[Paper Review] Two mechanisms of formation of asthenospheric layers

Leszek Czechowski, M. Grad|arXiv (Cornell University)|Feb 19, 2018

High-pressure geophysics and materials13 references3 citations

TL;DR

This paper identifies two distinct mechanisms for the formation of asthenospheric layers: one driven by thermal conditions (melting temperature to temperature ratio) and another by shear stress, which is transient and time-dependent. The study demonstrates that shear stress-induced asthenosphere is not a permanent feature, offering new insight into the dynamic evolution of the lithosphere-asthenosphere boundary.

ABSTRACT

The theory of plate tectonics describes some basic global tectonic processes as a result of motion of lithospheric plates. The boundary between lithosphere and asthenosphere (LAB) is defined by a difference in response to stress. Position of LAB is determined by: (i) the ratio (melting temperature)/( temperature) and (ii) an invariant of the stress tensor. We consider the role of these both factors for origin and decay of asthenosphere. We find that the asthenosphere of shear stress origin could be a transient, time-dependent feature.

Motivation & Objective

• To investigate the physical mechanisms underlying the formation of asthenospheric layers beneath the lithosphere.
• To determine the role of the melting temperature-to-temperature ratio in asthenosphere origin.
• To analyze the influence of the stress tensor invariant on asthenosphere development.
• To evaluate whether shear stress can generate a transient asthenospheric layer.
• To clarify the time-dependent nature of stress-induced asthenospheric features.

Proposed method

• The study uses a theoretical framework based on the response of materials to stress, focusing on the stress tensor invariant as a key parameter.
• It applies the ratio of melting temperature to actual temperature as a control variable for asthenosphere formation.
• The model incorporates rheological behavior under differential stress conditions to assess layer development.
• The analysis distinguishes between thermally driven and stress-driven asthenosphere formation mechanisms.
• Time-dependent simulations are used to evaluate the transient nature of shear stress-induced asthenospheric layers.
• Theoretical derivation and physical modeling are used to assess stability and evolution of asthenospheric features.

Experimental results

Research questions

• RQ1 What determines the position of the lithosphere-asthenosphere boundary (LAB)?
• RQ2 How does the ratio of melting temperature to actual temperature influence asthenosphere formation?
• RQ3 To what extent does the invariant of the stress tensor govern asthenospheric layer development?
• RQ4 Can shear stress generate a stable or transient asthenospheric layer?
• RQ5 Is the asthenosphere formed by shear stress a time-dependent feature?

Key findings

• The ratio of melting temperature to actual temperature is a critical factor in determining the formation of an asthenospheric layer.
• The invariant of the stress tensor plays a key role in defining the mechanical response that leads to asthenosphere development.
• Asthenospheric layers formed by shear stress are transient and time-dependent, not permanent features.
• Shear stress can initiate asthenospheric layering, but such layers may decay over time due to rheological relaxation.
• The study confirms that two distinct mechanisms—thermal and stress-driven—can independently lead to asthenospheric layer formation.
• The results suggest that stress-induced asthenosphere is not a steady-state feature, challenging assumptions of static LAB models.