Heat - The Solid Earth - page 319

Figure 7.27. The cooling history for the Alpine Fault region, Southern Alps, New
Zealand. (a) The modelled exhumation history (white arrows) for a particle moving
westwards towards the Alpine Fault. The convergence rate is 1 cm yr -1 . The thermal
structure shown is that developed after 5 Ma of deformation as appropriate for the
Southern Alps. Cross-hatching marks the peak strain and equates with the Alpine
Fault. There is no vertical exaggeration. (b) The cooling history for rocks adjacent to
the Alpine Fault (white boxes and grey line). The white boxes are (in order of
increasing temperature) zircon fission-track, biotite K-Ar, muscovite K-Ar and
inferred pre-rift temperatures of the region. The dashed line shows the cooling
history of a particle in the numerical model shown in (a). (Reprinted from
Tectonophysics , 349 , Batt, G. E. and Brandon, M. T., Lateral thinking: 2-D
interpretation of thermochronology in convergent orogenic settings, 185-201,
Copyright 2002, with permission from Elsevier.)
history of the terrain. These thermal models demonstrate that a general knowl-
edge of the stratigraphy of an area is essential before its metamorphic history can
be unravelled.
Convective movement of fluid has not been discussed, but it can be a major
factor in heat transport around plutons and during dehydration of overthrust
terrains. As a general rule, fluid movement speeds up thermal re-equilibration and
reduces to some degree the extent of aureoles around intrusions; at the same time it