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<p>Constraining the cooling timescales/rates of metamorphic rocks of orogens is critical for understanding their tectonic settings and geodynamic mechanisms, especially their links to plate tectonics and the formation of the continental lithosphere. The Orosirian period (2.1–1.8 Ga) is characterized by widespread orogenesis and is potentially linked to the onset of global plate tectonics, yet the metamorphic cooling histories of Orosirian orogens remain underexplored. This study applies a dual-constraint diffusion modeling approach, integrating both major (Fe, Mn, Mg, Ca) and trace elements (HREE + Y) in garnet. This is based on multi-mineral microprobe and laser ablation mapping to two metamorphic rocks from the Wutai–Fuping crustal section of the Trans-North China Orogen (TNCO). Sample 20FP09, collected from the Wanzi Supracrustal Rocks, records a two-stage retrograde <i>P–T</i> path: an isothermal decompression (ITD) from the M2 peak (725&#xa0;° C/0.9 GPa) to M3 decompression (725&#xa0;° C/0.6 GPa), followed by isobaric cooling (IBC) to M4 (550&#xa0;° C/0.4 GPa). Sample L17, from the Shizui Subgroup, preserves a single cooling segment from the M2T peak (680&#xa0;° C/0.6 GPa) to M3 (550&#xa0;° C/0.4 GPa). Diffusion modeling using multiple experimental datasets of diffusion coefficients yields an ITD duration of 1–4 Myr and an IBC duration of 11–31 Myr for sample 20FP09, and a single 35–50 Myr cooling interval for sample L17. Together, these results indicate a protracted cooling duration of 13–50 Myr, corresponding to a cooling rate of 2–13&#xa0;° C/Myr for the TNCO. Such rates are significantly slower than those of Phanerozoic orogens (&gt; 100&#xa0;° C/Myr). This implies that Orosirian orogenesis may have involved in prolonged thermal relaxation within a hot, weak Paleoproterozoic lithosphere, likely influenced by higher mantle temperatures and orogenic thermal structures. This study also demonstrates the importance of large datasets containing high spatial element maps for obtaining robust constraints on metamorphic timescales; and offers a first-order empirical estimate of Sc diffusivity in garnet, which remains experimentally unconstrained.</p>

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Protracted cooling in a long-lived Orosirian orogen: insights from major and trace element diffusion modeling in metamorphic garnet

  • 期刊论文

  • 发表日期：

    2026年1月20日

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  • Jia-Hui Liu,
  • Thorsten A. Markmann,
  • Hugo Dominguez,
  • Jinghui Guo,
  • Qian W. L. Zhang,
  • Liangliang Zhang,
  • Guochun Zhao,
  • Pierre Lanari

摘要

Constraining the cooling timescales/rates of metamorphic rocks of orogens is critical for understanding their tectonic settings and geodynamic mechanisms, especially their links to plate tectonics and the formation of the continental lithosphere. The Orosirian period (2.1–1.8 Ga) is characterized by widespread orogenesis and is potentially linked to the onset of global plate tectonics, yet the metamorphic cooling histories of Orosirian orogens remain underexplored. This study applies a dual-constraint diffusion modeling approach, integrating both major (Fe, Mn, Mg, Ca) and trace elements (HREE + Y) in garnet. This is based on multi-mineral microprobe and laser ablation mapping to two metamorphic rocks from the Wutai–Fuping crustal section of the Trans-North China Orogen (TNCO). Sample 20FP09, collected from the Wanzi Supracrustal Rocks, records a two-stage retrograde P–T path: an isothermal decompression (ITD) from the M2 peak (725 ° C/0.9 GPa) to M3 decompression (725 ° C/0.6 GPa), followed by isobaric cooling (IBC) to M4 (550 ° C/0.4 GPa). Sample L17, from the Shizui Subgroup, preserves a single cooling segment from the M2T peak (680 ° C/0.6 GPa) to M3 (550 ° C/0.4 GPa). Diffusion modeling using multiple experimental datasets of diffusion coefficients yields an ITD duration of 1–4 Myr and an IBC duration of 11–31 Myr for sample 20FP09, and a single 35–50 Myr cooling interval for sample L17. Together, these results indicate a protracted cooling duration of 13–50 Myr, corresponding to a cooling rate of 2–13 ° C/Myr for the TNCO. Such rates are significantly slower than those of Phanerozoic orogens (> 100 ° C/Myr). This implies that Orosirian orogenesis may have involved in prolonged thermal relaxation within a hot, weak Paleoproterozoic lithosphere, likely influenced by higher mantle temperatures and orogenic thermal structures. This study also demonstrates the importance of large datasets containing high spatial element maps for obtaining robust constraints on metamorphic timescales; and offers a first-order empirical estimate of Sc diffusivity in garnet, which remains experimentally unconstrained.