Energetics of the Earth:Mountain Building

Theresa Zajac, Haiyan Fu

Mountain Building model

Time Scales

The Solar System began to form about 6 billion years ago and the Earth and other planets about 4.5 billion years ago. mountain building events expend energy on time scales of several hundred million years. whereas others, like earthquakes, expend energy on time scales of a few seconds

Energy Source Mountain Building: Heat & Mechanical Energy

First, is mountain building resulting primarily from heat. The uplift comes because heat from inside the earth heats the overlying lithosphere, causing it to expand, lifting and swelling the surface upward.

The overall balance of energy in a steady state FTB:

Second is mechanical mountain building. tension (pulling apart) and compression (squeezing together). The relief (differences in elevation) come primarily because different blocks of earth move relative to each other, either falling or rising vertically, or one block being shoved (thrust) horizontally over another.

Mechanical Energy

Schematic cross -section of a critically tapered steady state fold-and-thrust belt(Dahlen F.A,1988)

WB: the rate of work on the base and front of the FTB

WD: the rate energy is dissipated against friction on the decollement fault

WS: the rate energy is dissipated by internal frictional processes within the deforming brittle wedge

WG: the rate of work against gravitational body forces

The static equilibrium equation:

Heat Budget

QT: total rate at which heat is conducted out of the top of the Wedge

QB: the total rate at which heat is conducted into the base of the wedge from the top of the basal decollement fault

QA: the total rate which heat is advected into the wedge across all the boundaries

HR: total rate of radiogenic heating

HS:the total rate of internal strain heatin

Schematic cross section of a steady state FTB and underlying subducting plate(Barr T.D,1989 )