Work Description

Date: 13 November, 2019

Dataset Title: Apatite fission track thermochronometry data from the Eastern Greater Caucasus, Azerbaijan

Dataset Creators: Tye, Alexander R, Niemi, Nathan A, Safarov, Rafig T, Kadirov, Fakhraddin A, Babayev, Gulam R

Dataset Contact: Alexander Tye (alextye@umich.edu)

Funding: EAR-1524304 (NSF), University of Michigan Rackham Graduate School, University of Michigan International Institute, University of Michigan Department of Earth and Environmental Sciences

Key Points:
- new apatite fission track thermochronometry data were collected from the Eastern Greater Caucasus mountain range of Azerbaijan
- the data constrain the cooling history of rocks exhumed within an active accretionary prism
- apatite fission track grain data are reported for 8 samples, 3 of which also have fission track length data

Research Overview:
Apatite fission track thermochronometry data were collected from the Eastern Greater Caucasus orogen, Azerbaijan. Thermochronometry data constrain the history of exhumation and deformation of rocks within the orogen, which is an active accretionary prism. Thermochronometry data record the timing of cooling of a rock sample beneath a given closure temperature. Given an assumed or inferred geothermal gradient, thermochronometric ages can be used to infer exhumation rates and make interpretations about rates of deformation in orogens. The apatite fission track data presented here are analyzed in concert with apatite (U-Th)/He and zircon (U-Th)/He ages reported in Tye et al., in prep., to characterize the exhumation history of the Eastern Greater Caucasus.

Methodology:
Uranium-238 undergoes spontaneous fission, leaving fission tracks in apatite grains, which incorporate uranium. These fission tracks are annealed over geologic timescales at temperatures greater than approximately 110 degrees C, so measuring the populations of fission tracks in natural apatite grains can constrain the time-temperature history of the apatites. Apatite grains were separated using standard magnetic and heavy liquid separation techniques. Grains were mounted and polished, then fission tracks were counted and used in combination with uranium concentrations inferred from induced fission (University of Arizona) or laser ablation inductively coupled plasma mass spectrometry (Apatite to Zircon, Inc.) to infer thermochronometric ages. Samples H3, H5, S1, S2, and S3 were analyzed at the University of Arizona using the external detector method in 2018. In the external detector method, the U concentration of measured apatites is estimated by irradiating the measured apatites along with a standard of known U concentration and counting the fission tracks in each medium induced by the radiation (see Donelick et al., 2005). Samples N1, N2, L2 were analyzed at Apatite to Zircon, Inc. in 2008-2010 using laser ablation inductively coupled plasma mass spectrometry to characterize apatite chemistry.

Files contained here:
There are eleven files, including eight spreadsheets of grain data (one spreadsheet of each sample) and three spreadsheets of track length data for applicable samples. Information found in each column is different depending on where the data were collected.

***
H3graindata.csv, H5graindata.csv, S1graindata.csv, S2graindata.csv, S3graindata.csv - These files report samples analyzed at the University of Arizona. They have a header with three lines:
-zeta factor +/- error--this is a user-specific parameter that is used to calibrate the fission tracks of a specific user to a standard
-Rho d (% relative error)--this is the density of induced fission tracks (# tracks/area) in a standard, used to calibrate inferred U concentration
-N d--this is the number of induced fission tracks in a standard, used to calibrate inferred U concentration

Below the header, each line corresponds to a specific apatite grain and the fission tracks measured in that grain. Column headers are:
N s--number of spontaneous (pre-existing, natural) fission tracks
N i--number of fission tracks induced by irradiation of the sample (used to estimate the uranium concentration in the sample)
Dpar--dimension of fission track etch figures in the long direction (microns)
Dper--dimension of fission track etch figures in the short direction (microns)
rho_s--spontaneous track density (# tracks/area)
rho_i--induced track density (# tracks/area)
rho_s/rho_i--ratio of rho_s to rho_i
U ppm--inferred uranium concentration in ppm from induced fission tracks
Age (Ma)--inferred fission track age for single grain in millions of years
Age error--error on inferred age in millions of years

The last line of each spreadsheet shows the pooled value of each column parameter for all analyzed grains. In these 5 spreadsheets, dashes (-) indicate values that could not be measured because a given grain had no fission tracks, resulting in an inferred thermochronometric age of 0.

***
N1graindata.csv, N2graindata.csv, L2graindata.csv - These files report samples analyzed at Apatite to Zircon, Inc. Each line corresponds to a different grain. Column headers are:
Grain number--an index for which grain is being analyzed
Natural tracks--number of spontaneous/natural fission tracks counted in a given area on the grain
Area (cmxcm)--area in which fission tracks were counted (in square cm)
FT_age (Ma)--inferred single grain fission track age in millions of years
1sigma (Ma)--inferred error on the fission track age in millions of years
Dpar (microns)--dimension of fission track etch figures in the long direction (microns)
Dper (microns)--dimension of fission track etch figures in the short direction (microns)
Uranium (ppm)--inferred uranium concentration in ppm from laser ablation inductively coupled plasma mass spectrometry

The last line of each file lists the zeta factor and error. As described above, the zeta factor is a user-specific parameter used to calibrate fission track counts.

***
N1tracklengths.csv, N2tracklengths.csv, L2tracklengths.csv - These files report the lengths of fission tracks from three samples analyzed at Apatite to Zircon, Inc. Fission track lengths can be used as an additional constraint on the time-temperature history of a given thermochronometry sample. Column headers are:
Track number--index of which fission track is being measured
Length (microns)--length of the fission track in microns
Angle_to_caxis (degrees)--the acute angle between the measured track and the c mineral axis of the apatite in which the track has been etched

Related publication(s):
Tye, A. R., Niemi, N. A., Safarov, R. T., Kadirov, F. A., and Babayev, G. R., Structural and thermochronometric data provide insight into strain accommodation within an active accretionary prism, the Eastern Greater Caucasus. In prep.

Use and Access:
This data set is made available under a Creative Commons Public Domain license (CC0 1.0).

To Cite Data:
Tye, A. R., Niemi, N. A., Safarov, R. T., Kadirov, F. A., and Babayev, G. R., Structural and thermochronometric data provide insight into strain accommodation within an active accretionary prism, the Eastern Greater Caucasus. In prep.

Reference:
Donelick, R. A., O’Sullivan, P. B., & Ketcham, R. A. (2005). Apatite fission-track analysis. Reviews in Mineralogy and Geochemistry, 58(1), 49-94.