Abstract
Faults and shear zones in orogens may be related to crustal shortening or extension or both. True extensional structures should ultimately intersect the Earth's surface when traced out in a direction opposite to that of hangingwall transport; the present dip of a fault in an orogen, and its relation to local layering, are unreliable guides. The observation of low-pressure metamorphic rocks structurally above high-pressure metamorphic rocks is not sufficient to diagnose crustal extension. A valid metamorphic criterion is the difference in pressure-time histories between footwall and hangingwall: if the footwall was decompressing faster than the hangingwall during shear zone movement, then the shear zone was truly extending the crust. The pressure-time history can be constrained via the temperature-time and pressure-temperature histories. Ideally, crustal extension inferred from structural data should be confirmed using diagnostic PTt information.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call