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熔体在地壳和地幔中怎样迁移及其动力学是地质学中的一个重要问题。作为地壳深融作用的产物 ,混合岩中的浅色体提供了一个极好的机会来探讨影响地壳熔体在中下地壳迁移的因素。为此 ,我们对美国加州南 Sierra Nevada岩基中典型的混合岩、变泥质岩及邻近的花岗闪长岩进行了详细的主要元素地球化学和野外构造变形分析 ,同时应用流体动力学理论估算了在中下地壳条件下 ,典型浅色体的迁移距离。南 Sierra Nevada岩基中的混合岩中的浅色体厚度为 1mm至 1cm。在部分熔融程度较高的区域 (>10 % ) ,浅色体相互连接而成网结状构造 ,应变的承载方式主要以 IWL(Interconnected Weak L ayers)形式进行 ,即熔融体表现为弱相而承载大部分的应变。相反地 ,在部分熔融程度较低的区域 (<5 % ) ,浅色体孤立地出现 ,应变的承载方式主要以 L BF(L oad- Bearing Frame-work)形式进行 ,即应变主要由非熔融体的基质来承担。这表明在混合岩形成过程中 ,熔体的出现强烈地制约着应变分解作用。应用 Shaw的岩石粘度模型 ,我们根据浅色体的主要元素地球化学成分计算了浅色体在熔融状态下的粘度。根据流体动力学原理 ,估算了浅色体在不同条件下的迁移距离。计算结果表明 :1和典型花岗岩相比 ,浅色体具有较高的粘度 ,为 10 9～ 10 1 2
How the melt migrates in the crust and the mantle and its kinetics is an important issue in geology. As a result of the crustal melting, the light-colored bodies in the mixed rocks provide an excellent opportunity to explore the factors that influence the migration of the crustal melt in the middle and lower crust. For this reason, we conducted detailed analysis of major element geochemical and field tectonic deformations of the typical mixed rocks, metamorphic rocks and adjacent granodiorites in the Sierra Nevada rock mass of the south of California, USA. At the same time, we applied the fluid dynamics theory The migration distance of a typical light-colored body is estimated under the conditions of the middle and lower crust. The light body thickness in the mixed rocks in the South Sierra Nevada rock base is 1 mm to 1 cm. In areas with a high degree of partial melting (> 10%), the light-colored bodies are connected to each other to form a network-like structure. The bearing of the strain is mainly in the form of an Interconnected Weak L ayers, ie, the melt behaves as a weak phase Carry most of the strain. In contrast, light-colored bodies appear in isolation in areas with a lower degree of partial melting (<5%), and the bearing modes of the strain are mainly in the form of L BF (L oad-Bearing Frame-work), ie, the strain mainly consists of non-melting Body matrix to bear. This indicates that the occurrence of melt strongly constrain the strain decomposition in the formation of mixed rocks. Using Shaw’s rock viscosity model, we calculated the viscosities of the light-colored bodies in the molten state based on the major elemental geochemical composition of the light-colored body. According to the principle of hydrodynamics, the migration distance of light body under different conditions is estimated. The calculation results show that: 1 Compared with the typical granite, the light-colored body has a higher viscosity of 10 9 ~ 10 1 2