Upper mantle structure of the Tonga‐Lau‐Fiji region from Rayleigh wave tomography
Upper mantle structure of the Tonga‐Lau‐Fiji region from Rayleigh wave tomography
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DOI：
10.1002/2016gc006656
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发表时间：
2016-11
期刊：
影响因子：
3.7
通讯作者：
S. S. Wei-S.;Y. Zha;W. Shen;D. Wiens;J. Conder;S. Webb
中科院分区：
文献类型：
--
作者：
S. S. Wei-S.;Y. Zha;W. Shen;D. Wiens;J. Conder;S. Webb
我们通过联合拟合来自环境噪声和双平面波层析成像的瑞利波相速度，研究了汤加-劳-斐济地区的上地幔地震结构。结果表明，劳盆地下方存在一个宽的低速区，最小SV速度约为3.7 ± 0.1 km/s，表明上涌的热软流层具有广泛的部分熔融。速度异常沿着刘氏扩张中心中部和东部的变化表明，地幔中存在不同程度的熔体孔隙。在北部的扩张中心远离汤加板块，推断熔融开始于约70公里的深度，并在地幔中形成一个倾斜带，倾斜到西部远离弧。这种模式表明，被动减压熔融过程提供的澳大利亚板块地幔从西方。在南部，由于来自澳大利亚地幔的供应受到劳岭岩石圈的阻碍，来自附近板片的水控制的通量熔融在弧后占主导地位。这种物质来源的变化导致了地球化学和轴向形态沿着扩张中心的快速转变。残留的劳海岭和斐济高原的特征是60-80公里厚的岩石圈，下面是低速软流圈。我们的研究结果表明，移动的岩石圈的东北部斐济高原-劳岭下面的活跃的塔韦乌尼火山。方位角各向异性表明，地幔流动方向从斐济下方的海沟垂直旋转到劳盆地下方的扩展垂直，这为地幔楔和萨摩亚柱的南向流动提供了证据。
We investigate the upper mantle seismic structure in the Tonga‐Lau‐Fiji region by jointly fitting the phase velocities of Rayleigh waves from ambient‐noise and two‐plane‐wave tomography. The results suggest a wide low‐velocity zone beneath the Lau Basin, with a minimum SV‐velocity of about 3.7 ± 0.1 km/s, indicating upwelling hot asthenosphere with extensive partial melting. The variations of velocity anomalies along the Central and Eastern Lau Spreading Centers suggest varying mantle porosity filled with melt. In the north where the spreading centers are distant from the Tonga slab, the inferred melting commences at about 70 km depth, and forms an inclined zone in the mantle, dipping to the west away from the arc. This pattern suggests a passive decompression melting process supplied by the Australian plate mantle from the west. In the south, as the supply from the Australian mantle is impeded by the Lau Ridge lithosphere, flux melting controlled by water from the nearby slab dominates in the back‐arc. This source change results in the rapid transition in geochemistry and axial morphology along the spreading centers. The remnant Lau Ridge and the Fiji Plateau are characterized by a 60–80 km thick lithosphere underlain by a low‐velocity asthenosphere. Our results suggest the removal of the lithosphere of the northeastern Fiji Plateau‐Lau Ridge beneath the active Taveuni Volcano. Azimuthal anisotropy shows that the mantle flow direction rotates from trench‐perpendicular beneath Fiji to spreading‐perpendicular beneath the Lau Basin, which provides evidence for the southward flow of the mantle wedge and the Samoan plume.