Information - TS7.4 HP / UHP (ultrahigh-pressure) nappes: exhumation mechanisms and tectonic implications
High-pressure and ultrahigh-pressure metamorphic rocks typically occur in collisional orogens. Most of them are derived from continental crust and they often form nappes sandwiched between lower-pressure units. Exhumation to Earth’s surface often took place during continent collision, at speeds comparable to plate velocities. The exhumation mechanisms and tectonic significance of HP and UHP rocks are still incompletely understood.
Open questions include: What circumstances lead to deep subduction of continental crust? How fast and how complete are metamorphic reactions during subduction and during exhumation? What is the maximum depth recorded by UHP rocks on Earth? How does a P-T-t path constrain the exhumation mechanism? How does the sedimentary record in foreland basins constrain the exhumation mechanism? What is the structural/textural record of HP/UHP exhumation? How are mantle rocks (garnet peridotites) introduced into UHP nappes? Did all rocks in a nappe experience the same maximum conditions or are HP/UHP blocks embedded in a lower-pressure matrix? Are all HP and UHP terranes exhumed by the same basic process? Is the material in the subduction channel strong or weak (weak enough to allow buoyant rise or even circulation)?
Welcome are contributions from all disciplines which can improve our understanding of the subduction/exhumation process, including structural geology, metamorphic petrology, detrital sediment studies, numerical and analogue modelling, geochronology, geophysics...
Preliminary List of Solicited Speakers
John Wheeler: Exhumation of HP/UHP tectonic units
P.J. O'Brien: Exhumation of UHP rocks: deciphering the petrologic and geochronologic evidence in Himalayan examples
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