Keller RA, Fisk MR, White WM
College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis 97331, USA.
Nature. 2000 Jun 8;405(6787):673-6. doi: 10.1038/35015057.
When a mantle plume interacts with a mid-ocean ridge, both are noticeably affected. The mid-ocean ridge can display anomalously shallow bathymetry, excess volcanism, thickened crust, asymmetric sea-floor spreading and a plume component in the composition of the ridge basalts. The hotspot-related volcanism can be drawn closer to the ridge, and its geochemical composition can also be affected. Here we present Sr-Nd-Pb isotopic analyses of samples from the next-to-oldest seamount in the Hawaiian hotspot track, the Detroit seamount at 51 degrees N, which show that, 81 Myr ago, the Hawaiian hotspot produced volcanism with an isotopic signature indistinguishable from mid-ocean ridge basalt. This composition is unprecedented in the known volcanism from the Hawaiian hotspot, but is consistent with the interpretation from plate reconstructions that the hotspot was located close to a mid-ocean ridge about 80 Myr ago. As the rising mantle plume encountered the hot, low-viscosity asthenosphere and hot, thin lithosphere near the spreading centre, it appears to have entrained enough of the isotopically depleted upper mantle to overwhelm the chemical characteristics of the plume itself. The Hawaiian hotspot thus joins the growing list of hotspots that have interacted with a rift early in their history.
当一个地幔柱与大洋中脊相互作用时，两者都会受到显著影响。大洋中脊可能会呈现出异常浅的水深、过量的火山活动、加厚的地壳、不对称的海底扩张以及洋脊玄武岩成分中的地幔柱成分。与热点相关的火山活动可能会被拉近到洋脊附近，其地球化学组成也会受到影响。在此，我们展示了对夏威夷热点轨迹中次古老海山——北纬51度的底特律海山——样本的锶-钕-铅同位素分析，结果表明，在8100万年前，夏威夷热点产生的火山活动具有与大洋中脊玄武岩难以区分的同位素特征。这种成分在夏威夷热点已知的火山活动中是前所未有的，但与板块重建的解释一致，即该热点在约8000万年前位于靠近大洋中脊的位置。由于上升的地幔柱在扩张中心附近遇到了热的、低粘度的软流圈和热的、薄的岩石圈，它似乎夹带了足够多同位素亏损的上地幔，从而掩盖了地幔柱本身的化学特征。因此，夏威夷热点加入了在其历史早期与裂谷相互作用的热点名单，且这一名单在不断增加。
