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Radiogenic strontium-87 as an index of geologic processes

C. E. Hedge·F.G. Walthall
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Abstract

The abundance of radiogenic Sr 87 relative to Sr 86 at the time of crystallization has been determined for 45 rocks. The total range in the ratio Sr 87 /Sr 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 87 /Sr 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 87 /Sr 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.

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C. E. Hedge, F.G. Walthall. 1963. Radiogenic strontium-87 as an index of geologic processes. https://doi.org/10.1126/science.140.3572.1214.b

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