A differential etching and magnetic separation approach to whole-rock potassium-argon dating of basaltic rocks.

Peter Horn; Dieter Müller-Sohnius

doi:10.2343/geochemj.22.115

A differential etching and magnetic separation approach to whole-rock potassium-argon dating of basaltic rocks.

GEOCHEMICAL JOURNAL ◽

10.2343/geochemj.22.115 ◽

1988 ◽

Vol 22 (3) ◽

pp. 115-128 ◽

Cited By ~ 9

Author(s):

Peter Horn ◽

Dieter Müller-Sohnius

Keyword(s):

Magnetic Separation ◽

Basaltic Rocks ◽

Argon Dating ◽

Differential Etching

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The Argon Surprise

Much Ado about (Practically) Nothing ◽

10.1093/oso/9780195393965.003.0017 ◽

2010 ◽

Author(s):

David Fisher

Keyword(s):

New York ◽

Mass Spectrometer ◽

East Pacific Rise ◽

Ocean Floor ◽

Fiscal Year ◽

State University ◽

Basaltic Rocks ◽

Argon Dating ◽

East Pacific ◽

Good Material

The first thing I did in Miami was to write a proposal to the National Science Foundation for a mass spectrometer, in order to test Hess’s idea of a spreading seafloor. Funding was not a problem in those halcyon and bygone days of yore. Once, I remember, Cesare came trotting down the hall calling out that it was the end of the fiscal year and the NSF was on the phone; they were calling to say they had two hundred thousand dollars left over from the budget, and did anyone want it? No one did, we all had enough money. Lordy, lordy. (Loud sigh.) And so the money for the mass spectrometer came through, but not before summer, and I was not about to spend July and August in the Miami furnace. Instead, I arranged to go up to the State University of New York at Stony Brook, where Ollie Schaeffer had become head of a new earth sciences department, to use his mass spectrometer to measure the ages on a suite of rocks brought back by one of my new friends at Miami, Enrico Bonatti, a marine geologist who had just returned from a research cruise with ocean floor samples that were perfect for testing the spreading seafloor hypothesis. He had dredged up basalts from the flanks of the East Pacific Rise and a half dozen other samples at various distances from it. So we should see young ages on the ridge rocks, and a spectrum of increasingly older ages as we moved outwards. Basalts are good material for normal potassium-argon dating, and those on the seafloor, we thought, should be even better. The basis of K/Ar dating is that you have a magma region somewhere inside the earth, with potassium continually decaying to argon. When the magma erupts, throwing out molten basaltic rocks, all the argon previously produced will bubble out and be lost to the atmosphere; as the lava cools into basaltic rocks, they will have potassium in them, but no argon, effectively setting the dating clock to zero.

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