Importance of initial buoyancy field on evolution of mantle thermal structure: Implications of surface boundary conditions
Importance of initial buoyancy field on evolution of mantle thermal structure: Implications of surface boundary conditions
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DOI：
10.1016/j.gsf.2014.05.004
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发表时间：
2015-01-01
影响因子：
8.9
通讯作者：
Forte, Alessandro M.
中科院分区：
文献类型：
--
作者：
Glisovic, Petar;Forte, Alessandro M.
虽然在地幔不均匀性的地震成像方面取得了重大进展，但仍有待解决的突出问题是，在遥远的地质历史中，地幔温度异常的分布情况不明，导致了全球层析成像模型推断出的现今异常。为了解决这个问题，我们提出了3-D对流模型在可压缩和自引力地幔初始化不同的假设温度模式。我们的前向对流模拟的一个显著特点是使用表面构造板块运动与底层地幔流的自洽耦合，而不施加规定的表面速度（即，板状边界条件）。作为一个近似的表面力学条件之前，板块构造开始运作，我们采用无滑移（刚性）边界条件。刚性边界条件表明，在地幔流演化过程中，初始的热控结构得以保留，其地理位置是固定的。考虑到不同假设的表面边界条件（刚性和板状）对地幔热不均匀性演化的影响，我们认为，七个超级地幔柱的内禀浮力最有可能在现今地幔热结构的层析图像中得到解决。我们的对流模拟与板状边界条件显示，在爪哇-印度尼西亚海沟系统下的初始冷异常的演变产生了一个长期的，稳定的模式的热不均匀性的最低地幔，类似于今天的大低剪切速度省（LLSVP），特别是在太平洋以下。然而，俯冲带的演化可能受到太古代以来深根和长寿的超级地幔柱驱动的地幔流的影响。这些对流模型还检测到的Perm异常，已被确定为一个独特的缓慢功能，从两个主要LLSVP的内在浮力。我们发现，没有必要在下地幔的密集的化学“桩”，以产生一个稳定的分布的温度异常，与LLSVP和Perm异常。我们的断层扫描为基础的对流模拟还表明，在东南太平洋板内火山活动可以解释为浅的小规模对流下的东太平洋隆起的超级羽流触发。(C)2014年，中国地质大学（北京）和北京大学。制作和主办Elsevier B. V.保留所有权利。
Although there has been significant progress in the seismic imaging of mantle heterogeneity, the outstanding issue that remains to be resolved is the unknown distribution of mantle temperature anomalies in the distant geological past that give rise to the present-day anomalies inferred by global tomography models. To address this question, we present 3-D convection models in compressible and self-gravitating mantle initialised by different hypothetical temperature patterns. A notable feature of our forward convection modelling is the use of self-consistent coupling of the motion of surface tectonic plates to the underlying mantle flow, without imposing prescribed surface velocities (i.e., plate-like boundary condition). As an approximation for the surface mechanical conditions before plate tectonics began to operate we employ the no-slip (rigid) boundary condition. A rigid boundary condition demonstrates that the initial thermally-dominated structure is preserved, and its geographical location is fixed during the evolution of mantle flow. Considering the impact of different assumed surface boundary conditions (rigid and plate-like) on the evolution of thermal heterogeneity in the mantle we suggest that the intrinsic buoyancy of seven superplumes is most-likely resolved in the tomographic images of present-day mantle thermal structure. Our convection simulations with a plate-like boundary condition reveal that the evolution of an initial cold anomaly beneath the Java-Indonesian trench system yields a long-term, stable pattern of thermal heterogeneity in the lowermost mantle that resembles the present-day Large Low Shear Velocity Provinces (LLSVPs), especially below the Pacific. The evolution of subduction zones may be, however, influenced by the mantle-wide flow driven by deeply-rooted and long-lived superplumes since Archean times. These convection models also detect the intrinsic buoyancy of the Perm Anomaly that has been identified as a unique slow feature distinct from the two principal LLSVPs. We find there is no need for dense chemical 'piles' in the lower mantle to generate a stable distribution of temperature anomalies that are correlated to the LLSVPs and the Perm Anomaly. Our tomography-based convection simulations also demonstrate that intraplate volcanism in the south-east Pacific may be interpreted in terms of shallow small-scale convection triggered by a superplume beneath the East Pacific Rise. (C) 2014, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. All rights reserved.