[sup 226]Ra-[sup 230]Th disequilibrium in axial and off-axis mid-ocean ridge basalts

Conference · Mon Mar 01 04:00:00 EST 1993 · Geochimica et Cosmochimica Acta; (United States)

OSTI ID:6430480

Volpe, A M; Goldstein, S J ^[1]

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1. Lawrence Livermore National Lab., CA (United States) Los Alamos National Lab., NM (United States)

The authors describe [sup 226]Ra-[sup 230]Th disequilibrium in mid-ocean ridge basalt (MORB) glasses from the Juan de Fuca, Gorda, and East Pacific ridges. These first mass spectrometric measurements of [sup 226]Ra in MORB glasses at sub-picogram abundance levels confirm the large excesses over [sup 230]Th determined by radon-emanation techniques and alpha spectrometry. All off-axis MORB glasses have [sup 226]Ra-[sup 230]Th and [sup 234]U-[sup 238]U in secular equilibrium. This suggests that magmatic processes, not secondary post-eruption alteration, generate [sup 238]U-series disequilibrium in these MORB. Least evolved, N-MORB from axial valleys have ([sup 226]Ra/[sup 230]Th) between 2.2-2.3. Differentiated and enriched E-type MORB have consistently low ([sup 226]Ra/[sup 230]Th) ratios compared with N-MORB from the same ridge sections. Ra-Th fractionation may be less pronounced, or magma residence-transit periods may be long for differentiated MORB. Also, E-MORB may be generated by different melt extraction volumes and rates. Estimated [sup 226]Ra-[sup 230]Th ages for N-MORB agree with location on and off ridge segments, and with Th-U model ages. These preliminary results show that [sup 226]Ra-[sup 230]Th disequilibrium could be used to quantify volcanic episodicity at ocean ridges. 39 refs., 6 figs., 4 tabs.

• OSTI ID: 6430480
• Report Number(s): CONF-911017--
• Conference Information: Journal Name: Geochimica et Cosmochimica Acta; (United States) Journal Volume: 57:6
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400102 -- Chemical & Spectral Procedures
54 ENVIRONMENTAL SCIENCES
540310* -- Environment
Aquatic-- Basic Studies-- (1990-)
ACTINIDE ISO
ACTINIDE ISOTOPES
ACTINIDE NUCLEI
AGE ESTIMATION
ALKALINE EARTH ISOTOPES
ALPHA DECAY RADIOISOTOPES
BASALT
CARBON 14 DECAY RADIOISOTOPES
EQUILIBRIUM
EVEN-EVEN NUCLEI
GEOLOGIC MODELS
HEAVY ION DECAY RADIOISOTOPES
HEAVY NUCLEI
IGNEOUS ROCKS
ISOTOPES
MAGNESIUM 28 DECAY RADIOISOTOPES
MASS SPECTROSCOPY
NEON 24 DECAY RADIOISOTOPES
NUCLEI
RADIOISOTOPES
RADIUM 226
RADIUM ISOTOPES
ROCKS
SEA BED
SPECTROSCOPY
SPONTANEOUS FISSION RADIOISOTOPES
THORIUM 230
THORIUM ISOTOPES
URANIUM 234
URANIUM 238
URANIUM ISOTOPES
VOLCANIC ROCKS
VOLCANISM
YEARS LIVING RADIOISOTOPES