Fission fragment tracks in apatite: recordable track lengths

The thermotectonic evolution of the East Alpine Rhenodanubian flysch zone (RDFZ) and the collisional history along the orogenic front is reconstructed using apatite fission-track (FT) thermochronology. The apatite FT data provides evidence for a burial depth of at least 6 km for the samples, which were totally reset. Burial was not deeper than 11 km, since the zircon fission-track system was not reset. The RDFZ represents an accretionary wedge with a complex burial and cooling history due to successive and differential accretion and exhumation. The sedimentary sequences were deposited along a convergent margin, where accretion started before Maastrichtian and lasted until Miocene. Accretion propagated from a central area (Salzburg±Ybbsitz) both to the west and to the east. In the west, accretion lasted from Middle Eocene to Early Oligocene, reflecting underplating of the RDFZ by the European continental margin sediments. In the east, where three nappes (Greifenstein, Kahlenberg and Laab nappes) can be distinguished, the exhumation started between Late Oligocene and Early Miocene. The Kahlenberg and Laab nappes show total resetting of the apatite FT ages, while in the Greifenstein nappe there is only partial resetting. According to a new paleogeographic reconstruction, the Kahlenberg and Laab nappes were placed on top of the Greifenstein nappe by an out-ofsequence thrust.

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“…For the track-length measurements Tints (track-in-track) and Tincles (track-in-cleavage) were considered (Bhandari et al 1971).…”

Section: Methodsmentioning

confidence: 99%

Accretionary history of the Rhenodanubian flysch zone in the Eastern Alps – evidence from apatite fission-track geochronology

Trautwein¹,

Dunkl²,

Frisch³

2001

Int J Earth Sci

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“…The nuclear fragments, moving in opposite directions through the lattice, produce a single ca. 20-μm long (Bhandari et al, 1971;Jonckheere, 2003a, b), b10-nm diameter (Afra et al, 2011;Jaskierowicz et al, 2004;Lang et al, 2015;Li et al, 2014;Miro et al, 2005;Paul and Fitzgerald, 1992;Schauries et al, 2014) fossil fission track. The number of tracks per unit volume (N S ) is proportional to the age (t) and 238 U content (U 238 ) of the sample and the spontaneous-fission rate (λ F ) of 238 U (Eq.…”

Section: Adjusted Age Equationmentioning

confidence: 99%

Standardless fission-track dating of the Durango apatite age standard

2015

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Five dating strategies were used for determining the standardless fission-track age of the Durango apatite. These use the same fossil-track densities but differ in the manner in which the induced-track densities are determined. A conventional age calculation, without correction for experimental factors, gives inconsistent ages with methodrelated differences N 15%. Correcting for these factors brings the ages in line with each other and with the reference age but leaves no room for a partial-annealing correction based on the confined-track lengths. Three further reasons suggest that a length correction is not appropriate. (1) The evidence for lengthbased corrections is inconclusive. (2) The plateau age of the Durango apatite is consistent with its apparent fission-track age to within 1%. (3) The calculated effective etchable length of the fossil tracks agrees within error with that of the induced tracks; both are further consistent with the measured mean length of confined induced tracks. The circumstance that the (U,Th)/He ages of the accepted and proposed apatite age standards are consistent with their reference ages leaves no margin for a lowered fission-track age resulting from partial annealing, although the case of the Durango apatite itself is inconclusive because of its exceptional crystal size. It is conjectured that the shortening of the fossil tacks in the Durango apatite is due to a lowering of the track etch rate over time. In this case, annealing equations fitted to induced-track data underestimate the extent of confined-track-length reduction in geological samples.

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“…4b [11,[26][27][28][29][30]) and the calculated summed fissionfragment ranges (21.2 lm [12]). A somewhat lower but nonnegligible value (1.8 lm) is implicit in the earlier work of [31].…”

Section: Discussionmentioning

confidence: 97%