Massentransporte und Massenverteilungen im System Erde  
    Classification of different types of geoid at top of the plume  Classification of different types of geoid at top of the plume   
 

 

Classification of different types of geoid at top of the plume

We classified different plume types in terms of their geoid signals. These calculations have been done using a Finite Element convection code in axi-symmetric spherical shell geometry, where the plumes developed at the pole. We ran simulations of sixteen different viscosity distributions for three different Rayleigh numbers. They illustrate scenarios where hot plumes have a larger or smaller influence on the geoid and topography compared to the constant viscosity case. We now are able to define different classes of plumes by classifying their geoid signals.

 

Class 1). Mainly depth dependent viscosity:

 

A viscosity which changes essentially with depth has a completely different effect on the shape of the geoid. For strongly depth dependent cases, a geoid with negative sign shows up and for less depth dependent viscosity, a positive sign with small amplitude geoid appears. This can be considered as a transition between strongly depth dependent and constant viscosity case.

 

Figure 1. Temperature field (left) and Geoid anomaly above the plume (right) of class 1 model

Class 2). Temperature dependent viscosity:

 

Temperature dependent models become more chaotic when the activation energy is increased. This increase is associated with increasing mantle temperature, too. Consequently, the flow in the hot, lower mantle becomes strongly time dependent as well as the total geoid. In this category, all geoids associated with the first arriving plumes and typical plume after reaching steady state are bell shaped with decreasing amplitude.

Figure 2. Temperature field (left) and Geoid anomaly above the plume (right) of class 2 model

Class 3). Temperature – pressure dependent viscosity

 

The combination of depth and temperature dependent viscosity can be divided into three different types by itself: 1) depth dominant 2) temperature dominant and 3) compensation cases

Whereas there is a lid at the top surface as a result of temperature dependence with different thickness the geoid anomalies in these cases are surprisingly similar although they have strongly different rheology.

Figure 3. Temperature field (left) and Geoid anomaly above the plume (right) of class 3 model

For more details, see Shahraki and Schmeling, 2010, submitted