A 1.5 Ma record of plume-ridge interaction at the Western Galápagos Spreading Center (91°40′–92°00′W). (15th July 2016)

• Record Type: Journal Article
• Authors: Herbrich, Antje; Hauff, Folkmar; Hoernle, Kaj; Werner, Reinhard; Garbe-Schönberg, Dieter; White, Scott
• Is Part Of: Geochimica et cosmochimica acta. Volume 185(2016:Jul. 15)
• Page Start: 141
• Page End: 159
• Publication Date: 2016-07-15
• Subjects: Galápagos plume -- Plume ridge interaction -- Galápagos Spreading Center -- Magmatic geochemistry; Geochemistry -- Periodicals; Meteorites -- Periodicals; Géochimie -- Périodiques; Météorites -- Périodiques; Geochemie; Astrochemie; Electronic journals; 551.905
• DOI: 10.1016/j.gca.2016.04.036
• Languages: English
• ISSNs: 0016-7037

Abstract

Abstract: Shallow (elevated) portions of mid-ocean ridges with enriched geochemical compositions near hotspots document the interaction of hot, geochemically-enriched plume mantle with shallow depleted upper mantle. Whereas the spatial variations in geochemical composition of ocean crust along the ridge axis in areas where plume-ridge interaction is taking place have been studied globally, only restricted information exists concerning temporal variations in geochemistry of ocean crust formed through plume-ridge interaction. Here we present a detailed geochemical study of 0–1.5 Ma ocean crust sampled from the Western Galápagos Spreading Center (WGSC) axis to 50 km north of the axis, an area that is presently experiencing a high influx of mantle material from the Galápagos hotspot. The tholeiitic to basaltic andesitic fresh glass and few bulk rock samples have incompatible element abundances and Sr–Nd–Pb isotopic compositions intermediate between depleted normal mid-ocean-ridge basalt (N-MORB) from >95.5°W along the WGSC and enriched lavas from the Galápagos Archipelago, displaying enriched (E-)MORB type compositions. Only limited and no systematic geochemical variations are observed with distance from the ridge axis for <1.0 Ma old WGSC crust, whereas 1.0–1.5 Ma old crust trends to more enriched isotopic compositions in 87 Sr/ 86 Sr, 143 Nd/ 144 Nd, 207 Pb/ 204 Pb and 208 Pb/ 204 Pb isotope ratios. On isotope correlation diagrams, the data set displays correlations between depleted MORB and two enriched components. Neither the geographically referenced geochemical domains of the Galápagos Archipelago nor the end members used for principal component analysis can successfully describe the observed mixing relations. Notably an off-axis volcanic cone at site DR63 has the appropriate composition to serve as the enriched component for the younger WGSC and could represent a portion of the northern part of the Galápagos plume not sampled south of the WGSC. Similar compositions to samples from volcanic cone DR63 have been found in the northern part of the 11–14 Ma Galápagos hotspot track offshore Costa Rica, indicating that this composition is derived from the northern portion of the Galápagos plume. The older WGSC requires involvement of an enriched mantle two (EMII) type source, not recognized thus far in the Galápagos system, and is interpreted to reflect entrained material either from small-scale heterogeneities within the upper mantle or from the mantle transition zone. Overall the source material for the 0–1.5 Ma WGSC ocean crust appears to represent mixing of depleted upper mantle with Northern Galápagos Plume material of relatively uniform composition in relatively constant proportions.