Ancellin M. A., Samaniego Pablo, Vlastelic I., Nauret F., Gannoun A., Hidalgo S. (2017). Across-arc versus along-arc Sr-Nd-Pb isotope variations in the Ecuadorian volcanic arc. Geochemistry Geophysics Geosystems, 18 (3), p. 1163-1188. ISSN 1525-2027.
Titre du document
Across-arc versus along-arc Sr-Nd-Pb isotope variations in the Ecuadorian volcanic arc
Ancellin M. A., Samaniego Pablo, Vlastelic I., Nauret F., Gannoun A., Hidalgo S.
Source
Geochemistry Geophysics Geosystems, 2017,
18 (3), p. 1163-1188 ISSN 1525-2027
Previous studies of the Ecuadorian arc (1 degrees N-2 degrees S) have revealed across-arc geochemical trends that are consistent with a decrease in mantle melting and slab dehydration away from the trench. The aim of this work is to evaluate how these processes vary along the arc in response to small-scale changes in the age of the subducted plate, subduction angle, and continental crustal basement. We use an extensive database of 1437 samples containing 71 new analyses, of major and trace elements as well as Sr-Nd-Pb isotopes from Ecuadorian and South Colombian volcanic centers. Large geochemical variations are found to occur along the Ecuadorian arc, in particular along the front arc, which encompasses 99% and 71% of the total variations in Pb-206/Pb-204 and Sr-87/Sr-86 ratios of Quaternary Ecuadorian volcanics, respectively. The front arc volcanoes also show two major latitudinal trends: (1) the southward increase of Pb-207/Pb-204 and decrease of Nd-143/Nd-144 reflect more extensive crustal contamination of magma in the southern part (up to 14%); and (2) the increase of Pb-206/Pb-204 and decrease of Ba/Th away from similar to 0.5 degrees S result from the changing nature of metasomatism in the subarc mantle wedge with the aqueous fluid/siliceous slab melt ratio decreasing away from 0.5 degrees S. Subduction of a younger and warmer oceanic crust in the Northern part of the arc might promote slab melting. Conversely, the subduction of a colder oceanic crust south of the Grijalva Fracture Zone and higher crustal assimilation lead to the reduction of slab contribution in southern part of the arc.
Plan de classement
Géologie et formations superficielles [064]
;
Géophysique interne [066]
