Lithospheric cooling trends and deviations in oceanic PP-P and SS-S differential traveltimes
Lithospheric cooling trends and deviations in oceanic PP-P and SS-S differential traveltimes
复制标题
海洋 PP-P 和 SS-S 差动时间的岩石圈冷却趋势和偏差
作者：
Goes S
大洋岩石圈的热结构和成分结构对板块运动具有重要的控制作用，但至今仍存在争议。我们的60，000个PP ‐PandSS‐Straveltime差与海洋PP和SS反弹点的集合提供了对纵波和横波速度的良好约束。通过计算旅行时的热模型转换为地震结构的热力学方法，我们测试是否岩石圈冷却可以解释PP-PandSS-Straveltime的变化与板块年龄。当PP波和SS波从逐渐变老的洋壳反射时，PP-和SS-应变时间有很大的分散性，但平均分别减少0.2和0.7 s/Myr½。具有大洋中脊玄武岩源地幔位温（1315° ± 50°C）的半空间和板块冷却模型都解释了PP-PandSS-Sanomalies的平均值及其随着板块年龄的下降。相对于冷却模型的残差PP ‐PandSS‐反常现象揭示了大尺度模式。沿着几条路径（例如，汤加-斐济到北美西部），深部地幔的地震不均匀性是造成PP-和SS-Straveltime变化的重要原因。大多数异常可能对应于上地幔的广泛温度变化，例如非常缓慢的中-北太平洋（可能需要100°C的额外温度）以及分别与深和浅水深相关的沿着脊的高速和低速异常。
The thermal and compositional structure of oceanic lithosphere, which exerts an important control on plate behavior, is still debated. Our set of 60,000PP‐PandSS‐Straveltime differences with oceanicPPandSSbounce points provides a good constraint on both compressional‐ and shear‐wave velocity. By calculating traveltimes for thermal models that are converted to seismic structures with a thermodynamic approach, we test whether lithospheric cooling can explainPP‐PandSS‐Straveltime variations with plate age. ThePP‐PandSS‐Straveltimes have substantial scatter but, on average, decrease by 0.2 and 0.7 s/Myr½, respectively, when thePPandSSwaves reflect off progressively older oceanic crust. Both a half‐space and a plate cooling model with a mid‐ocean ridge basalt‐source mantle potential temperature (1315° ± 50°C) explain the average values of thePP‐PandSS‐Sanomalies and their decrease with plate age. ResidualPP‐PandSS‐Sanomalies relative to a cooling model reveal large‐scale patterns. Along a few paths (e.g., Tonga–Fiji to western North America), seismic heterogeneity in the deep mantle is responsible for a significant fraction of thePP‐PandSS‐Straveltime variation. Most anomalies probably correspond to broad temperature variations in the upper mantle, such as a very slow central–northern Pacific (which may require a 100°C excess temperature) and high‐ and low‐velocity anomalies along the ridges that correlate with deep and shallow bathymetry, respectively.