HR: 08:00h
AN: T11D-01 INVITED    [Abstracts]
TI: Progress in our Understanding of High- and Ultrahigh-pressure Metamorphism
AU: * Ernst, W G
EM: ernst@geo.stanford.edu
AF: Stanford University, Depaartment of Geological & Environmental Sciences, Stanford, CA 94305-2115, United States
AU: Liou, J G
EM: jliou@stanford.edu
AF: Stanford University, Depaartment of Geological & Environmental Sciences, Stanford, CA 94305-2115, United States
AB: Fifty years ago on what we regarded as a relatively immobile Earth, the physical conditions and geologic environments that produced blueschists, eclogites, and garnet lherzolites, although surmised, were quantitatively unknown. With the advent of high-pressure synthesis equipment and more precise calorimetry, minerals such as jadeite, aragonite, pyrope, and dense polymorphs of silica and carbon were shown to be stable at elevated pressures and low-to-moderate temperatures. Geothermal gradients required by the P-T stability ranges of these phases are only explicable on a dynamic planet typified by mantle circulation and lithospheric subduction. Integration of experimental studies with plate tectonics has elucidated the genesis of both oceanic and continental crust. Combined with geochemical, geophysical, and isotopic data, high-pressure phase equilibria now are providing new constraints on the constitution and differentiation of the controlling mantle. Circumpacific-type blueschists and eclogites form in penetratively deformed allochthonous slabs and nappes that are overturned seaward, requiring profound descent of oceanic basement of at least 30-50 km during metamorphism. Neoblastic coesite and microdiamond inclusions in tough, rigid host minerals demonstrate that Alpine-type continental collision involves incomplete recovery of rocks subducted yet more deeply, up to 100-130 km. More surprising still, garnet lherzolites from the central Alps, east-central China, western Norway, and Bohemia display mineral intergrowths and exsolution lamellae reflecting the former presence of majoritic garnet and other ultrahigh-pressure phases, requiring depths of origin of host peridotites exceeding 300 km. Nano- minerals hold another key to quantifying the recovered depths of subduction and/or mantle return flow. Times of storage at great depth and exhumation rates remain current problems. Fluid-rock and lithosphere-asthenosphere interactions have recycled volatiles to the deep Earth through the subduction of both hydrous and nominally anhydrous phases. Mantle petrochemistry and the dynamics of plumes + plates control the evolving architecture of the crust and the dependent biosphere, hence investigations utilizing advanced technologies on condensed high- and ultrahigh-pressure materials will lead to a fuller understanding of the deep Earth in time and space
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 3613 Subduction zone processes (1031, 3060, 8170, 8413)
DE: 8021 Melanges
DE: 8104 Continental margins: convergent
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting