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Cosmogenic 3He exposure ages and geochemistry of basalts from Ascension Island, Atlantic Ocean

Lookup NU author(s): Dr Anne-Sophie Meriaux

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Abstract

The chronology and origin of volcanism of Ascension Island, South Atlantic Ocean, is poorly resolved. Here we use in situ produced cosmogenic 3He in olivine and pyroxene phenocrysts from well-preserved lava flows to date the main sub-aerial basalt volcanism on the island. Etching olivine separates in HF/HNO3 appears to remove a significant proportion of the implanted radiogenic 4He contribution. Average exposure ages of each flow corrected for radiogenic He range from 328 ka to 186 ka and are used to refine the chronology and stratigraphy of the island. Magmatic 3He/4He ratios derived from in vacuo crushing are in the range of 6.3–7.3 RA. This range is lower than the neighbouring Mid-Atlantic Ridge segment (6–8°S) but slightly higher than measured in regional ocean islands of St. Helena, Tristan da Cunha and Gough. Combining these data with new trace element data and published radiogenic isotope ratios it appears that the Ascension Island magmatism is a mix of HIMU mantle material, typified by basalts from St. Helena, and depleted MORB-source mantle.


Publication metadata

Author(s): Ammon K, Dunai TJ, Stuart FM, Mériaux A-S, Gayer E

Publication type: Article

Publication status: Published

Journal: Quaternary Geochronology

Year: 2009

Volume: 4

Issue: 6

Pages: 525-532

ISSN (print): 1871-1014

Publisher: Elsevier BV

URL: http://dx.doi.org/10.1016/j.quageo.2009.09.003

DOI: 10.1016/j.quageo.2009.09.003


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