Open AccessGeochemical evidence for low magma supply and inactive propagation at the Galápagos 93.25°W overlapping spreading center
Author(s) -
Rotella Melissa D.,
Sinton John M.,
Mahoney John J.,
Chazey William
Publication year - 2009
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2009gc002445
Subject(s) - geology , plagioclase , mantle (geology) , incompatible element , trace element , geochemistry , magma , melt inclusions , olivine , mineralogy , volcano , partial melting , paleontology , quartz
Major and trace element concentrations; Sr, Nd, and Pb isotopic ratios; and plagioclase and olivine compositions of samples from 92°35′W to 94°10′W on the Galápagos Spreading Center (GSC) constrain magmatic processes associated with the 93.25°W overlapping spreading center (OSC). Significant variations in parental magma compositions and extent of low‐pressure fractionation over short along‐axis distances suggest small, discontinuous, or poorly mixed magma chambers. Mineralogical, petrological, and geochemical data indicate this OSC is characterized by low overall melt supply. Regional along‐axis geochemical gradients along the western GSC (e.g., in 206 Pb/ 204 Pb, Nb/Zr, and La (8) /Sm (8) ) are interrupted by increased variability within the OSC, consistent with less efficient mixing of melts in this region. Despite a long‐term history of westward propagation, bathymetric and geochemical data are inconsistent with recent propagation of this offset; the eastern limb appears to have recently retreated and left behind a series of abandoned ridges within the overlap zone. The eastern limb shows two progressive westward trends of decreasing ratios of highly to moderately incompatible elements, one outside and one within the overlap zone. The overlapping portion of the western limb also has low ratios of these elements. These patterns are consistent with previously depleted mantle being preferentially melted beneath this offset.