Mathematics – Logic
Scientific paper
May 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995e%26psl.132...43l&link_type=abstract
Earth and Planetary Science Letters, vol. 132, Issue 1-4, pp.43-51
Mathematics
Logic
3
Scientific paper
In order to test the usefulness of the helium method for detecting young geological events in hematite, U, Th and 4 He concentrations were analyzed in five specularite samples from Rio Marina-type hematite deposits (northeastern Elba, Italy). Four specularite samples define a isochron age of 5.39 ± 0.46 Ma (2 ). The isochron intercepts the 4 He axis at 49 ± 88 pl/g (2 ). Adularia, which is paragenetic with specularite in one sample used for the isochron, gives a mean age of 5.32 ± 0.11 Ma. In addition, two specularite samples, one from Rio Marina and one from Terra Nera (southeastern Elba) give helium model ages of 6.4 ± 0.4 and 7.3 ± 0.4 Ma respectively. Depending on the model of genesis, the high ages reflect incomplete 4 He degassing and/or 4 He excess . The study demonstrates that geologically meaningful helium ages as young as Pliocene can be obtained from specularite in spite of expected interferences from initial helium. If the 4 He axis intercept is a general measure of initial 4 He in hematite its effect on the calculated ages in Mesozoic hematites in previous studies is negligible. The age concordance implies that similar concordance should exist in samples with a known thermal history much older than Pliocene. Moreover, the helium method could also work on specularite with a thermal history younger than Pliocene.
Bähr Roland
Lippolt Hans J.
Wernicke Rolf S.
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