Radiogenic Strontium-87 as an Index of Geologic Processes
The abundance of radiogenic Sr/sup 87/ relative to Sr/sup 86/ at the time of crystallization has been determined for 45 rocks. The total range in the ratio Sr/sup 87//Sr/sup 86/ is less than 2 percent. Ratios for recent lavas range from 0.702 to 0.711. Oceanic basalts are closely grouped at 0.703, whereas ratios for continental volcanic rocks spread from 0.702 to 0.711. Among the volcanic rocks, ranging from basalt to rhyolite, no correlation was found between original ratio and rock type. Older mafic and felsic rocks that include both plutonic and extrusive types also cover this same range in original Sr/sup 87//Sr/ sup 86/ ratios; however, there is a definite trend with geologic time. Precambrian rocks give values as low as 0.700. The data indicate that Sr/sup 87// Sr/sup 86/ of the weathering crust has changed 1.1 percent in 3000 million years, while the ratio in the mantle has changed no more than 0.5 percent.
- Research Organization:
- U.S. Geological Survey, Washington, D.C.
- Sponsoring Organization:
- USDOE
- NSA Number:
- NSA-17-027582
- OSTI ID:
- 4687747
- Journal Information:
- Science, Journal Name: Science Journal Issue: 3572 Vol. 140; ISSN 0036-8075
- Publisher:
- AAAS
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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