Composition of the depleted mantle

Abstract

[1] We present an estimate for the composition of the depleted mantle (DM), the source for mid-ocean ridge basalts (MORBs). A combination of approaches is required to estimate the major and trace element abundances in DM. Absolute concentrations of few elements can be estimated directly, and the bulk of the estimates is derived using elemental ratios. The isotopic composition of MORB allows calculation of parent-daughter ratios. These estimates form the ''backbone'' of the abundances of the trace elements that make up the Coryell-Masuda diagram (spider diagram). The remaining elements of the Coryell-Masuda diagram are estimated through the composition of MORB. A third group of estimates is derived from the elemental and isotopic composition of peridotites. The major element composition is obtained by subtraction of a low-degree melt from a bulk silicate Earth (BSE) composition. The continental crust (CC) is thought to be complementary to the DM, and ratios that are chondritic in the CC are expected to also be chondritic in the DM. Thus some of the remaining elements are estimated using the composition of CC and chondrites. Volatile element and noble gas concentrations are estimated using constraints from the composition of MORBs and ocean island basalts (OIBs). Mass balance with BSE, CC, and DM indicates that CC and this estimate of the DM are not complementary reservoirs.Components: 13,973 words, 9 figures, 8 tables, 2 datasets.

The mean composition of ocean ridge basalts

“…This was first shown by Salters and Stracke [2004], as their estimate of D-MORB is similar to (and slightly more enriched than) the N-MORB of Sun and McDonough [1989]. The new D-MORB composition (Table 3), however, is even more enriched relative to the N-MORB value of Sun and McDonough [1989], demonstrating the extreme depletion in this early N-MORB estimate.…”

“…[3] Early estimates of the average composition of MORB were calculated on a small number of samples [e.g., Hofmann, 1988;Sun and McDonough, 1989]. More recently, multiple groups have calculated averages using a more extensive set of compositions [Salters and Stracke, 2004;Rubin and Sinton, 2007;McDonough, 2010, hereafter referred to as AM, 2010]. These global studies, however, either averaged individual samples to estimate a mean composition [AM, 2010;Salters and Stracke, 2004], a method prone to sampling bias, or averaged samples from 37 "ridge sections" to explore variations with spreading rate without addressing the question of the global average composition [Rubin and Sinton, 2007].…”

Patterns in Galápagos Magmatism Arising from the Upper Mantle Dynamics of Plume‐Ridge Interaction

“…The concentration of an incompatible trace element in the melt produced from EC and DC are governed by modal, fractional melting using partition coefficients of Salters and Stracke [2004] and modal proportions of Ito and Mahoney [2005a], which vary with extent of melting, …”

Morphology of seismically slow lower-mantle structures

“…We follow the approach ofŠramek et al (2013) and estimate the enrichment factor of such a lower-mantle enriched reservoir by apportioning a bulk mantle reservoir (obtained by extracting the crust from a bulk silicate Earth model) between a depleted and enriched reservoir. We consider a range of compositions for the depleted reservoir, represented by three recent studies (Salters & Stracke 2004;Workman & Hart 2005;Arevalo & McDonough 2010). We note that this analysis is primarily intended to be illustrative, rather than advocating a particular interpretation of the LLSVP composition.…”