Seismic shear wave structure of the uppermost mantle beneath the Mohns Ridge
Seismic shear wave structure of the uppermost mantle beneath the Mohns Ridge
复制标题
莫恩斯海岭下方最上地幔的地震剪切波结构
DOI：
10.1029/2011gc003792
复制
发表时间：
2011
期刊：
影响因子：
3.7
通讯作者：
R. Dunn
中科院分区：
文献类型：
--
作者：
M. M. Conley;R. Dunn
在大洋中脊产生的地壳，其完全扩展速率小于1.20毫米/年，据观察只有0-4公里厚，远低于全球平均水平，即以更快的扩展速率产生的6-7公里厚的洋壳。这种差异的起源是未知的，但据推测，在最慢的蔓延脊的轴，无论是抑制浅熔化或熔体提取较厚的热边界层。我们提出了一个区域宽带数据的分析，主要是爱和瑞利波，收集沿着非常缓慢的扩展莫恩斯海岭（地壳厚度为104公里）在挪威-格陵兰海。地震数据约束岩石圈和软流圈的岩石圈年龄为0至25 Ma的速度。我们发现岩石圈厚度与一个简单的脊半空间热模型（通过温度和压力对地幔物质地震性质的影响）的预测非常匹配。软流圈剪切波速度与这个热模型一致，加上最年轻时≤2%的熔化。就在地幔的顶部，一个薄的区域，速度介于地幔和辉长岩之间，这表明一些熔体被冻结到地幔中，如果一个薄的轴向岩石圈盖抑制熔体从地幔中提取，熔体随后被冻结到地幔中，可能会发生这种情况。如果这一过程在某种程度上发生在所有缓慢到非常缓慢的扩张脊，那么可能有空间上的大水库的原因不明的辉长岩熔体冻结到地幔中的许多海洋盆地。
Crust produced at mid‐ocean ridges with full spreading rates less than ∼20 mm/yr is observed to be only 0–4 km thick, well below the global average of 6–7 km for oceanic crust produced at faster spreading rates. The origin of this difference is unknown, but is speculated to result from a thicker thermal boundary layer at the axis of the slowest spreading ridges that either inhibits shallow melting or melt extraction. We present an analysis of regional broadband data, predominately Love and Rayleigh waves, collected along the very slow spreading Mohns Ridge (where crustal thickness is ∼4 km) in the Norwegian‐Greenland Sea. The seismic data constrain lithospheric and asthenospheric velocities for lithospheric ages from 0 to 25 Ma. We find lithospheric thickness to closely match the prediction of a simple ridge half‐space thermal model (via the temperature and pressure effects on the seismic properties of mantle materials). Asthenospheric shear wave velocities are consistent with this thermal model plus ≤2% melt at the youngest ages. Just at the top of the mantle, a thin zone with velocities intermediate between those of mantle and gabbroic rocks suggests that some melt is frozen into the mantle as might occur if a thin axial lithospheric lid inhibits melt extraction from the mantle and the melt is subsequently frozen into the mantle. If this process occurs to some degree at all slow to very slow spreading ridges, then there may be spatially large reservoirs of unaccounted for gabbroic melt frozen into the mantle throughout many ocean basins.