Modeling the dynamic process of slab subduction based on temperature-dependent thermal coefficients
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摘要: 热传导系数和热膨胀系数是影响板块俯冲动力学过程的两个重要参数. 由于地球介质的不均匀性，热系数也会随深度发生变化.然而，这种变化在地球动力学模拟研究中往往被忽略.本文针对随温度变化的热传导系数和热膨胀系数， 模拟板块俯冲的动力学过程，分析热系数、黏度对板块俯冲形态的影响及其对应的地幔对流特征.结果表明，依温度变化的热传导系数和热膨胀系数会影响地幔温度及黏度分布，进而改变板块的俯冲角度；黏度是控制板块俯冲动力学演化过程的重要因素；地幔对流受黏度结构的影响，呈现分层对流及局部多个对流环等多种不同形态的对流场特征.Abstract: The thermal conductivity and expansion coefficients are two significant parameters that have influence on the dynamic process of slab subduction. Due to the heterogeneity of Earth medium, these two coefficients are usually variable with depth. Unfortunately, such variations are often ignored in current modeling studies of geodynamics. The present study refers to the temperature-dependent thermal conductivity and expansion to simulate the dynamic process of slab subduction. The impact of thermal parameters and viscosity on slab geometry and the corresponding characteristics of mantle convection are analyzed. The modeling results show that the temperature-dependent thermal conductivity and expansion affect the subduction angle by changing the thermal and viscosity structure. The viscosity plays a critical role in controlling the slab dynamic evolution. The mantle convection is affected by viscosity structure and exhibits different patterns, such as layered convection and local multiple convection loops, etc.
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Keywords:
- slab subduction /
- viscosity structure /
- mantle convection /
- numerical modeling
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图 2 模型1的热结构(a)及黏度(b)演化. 白色实线表示上、 下地幔的分界线，箭头表示流速
Figure 2. Temperature(a) and viscosity(b)evolution for model 1 The white line denotes the boundary of upper and lower mantle，and the arrows represent fluid velocities
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图 3 热系数对板块俯冲演化的影响(a)、(b)分别为模型1(黑色实线)和模型2(红色虚线)的热结构和黏度结构，(c)为俯冲经历5，15和25 Ma后模型2的黏度演化. 图中白色实线表示上、下地幔的分界线，箭头表示流速
Figure 3. Influence of thermal coefficients on slab subduction evolution (a)-(b)Temperature and viscosity depth profiles for model 1(black solid line) and model 2(red dashed line);(c)Viscosity profiles for model 2 after 5，15 and 25 Ma evolution. The white line denotes the boundary of upper and lower mantle，and the arrows represent fluid velocities
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图 3 地幔黏度结构对板块俯冲演化的影响(a)模型3，ηl/ηu=1；(b)模型4，ηl/ηu=100.白色实线表示上、下地幔的分界线，箭头表示流速
Figure 3. Influence of mantle viscosity structure on slab subduction evolution(a)Model 3 with ηl/ηu=1;(b)Model 4 with ηl/ηu=100. The white line denotes the boundary of upper and lower mantle，and the arrows represent fluid velocities
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图 5 板块边界剪切带黏度对板块俯冲演化的影响(a)模型5，ηsz=5×1020 Pa · s，(b)模型6，ηsz=3×1021 Pa · s. 白色实线表示上、 下地幔的分界线，箭头表示流速
Figure 5. Influence of the shear zone viscosity at the plate boundary on slab subduction evolution(a)Model 5 with ηsz=5×1020 Pa · s;(b)Model 6 with ηsz=3×1021 Pa · s. The white line denotes the boundary of upper and lower mantle，and the arrows represent fluid velocities
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图 6 不同模型对应的地幔对流场(黑色线为流线，箭头表示流速)(a)模型1;(b)模型2;(c)模型3;(d)模型4;(e)模型5;(f)模型6
Figure 6. Mantle flow with different models where black lines are streamlines and arrows represent fluid velocities(a)Model 1;(b)Model 2;(c)Model 3;(d)Model 4;(e)Model 5;(6)Model 6 900 km
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