的主要证据。为了确定这些侵入是否与火山口事件有关，或者是否属于晚期元古代的比纳阿尔斯河碱性复合体（PRAC）具有重要的区域意义，从火山口地区和火山口环境中选取了侵入岩样品用Rb-Sr同位素法测定日期。这些结果无疑证明，火山口边缘的侵入是区域岩浆事件的一部分，该事件似乎发生在1.3 Ga之前，并且包括了PRAC的所有侵入。因此，没有理由将侵入岩浆作用与最近火山口结构的形成联系起来。

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