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Title: Zircon U-Pb geochronology data from the Colorado Mineral Belt, Front Range, Colorado, USA Open Access Deposited

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  • Zircon U/Pb geochronology analyses were conducted by laser ablation multicollector inductively coupled plasma mass spectrometry (LA-ICP-MS) at the Arizona LaserChron Center using an Element2 HR ICP-MS, following the methods of Gehrels et al. (2008). Approximately 50 zircon grains from each CMB sample were mounted in a 1-inch epoxy mount with zircon standards. Mounts were sanded to a depth of ~20 µm and then polished. In order to locate analysis sites and provide context for interpreting results, we imaged mounts at the University of Michigan using a JEOL 7800FE SEM equipped with a CL detector system. For isotopic analyses, a Photon Machines Analyte G2 excimer laser equipped with HelEx ablation cell ablated zircon crystals using a spot diameter of 20 µm. The ablated material was carried in He into the plasma source of the Element2, which sequences rapidly through U, Th, and Pb isotopes. For the CMB samples, weighted mean 206Pb/238U ages (Table 1, 2) were calculated using the routines in Isoplot (Ludwig, 2008). The final uncertainty for the CMB samples determined by quadratic addition of the weighted mean and external uncertainties. Christine Smith Siddoway prepared detrital zircon grains from Tavakaiv Quartzite sample AP6317 (Table 3) for processing and analysis at the Arizona LaserChron Center following the procedures outlined above. Gehrels, G.E., Valencia, V.A. and Ruiz, J., 2008. Enhanced precision, accuracy, efficiency, and spatial resolution of U‐Pb ages by laser ablation–multicollector–inductively coupled plasma–mass spectrometry. Geochemistry, Geophysics, Geosystems, 9(3). Ludwig, K.R., 1988. ISOPLOT for MS-DOS, a plotting and regression program for radiogenic-isotope data, for IBM-PC compatible computers, version 1.00 (No. 88-557). US Geological Survey,.
Description
  • The Front Range of the Southern Rocky Mountains near Boulder, CO contains a rock record that spans nearly 1.7 billion years. Zircon U-Pb geochronology is an isotopically-based chronometer for measuring deep earth time. We apply this method to a series of small igneous intrusive bodies from the Front Range west of Boulder, CO. These instrusives are collectively known as the Colorado Mineral Belt (CMB) for the economic mineral deposits associated with the instrusives. Past geochronological methods have provided only rudimentary constraints on the geologic timing of emplacement of these bodies. We demonstrate the CMB magmatic activity in the Front Range occurred in two discrete pulses, one at ~67 Ma (million years ago) and one at ~47 Ma. Additional application of the same methodology to a sedimentary rock, the Neoproterozoic Tavakiav Quartzite, uses the zircon U-Pb ages as tracers to constrain the provenance and depositional age of this unique sand body.
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  • National Science Foundation (NSF)
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Date coverage
  • 2017-06-01
Citations to related material
  • Murray, K. E., Niemi, N. A., & Clark, M. K. (2025). Evidence for the Neoproterozoic rifting of Rodinia in the Rocky Mountain Front Range. Tectonics, 44, e2023TC008216.
Related items in Deep Blue Documents
  • Murray, K. E., Niemi, N. A., Clark, M. C. (2022). Apatite and Zircon (U-Th)/He Thermochronometry Data from the Colorado Front Range, Boulder County, Colorado, USA [Data set], University of Michigan - Deep Blue Data. https://doi.org/10.7302/g4eg-vr84
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  • 02/20/2025
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  • 02/20/2025
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  • https://doi.org/10.7302/xjts-pd98
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To Cite this Work:
Murray, K. E., Niemi, N. A., Clark, M. K., Siddoway, C. (2025). Zircon U-Pb geochronology data from the Colorado Mineral Belt, Front Range, Colorado, USA [Data set], University of Michigan - Deep Blue Data. https://doi.org/10.7302/xjts-pd98

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Files (Count: 2; Size: 112 KB)

Thumbnailthumbnail-column Title Original Upload Last Modified File Size Access Actions
Murray_et_al_CMB_Zircon_U-Pb_Tables.xlsx 2025-02-18 2025-02-18 105 KB Open Access
Murray_Front_Range_Zircon_README.txt 2025-02-18 2025-02-20 6.14 KB Open Access

Date: 18 February, 2025

Dataset Title: Zircon U-Pb geochronology data from the Colorado Mineral Belt, Front Range, Colorado, USA

Dataset Contact: Nathan Niemi [email protected]

Dataset Creators:
Name: Kendra Murray
Email: [email protected]
Institution: Idaho State University, Department of Geosciences
ORCID: https://orcid.org/0000-0003-4008-1645

Name: Nathan A Niemi
Email: [email protected]
Institution: University of Michigan, Department of Earth and Environmental Sciences
ORCID: https://orcid.org/0000-0002-3380-3024

Name: Marin K. Clark
Email: [email protected]
Institution: University of Michigan, Department of Earth and Environmental Sciences
ORCID: https://orcid.org/0000-0002-6141-8422

Name: Christine Siddoway
Email: [email protected]
Institution: Colorado College, Geology Department
ORCID: https://orcid.org/0000-0003-0478-6138

Funding: NSF-EAR-2140480, NSF-EAR-1151247, NSF-EAR-1649254

Key Points:
- We provide zircon U-Pb geochronologic ages on instrusive rocks associated with the Colorado Mineral Belt near Boulder, CO
- These ages delineate two distinct episodes of magmatic activity, at ~47 Ma and 67 Ma
- Detrital zircon U-Pb ages from the Tavakiav Quartzite provide information on its depositional age and provenance

Research Overview:
The Front Range of the Southern Rocky Mountains near Boulder, CO contains a rock record that spans nearly 1.7 billion years. Zircon U-Pb geochronology is an isotopically-based chronometer for measuring deep earth time. We apply this method to a series of small igneous intrusive bodies from the Front Range west of Boulder, CO. These instrusives are collectively known as the Colorado Mineral Belt (CMB) for the economic mineral deposits associated with the instrusives. Past geochronological methods have provided only rudimentary constraints on the geologic timing of emplacement of these bodies. We demonstrate the CMB magmatic activity in the Front Range occurred in two discrete pulses, one at ~67 Ma (million years ago) and one at ~47 Ma. Additional application of the same methodology to a sedimentary rock, the Neoproterozoic Tavakiav Quartzite, uses the zircon U-Pb ages as tracers to constrain the provenance and depositional age of this unique sand body.

Methodology:
Rock samples were processed using standard rock crushing followed by density and magnetic mineral separation techniques. Zircon U/Pb geochronology analyses were conducted by laser ablation multicollector inductively coupled plasma mass spectrometry (LA-ICP-MS) at the Arizona LaserChron Center using an Element2 HR ICP-MS, following the methods of Gehrels et al. (2008). Approximately 50 zircon grains from each CMB sample were mounted in a 1-inch epoxy mount with zircon age standards. Mounts were sanded to a depth of ~20 µm and then polished. In order to locate analysis sites and provide context for interpreting results, we imaged mounts at the University of Michigan using a JEOL 7800FE SEM equipped with a CL detector system. For isotopic analyses, a Photon Machines Analyte G2 excimer laser equipped with HelEx ablation cell ablated zircon crystals using a spot diameter of 20 µm. The ablated material was carried in He into the plasma source of the Element2, which sequences rapidly through U, Th, and Pb isotopes. For the CMB samples, weighted mean 206Pb/238U ages were calculated using the routines in Isoplot (Ludwig, 2008). The final uncertainty for the CMB samples determined by quadratic addition of the weighted mean and external uncertainties. Christine Smith Siddoway prepared detrital zircon grains from Tavakaiv Quartzite sample AP6317 (Table S3, Fig. S3) for processing and analysis at the Arizona LaserChron Center following the procedures outlined above. Zircon 238U/206Pb ages of the CMB stocks are reported with 2σ uncertainties.

Date Coverage: 2017.

Instrument and/or Software specifications: NA

Files contained here:

Table 1 CMB Ages - this file contains a summary of the emplacement age of 6 Colorado Mineral Belt intrusives
- Pluton (common name of the intrusive body sampled)
- Name (Sample ID of the sample collected)
- Lat (Latitude - unit: °N on WGS84 spheroid)
- Long (Longitude - unit: °E on WGS84 spheroid)
- Elevation (unit: m)
- Age (unit: Ma)
- ±2σ (unit: Ma)
- 4He error (unit: ncc)

Table 2 CMB Data - this file contains detailed analytical data for 6 Colorado Mineral Belt intrusives
- Analysis (individual laser spot analysis number)
- U ppm (unit: ppm)
Isotope Ratios
- 206Pb/204Pb (ratio of 206Pb isotope to 204Pb isotope)
- U/Th (ratio of uranium content to thorium content)
- 206Pb*/207Pb* (ratio of 206Pb* isotope to 207Pb* isotope, corrected for common lead)
- ± (unit: %)
- 207Pb*/235U* (ratio of 207Pb* isotope to 235U* isotope, corrected for common lead)
- ± (unit: %)
- 206Pb*/238U* (ratio of 206Pb* isotope to 238U* isotope, corrected for common lead)
- ± (unit: %)
- Error Corr.
Apparent Ages (Ma)
- 206Pb*/238U* (unit: Ma)
- ± (unit: Ma)
- 207Pb*/235U* (unit: Ma)
- ± (unit: Ma)
- 206Pb*/207Pb* (unit: Ma)
- ± (unit: Ma)
-Best age (unit: Ma)
- ± (unit: Ma)
- Conc (unit: %)

Table 3 Tava Data - this file contains detailed analytical data for 1 sample of Tavakiav Quartzite
- Analysis (individual laser spot analysis number)
- U ppm (unit: ppm)
Isotope Ratios
- 206Pb/204Pb (ratio of 206Pb isotope to 204Pb isotope)
- U/Th (ratio of uranium content to thorium content)
- 206Pb*/207Pb* (ratio of 206Pb* isotope to 207Pb* isotope, corrected for common lead)
- ± (unit: %)
- 207Pb*/235U* (ratio of 207Pb* isotope to 235U* isotope, corrected for common lead)
- ± (unit: %)
- 206Pb*/238U* (ratio of 206Pb* isotope to 238U* isotope, corrected for common lead)
- ± (unit: %)
- Error Corr.
Apparent Ages (Ma)
- 206Pb*/238U* (unit: Ma)
- ± (unit: Ma)
- 207Pb*/235U* (unit: Ma)
- ± (unit: Ma)
- 206Pb*/207Pb* (unit: Ma)
- ± (unit: Ma)
-Best age (unit: Ma)
- ± (unit: Ma)
- Conc (unit: %)

Related publication(s):
Murray, K. E., Niemi, N. A., & Clark, M. K. (2025). Evidence for the Neoproterozoic rifting of Rodinia in the Rocky Mountain Front Range. Tectonics, 44, e2023TC008216.

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

To Cite Data:
Murray, K. E., Niemi, N. A., & Clark, M. K. (2025). Zircon U-Pb geochronology data from the Colorado Mineral Belt, Front Range, Colorado, USA [Data set]. University of Michigan - Deep Blue. https://doi.org/10.7302/g4eg-vr84

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