Helium- and lead-isotope geochemistry of oceanic volcanic rocks from the East Pacific and South Atlantic. Doctoral thesis
Technical Report
·
OSTI ID:6967820
Glassy basalts erupted at young Pacific seamounts and along the mid-ocean ridge in the South Atlantic, and volcanic rocks from the island of St. Helena were studied for He and Pb isotopes. (U+TH)/He ages of seamount alkali basalts were determined from the isotope disequilibrium of (3)He/(4)He between He trapped in vesicles and that dissolved in the glass phase. The method allows alkalic lavas to be dated in the age range of 103 to 106 years. Tholclites at the EPR seamounts have He, Pb, Sr and Nd isotope compositions indistinguishable from MORB, while associated alkali basalts show more radiogenic signatures. The low (3)He/(4)He in the vesicles of alkali basalts (1.2-2.6 RA), their low helium concentrations, and systematic variations with extent of differentiation suggest that magmatic processes influence (3)He/(4)He in these alkalic lavas. Pb-Sr-Nd isotopes at Shimada seamount (17 deg N, 117 deg W) indicate the presence of enriched mantle beneath the East Pacific which resembles that beneath Samoa. Low (3)He/(4)He (4-5 RA) appears to be an inherent characteristic of the component. Much of the South Atlantic ridge axis displays (3)He/(4)He lower than normal MORB, and is apparently contaminated by off-axis hotspots. He-Pb systematics along the ridge suggest that (3)He/(4)He at St. Helena is less than MORB, consistent with values measured by in vacuo crushing of olivine and pyroxene in St. Helena rocks (approx. 5.8 RA).
- Research Organization:
- Woods Hole Oceanographic Institution, MA (USA)
- OSTI ID:
- 6967820
- Report Number(s):
- PB-88-175906/XAB; WHOI-87-36
- Country of Publication:
- United States
- Language:
- English
Similar Records
The Cobb-Eickelberg seamount chain: Hotspot volcanism with mid-ocean ridge basalt affinity
Sources of oceanic basalts: radiogenic isotopic evidence
Helium isotopes in lithospheric mantle: Evidence from Tertiary basalts of the western USA
Journal Article
·
Fri Aug 10 00:00:00 EDT 1990
· Journal of Geophysical Research; (United States)
·
OSTI ID:5085718
Sources of oceanic basalts: radiogenic isotopic evidence
Journal Article
·
Thu Jan 31 23:00:00 EST 1985
· Geology; (United States)
·
OSTI ID:5486834
Helium isotopes in lithospheric mantle: Evidence from Tertiary basalts of the western USA
Journal Article
·
Mon Nov 30 23:00:00 EST 1998
· Geochimica et Cosmochimica Acta
·
OSTI ID:343754