Abstract
Volatile and stable isotope data provide tests of mantle processes that give rise to mantle heterogeneity. New data on enriched mid-oceanic ridge basalts (MORB) show a diversity of enriched components. Pacific PREMA-type basalts (H2O/Ce = 215 ± 30, δDSMOW = −45 ± 5 ‰) are similar to those in the northern Atlantic (H2O/Ce = 220 ± 30; δDSMOW = −30 to −40 ‰). Basalts with EM-type signatures have regionally variable volatile compositions. Northern Atlantic EM-type basalts are wetter (H2O/Ce = 330 ± 30) and have isotopically heavier hydrogen (δDSMOW = −57 ± 5 ‰) than northern Atlantic MORB. Southern Atlantic EM-type basalts are damp (H2O/Ce = 120 ± 10) with intermediate δDSMOW (−68 ± 2 ‰), similar to δDSMOW for Pacific MORB. Northern Pacific EM-type basalts are dry (H2O/Ce = 110 ± 20) and isotopically light (δDSMOW = −94 ± 3 ‰). A multistage metasomatic and melting model accounts for the origin of the enriched components by extending the subduction factory concept down through the mantle transition zone, with slab temperature a key variable. Volatiles and their stable isotopes are decoupled from lithophile elements, reflecting primary dehydration of the slab followed by secondary rehydration, infiltration, and re-equilibration by fluids derived from dehydrating subcrustal hydrous phases (e.g., antigorite) in cooler, deeper parts of the slab. Enriched mantle sources form by addition of <1% carbonated eclogite ± sediment-derived C-O-H-Cl fluids to depleted mantle at 180–280 km (EM) or within the transition zone (PREMA).
Original language | English (US) |
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Pages (from-to) | 3801-3839 |
Number of pages | 39 |
Journal | Geochemistry, Geophysics, Geosystems |
Volume | 18 |
Issue number | 11 |
DOIs | |
State | Published - Nov 2017 |
Keywords
- mantle geochemistry
- metasomatism
- oceanic basalt
- stable isotopes
- subduction
- volatiles
ASJC Scopus subject areas
- Geophysics
- Geochemistry and Petrology