Th isotope and U-series studies of subduction-related volcanic rocks
- Univ. of California, Santa Cruz (USA)
The activities of 6-7 radionuclides measured by alpha spectrometry are reported for 35 samples of recent volcanic rocks from 24 volcanoes in 9 arcs. These include continental margins (Cascades, Alaska, Costa Rica), island arcs (the Sunda, Banda, and Sangihe arcs of Indonesia, Marianas, Japan, Aleutians, Antilles, Tonga), and a backarc basin (Lau Basin). Enrichment of {sup 238}U over {sup 230}Th is more common and greater in these subduction-related volcanics than in those from other tectonic environments. {sup 230}Th/{sup 232}Th ratios also extend to higher values, both in absolute numbers and relative to other isotope ratios. Enrichment of {sup 210}Po and {sup 226}Ra over {sup 230}Th is widespread and is more common and greater in island arcs than continental margins. The level of Po or Ra enrichment is similar to that in ocean island and ridge basalts and deceases with differentiation. The differences in Th-U systematics between subduction-related and other volcanic rocks are attributed to variations in the process of melt extraction, changes in bulk partition coefficients within the mantle wedge, or preferential addition of U from subducted lithosphere. Ra enrichments are attributed to partial melting processes which are similar to those at ocean ridges. Smaller excesses at continental margins are attributed either to slower ascent or to differences in the process of melt formation beneath continents.
- OSTI ID:
- 6243836
- Journal Information:
- Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 54:5; ISSN GCACA; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
Similar Records
Tectonic significance of bimodal volcanism in the Archean Michipicoten greenstone belt, Ontario
Basin formation and Neogene sedimentation in a backarc setting, Halmahera, eastern Indonesia
Related Subjects
580000* -- Geosciences
ACTINIDE ISOTOPES
ACTINIDE NUCLEI
ALPHA DECAY RADIOISOTOPES
ALPHA SPECTROSCOPY
CHEMISTRY
EVEN-EVEN NUCLEI
GEOCHEMISTRY
HEAVY ION DECAY RADIOISOTOPES
HEAVY NUCLEI
IGNEOUS ROCKS
ISOTOPE RATIO
ISOTOPES
MAGMATISM
NEON 24 DECAY RADIOISOTOPES
NUCLEI
PETROCHEMISTRY
PETROGENESIS
RADIOISOTOPES
ROCKS
SPECTROSCOPY
SUBDUCTION ZONES
THORIUM 230
THORIUM 232
THORIUM ISOTOPES
URANIUM 238
URANIUM ISOTOPES
VOLCANIC ROCKS
YEARS LIVING RADIOISOTOPES