Inferences of mantle viscosity based on ice age data sets: Radial structure
Inferences of mantle viscosity based on ice age data sets: Radial structure
复制标题
基于冰河时代数据集的地幔粘度推论：径向结构
DOI：
--
复制
发表时间：
2016
期刊：
影响因子：
--
通讯作者：
K. Latychev
中科院分区：
文献类型：
--
作者：
H. Lau;J. Mitrovica;J. Austermann;O. Crawford;D. Al;K. Latychev
我们对冰川均衡调整（GIA）数据进行了联合非线性反演，包括：加拿大和斯堪的纳维亚的冰期后衰减时间、芬诺斯坎德弛豫谱（FRS）、晚全新世海平面差（DSL）最高分（基于澳大利亚海平面历史的最新汇编），以及地球势的2度纬向谐波（J2）的变化率。解析能力分析表明：(1)FRS约束上地幔平均粘度为~ 3 × 1020 Pa s，(2)冰期后衰变时间数据要求地幔顶部~ 1500 km的平均粘度为1021 Pa s， (3) J2基准约束下地幔平均粘度为~ 5 × 1021 Pa s。为了调和(2)和(3)，地幔深部粘度必须增加到1022 ~ 1023 Pa s。我们的分析强调了精确校正J2观测对现代冰川融化的重要性，以便可靠地推断深部地幔粘度。我们还进行了大量的正演计算，以研究GIA数据集与下地幔内粘度跳跃的兼容性，正如地球动力学和地震研究所建议的那样，并得出结论，GIA数据可以容纳在1000-1700公里深度范围内的边界上粘度的1-2个数量级的急剧跳跃，但不需要这样的特征。最后，我们发现没有1 - D粘度剖面能够同时与DSL高位数据相协调，并表明这种不一致可能是由于横向不均匀的地幔粘度，这是我们在一项伴随研究中探讨的问题。
We perform joint nonlinear inversions of glacial isostatic adjustment (GIA) data, including the following: postglacial decay times in Canada and Scandinavia, the Fennoscandian relaxation spectrum (FRS), late‐Holocene differential sea level (DSL) highstands (based on recent compilations of Australian sea level histories), and the rate of change of the degree 2 zonal harmonic of the geopotential, J2. Resolving power analyses demonstrate the following: (1) the FRS constrains mean upper mantle viscosity to be ∼3 × 1020 Pa s, (2) postglacial decay time data require the average viscosity in the top ∼1500 km of the mantle to be 1021 Pa s, and (3) the J2 datum constrains mean lower mantle viscosity to be ∼5 × 1021 Pa s. To reconcile (2) and (3), viscosity must increase to 1022–1023 Pa s in the deep mantle. Our analysis highlights the importance of accurately correcting the J2 observation for modern glacier melting in order to robustly infer deep mantle viscosity. We also perform a large series of forward calculations to investigate the compatibility of the GIA data sets with a viscosity jump within the lower mantle, as suggested by geodynamic and seismic studies, and conclude that the GIA data may accommodate a sharp jump of 1–2 orders of magnitude in viscosity across a boundary placed in a depth range of 1000–1700 km but does not require such a feature. Finally, we find that no 1‐D viscosity profile appears capable of simultaneously reconciling the DSL highstand data and suggest that this discord is likely due to laterally heterogeneous mantle viscosity, an issue we explore in a companion study.