Superplume, supercontinent, and post-perovskite: Mantle dynamics and anti-plate tectonics on the Core–Mantle Boundary
Superplume, supercontinent, and post-perovskite: Mantle dynamics and anti-plate tectonics on the Core–Mantle Boundary
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DOI：
10.1016/j.gr.2006.06.003
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发表时间：
2007
影响因子：
6.1
通讯作者：
S. Maruyama;M. Santosh;Dapeng Zhao
中科院分区：
文献类型：
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作者：
S. Maruyama;M. Santosh;Dapeng Zhao
西太平洋三角带（WPTZ）是一个未来超大陆的边界，将在250 Ma后形成。西太平洋断裂带东部和南部具有双面俯冲带的特征，至少自200 Ma以来，西太平洋断裂带是一个以大量制冷和向地幔楔供水为主的区域。WPTZ下的中地幔边界层（MBL, 410-660 km）存在长度超过1200 km的长滞流板块，而在核心-地幔边界（CMB, 2700-2900 km）存在厚的高v异常，可能代表着板块墓地。为了解释D″层冷异常，必须对MBL中曾经停滞的板块进行灾难性塌陷，这种塌陷可能发生在30-20 Ma，作为打开一系列弧后盆地、热区、小海洋盆地的触发器，并可能形成一系列海洋和大陆的微板块。这些事件是上地幔被来自下地幔的更热、更肥沃的物质所取代的结果。利用洋中脊玄武岩（MORB）和软锰矿相图，结合410 ~ 660 km的地震不连续面、D″层厚度和超低速度带（ULVZ）的分布，估算了固体地球的热结构。结果清楚地表明存在两个主要的超羽流和一个下流。除了D″层外，地球的热结构似乎受180 Ma以来俯冲历史的控制。D″层的热结构似乎是由更古老的石板墓地控制的，正如对700 Ma的Laurasia， Gondwana和Rodinia的古地理重建所期望的那样。对比太平洋超级羽流和西太平洋带下方的地幔层析成像表明，随着时间的推移，一个寒冷的板块墓地转变为一个大规模的地幔上涌。太平洋超级羽流诞生于1.0-0.75 Ga超大陆Rodinia下方最冷的CMB，在那里，超过12个大陆通过碰撞合并积累了大量的冷板块。在全地幔尺度上的高速p波异常显示出局限于环太平洋和特提斯地区MBL的停滞板块。高速带可以在太平洋地区清楚地识别出来，这表明在比罗迪尼亚分裂更古老的地质时期形成的平板墓地的存在。我们推测主要的俯冲发生在冈瓦纳形成时期，在600 - 540 Ma期间非常活跃，在泛大陆北半部（月桂陆）形成期间400 - 300 Ma再次出现。我们将三个主要的板块墓地与地球历史上三个主要的造山运动联系起来，新出现的图像表明，今天的太平洋超级羽流位于罗丁板块墓地的中心。通过对比西太平洋三角带（WPTZ）、亚洲的Laurasia、非洲的Gondwana和太平洋的Rodinia的地幔热结构，结合地震层析成像，推测了超羽流的形成机制。最冷的地幔通过广泛的俯冲形成一个超大陆，随着几亿年的时间变化到超大陆下面最热的地幔。太平洋超级羽流是由边缘陡峭的速度梯度严格定义的，特别是有很好的记录的s波速度。超级羽流最外层区域的特征是罗迪尼亚板墓地，形成一个甜甜圈形状。我们为太平洋超级羽流建立了一个岩石学模型，并展示了如何……
The Western Pacific Triangular Zone (WPTZ) is the frontier of a future supercontinent to be formed at 250 Ma after present. The WPTZ is characterized by double-sided subduction zones to the east and south, and is a region dominated by extensive refrigeration and water supply into the mantle wedge since at least 200 Ma. Long stagnant slabs extending over 1200 km are present in the mid-Mantle Boundary Layer (MBL, 410–660 km) under the WPTZ, whereas on the Core–Mantle Boundary (CMB, 2700–2900 km depth), there is a thick high-V anomaly, presumably representing a slab graveyard. To explain the D″ layer cold anomaly, catastrophic collapse of once stagnant slabs in MBL is necessary, which could have occurred at 30–20 Ma, acting as a trigger to open a series of back-arc basins, hot regions, small ocean basins, and presumably formation of a series of microplates in both ocean and continent. These events were the result of replacement of upper mantle by hotter and more fertile materials from the lower mantle. The thermal structure of the solid Earth was estimated by the phase diagrams of Mid Oceanic Ridge Basalt (MORB) and pyrolite combined with seismic discontinuity planes at 410–660 km, thickness of the D″ layers, and distribution of the ultra-low velocity zone (ULVZ). The result clearly shows the presence of two major superplumes and one downwelling. Thermal structure of the Earth seems to be controlled by the subduction history back to 180 Ma, except in the D″ layer. The thermal structure of the D″ layer seems to be controlled by older slab-graveyards, as expected by paleogeographic reconstructions for Laurasia, Gondwana and Rodinia back to 700 Ma. Comparison of mantle tomography between the Pacific superplume and underneath the WPTZ suggests the transformation of a cold slab graveyard to a large-scale mantle upwelling with time. The Pacific superplume was born from the coldest CMB underneath the 1.0–0.75 Ga supercontinent Rodinia where huge amounts of cold slabs had accumulated through collision-amalgamation of more than 12 continents. A high velocity P-wave anomaly on a whole-mantle scale shows stagnant slabs restricted to the MBL of circum-Pacific and Tethyan regions. The high velocity zones can be clearly identified within the Pacific domain, suggesting the presence of slab graveyards formed at geological periods much older than the breakup of Rodinia. We speculate that the predominant subduction occurred through the formation period of Gondwana, presumably very active during 600 to 540 Ma period, and again from 400 to 300 Ma during the formation of the northern half of Pangea (Laurasia). We correlate the three dominant slab graveyards with three major orogenies in earth history, with the emerging picture suggesting that the present-day Pacific superplume is located at the center of the Rodinian slab graveyard. We speculate the mechanism of superplume formation through a comparison of the thermal structure of the mantle combined with seismic tomography under the Western Pacific Triangular Zone (WPTZ), Laurasia (Asia), Gondwana (Africa), and Rodinia (Pacific). The coldest mantle formed by extensive subduction to generate a supercontinent, changes with time of the order of several hundreds of million years to the hottest mantle underneath the supercontinent. The Pacific superplume is tightly defined by a steep velocity gradient on the margin, particularly well documented by S-wave velocity. The outermost region of the superplume is characterized by the Rodinia slab graveyard forming a donut-shape. We develop a petrologic model for the Pacific superplume and show how …