Data from: Exhumation history of the Sangre de Cristo Range, Colorado, from mid- to low-temperature thermochronology: New insights into Laramide contraction and Oligocene–Miocene extension in the northern Rio Grande rift, USA
Data files
Jun 24, 2026 version files 1.47 MB
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File_1_Sangre_de_Cristo_thermochronology_samples_and_date_summary.xlsx
14.22 KB
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File_2_U-Th_He_thermochronology_data.xlsx
82.75 KB
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File_3_Ar-Ar_thermochronology_data.xlsx
924.35 KB
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File_4_Fission_track_data.xlsx
435.10 KB
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README.md
12.82 KB
Abstract
This dataset consists of thermochronologic data that form the basis of a 2026 Tectonics manuscript titled “Exhumation history of the Sangre de Cristo Range, Colorado, from mid- to low-temperature thermochronology: New insights into Laramide contraction and Oligocene–Miocene extension in the northern Rio Grande rift, USA.” Data from samples collected in the Sangre de Cristo Range in southern Colorado include zircon (U-Th)/He dates (21 samples, 97 grains), apatite (U-Th)/He dates (16 samples, 73 grains), zircon fission dates (6 samples), apatite fission track dates (2 samples), K-feldspar 40Ar/39Ar data (4 samples), and biotite 40Ar/39Ar data (1 sample). These thermochronologic data provide insight into the polyphase deformation history and spatiotemporal patterns of extensional exhumation in the Sangre de Cristo Mountains in southern Colorado. Key findings based on these data include: a) The Alvarado fault along the northeastern range flank initiated as a Laramide reverse fault and was reactivated as a normal fault in the early Miocene; b) The onset of rapid cooling due to extensional exhumation is 20–16 Ma along northeastern flank of the range, 18–14 Ma near the range crest, and 14–10 Ma along southwestern flank of the range; c) The Sangre de Cristo Range underwent limited cooling between the Oligocene inception of extension and Miocene onset of rapid cooling associated with slip on range-bounding faults; and d) The southwestern flank of the range was exhumed from temperatures of ~240±25°C at the onset of Miocene rapid cooling, consistent with ~7–9 km displacement across the Sangre de Cristo fault system.
Dataset DOI: 10.5061/dryad.tdz08kqdq
Description of the data and file structure
These files include: a) apatite and zircon (U-Th)/He thermochronologic data, b) K-feldspar and biotite 40Ar/39Ar thermochronologic data, and c) zircon and apatite thermochronologic data. The (U-Th)/He data for samples beginning in 19–24 were collected at the Thermochronology Research and Instrumentation Laboratory at the University of Colorado Boulder following protocols outlined in Flowers et al. (2020) and Stanley and Flowers (2020), whereas the samples beginning with MC or 8 were analyzed at the Arizona Radiogenic Helium Dating Laboratory at the University of Arizona following protocols outlined in Guenther et al. (2016). The K-feldspar and biotite samples were irradiated at the Oregon State University TRIGA experimental reactor and later analyzed via the 40Ar/39Ar step heating method at the Nevada Isotope Geochronology Laboratory (at the University of Nevada Las Vegas) using an IsotopX NGX-600 noble gas multi-collector mass spectrometer with a high-vacuum HEINE furnace. Age determinations and errors were calculated using ArArCalc v. 2.7.0 (Koppers, 2002). The fission track analyses were performed at GeoSep Services using standard procedures for the laser-ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) method following analytical procedures outlined in Donelick et al., (2005).
References
Donelick, R. A., O’Sullivan, P. B., & Ketcham, R. A. (2005). Apatite fission-track analysis. Reviews in Mineralogy and Geochemistry, 58(1), 49-94.
Flowers, R. M., Macdonald, F. A., Siddoway, C. S., & Havranek, R. (2020). Diachronous development of great unconformities before Neoproterozoic snowball Earth. Proceedings of the National Academy of Sciences of the United States of America, 117(19), 10172–10180.
Guenthner, W.R., Reiners, P.W., Ketcham, R.A., Nasdala, L., & Giester, G. (2013). Helium diffusion in natural zircon: Radiation damanage, anisotropy and the interpretation of zircon (U-Th)/He thermochronology. American Journal of Science, 313, 145-198.
Koppers, A. A. (2002). ArArCALC—software for 40Ar/39Ar age calculations. Computers & Geosciences, 28(5), 605-619
Stanley, J. R., & Flowers, R. M. (2020). Mesozoic denudation history of the lower Orange River and eastward migration of erosion across the southern African Plateau. Lithosphere, 12(1), 74-87.
Files and variables
File: File_1_Sangre_de_Cristo_thermochronology_samples_and_date_summary.xlsx
Description: Sample locations and date summary
Variables
- Sample: name of sample
- Lithology: rock type of sample
- UTM X, UTM Y: UTM coordinates in WGS 84 (X = easting, Y = northing)
- Distance from SdC fault (km): sample distance ENE of the Sangre de Cristo fault in kilometers
- Elev. (m): elevation of sample in meters.
- Zircon and Apatite (U-Th)/He dates, Avg. date (Ma) = average date, Std.dev. = standard deviation of dates, Aliq. = number of grains used in average age calculation compared to the total number of grains analyzed
File: File_2_U-Th_He_thermochronology_data.xlsx
Description: Zircon and apatite (U-Th)/He data
Variables
- Sample Name and Aliquot: sample name corresponds to samples from File 1.
- length 1 (µm), width 1 (µm), length 2 (µm), width 2 (µm): Length is measured parallel to the c-axis and includes pyramidal terminations. It is measured twice on two perpendicular sides.
- Geom: Geometry is defined as described as in Figure 3 of Ketcham et al. (2011).
- Np: describes the number of pyramidal terminations of the grain.
- 4He (fmol): Blank-corrected 4He
- ±: Uncertainties on 4He, U, Th, and Sm are reported as the 1s standard deviation and include the propagated uncertainties on the measurements of the sample, blank, spike, and standard.
- U (ng): Total blank-corrected ng of 238U and 235U. Total 238U is measured and 235U is calculated assuming 235U = 238U/137.818 after Hiess et al. (2012).
- Th (ng): Total blank-corrected ng of 232Th
- 147Sm (ng): Total blank-corrected ng of 147Sm. In some cases Sm may not be measured, for example in minerals like zircon with negligible Sm. n.m. indicates when Sm is not measured.
- ESR Ft (µm): equivalent spherical radius of a sphere with an equivalent alpha-ejection correction as the grain, calculated using equation A6 in Cooperdock et al. (2019)
- Mass (µg): Mass is the mass of the crystal. Determined from the measured grain dimensions, the volume assuming the reported grain geometry, and the volume equations and mineral densities in Ketcham et al. (2011).
- 4He (nmol/g),U (ppm), Th (ppm), Sm (ppm): Concentration of each element (He, U, Th, and Sm) computed from the mass and the absolute amount of the measured isotopes (where 147Sm is 0.15 of the total Sm reported here). In some cases, Sm may not be measured, for example, in minerals like zircon with negligible Sm. n.m. indicates when Sm is not measured.
- Uncorr Date (Ma): Uncorrected (U-Th)/He date is calculated iteratively using the 4He production equation defined as equation 1 in Wolf et al. (1998), modified to include He produced from Sm decay and assuming secular equilibrium.
- TAU ± (Ma) 2s: Uncertainty on the uncorrected (U-Th)/He date is reported at 2s and includes the propagated total analytical uncertainties (TAU) on the U, Th, Sm and He measurements. Uncertainty propagation done using HeCalc (Martin et al., 2023).
- Comb Ft: The combined alpha-ejection correction for the crystal calculated from the parent isotope-specific FT corrections, the proportion of U and Th contributing to 4He production, and assuming homogeneous parent isotope distributions using equation A4 in Cooperdock et al. (2019). The parent isotope-specific alpha ejection corrections were computed assuming the reported grain geometry in this table and the equations and alpha-stopping distances in Ketcham et al. (2011).
- Corrected Date (Ma): The corrected (U-Th)/He date is calculated iteratively using the absolute values of He, U, Th, and Sm, the isotope-specific FT corrections, and equation 34 in Ketcham et al. (2011), assuming secular equilibrium.
- ± TAU (Ma) 2σ: Uncertainty on the corrected (U-Th)/He date is reported at 2s and includes the propagated total analytical uncertainties (TAU) on the U, Th, Sm and He measurements. Uncertainty propagation done using HeCalc (Martin et al., 2023).
- IE: The proportion of Helium extracted in the initial extraction.
File: File_3_Ar-Ar_thermochronology_data.xlsx
Description: K-feldspar and biotite 40Ar/39Ar data from incremental step-heating analyses of samples 19-7-9 (two different K-feldspar separates), 20-9-SC1 (two different K-feldspar separates), 21-9-AF3 (K-feldspar), 24-DF162 (K-feldspar), and 24-DF162 (biotite). Analyses was performed at the Nevada Isotope Geochronology Laboratory, University of Nevada, Las Vegas. Samples were irradiated at the Oregon State TRIGA Reactor with Fish Canyon Tuff sanidine (FC-2) standards. This file is provided largely as output from ArArCalc software; users seeking full documentation of all software-generated variables are referred to the ArAr Calc v. 2.7.0 user documentation (Koppers, 2002).
Variables for primary step heating results in columns 1–20
- Column 1: Sample name and analysis number
- Column 2: Step heating temperature in °C
- Columns 3, 4: amount of 36Ar gas in mV ± %1σ
- Columns 5, 6: amount of 37Ar gas in mV ± %1σ
- Columns 7, 8: amount of 38Ar gas in mV ± %1σ
- Columns 9, 10: amount of 39Ar gas in mV ± %1σ
- Columns 11, 12: amount of 40Ar gas in mV ± %1σ
- Columns 13, 14: 40Ar/39Ar ± 2σ
- Column 15, 16: 40Ar/39Ar age in Ma ± 2σ (the apparent age calculated from this ratio)
- Column 17: 40Ar (r)%, the percentage total of 40Ar that is radiogenic
- Column 18: 39Ar (r)%, the percentage total of 39Ar that is radiogenic
- Columns 19, 20: K/Ca ± 2σ, potassium-to-calcium ratio (±2σ), a proxy for the mineralogical domain being degassed
Additional data columns are outlined below:
Normal Isochron (columns 21–27): Data for reconstructing a normal isochron plot (39Ar(k)/40Ar(a) vs. 40Ar(a+r)/36Ar(a)), used to evaluate the initial 40Ar/36Ar ratio and check for excess argon. The column r.i. is the relative inverse variance weighting used in isochron regression.
Inverse Isochron (columns 28–34): Data for constructing an inverse isochron plot (39Ar(k)/40Ar(a+r) vs. 36Ar(a)/40Ar(a+r), an alternative representation that more directly resolves the trapped argon component.
Degassing Patterns (columns 35–68): Breakdown of each argon isotope signal into its source components per heating step. Subscript notation indicates source: (a) = atmospheric, (c) = cosmogenic, (ca) = calcium-derived, (cl) = chlorine-derived. All values in mV with associated 1%σ uncertainties.
Additional Parameters (columns 69–78): Supplementary calculated quantities including isotope ratios, timing parameters, decay corrections, and molar quantities of argon, as generated by ArArCalc.
Procedure Blanks, Intercept Values, Sample Parameters, and Irradiation Constants (columns 79–171): Laboratory metadata sections generated by ArArCalc documenting blank corrections applied during analysis, regression intercept values, sample preparation details (analyst, standard used, J-value, sensitivity, irradiation information), and the interference correction factors used to correct for reactor-produced argon isotopes.
File: File_4_Fission_track_data.xlsx
Description: Zircon and apatite fission track data. There are two worksheets for each sample: one for the fission track data and one for the U-Pb data
File: File_4_Fission_track_data.xlsx
Description: Zircon and apatite fission track data. There are two worksheets for each sample: one for the fission track data and one for the U-Pb data
Variables for the fission track data
- Column A: Spot Name
- Column B: Spot Index
- Column C: FT Age (Ma): fission track age for spot in Ma
- Column D: 95%-CI (Ma): lower age error in Ma at 95% confidence interval
- Column E: 95%+CI (Ma): upper age error in Ma at 95% confidence interval
- Column F: UPb Age (Ma): U-Pb age for spot in Ma
- Column G: UPb 2 -sigma: - error on U-Pb age in Ma
- Column H: UPb 2 +sigma: +error on U-Pb age in Ma
- Column I: Ns: number of spontaneous fission track counted over area
- Column J: Area cm^2: area (in cm2) over which fission tracks were counted
- Column K: U/Cation
- Column L: +/- 1 sig: 1σ error of U/Cation
Variables of U-Pb data worksheets
(A) Analysis Name, (B) Preferred Age (Ma), (C) 2 -sigma, (D) 2 +sigma, (E) Age Type, (F) Concordant Scan, (G) Discordant Scans, (H) Analysis Name, (I) 207Pb/235Uc Ratio, (J) 2 sigma, (K) 206Pb/238U Ratio, (L) 2 sigma, (M) Error Correlation, (N) 238U/206Pb Ratio, (O) 2 sigma, (P) 207Pb/206Pb Ratio, (Q) 2 sigma, (R) Error Correlation, (S) 207Pb/235U Ratio, (T) 2 sigma, (U) 208Pb/232Th Ratio, (V) 2 sigma, (W) Analysis Name, (X) 207Pb/235U Age (Ma), (Y) 2 -sigma, (Z) 2 +sigma, (AA) 207Pb/235Uc Age (Ma), (AB) 2 -sigma, (AC) 2 +sigma, (AD) 206Pb/238U Age (Ma), (AE) 2 -sigma, (AF) 2 +sigma, (AG) 207Pb/206Pb Age (Ma) (AH) 2 -sigma, (AI) 2 +sigma, (AJ) 208Pb/232Th Age (Ma), (AK) 2 -sigma, (AL) 2 +sigma, (AM) Pbc-corrected (Ma), (AN) 2 -sigma, (AO) 2 +sigma, (AP) 207Pbc/206Pbc, (AQ) 207Pbc/207Pb, (AR) Analysis Name, (AS) 207Pb/235Uc Ratio, (AT) 2 sigma, (AU) 206Pb/238U Ratio, (AV) 2 sigma, (AW) Error Correlation, (AX) 238U/206Pb Ratio, (AY) 2 sigma, (AZ) 207Pb/206Pb Ratio, (BA) 2 sigma, (BB) Error Correlation, (BC) 207Pb/235U Ratio, (BD) 2 sigma, (BE) 208Pb/232Th Ratio, (BF) 2 sigma, (BG) Analysis Name, (BH) 207Pb/235U Age (Ma), (BI) 2 -sigma, (BJ) 2 +sigma, (BK) 207Pb/235Uc Age (Ma), (BL) 2 -sigma, (BM) 2 +sigma, (BN) 206Pb/238U Age (Ma), (BO) 2 -sigma, (BP) 2 +sigma, (BQ) 207Pb/206Pb Age (Ma), (BR) 2 -sigma, (BS) 2 +sigma, (BT) 208Pb/232Th Age (Ma), (BU) 2 -sigma, (BV) 2 +sigma, (BW) Pbc-corrected (Ma), (BX) 2 -sigma, (BY) 2 +sigma, (BZ) 207Pbc/206Pbc, (CA) 207Pbc/207Pb
Code/software
No software is needed to view these data, which are all organized in spreadsheets.
Access information
Other publicly accessible locations of the data:
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