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Compositional effects on etching of fossil confined fission tracks in apatite

Hongyang Fu, Florian Trilsch, Raymond Jonckheere and Lothar Ratschbacher
Compositional effects on etching of fossil confined fission tracks in apatite
American Mineralogist (May 2024) 109 (12): 2026-2036

Abstract

Fission-track analysis is a thermochronologic method for dating rocks and reconstructing their low-temperature thermal histories. We investigate the influence of the apatite composition on the etching of fossil confined fission tracks, and its consequences for the fission-track method. We conducted step-etch experiments with 5.5 M HNO (sub 3) at 21 degrees C on samples with etch pit diameters (Dpar) spanning most of the range for natural apatites (Panasqueira: 1.60 mu m, Slyudyanka: 2.44 mu m, Brazil: 3.92 mu m, and Bamble: 4.60 mu m) to determine their apatite etch rates v (sub R) (the rate at which each lattice plane is displaced parallel to itself) as a function of crystallographic orientation (Phi '). Our measurements revealed significant differences between the four samples. We fitted three-parameter functions, v (sub R) = a(Dpar)Phi ' e (super b(Dpar)Phi ') + c, describing v (sub R) as a function of the angle to the apatite c-axis for our hexagonal samples (excluding Bamble) and Durango apatite. The parameters a and b both exhibit a linear correlation with Dpar, whereas the constant c is small ( approximately 0.1 mu m min (super -1) ) and its between-sample variation negligible at the resolution of our measurements. Bamble exhibits a different, bimodal relationship between v (sub R) and Phi ', which we fitted with a sum of two sine functions. In all cases, including Bamble, there is a striking correlation between the angular frequencies of horizontal confined tracks and the magnitude of the apatite etch rate v (sub R) perpendicular to the track axes. This shows that the sample of confined tracks selected for measurement and modeling is to a much greater degree determined by the etching properties of the apatite sample than by geometric or subjective biases. The track etch rate v (sub T) is constant along most of the track length but varies from track to track. The mean v (sub T) correlates with Dpar, so that tracks etch to their full lengths in a shorter time in faster etching apatites. The mean rate of length increase between etch steps, v (sub L) , also correlates with Dpar. The length increments of individual tracks are however irregular. This points to an intermittent structure at the ends of the tracks.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 109
Serial Issue: 12
Title: Compositional effects on etching of fossil confined fission tracks in apatite
Affiliation: China University of Geosciences, Ministry of Education, Key Laboratory of Tectonics and Petroleum Resources, Wuhan, China
Pages: 2026-2036
Published: 20240509
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 49
Accession Number: 2024-045299
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 5 tables
Secondary Affiliation: TU Bergakademie Freiberg, Endogene Geologie, DEU, Germany
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2024, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 202427
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