Martinez Fernando, Taylor Brian
Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA.
Nature. 2002 Mar 28;416(6879):417-20. doi: 10.1038/416417a.
At mid-ocean ridges, plate separation leads to upward advection and pressure-release partial melting of fertile mantle material; the melt is then extracted to the spreading centre and the residual depleted mantle flows horizontally away. In back-arc basins, the subducting slab is an important control on the pattern of mantle advection and melt extraction, as well as on compositional and fluid gradients. Modelling studies predict significant mantle wedge effects on back-arc spreading processes. Here we show that various spreading centres in the Lau back-arc basin exhibit enhanced, diminished or normal magma supply, which correlates with distance from the arc volcanic front but not with spreading rate. To explain this correlation we propose that depleted upper-mantle material, generated by melt extraction in the mantle wedge, is overturned and re-introduced beneath the back-arc basin by subduction-induced corner flow. The spreading centres experience enhanced melt delivery near the volcanic front, diminished melting within the overturned depleted mantle farther from the corner and normal melting conditions in undepleted mantle farther away. Our model explains fundamental differences in crustal accretion variables between back-arc and mid-ocean settings.
在大洋中脊，板块分离导致富源地幔物质向上平流并减压部分熔融；熔体随后被抽取到扩张中心，残余的亏损地幔则水平流走。在弧后盆地，俯冲板块对幔流平流和熔体抽取模式以及成分和流体梯度具有重要控制作用。模拟研究预测，地幔楔对弧后扩张过程有显著影响。在此我们表明，劳弧后盆地的各种扩张中心表现出岩浆供应增强、减弱或正常的情况，这与距弧火山前沿的距离相关，而与扩张速率无关。为解释这种相关性，我们提出，在地幔楔中因熔体抽取而产生的亏损上地幔物质被翻转，并通过俯冲诱导的角向流重新引入弧后盆地之下。扩张中心在火山前沿附近经历增强的熔体供应，在距角部较远的翻转亏损地幔内熔融减弱，而在更远的未亏损地幔中处于正常熔融条件。我们的模型解释了弧后与大洋环境之间地壳增生变量的根本差异。
