Contrasting Thermal Evolution within the Ross Orogen, Antarctica: Evidence from Mineral $$^{40}Ar/^{39}Ar$$ Ages
Contrasting Thermal Evolution within the Ross Orogen, Antarctica: Evidence from Mineral $$^{40}Ar/^{39}Ar$$ Ages
复制标题
南极洲罗斯造山带内的热演化对比：来自矿物 $$^{40}Ar/^{39}Ar$$ 年龄的证据
DOI：
--
复制
发表时间：
1996
期刊：
影响因子：
--
通讯作者：
R. D. Dallmeyer
中科院分区：
文献类型：
--
作者：
J. Goodge;R. D. Dallmeyer
横贯北极山脉中部的Nimrod群和南极维多利亚大陆北部的Lanterman变质杂岩构成了罗斯造山带的内部变质基底地体，在岩性、构造和变质作用方面具有许多一级相似之处。然而，从地质学家(Nimrod群)和Lanterman山脉(Lanterman杂岩)的构造岩中确定的角闪石和白云母冷却年龄表明，这两个地体经历了不同的运动后冷却历史。来自火成岩和沉积原岩的尼姆罗韧性L-S构造岩的角闪石冷却年龄为524~495 Ma，白云母冷却年龄为499~496 Ma。这些年龄被解释为同变质韧性变形后的冷却。结合40Ar/39Ar年龄数据和现有的U-Pb年龄数据，尼姆罗德构造岩的平均运动后冷却速率约为10°C/m.y。兰特曼杂岩的变质沉积L-S构造岩获得了约486 Ma(角闪石)和约482 Ma(白云母)的冷却年龄。这些冷却年龄表明，兰特曼运动后的平均冷却速率约为30℃/m.y。我们解释说，这些地区不同的热历史是沿造山带不同模式吸积的结果，部分原因是东南极克拉通之下的古太平洋岩石圈倾斜俯冲。在横贯北极的中部山脉，尼姆罗德冷却速率表明构造后剥蚀速率相对较低(约0.4 mm/a)，这是由于上板块边缘背景下的地壳增厚造成的。相邻大陆边缘上壳层序的收缩不涉及明显的俯冲作用，这可能是边缘平行平移的高分量的结果。相比之下，明显较快的Lanterman冷却速度表明维多利亚陆地北部增厚的地壳剥蚀速度更快(约1.2 mm/a)。来自Lanterman杂岩的运动学和降温速率数据表明，下古生代火山弧和陆隆组合的外侧增生涉及结晶基底下方近垂直的俯冲，最终导致快速构造剥蚀。
The Nimrod Group in the central Transantarctic Mountains and the Lanterman Metamorphic Complex in northern Victoria Land of Antarctica constitute internal metamorphic basement terrains of the Ross orogen that share many first-order similarities in lithology, structure, and metamorphism. However, new $$^{40}Ar/^{39}Ar$$ cooling ages determined for hornblende and muscovite from tectonites in the Geologists (Nimrod Group) and Lanterman ranges (Lanterman complex) indicate that these terrains experienced different post-kinematic cooling histories. Nimrod ductile L-S tectonites derived from igneous and sedimentary protoliths yield $$^{40}Ar/^{39}Ar$$ hornblende cooling ages of 524-495 Ma and muscovite cooling ages of 499-496 Ma. These ages are interpreted to date the cooling following syn-metamorphic ductile deformation. Combined $$^{40}Ar/^{39}Ar$$ and existing U-Pb age data yield an average post-kinematic cooling rate for the Nimrod tectonites of ~10°C/m.y. Metasedimentary L-S tectonites of the Lanterman complex yield $$^{40}Ar/^{39}Ar$$ cooling ages of ca. 486 Ma (hornblende) and ca. 482 Ma (muscovite). These cooling ages indicate an average post-kinematic Lanterman cooling rate of ~30°C/m.y. We interpret the contrasting thermal histories of these terrains to be the result of different modes of accretion along the orogen, due in part to oblique subduction of paleo-Pacific lithosphere beneath the East Antarctic craton. In the central Transantarctic Mountains, Nimrod cooling rates indicate relatively modest post-tectonic denudation rates (~0.4 mm/a), resulting from crustal thickening in an upper plate-margin setting. Contraction of adjacent continental-margin supracrustal sequences did not involve significant under-thrusting, possibly as a result of a high component of margin-parallel translation. In contrast, markedly faster Lanterman cooling rates indicate more rapid denudation (~1.2 mm/a) of thickened crust in northern Victoria Land. Kinematic and cooling-rate data from the Lanterman complex indicate that accretion of outboard lower Paleozoic volcanic arc and continental-rise assemblages involved near-orthogonal underthrusting beneath crystalline basement, leading ultimately to rapid tectonic denudation.