Effects of a realistic mantle thermal conductivity on the patterns of 3-D convection
Effects of a realistic mantle thermal conductivity on the patterns of 3-D convection
复制标题
真实地幔热导率对 3-D 对流模式的影响
DOI：
10.1016/s0012-821x(99)00165-x
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发表时间：
1999
影响因子：
5.3
通讯作者：
M. Rabinowicz
中科院分区：
文献类型：
--
作者：
F. Dubuffet;D. Yuen;M. Rabinowicz
A. M. Hofmeister [Science 283（1999）1699-1706]最近提出了一个描述地幔热导率随温度和压力变化的物理模型。我们数值研究了这种温度和压力依赖的热导率对三维常粘性对流的影响。对于瑞利数大于104到106的情况，采用了4 × 4 × 1的大纵横比盒。幂律指数支配声子对热导率的贡献控制对流的风格。对于硅酸盐，对流的模式是非常不同的，从恒定的电导率，而对流模式与氧化物的导电性是接近的情况下，恒定的电导率。Boussinesq和扩展的Boussinesq模型与粘性和绝热加热进行了研究。变热导率对地幔对流的主要影响是：（1）下地幔的加热;（2）长波长的Boussinesq对流;（3）短波长的扩展Boussinesq对流;（4）厚的稳定羽流和大的羽流头;（5）在地幔底部厚约500 km的热边界层。由于能量方程中的可变电导率，新项的贡献的大小是边界层处的绝热加热的几倍。一个大区域的超绝热下地幔约400至600 K的过剩是由可变的热导率。这一发现对最近地震发现的下地幔深部密度较轻具有有趣的意义。
A physical model describing the temperature and pressure dependences of mantle thermal conductivity has recently been provided by A.M. Hofmeister [Science 283 (1999) 1699–1706]. We have studied numerically the influences of such a temperature- and pressure-dependent thermal conductivity on 3-D constant viscosity convection. A large aspect-ratio box of 4 × 4 × 1 has been taken for Rayleigh numbers greater than 104to 106. The power-law index governing the phonon contribution to the thermal conductivity controls the style of convection. For silicates, the pattern of convection is quite different from that of constant conductivity, whereas the pattern of convection associated with conductivity of oxides is close to the case for constant conductivity. Both Boussinesq and extended-Boussinesq models with viscous and adiabatic heatings have been examined. Major effects of variable thermal conductivity on mantle convection are: (1) heating up of the lower mantle; (2) longer-wavelength Boussinesq convection; (3) shorter wavelength for extended-Boussinesq convection; (4) thick stable plumes with large plumeheads; (5) thicker thermal boundary layer of around 500 km at the base of the mantle. The contributions from the new terms due to the variable conductivity in the energy equation have magnitudes several times that of chondritic heating at the boundary layers. A large region of superadiabatic lower mantle with about a 400 to 600 K excess is caused by variable thermal conductivity. This finding has an interesting implication on the recent seismic finding of a lighter density in the deep portion of the lower mantle.