Variable modification of continental lithosphere during the Proterozoic Grenville orogeny: Evidence from teleseismic P-wave tomography
Variable modification of continental lithosphere during the Proterozoic Grenville orogeny: Evidence from teleseismic P-wave tomography
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DOI：
10.1016/j.epsl.2019.115763
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发表时间：
2019-11
影响因子：
5.3
通讯作者：
A. Boyce;I. Bastow;E. Golos;S. Rondenay;S. Burdick;R. D. van der Hilst
中科院分区：
文献类型：
--
作者：
A. Boyce;I. Bastow;E. Golos;S. Rondenay;S. Burdick;R. D. van der Hilst
克拉通是大陆的古老核心，在多次威尔逊旋回的热和机械侵蚀中幸存下来，但其边缘在大陆汇聚期间经受住修改的能力存在争议。元古代格伦维尔造山作用于原北美大陆劳伦西亚东部边缘的≥300Myr，其年龄从碰撞时的∼1.5Gyr至0.25Gyr从北至南不等。保存完好的格伦维尔省位于阿巴拉契亚地体以西，自形成以来，在很大程度上保持了构造静止期。位于这些元古界之下的厚而冷的地幔岩石圈通常以地震速度升高为特征，但俯冲带上方流体/熔体来源的交代作用对岩石圈的改造可以导致V-P的降低，而对V-S和密度的影响不大。因此，绝对P波速约束是对现有的北美S波层析成像模型的重要补充，用于研究格伦维尔造山带的克拉通边缘改造机制。北美大陆的新P波层析成像受益于加拿大地盾区域网络部署到达时间处理方面的最新进展，揭示了格伦维尔造山带沿走向波的速度变化。在北部，高地震波速度(深达250公里)向东延伸，从北美的太古宙核心到加拿大格伦维尔省下方。相比之下，在美国南部以下，高岩石圈波速仅限于格伦维尔省以西，特别是在深度不到150公里的地方。我们认为，东部劳伦蒂亚之下俯冲衍生的交代作用在热稳定之前对格伦维尔南部进行了改造，并可能形成了地幔龙骨。在格伦维尔北部之下，厚厚的、枯竭的劳伦斯岩石圈抵制了广泛的交代作用。格伦维利亚地体沿走向的年龄差异和由此产生的交代变质历史表明，元古代岩石圈至少需要250Myr才能获得抵抗变质的能力。
Cratons, the ancient cores of the continents, have survived thermal and mechanical erosion over multiple Wilson cycles, but the ability of their margins to withstand modification during continental convergence is debated. The Proterozoic Grenville orogeny operated for≥ 300 Myr along the eastern edge of the proto-North American continent Laurentia, whose age varied north-to-south from∼ 1.5− 0.25 Gyr at the time of collision. The preserved Grenville Province, west of the Appalachian terranes, has remained largely tectonically quiescent since its formation. Thick, cool, mantle lithosphere that underlies these Proterozoic regions is typically identified by elevated seismic velocities but lithospheric modification by fluid/melt-derived metasomatic enrichment above a subduction zone, can lead to a reduction in V P with little effect on V S and density. Absolute P-wavespeed constraints are therefore a vital complement to existing S-wave tomographic models of North America to investigate craton edge modification mechanisms in the Grenville orogen. New P-wave tomographic imaging of the North American continent, which benefits from recent developments in arrival-time processing of regional network deployments from the Canadian shield, reveals along strike wavespeed variation in the Grenville orogen. In the north, high seismic wavespeeds (to depths of 250 km) extend eastwards, from the Archean core of North America to beneath the Canadian Grenville Province. In contrast, below the southern US, high lithospheric wavespeeds are restricted to west of the Grenville Province, in particular at depths less than 150 km. We argue that subduction-derived metasomatism beneath eastern Laurentia modified the southern Grenville, prior to thermal stabilization and perhaps mantle keel formation. Beneath the northern Grenville, the thick, depleted Laurentian lithosphere resisted extensive metasomatism. Along strike age differences in Grenvillian terranes and their resulting metasomatic modification histories suggests that at least 250 Myr is required for Proterozoic lithosphere to gain resistance to modification.