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The nature and origin of upper mantle heterogeneity beneath the Mid-Atlantic Ridge 33-25°N: A Sr-Nd-Hf isotopic perspective

Guo, Pengyuan and Niu, Yaoling and Sun, Pu and Zhang, Junjie and Chen, Shuo and Duan, Meng and Gong, Hongmei and Wang, Xiaohong (2021) 'The nature and origin of upper mantle heterogeneity beneath the Mid-Atlantic Ridge 33-25°N: A Sr-Nd-Hf isotopic perspective.', Geochimica et Cosmochimica Acta, 307 . pp. 72-85.

Abstract

We present new Sr-Nd-Hf isotopic data on mid-ocean ridge basalts from two ridge segments (OH-1, OH-3) between the Oceanographer and Hayes fracture zones at the Mid-Atlantic Ridge 33-35°N to constrain the nature and origin of upper mantle heterogeneity beneath the Mid-Atlantic Ridge. Together with the major and trace elements data (Niu et al., 2001), the new Sr-Nd-Hf isotopic data illustrate that the mantle sources of these lavas comprise three components, i.e., a depleted mantle with high radiogenic Hf isotopic compositions (ADM), an incompatible elemental enriched component with radiogenic Sr and un-radiogenic Nd-Hf isotopic compositions (E-type I), and an incompatible element depleted component with variably enriched Sr-Nd-Hf isotope compositions (i.e., E-type II). The ADM and E-type I components may be understood as representing ancient mantle melting residues and metasomatic veins developed at the base of the thickening oceanic lithosphere, respectively. The unique E-type II component is best explained as recent mantle melting residues of a geochemically enriched mantle, probably associated with the Azores mantle plume to the north. Taking together, we interpret the E-MORB dominated OH-1 lavas as resulting from a relatively higher degree melting of a mantle source composed of ADM matrix and E-type I material, whereas the N-MORB dominated OH-3 lavas resulting from lower degree melting of the mantle source primarily comprising ADM and E-type II components. Such a petrological and geochemical understanding explains the contrast in crustal thickness, ridge morphology and tomography, and mantle Bouguer anomalies between the two ridge segments.

Item Type:Article
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1016/j.gca.2021.05.033
Publisher statement:© 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Date accepted:17 May 2021
Date deposited:17 May 2021
Date of first online publication:23 May 2021
Date first made open access:13 August 2021

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