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Cosmogenic 3He exposure ages and geochemistry of basalts from Ascension Island, Atlantic Ocean.
- Source :
- Quaternary Geochronology; Dec2009, Vol. 4 Issue 6, p525-532, 8p
- Publication Year :
- 2009
-
Abstract
- Abstract: The chronology and origin of volcanism of Ascension Island, South Atlantic Ocean, is poorly resolved. Here we use in situ produced cosmogenic <superscript>3</superscript>He 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/HNO<subscript>3</subscript> appears to remove a significant proportion of the implanted radiogenic <superscript>4</superscript>He contribution. Average exposure ages of each flow corrected for radiogenic He range from 328ka to 186ka and are used to refine the chronology and stratigraphy of the island. Magmatic <superscript>3</superscript>He/<superscript>4</superscript>He ratios derived from in vacuo crushing are in the range of 6.3–7.3 R <subscript>A</subscript>. 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. [Copyright &y& Elsevier]
- Subjects :
- COSMOGENIC nuclides
GEOCHEMISTRY
HELIUM isotopes
GEOCHRONOMETRY
BASALT
MAGMATISM
Subjects
Details
- Language :
- English
- ISSN :
- 18711014
- Volume :
- 4
- Issue :
- 6
- Database :
- Supplemental Index
- Journal :
- Quaternary Geochronology
- Publication Type :
- Academic Journal
- Accession number :
- 45220660
- Full Text :
- https://doi.org/10.1016/j.quageo.2009.09.003