Mathematics – Logic
Scientific paper
Sep 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007gecoa..71.4512s&link_type=abstract
Geochimica et Cosmochimica Acta, Volume 71, Issue 18, p. 4512-4537.
Mathematics
Logic
3
Scientific paper
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.
Gleadow Andrew
Kohn Barry
Rainer Thomas
Raza Asaf
Spiegel Cornelia
No associations
LandOfFree
The effect of long-term low-temperature exposure on apatite fission track stability: A natural annealing experiment in the deep ocean does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with The effect of long-term low-temperature exposure on apatite fission track stability: A natural annealing experiment in the deep ocean, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The effect of long-term low-temperature exposure on apatite fission track stability: A natural annealing experiment in the deep ocean will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-965632