Open AccessMagmatic processes and segmentation at a fast spreading mid‐ocean ridge: Detailed investigation of an axial discontinuity on the East Pacific Rise crest at 9°37′N
Author(s) -
Smith Matthew C.,
Perfit Michael R.,
Fornari Daniel J.,
Ridley W. Ian,
Edwards Margo H.,
Kurras Gregory J.,
Von Damm Karen L.
Publication year - 2001
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2000gc000134
Subject(s) - geology , lava , seafloor spreading , hydrothermal circulation , mid ocean ridge , volcano , basalt , ridge , crest , flood basalt , rift , trough (economics) , igneous rock , geochemistry , paleontology , tectonics , volcanism , macroeconomics , physics , quantum mechanics , economics
Geophysical and petrological boundaries on mid‐ocean ridges provide ideal locations to study the relationships between magmatic, tectonic, and hydrothermal processes. Alvin‐based observational data and geochemical data for basalts and hydrothermal fluids are used to investigate these relationships at an axial discontinuity on the East Pacific Rise (EPR) crest between ∼9°36′N and 9°38′N. This ridge‐crest discontinuity is morphologically expressed by the overlap of an eastern and western axial summit collapse trough (ASCT) that delimits the primary volcanic and hydrothermal loci along the ridge crest in this area. The ASCTs overlap by ∼3 km and are offset in a right‐lateral sense by 0.45 km. Near‐bottom imaging of this area in 1989 and 1991 shows changes in volcanic morphology and increases in hydrothermal and biological activity consistent with the occurrence of a magmatic event during that time interval. When combined with the inferred age and structure of the seafloor, basalt geochemistry, and hydrothermal fluid chemistry, these temporal changes suggest active southward propagation of the eastern ASCT and show that the western ASCT was unaffected by the recent magmatic event. Numerous extinct hydrothermal vents and older‐looking lava flow surfaces suggest waning of magmatic activity in the western ASCT.Young‐looking lava flows within or proximal to the eastern ASCT have anomalously high Mg numbers relative to the regional trend and are chemically similar to lava erupted in 1991 along the 9°46′–52′N EPR region. We propose that the young‐looking lava flows in the eastern ASCT are related to the 1991 eruption. Data show that the 9°37′N axial discontinuity marks a magmatic and hydrothermal boundary along the EPR ridge‐crest, and we argue that it be classified as a third‐order discontinuity. This result is consistent with geophysical evidence suggesting fundamental differences in the crust and upper mantle north and south of the 9°37′N discontinuity.