What Is Mantle Convection?

Due to the increase of heat, the mantle material in the stratosphere decreases in density and expands in volume to generate a rising heat flow. The rising mantle material diverges around the bottom of the crust. As the temperature decreases, the density of the mantle material increases and it sinks into the mantle This process is called mantle convection.

Mantle convection :

Mantle convection is a hypothesis inferred from the knowledge of the earth. As early as 1881, Fisher (O. Fisher) in his book "Crust Physics" raised the idea that convection might exist in the mantle. In the 1930s, British geologist A. Holmes tried to explain the driving mechanism of continental drift by mantle convection. In the 1960s, the idea of mantle convection became

According to the rheological properties, the upper layers of the earth should be divided into rock layers (spheres) and soft stratospheres (spheres). The mantle material in the stratosphere has fluid-like properties due to partial melting. The thermal convection driven by the density difference (or temperature difference) in the fluid layer of limited thickness is generally a honeycomb structure. Each honeycomb has upflow, downflow and horizontal flow, which constitute a complete convection unit. The convection unit in a two-dimensional problem is called a convection ring. The convection ring in the completely fluid layer is generally rectangular. Based on deep source seismic data and estimates of the mantle phase change zone and rheological parameters, most scholars believe that the maximum depth of the mantle troposphere is about 700 km. Therefore, there are several or even a dozen convection rings below a plate. The direction of flow in adjacent convection rings is opposite, and the drag forces on the rock plates floating on them are also opposite, causing the drag forces to cancel each other out (Figure 1). This is the so-called aspect ratio in mantle convection research. shield".

Some people believe that the basis for limiting mantle convection to the upper mantle at a depth of 700 kilometers is insufficient, and therefore advocate full mantle convection. As the depth of the troposphere extends to a depth of 2900 km at the core-mantle boundary (Figure 2), the ratio of the plate's horizontal scale to the depth of the troposphere is on the order of 1, and the contradiction of aspect ratio can be resolved. In the late 1970s and early 1980s, research on whole-mantle convection was very active, including exploring the characteristics of whole-mantle convection and its relationship with surface observation data. Especially, three-dimensional effects have begun to be considered. But whether the whole-mantle convection hypothesis is true depends on whether it can interpret various geophysical observations.

The rock layer plate is generated by the hot mantle material in the mid-ocean ridge and returns to the mantle at the trench. Therefore, the horizontally moving rock layer plate is a component of the mantle convection. Convective systems should contain both rock layers and stratospheres with different rheological properties. Preliminary calculation results show that the appearance of rock layers in the convection system also makes the aspect ratio of the convection ring more reasonable. In the late 1970s, research in this area continued to improve with a view to obtaining more consistent results with surface observations. ^[2]

The upwelling flow in the mantle convection is of great significance to geophysics. It is the main way to transfer energy, momentum and mass from the inside of the earth to the surface. It is called the mantle upwelling flow or hot column. The columnar mantle current is sometimes called the mantle current. Upwelling flows are closely related to the formation of mid-ocean ridge rifts and continental rifts, surface hotspots and volcanic phenomena, and are therefore valued.