Receiver function analysis of the North American crust and upper mantle

Abstract

Data from 27 permanent broad-band stations spread over North America and sampling diverse tectonic regimes of varying ages from the Archaean to the Phanerozoic, were analysed using the receiver function approach. Receiver functions, a few hundred at most of the locations, provide valuable constraints on the composition of the crust shaped by diverse processes characteristic of their time of formation. The chemically inert and stable nature of the Archaean domains of Canada is well manifested in their low Poisson ratio (0.26, felsic, lower than global averages for Precambrian age crust) accompanied by a thicker than global average (>35 km) Archaean crust. Data from the Canadian Cordillera and Innuitian orogens of Phanerozoic times indicate the possible operation of two distinctly different crustal processes resulting in thin crusts (<35 km) with dominantly felsic and more mafic compositions, respectively. These processes are restricted to the region above 410 km without disturbing the integrity of the mantle transition zone (MTZ), which is evident from the remarkably homogeneous nature of the 410 and 660 km discontinuities beneath the Canadian landmass. Contrastingly, the thermally complex Phanerozoic southern California region suggests the presence of a heterogeneous mantle transition zone possibly owing to localized 660 topography with a relatively uniform 410 overlain by a crust heterogeneous in composition and perhaps maturing to that of a continent.