Gravity anomalies, flexure and mantle rheology seaward of circum-Pacific trenches
Gravity anomalies, flexure and mantle rheology seaward of circum-Pacific trenches
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DOI：
10.1093/gji/ggw275
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发表时间：
2016-10
影响因子：
2.8
通讯作者：
J. Hunter;A. Watts
中科院分区：
文献类型：
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作者：
J. Hunter;A. Watts
我们使用卫星导出的自由空间重力异常数据的集合平均值，结合逆模型技术，来确定环太平洋俯冲洋岩石圈的有效弹性厚度Te及其与板块年龄的关系。合成模型测试表明，使用重力异常，而不是水深测量，数据和至少750公里长的剖面，可以最好地恢复T e。基于均匀Te弹性板的反演模型表明，Te随俯冲大洋岩石圈年龄的增加而增加，并近似由基于冷却板模型的390 ± 10 ℃海洋等温线的深度给出。如果在海沟轴线和外部隆起之间包括一个机械薄弱区，则观测到的重力异常和计算出的重力异常之间的不匹配将得到显著改善。这一弱带与弯曲断裂和地震活动的观测结果是一致的。反向模型显示，外海隆向陆地的T e通常比外海隆向海的T e小40- 65%。向陆和向海的Te都随着岩石圈年龄的增加而增加，并分别由342-349 ℃和671-714 ℃海洋等温线的深度给出。的依赖性的T-电子年龄是一致的海洋岩石圈的冷却模型，因为它远离洋中脊和温度依赖的韧性蠕变的海洋岩石圈矿物，如橄榄石。通过比较观测到的T-E预测T-E的基础上，实验室推导的屈服强度信封和假设的弹塑性变形，我们试图约束海洋岩石圈的流变学。无论假设的摩擦系数如何，干橄榄石的低温塑性遵循Goetze，Evans & Goetze，Rateron等人的定律。和Mei et al .所有这些都为环太平洋俯冲带的观测T e提供了相当好的拟合。这一结果与夏威夷群岛形成了鲜明对比，夏威夷群岛的这些湍流定律通常过于强大，无法适应观测结果。Pacific接骨板内的流变学差异可能是由加载时间尺度的差异以及所发生的粘弹性应力松弛量的差异引起的。其他的可能性包括夏威夷群岛的热再生和岩浆辅助的再生。
SUMMARY We have used ensemble averages of satellite-derived free-air gravity anomaly data, together with inverse modelling techniques, to determine the effective elastic thickness, T e , of circum-Pacific subducting oceanic lithosphere and its relationship to plate age. Synthetic modelling tests show that T e can be recovered best using gravity anomaly, rather than bathymetry, data and profiles that are at least 750 km long. Inverse modelling based on a uniform T e elastic plate suggests that T e increases with age of the subducting oceanic lithosphere and is given approximately by the depth to the 390 ± 10 ◦ C oceanic isotherm based on a cooling plate model. Misfits between the observed and calculated gravity anomalies are significantly improved if a mechanically weak zone is included between the trench axis and the outer rise. This weak zone is coincident with observations of bend-faulting and seismicity. Inverse modelling shows that T e landward of the outer rise is generally 40–65 per cent less than the T e seaward of the outer rise. Both landward and seaward T e increases with age of the lithosphere and are given by the depth to the 342–349 ◦ C and 671–714 ◦ C oceanic isotherm, respectively. A dependence of T e on age is consistent with models for the cooling of oceanic lithosphere as it moves away from a mid-ocean ridge and the temperature-dependent ductile creep of oceanic lithospheric minerals such as olivine. By comparing the observed T e to the predicted T e based on laboratory-derived yield strength envelopes and an assumption of elastic-perfectly plastic deformation, we have attempted to constrain the rheology of oceanic lithosphere. Regardless of the assumed friction coefficient, the dry-olivine low-temperature plasticity flow laws of Goetze, Evans & Goetze, Raterron et al . and Mei et al . all provide quite a good fit to the observed T e at circum-Pacific subduction zones. This result contrasts with the Hawaiian Islands, where these flow laws are generally too strong to fit the observations. The discrepancy in rheology within Pacific plate may be caused by differences in the timescale of loading and therefore the amount of viscoelastic stress relaxation that has occurred. Other possibilities include thermal rejuvenation and magma-assisted flexure at the Hawaiian Islands.