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The Condor seamount at Mid-Atlantic Ridge as a supplementary source of trace and rare earth elements to the sediments

AuthorsCaetano, Miguel; Vale, Carlos; Anes, Bárbara; Raimundo, Joana; Drago, Teresa; Schimdt, Sabine; Nogueira, Marta; Oliveira, Anabela; Prego, R.
KeywordsCondor seamount
Rare earth elements
Pb isotopes
Azores archipelago
North Atlantic Ocean
Issue Date2013
CitationDeep Sea Research - Part II - Topical Studies in Oceanography 98(PA): 24-37 (2013)
AbstractThe Condor Seamount rises from seabed to 180 m water depth, being located 10 nautical miles southwest of the island of Faial, Azores Archipelago at the Mid-Atlantic Ridge (MAR). The vertical distribution of major, minor, trace and rare earth elements (REE) and Pb isotopes was studied in four sediment cores: one from the top of the Condor Seamount (200 m, MC9), two from the seamount base (1400 m, MC2 and MC4), and one from a deep area (1900 m, MC8). Sediments from the top of the Condor were composed by coarser particles being the fine fraction lower than 1%. Conversely the other sediments were constituted by 51–92% of fine particles (<63 μm). Individual fragments of volcanic material (>2 mm) were found at several depths of the cores sampled at the base of the seamount. The core collected in the top of the Condor showed higher carbonate content (76–86%) compared with the other cores (41–64%). The chemical compositions of MC2 and MC4 point to an enhancement of V, Cr, Co, Ni and Fe concentrations. Lower concentrations in MC8 hypothesis that Condor seamount constitutes a supplementary source of trace elements. The most plausible explanation for the enhancement found in sediments of the seamount base is the weathering of slopes with volcanic activities, which supply particles with higher element concentrations than pelagic sediments. This hypothesis is corroborated by REE data, showing increased chondrite normalized ratios in MC2 and MC4. Moreover, the REE pattern found in those cores was comparable to that existing in volcanic material with Light REE enrichment in comparison to Heavy REE. These results indicate a substantial contribution of particles derived from volcanic activities to sediments settled in the vicinity of the Condor Seamount. It is argued the potential use of REE in sediments from this region as tracers of volcanic activities. Depth profiles of 206Pb/207Pb and 206Pb/208Pb showed lower ratios in the first 8 cm sediment layers, reflecting atmospheric input of anthropogenic Pb in the last century. On the basis of Pb profiles it is proposed a baseline Pb concentration of 3.6±0.2 μg g−1 for pelagic sediments of the region with an isotopic signature of 206Pb/207Pb=1.227±0.003 and 206Pb/208Pb=0.492±0.001 signature. The isotope plots of 206Pb/207Pb versus 208Pb/206Pb showed a linear trend indicating the mixing between more radiogenic pre-industrial end-members and less radiogenic anthropogenic lead. The Pb isotope composition of sediments from the Condor area falls closer to North Atlantic Sediment Line. Sediments showed a 206Pb/204Pb signature closer to the basalts of the Capelo volcanic complex than from Mid-Ocean Ridge Basalts (MORB), which suggests the contribution of similar geological formations to sedimentary material.
Description14 páginas, 8 figuras, 3 tablas
Publisher version (URL)http://dx.doi.org/10.1016/j.dsr2.2013.01.009
Appears in Collections:(IIM) Artículos
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