Continental Magmatism and Dynamic Topography
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Isostasy, flexure and dynamic processes all influence the shape of the Earth’s surface. While the first two processes are well understood, dynamic topography remains controversial. On the continents, dynamic uplift is often expressed by positive long-wavelength gravity anomalies, radial drainage patterns, and slow seismic velocity anomalies within the upper mantle. Volcanic activity and elevated heat flow are also often observed. The aim of this study is to investigate the link between geochemical compositions of intracontinental magmatism and geophysical, geomorphological and geodetic observations of dynamic uplift. Three volcanic regions are considered in detail: western North America, northeast Brazil and Madagascar. The combined database includes 348 new whole-rock geochemical analyses. Rare earth element concentrations of mafic, asthenospheric-derived volcanic samples are exploited to calculate the depth and temperature of melt generation by inverse modelling. A sensitivity test of this modelling scheme is carried out. Lithospheric thickness and mantle temperature are independently determined from shear wave velocity models. Beneath western North America, a negative correlation between shear wave velocities at depths of 70–150 km and degree of melting is observed. Temperatures obtained from igneous compositions and from shear wave velocity profiles beneath volcanic fields closely agree. Melts are produced within, or close to, the spinel-garnet transition zone at depths shallower than $\sim
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Maclennan, John