Geodynamic models of the West Antarctic Rift System: Implications for the mantle thermal state
Geodynamic models of the West Antarctic Rift System: Implications for the mantle thermal state
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南极西部裂谷系统的地球动力学模型：对地幔热状态的影响
DOI：
10.1130/ges01594.1
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发表时间：
2018
期刊：
影响因子：
2.5
通讯作者：
Jha, Sumant
中科院分区：
文献类型：
--
作者：
Harry, Dennis L.;Anoka, Jourdan L.;Jha, Sumant
模拟南极西部裂谷系统扩展的二维有限元模型显示出三类行为，这些行为依赖于裂谷前上地幔的热状态。所有的模型都是从相对凉爽的东南极洲岩石圈和温暖的西南极洲并列开始的。这些模型都经历了一个最初的扩展期，这个扩展期广泛分布在各个战争中。在离东南极洲最远的模式边缘突然形成岩石圈颈部之前，第一类模式继续以这种方式延伸超过80海里。第一类模式的行为是由温暖的战争岩石圈和较冷的东南极洲岩石圈并置引起的水平温度梯度所主导的。这就产生了一个相应的强度梯度，导致脖子最终在模型的温暖、脆弱的边缘发育。1类模型在地壳底部具有相对较高的裂前温度（约800°C），这抑制了拉伸前80毫秒的应变聚焦。在第2类模型中，裂谷轴在战争的内部发展。第2类模型与第1类模型的不同之处在于，地壳的净产热在确定裂陷之前和期间地幔顶部的温度方面起着更大的作用。这些模型边缘的缩进受到抑制，因为地壳变薄导致模型边缘的岩石圈冷却和加强。这导致延伸的轨迹向战争较弱的内部转移。在第3类模式中，裂谷轴形成于裂谷前岩石圈在相对较冷较厚的东南极洲和较暖较薄的西南极洲之间过渡的地方。在这些模型中，岩石圈的同张性冷却和加强导致应变轨迹转移到过渡区，而不是战争的内部。第3类模式类似于晚白垩世至晚古近纪的大范围伸展和新近纪在西南极洲/东南极洲边界附近更为集中的伸展。所有3类模型均要求晚白垩世至古近纪大伸展阶段的地幔势温不大于1270°C，表明伸展早期在WARS下方不存在活动的地幔柱。
Two-dimensional finite element models simulating extension of the West Antarctic Rift System (WARS) exhibit three classes of behavior, which are dependent upon the pre-rift thermal state of the upper mantle. All of the models begin with relatively cool East Antarctica lithosphere juxtaposed against warmer West Antarctica. The models all undergo an initial period of extension that is broadly distributed across the WARS. Class 1 models continue to extend in this way for more than 80 m.y. before abruptly developing a lithospheric neck at the edge of the model furthest from East Antarctica. The behavior of Class 1 models is dominated by a horizontal temperature gradient caused by juxtaposition of the warm WARS lithosphere against the cooler East Antarctica lithosphere. This produces a corresponding strength gradient, which causes a neck to eventually develop at the warm, weak edge of the model. Class 1 models have relatively high pre-rift temperatures at the base of the crust (>800 °C), which inhibits focusing of strain during the first 80 m.y. of extension. In Class 2 models the rift axis develops within the interior of the WARS. Class 2 models differ from Class 1 models in that the net heat production in the crust plays a larger role in determining the temperature at the top of the mantle prior to and during rifting. Necking at the edge of these models is inhibited because crustal thinning leads to cooling and strengthening of the lithosphere at the edge of the model. This causes the locus of extension to shift toward the weaker interior of the WARS. In Class 3 models, the rift axis forms where the pre-rift lithosphere transitions between relatively cool and thick East Antarctica and warmer and thinner West Antarctica. In these models, syn-extensional cooling and strengthening of the lithosphere causes the locus of strain to shift into the transitional region rather than the interior of the WARS. Class 3 models resemble the evolution of the WARS, which underwent a period of broad extension during the Late Cretaceous through late Paleogene Periods and more focused extension near the West Antarctica/East Antarctica boundary during the Neogene Period. All Class 3 models require the mantle potential temperature during the Late Cretaceous through Paleogene phase of broad extension to be no greater than 1270 °C, suggesting that an active mantle plume was not present beneath the WARS during the early stages of extension.
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