The effect of long term low temperature exposure on apatite fission track stability; a natural annealing experiment in the deep ocean

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doi: 10.1016/j.gca.2007.06.060
Author(s): Spiegel, Cornelia; Kohn, Barry; Raza, Asaf; Rainer, Thomas; Gleadow, Andrew
Author Affiliation(s): Primary:
Universität Bremen, Geowissenschaften, Bremen, Federal Republic of Germany
University of Melbourne, Australia
Montanuniversität Leoben, Austria
Volume Title: Geochimica et Cosmochimica Acta
Source: Geochimica et Cosmochimica Acta, 71(18), p.4512-4537. Publisher: Elsevier, New York, NY, International. ISSN: 0016-7037 CODEN: GCACAK
Note: In English. 85 refs.; illus., incl. 7 tables
Summary: Since studies on deep-sea cores were carried out in the early 1990s it has been known that ambient temperature may have a marked affect on apatite fission track annealing. Due to sluggish annealing kinetics, this effect cannot be quantified by laboratory annealing experiments. The unknown amount of low-temperature annealing remains one of the main uncertainties for extracting thermal histories from fission track data, particularly for samples which experienced slow cooling in shallow crustal levels. To further elucidate these uncertainties, we studied volcanogenic sediments from five deep-sea drill cores, that were exposed to maximum temperatures between ∼10° and 70°C over geological time scales of ∼15-120 Ma. Mean track lengths (MTL) and etch pit diameters (Dpar) of all samples were measured, and the chemical composition of each grain analysed for age and track length measurements was determined by electron microprobe analysis. Thermal histories of the sampled sites were independently reconstructed, based on vitrinite reflectance measurements and/or 1D numerical modelling. These reconstructions were used to test the most widely used annealing models for their ability to predict low-temperature annealing. Our results show that long-term exposure to temperatures below the temperature range of the nominal apatite fission track partial annealing zone results in track shortening ranging between 4 and 11%. Both chlorine content and Dpar values explain the downhole annealing patterns equally well. Low chlorine apatite from one drill core revealed a systematic relation between Si-content and Dpar value. The question whether Si-substitution in apatite has direct and systematic effects on annealing properties however, cannot be addressed by our data. For samples, which remained at temperatures <30°C, and which are low in chlorine, the Laslett et al. [Laslett G., Green P., Duddy I. and Gleadow A. (1987) Thermal annealing of fission tracks in apatite. Chem. Geol. 65, 1-13] annealing model predicts MTL up to 0.6 µm longer than those actually measured, whereas for apatites with intermediate to high chlorine content, which experienced temperatures >30°C, the predictions of the Laslett et al. (1987) model agree with the measured MTL data within error levels. With few exceptions, predictions by the Ketcham et al. [Ketcham R., Donelick R. and Carlson W. (1999) Variability of apatite fission-track annealing kinetics. III: Extrapolation to geological time scales. Am. Mineral. 84/9, 1235-1255] annealing model are consistent with the measured data for samples which remained at temperatures below ∼30°C. For samples which experienced maximum temperatures between ∼30 and 70°C, and which are rich in chlorine, the Ketcham et al. (1999) model overestimates track annealing. Abstract Copyright (2007) Elsevier, B.V.
Year of Publication: 2007
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 07 Marine Geology and Oceanography; Annealing; Apatite; Atlantic Ocean; Atlantic Ocean Islands; Bermuda Rise; Broken Ridge; Canary Islands; Caribbean Sea; Crystal chemistry; DSDP Site 397; Deep Sea Drilling Project; Deep-sea environment; Experimental studies; Fission tracks; Geochemistry; IPOD; Indian Ocean; Kinetics; Leg 121; Leg 129; Leg 165; Leg 47; Low temperature; Marine environment; Marine sediments; Models; North Atlantic; North Pacific; Northwest Pacific; ODP Site 755; ODP Site 800; ODP Site 999; Ocean Drilling Program; Pacific Ocean; Phosphates; Pigafetta Basin; Prediction; Sediments; Temperature; Thermal history; Vitrinite reflectance; West Pacific
Coordinates: S310148 S310147 E0933249 E0933248
N124437 N124437 W0784422 W0784422
N265042 N265042 W0151048 W0151048
N215522 N215523 E1521920 E1521919
Record ID: 2008044606
Copyright Information: GeoRef, Copyright 2017 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands