Mixing two enriched and distinct mantle sources beneath Lucky Strike segment, 37N on the Mid-Atlantic Ridge (abstract of paper presented at 15th Annual V.M. Goldschmidt Conference, Moscow, Idaho, , May 2005)


Ferreira, P.L., Murton, B.J. and Boulter, C. (2005) Mixing two enriched and distinct mantle sources beneath Lucky Strike segment, 37N on the Mid-Atlantic Ridge (abstract of paper presented at 15th Annual V.M. Goldschmidt Conference, Moscow, Idaho, , May 2005). Geochimica et Cosmochimica Acta, 69, (10S), A102.

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Description/Abstract

New major and trace element, and Nd-Sr isotopic, data on samples from the Lucky Strike Segment are presented. All samples studied are enriched mid-ocean ridge basalts (E-MORB), but different degrees of enrichment are identified. Three distinct compositional groups can be established: - in Group 1, the lavas have the highest “more incompatible/less incompatible” (MI/LI) element ratios, 87Sr/86Sr and the lowest 143Nd/144Nd ratios. These lavas have a degree of enrichment between those of E-MORB and OIB and are spatially restricted to the central part of the axial volcano. Group 3 lavas have the smallest “MI/LI”, 87Sr/86Sr and the highest 143Nd/144Nd ratios. The lavas present REE and multi-element patterns typical of E-MORB and were collected throughout the Lucky Strike segment (from 37º12,0’ to 37º27,3’ in latitude). Group 2 lavas have chemical characteristics intermediate between those of groups 1 and 3 in terms of trace and isotope compositions, have the maximum dispersion in the different element or element ratios, and present an enrichment degree between those of group 1 and 3 lavas.

Relationships between various incompatible trace element ratios (e.g. La/Sm versus Nb/Zr), together with Sr and Nd isotopic ratios, or between both (e.g. La/Sm versus
143Nd/144Nd) show clearly a continuous chemical trend, defined by group 2 basalts, progressively connecting the chemical characteristics shown by groups 1 and 3. The justification for that trend being the result of mixing processes was tested, and a good fit of the mixing lines to the data was obtained. Moreover, since the mixing processes between a depleted mantle source (N-MORB type), and a highly enriched source (Plume type) are frequently postulated to explain the origin of E-MORB type basalts (identical to those of group 3), calculation of the mixing lines were extended to a N-MORB end-member, and good fits were also obtained.
These results show that mixing could be invoked to explain the chemical diversity among the Lucky Strike segment magmas, involving an N-MORB type source end-member and an enriched end-member similar to that assumed to generate the basalts from group 1. Hence, the existence of two distinct (both enriched) mantle sources beneath Lucky Strike segment could be postulated.

Item Type: Article
Subjects: Q Science > QE Geology
Divisions: University Structure - Pre August 2011 > School of Ocean & Earth Science (SOC/SOES)
University Structure - Pre August 2011 > National Oceanography Centre (NERC)
ePrint ID: 20389
Date Deposited: 23 Feb 2006
Last Modified: 27 Mar 2014 18:10
URI: http://eprints.soton.ac.uk/id/eprint/20389

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