HR: 17:15h
AN: V54B-06 [Abstracts]
TI: Incipient orogeny and UHP rocks: a genetic link
AU: Perchuk, L L
EM: llp@msu.ru
AF: Department of Petrology, Moscow State University, Leninskie Gory, Moscow, 119992
Russian Federation
AU: Perchuk, L L
EM: llp@msu.ru
AF: Institute of Experimental Mineralogy, Russian Academy of Sciences, Chernogolovka, Moscow, 142432
Russian Federation
AU: * Gerya, T V
EM: taras.gerya@erdw.ethz.ch
AF: Department of Earth Sciences, Swiss Federal Institute of Technology, Zrich, Sonneggstrasse 5, Zurich,
CH-8092
Switzerland
AU: * Gerya, T V
EM: taras.gerya@erdw.ethz.ch
AF: Institute of Experimental Mineralogy, Russian Academy of Sciences, Chernogolovka, Moscow, 142432
Russian Federation
AU: Burg, J
EM: jean-pierre.burg@erdw.ethz.ch
AF: Department of Earth Sciences, Swiss Federal Institute of Technology, Zrich, Sonneggstrasse 5, Zurich,
CH-8092
Switzerland
AB:
Initial stages of orogeny are often manifested by variety of geodynamic processes such as transition from subduction to
continental collision, break off of subducted slab, lithospheric delamination, deep subduction and exhumation of the
continental crust playing crucial role for the generation of geological structure of resulting orogenic system. Indeed, these
initial stages are still very poorly understood. On the basis of well known P-T-t paths and using two-dimensional numerical
modeling of transition from subduction of an oceanic slab to continent-continent collision we found a genetic link between
initiation of orogeny and formation and exhumation of coesite- and diamond-bearing UHP rocks metamorphosed at T>700°C
in presence of the dense supercritical silicate fluid and/or melts. Formation of these rocks is explained by a ``hot channel
effect''. This process involves the transient formation of a hot tectonic channel in crustal and mantle rocks at the
beginning of collision. The channel formed along the plate interface and could penetrate toward the bottom of the lithosphere
of the overriding plate (150-200 km) within the range of 700 and 1000°C. Anomalously high temperature is caused by
intense viscous and radiogenic heating produced in the channel by deeply subducted radiogenic upper-crustal rocks (e.g.,
sediments of passive margin origin). Heating is also associated with intense aqueous fluid flow released in the course of
rapid dehydration (deserpentinization) of the mantle lithosphere of the overriding plate that has been hydrated during
previous subduction stages. Lower effective viscosity of rocks subjected to increased temperature, partial melting, and fluid
infiltration promotes the mlange of hydrated mantle and crustal rocks within the hot channel. This channel may exist only
at the earliest stages of orogeny and producing rapidly large amounts of UHP-HT rocks. Further collision closes the channel
through squeezing rheologically weak (partially molten) buoyant rocks between the rigid lithospheric mantle and two colliding
plates. An assemblage of complicated P-T paths with repetitive loops characterizes the exhumation of UHP rocks during in the
hot channel.
DE: 3652 Pressure-temperature-time paths
DE: 3654 Ultra-high pressure metamorphism
DE: 8020 Mechanics, theory, and modeling
DE: 8104 Continental margins: convergent
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005