Geochemical and geophysical estimates of lithospheric thickness variation beneath Galapagos
Geochemical and geophysical estimates of lithospheric thickness variation beneath Galapagos
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DOI：
10.1016/j.epsl.2010.10.002
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发表时间：
2010-12-01
影响因子：
5.3
通讯作者：
Geist, D.
中科院分区：
文献类型：
--
作者：
Gibson, S. A.;Geist, D.
加拉帕戈斯群岛的活火山活动范围远比其他与热点相关的群岛，如夏威夷群岛（类似于20,000公里）广泛得多（约40,000公里）。在这里，我们使用地球化学和地球物理模型来约束这种大空间范围的熔体生成的原因和喷发玄武岩的不同成分。玄武岩岩浆中不相容的微量元素比例提供了对加拉帕戈斯群岛下熔融状态的物理和化学性质的洞察，以及火山活动相对广泛、非线性年龄递进分布的原因。虽然来自加拉帕戈斯群岛各个火山的玄武岩的这些（和同位素）比率的变化是有限的，但在整个群岛上喷发的玄武岩中已经观察到相当大的差异。我们利用稀土元素反演模型对以“羽流”和枯竭的MORB地幔成分为主的玄武岩进行了模拟，以限制不同加拉帕戈斯火山下熔体柱顶部的深度。通过转换最近发表的层析实验中的s波数据[Villagomez， dr . et al., 2007]。加拉帕戈斯群岛表面波层析成像下的上地幔结构。j .地球物理学。[参考文献112]到温度，我们已经能够绘制出加拉帕戈斯岩石圈的底部，即地幔潜在温度为1315摄氏度的地热与无水橄榄岩固体相交的地方。我们的地球物理模型和地球化学模型的结果之间存在着极好的相关性。这些预测表明，岩石圈厚度的变化范围从加拉帕戈斯群岛西南部岛屿（如费尔南迪纳岛和伊莎贝拉岛）地下60公里到东北部岛屿（如吉诺维萨岛、马尔切纳岛、圣地亚哥东部和圣克鲁斯北部）地下45公里不等。远离现今地幔柱轴假定位置的较薄的岩石圈，加上地幔柱的横向偏转，导致了相对大片地区的活火山活动。岩石圈厚度相对于离加拉帕戈斯扩张中心的距离的不均匀变化与太平洋这部分海底岩石圈的复杂性质是一致的，可能是由于脊跳。(C) 2010 Elsevier B.V.版权所有
Active volcanism in Galapagos is far more widespread (>40,000 km(2)) than in other hotspot-related archipelagos, such as Hawaii (similar to 20,000 km(2)). Here we employ both geochemical and geophysical models to constrain the causes of this large spatial extent of melt generation and the diverse compositions of erupted basalts. Insight in to the physical as well as the chemical nature of the melting regime beneath Galapagos - and the cause of the relatively widespread, non-linear age-progressive distribution of volcanism - is provided by incompatible-trace-element ratios of basaltic magmas. Whilst variations in these (and isotopic) ratios of basalts from individual Galapagos volcanoes are limited, considerable differences have been observed in basalts erupted across the archipelago. We have used rare-earth-element inversion modelling for basalts dominated by "plume" and depleted MORB mantle components to constrain the depth to the top of the melt column beneath different Galapagos volcanoes. By converting S-wave data from a recently published tomographic experiment [Villagomez, D.R. et al., 2007. Upper mantle structure beneath the Galapagos Archipelago from surface wave tomography. J. Geophys. Res. 112] to temperature we have been able to map the base of the Galapagos lithosphere, i.e. where the geotherm, with a mantle potential temperature of 1315 degrees C, intersects the anhydrous peridotite solidus.An excellent correlation exists between the results of our geophysical and geochemical models. These predict that lithospheric thickness varies from similar to 60 km beneath islands in the south west of the Galapagos Archipelago (e.g. Fernandina and Isabela) to similar to 45 km below those in the northeast (e.g. Genovesa, Marchena, eastern Santiago and northern Santa Cruz). The thinner lithosphere away from the postulated site of the present-day plume axis, combined with the lateral deflection of the plume, is responsible for active volcanism over a relatively large area. Non-uniform variations in lithospheric thickness relative to distance from the Galapagos Spreading Centre are consistent with the complex nature of the oceanic lithosphere beneath this part of the Pacific, perhaps due to ridge jumps. (C) 2010 Elsevier B.V. All rights reserved.