高温高压条件下榴辉岩和超硅石榴石热传导性质研究:对俯冲带热结构的启示

The thermal structure of subduction zone has attracted widespread attentions since the 1960s for its important implications in the stability of hydrous minerals, deep seismicity, metamorphic reactions and arc magmatism. It is well kown that thermal transport properties (including thermal conductivity and thermal diffusivity) of eclogite and majoritic garnet, which is the major components of subcuting slab, strongly controled the thermal structure of subdution zone. However, few data was reported untill now. In this proposal, we intend to study the thermal transport properties eclogite and majoritic garnet under high pressure and high temperature conditions (0-22GPa, 300-1500K), which will provide great constraints on the thermal structure and deep earthquake. The experimental results will benifit us in understanding the thermal structure of Western Pacific subduction zone and its connection to the destruction of North China cration and the complex-shaped velocity discontinuities around a depth of 410 km and 660 km under Eastern China.

俯冲带热结构制约着俯冲带中含水矿物的稳定范围，变质作用和岩浆的产生等地质过程。俯冲带物质（榴辉岩和超硅石榴石）的热传导性质是影响俯冲带热结构的重要因素之一，但目前相关研究却基本处于空白状态。本项目拟在高温高压条件下(0-22GPa, 300-1500K)查明榴辉岩和超硅石榴石的热传导性质（热导率、热扩散率），为合理的模拟俯冲带热结构提供基础实验数据和约束条件，探讨西太平洋俯冲带与华北克拉通破坏和中国东部420km、510km、660km复杂的地震波不连续面之间的关系。

俯冲带热结构制约着俯冲带中含水矿物的稳定范围，变质作用和岩浆的产生等地质过程。俯冲带物质(榴辉岩和超硅石榴石)的热传导性质是影响俯冲带热结构的重要因素之一，但目前相关研究却基本处于空白状态。本项目在高温高压条件下(0-16GPa, 300-1000K) 查明了榴辉岩和超硅石榴石的热传导性质(热导率、热扩散率)。我们的研究结果显示：.1..相对于俯冲洋幔，俯冲洋壳具有较低的热导率，相当于俯冲带的绝热层，可以有效的减少从周围地幔传入俯冲带的热量。通过模拟计算俯冲带的热结构发现，如果考虑大洋地壳的隔热贡献，那么俯冲带的实际温度要比前人认为的低50-120K，相应的俯冲带中亚稳态橄榄石的含量将增加约30-50%。同理，也会有更多的蛇纹石可以相变为Phase A(一种含水矿物)继而将一定量的水带入地幔转换带。.2..常温高压条件下超硅石榴石+斯石英组合（俯冲洋壳高压相）的热导率和热扩散率分别为2.77 W m^-1 K^-1和0.87mm^2 s^-1，远低于林伍德石的热导率（9.83 W m^-1 K^-1）和热扩散率 (3.09 mm^2 s^-1)。虽然由于实验技术原因我们目前无法获得高温条件下超硅石榴石+斯石英组合的热导率，但常温条件下的测试结果表明，俯冲洋壳的存在是俯冲板片在进入转换带以后仍能保持低温的重要因素之一。.