Autori: Ducea, M.N., Barton, M.D.

Editorial: Geology, 35 (11), p.1047-1050, 2007.

Rezumat:

A compilation of age, Sr, Nd and O isotopic analyses of plutonic rocks from the western North American Cordillera shows that the high-flux pulses of magmatism that make up most of the exposed North American arcs are dominated by upper plate lithospheric mass. Oceanic crustal (basalts and sediments) melting cannot be a principal mechanism responsible for arc magmatism. Mass balance calculations show that no more than 50% of that mass can be mantle-derived. The mechanisms responsible for igniting high-flux magmatism in these batholiths remain elusive, but flare-ups must have fundamentally developed in response to crustal/lithospheric thickening. These arcs represent the sites of crustal differentiation and contribute to net continental growth only if dense residual lower crust was returned to the convective mantle. Isotopic data shown here suggest that if convective removal of batholithic roots does take place, it must be a consequence and not a cause of episodic flare-ups, and therefore it postdates high-flux magmatic events. The Altiplano-Puna Volcanic Complex in South America may be the most recent continental arc segment in flare-up mode.

Cuvinte cheie: arc magmatism, flare-up events