Open AccessOrigin of MORB enrichment and relative trace element compatibilities along the Mid‐Atlantic Ridge between 10° and 24°N
Author(s) -
Hémond Christophe,
Hofmann Albrecht W.,
Vlastélic Ivan,
Nauret François
Publication year - 2006
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2006gc001317
Subject(s) - peridotite , basalt , trace element , geology , incompatible element , geochemistry , mantle (geology) , seamount , metasomatism , mid ocean ridge , mid atlantic ridge , mantle plume , partial melting , ridge , lithosphere , paleontology , tectonics
The origin of chemically and isotopically enriched basalts along mid‐ocean ridges (E‐MORB) has been the subject of recent interest, particularly in cases where they are not related to a specific mantle plume. We present new isotope dilution analyses for Th, U, La, Ce, and Pb in 26 mostly glassy tholeiite samples dredged from the Mid‐Atlantic Ridge (MAR) between 10° and 24°N. We interpret these data in combination with other previously published trace element data and isotope ratios for the same samples. We focus on the region at 14°–15°N, where incompatible trace element abundances are enriched by as much as factors of 40, relative to the depleted basalts found to the north and the south of this region. We invoke simple recycling of alkali basalts found on oceanic islands and seamounts as an alternative E‐MORB origin to a recently published metasomatic enrichment model. A small amount of recycled alkali basalt is added to the local depleted mantle peridotite. Melting of such mixed sources can produce the observed E‐MORB at 14°–15°N MAR and elsewhere. The bulk partition coefficients of Nb, Ta, K, and Pb (relative to other trace elements) are geochemically important because these elements are widely used as tracers of source chemistry. We evaluate their partitioning using simple log‐log plots, and we compare the 10°–24° MAR basalts with a similar suite from the CIR 18°–20°S. In both suites, Nb (bulk) partitioning is close to Th, and Pb is close to Pr. Tantalum partitioning is also very close to Nb in the MAR setting but between U and K in the CIR setting. Potassium is slightly more compatible than U in the MAR suite but less compatible in the CIR setting. Thus, although the bulk partition coefficients of these elements do vary slightly in different regions, their overall consistency is remarkable considering that the partitioning of the individual elements is governed by different mineral phases.