Effects of plate boundary geometry and kinematics on mantle melting beneath the back-arc spreading centers along the Lau Basin
Effects of plate boundary geometry and kinematics on mantle melting beneath the back-arc spreading centers along the Lau Basin
复制标题
板块边界几何和运动学对劳盆地弧后扩张中心下方地幔熔融的影响
DOI：
10.1016/j.epsl.2010.08.004
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发表时间：
2010
影响因子：
5.3
通讯作者：
D. Blackman
中科院分区：
文献类型：
--
作者：
N. Harmon;D. Blackman
弧后扩张中心，沿着劳盆地的轴向形态，地壳厚度和地球化学的趋势，这是相反的，通常观察到在大洋中部扩张中心。我们开发的地幔流，热结构和熔融的劳后弧汤加俯冲系统的三个劳扩张中心-Valu Fa岭，东部劳，中央劳的二维数值模型。我们的目标是确定是否沿走向的循环模式或地幔楔内的水合作用的变化可以解释所观察到的趋势。我们使用现今的板块和俯冲板的几何形状和速度，探讨了一系列的地幔潜在温度和水含量的情况下，并测试预测是否符合观测地壳厚度和水含量的岩浆爆发在扩张的山脊。在测试的地幔参数范围内，我们发现，1300°C的潜在温度和大于0.22%wt的源水含量需要匹配观测到的地壳厚度和熔岩水含量在Valu Fa。在相同或更高的地幔位温下，与东劳和中劳观测结果相匹配，需要在弧下地幔源中的水少得多。一个小的背景水化的0.01%重量水在地幔楔需要匹配的水在中央刘岩浆的观察。我们预测，弧和弧后熔融区是相互连接的所有潜在的温度和亚弧水含量在东劳扩展中心和Valu Fa脊，而在中央劳，他们只连接的情况下，地幔位温为1400°C或更高。我们推测，寿命较长的东劳和中央劳裂谷和轴向火山作用可能脱水的地幔楔和减缓这些扩展中心下的熔体生产。Valu Fa山脊，这是积极传播到一个更多的水化楔与Tofua弧，经验增强熔融相对于其他两个扩展中心。对于Valu Fa的情况下，我们表明，快速俯冲结合附近的沟槽和扩展中心的结果，在增强的上升流，因此，增加地壳生产。俯冲速度较慢，收敛速率为45毫米/年，地幔干燥，地幔位温为1350°C，使中央劳和瓦鲁法之间的地壳厚度差缩小到1.2公里以内。相比之下，对于现今的运动学，地幔干燥，地幔位温为1350°C，我们的模型预测Valu Fa的地壳厚度比Central Lau厚3.1km，更接近观测值。
The back-arc spreading centers that extend along the Lau Basin exhibit trends in axial morphology, crustal thickness, and geochemistry, which are opposite those typically observed at mid ocean spreading centers. We develop 2D numerical models of mantle flow, thermal structure and melting of the Lau back-arc–Tonga subduction system for each of three Lau spreading centers—Valu Fa Ridge, the Eastern Lau, and the Central Lau. Our goal is to determine whether along-strike variability in the circulation pattern or hydration within the mantle wedge could explain the trends observed. We use present-day plate and subducted slab geometries and velocities to explore a range of mantle potential temperature and water content scenarios and test whether predictions match observations of crustal thickness and water content of the magmas erupted at the spreading ridges. Within the range of mantle parameters tested, we find that a potential temperature of 1300°C and source water contents greater than 0.22% wt are required to match observed crustal thickness and lava water contents at Valu Fa. Substantially less water in the sub arc mantle source is required to match the Eastern Lau and Central Lau observations at the same or higher mantle potential temperatures. A small background hydration of 0.01% wt water in the mantle wedge is required to match the observations of water in the Central Lau magmas. We predict that the arc and back-arc melting regions are interconnected for all potential temperatures and sub arc water contents at the Eastern Lau spreading center and at the Valu Fa Ridge, while at the Central Lau, they are only connected for cases when mantle potential temperature is 1400°C or greater. We hypothesize that the longer-lived Eastern Lau and Central Lau rifting and axial volcanism may have dehydrated the mantle wedge and slowed melt production beneath these spreading centers. The Valu Fa Ridge, which is actively propagating into a more hydrated wedge associated with the Tofua arc, experiences enhanced melting relative to the other two spreading centers. For the Valu Fa case, we show fast subduction in combination with the proximity of the trench and spreading center results in enhanced upwelling and, therefore, increased crustal production. Slower subduction, with a convergence rate of 45mm/yr, a dry mantle, and a 1350°C mantle potential temperature reduces the difference in crustal thickness between the Central Lau and Valu Fa to within 1.2km. In contrast, for present-day kinematics with a dry mantle and 1350°C mantle potential temperature, our models predict the crustal thickness at Valu Fa to be 3.1km thicker than Central Lau, much closer to the observed values.