Petrogenetic relations and compositional characteristics of U-Pb geochronometers in a Mesoarchean late magmatic zircon-apatite vein: Maniitsoq region, SW Greenland
By: J.H. Marsh 1, T.R.C. Jørgensen 1, N.J. Evans 2, C.L. Kirkland 2, M.A. Hamilton 3, A. Vezinet 4, D. Harlov 5, and D.R. Mole 11. Mineral Exploration Research Centre, Laurentian University, 935 Ramsey Lake Rd., Sudbury, ON P3E 2C6, Canada 2. School of Earth and Planetary Sciences, Curtin University, Perth, Bentley, WA 6102, Australia 3. Jack Satterly Geochronology Laboratory, Department of Geology, University of Toronto, Toronto, ON M5S 3B1, Canada 4. Department of Earth and Atmospheric Sciences, University of Alberta, 1-26 Earth Sciences Building, Edmonton, AB T6G 2E3, Canada 5. Chemistry and Physics of Earth Materials, Deutsches GeoForschungsZentrum-GFZ, Telegrafenberg, Potsdam, 14473, Germany
Abstract
A mm-scale vein, composed of megacrystic zircon and interstitial apatite with abundant monazite inclusions, within a Mesoarchean metagabbro in the Akia Terrane of SW Greenland has been investigated to determine petrogenetic relationships and compositional characteristics of the U-bearing minerals. Zircon are dominated by oscillatory-zoned interiors, locally cut by thin, CL-bright veinlets and rims. CA-ID-TIMS yields a concordia age of 3008.7 ± 0.75 Ma. LA-MC-ICPMS analyses yield slightly discordant intercept ages of 3008.4 ± 0.67 Ma for pristine interiors and 2996.8 ± 1.9 Ma for rims, whereas veinlet-bearing (mixed) analyses yield variably discordant 207Pb/206Pb dates between ~2975-2700 Ma. The Hf isotopic composition is homogeneous across all domains, with LA and solution MC-ICPMS analyses yielding 176Hf/177Hfi = 0.280829 ± 10 and 0.280827 ± 11, respectively (εHfi = -0.60 ± 0.38). The interior trace element composition is consistent with magmatic zircon, with rim composition trending toward a zircon fractionated, more H2O-rich environment.
Apatite have decreasing Y, REE, Th and U from interior to rims, with trends suggesting variable alteration of primary apatite formed in a mafic magma. CL imaging shows a granular internal microstructure and halos surrounding monazite inclusions, interpreted as a dissolution-precipitation (D-P) network and zones of LREE-Th-U depletion associated with monazite exsolution, respectively. Apatite exhibit a spread in Pb0/Pb*, correlating with REE concentration, and defining a discordia with lower intercept of 1808 ± 53 Ma and upper intercept 207Pb/206Pb of 1.103 (i.e. model Pb composition in the Mesoarchean). Monazite exhibit multiple age/compositional domains with 207Pb/206Pb dates ranging from ~2900 to 2700 Ma, forming a slightly discordant array with lower intercept ~2050 Ma. The results suggest crystallization of zircon and apatite from a slightly evolved magma at ~3009 Ma was followed by zircon recrystallization at ~2997 Ma, zircon veining and local Pb-loss, along with D-P-enhanced monazite exsolution from apatite between ~2900-2700 Ma, and resetting the U-Pb systems in apatite (and monazite to some degree?) between ~2050-1800 Ma. Thus, each chronometer records multiple aspects of a complex tectono-thermal history previously defined in the Akia Terrane.
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| Last Updated | March 25, 2026, 02:06 (UTC) |
| Created | March 25, 2026, 02:06 (UTC) |
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Title
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Petrogenetic relations and compositional characteristics of U-Pb geochronometers in a Mesoarchean late magmatic zircon-apatite vein: Maniitsoq region, SW Greenland |
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Description
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By: J.H. Marsh 1, T.R.C. Jørgensen 1, N.J. Evans 2, C.L. Kirkland 2, M.A. Hamilton 3, A. Vezinet 4, D. Harlov 5, and D.R. Mole 1
1. Mineral Exploration Research Centre, Laurentian University, 935 Ramsey Lake Rd., Sudbury, ON P3E 2C6, Canada 2. School of Earth and Planetary Sciences, Curtin University, Perth, Bentley, WA 6102, Australia 3. Jack Satterly Geochronology Laboratory, Department of Geology, University of Toronto, Toronto, ON M5S 3B1, Canada 4. Department of Earth and Atmospheric Sciences, University of Alberta, 1-26 Earth Sciences Building, Edmonton, AB T6G 2E3, Canada 5. Chemistry and Physics of Earth Materials, Deutsches GeoForschungsZentrum-GFZ, Telegrafenberg, Potsdam, 14473, Germany Abstract A mm-scale vein, composed of megacrystic zircon and interstitial apatite with abundant monazite inclusions, within a Mesoarchean metagabbro in the Akia Terrane of SW Greenland has been investigated to determine petrogenetic relationships and compositional characteristics of the U-bearing minerals. Zircon are dominated by oscillatory-zoned interiors, locally cut by thin, CL-bright veinlets and rims. CA-ID-TIMS yields a concordia age of 3008.7 ± 0.75 Ma. LA-MC-ICPMS analyses yield slightly discordant intercept ages of 3008.4 ± 0.67 Ma for pristine interiors and 2996.8 ± 1.9 Ma for rims, whereas veinlet-bearing (mixed) analyses yield variably discordant 207Pb/206Pb dates between ~2975-2700 Ma. The Hf isotopic composition is homogeneous across all domains, with LA and solution MC-ICPMS analyses yielding 176Hf/177Hfi = 0.280829 ± 10 and 0.280827 ± 11, respectively (εHfi = -0.60 ± 0.38). The interior trace element composition is consistent with magmatic zircon, with rim composition trending toward a zircon fractionated, more H2O-rich environment. Apatite have decreasing Y, REE, Th and U from interior to rims, with trends suggesting variable alteration of primary apatite formed in a mafic magma. CL imaging shows a granular internal microstructure and halos surrounding monazite inclusions, interpreted as a dissolution-precipitation (D-P) network and zones of LREE-Th-U depletion associated with monazite exsolution, respectively. Apatite exhibit a spread in Pb0/Pb*, correlating with REE concentration, and defining a discordia with lower intercept of 1808 ± 53 Ma and upper intercept 207Pb/206Pb of 1.103 (i.e. model Pb composition in the Mesoarchean). Monazite exhibit multiple age/compositional domains with 207Pb/206Pb dates ranging from ~2900 to 2700 Ma, forming a slightly discordant array with lower intercept ~2050 Ma. The results suggest crystallization of zircon and apatite from a slightly evolved magma at ~3009 Ma was followed by zircon recrystallization at ~2997 Ma, zircon veining and local Pb-loss, along with D-P-enhanced monazite exsolution from apatite between ~2900-2700 Ma, and resetting the U-Pb systems in apatite (and monazite to some degree?) between ~2050-1800 Ma. Thus, each chronometer records multiple aspects of a complex tectono-thermal history previously defined in the Akia Terrane. |
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102.17 |
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2021-03-22 |
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public |
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https://metalearth.geohub.laurentian.ca/datasets/914d4ed86c194f9ca829c08d8dd0c642 |
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MetalEarth |
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MetalEarth |
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2021-03-23 |
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914d4ed86c194f9ca829c08d8dd0c642 |
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English |
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https://metalearth.geohub.laurentian.ca/datasets/914d4ed86c194f9ca829c08d8dd0c642 |
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None |
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