HR: 0800h
AN: U11A-0011    [Abstracts]
TI: Visco-elastic Models of Neo-Hadean and Archean Greenstone Belt Formation by Diapiric Density Inversion
AU: * Robin, C M
EM: crobin@physics.utoronto.ca
AF: University of Toronto, Depts. of Physics & Geology, 60 St. George St., Toronto, ON M5S 1A7, Canada
AU: Bailey, R C
EM: bailey@physics.utoronto.ca
AF: University of Toronto, Depts. of Physics & Geology, 60 St. George St., Toronto, ON M5S 1A7, Canada
AB: Diapirism as a model for the formation of Archean granite-greenstone terrains has been periodically in and out of favour since it was first suggested in 1951. Recently, there has been renewed interest in diapirism to explain Archean terrains, which has re-ignited the debate over the importance of vertical vs. horizontal tectonics in the Archean, or at least, the debate over when the change from one to the other is likely to have occurred. In 1980, Mareschal and West performed numerical calculations which tested the physics of crustal diapirism, and were able to simulate the bulk features of many granite-greenstone sequences. However, due to computational restrictions at the time, their rheologies were over-simplified, and recent information on mantle and crustal heat flow suggest they overestimated Archean thermal inputs. Here we present results modeling diapiric overturn using a moving mesh visco-elastic finite-element solver. We test a range of non-Newtonian rheologies, thermal parameters, and supracrustal volcanic thicknesses. Comparison of our results with field observation constrains the range of plausible models. We find that the formation of dome-and-keel structures occurs easily and rapidly (~ 10 Ma or less), even using conservatively cool estimates for Archean thermal profiles, implying that this process may have been important in the Neo-Hadean and Meso-Archean. Indeed, the ubiquity of dome-and-keel structures in Archean terrains suggests that diapirism may have been a dominant crustal process in hotter geological times. We speculate on what the predominance of such a mechanism implies for early crustal and lithospheric evolution.
DE: 8003 Diapir and diapirism
DE: 8020 Mechanics, theory, and modeling
DE: 8122 Dynamics: gravity and tectonics
DE: 8125 Evolution of the Earth (0325)
DE: 8159 Rheology: crust and lithosphere (8031)
SC: Union [U]
MN: 2007 Fall Meeting