Evolution of spinel-bearing ultrahigh-temperature granulite in the Jining complex, North China Craton: constrained by phase equilibria and Monte Carlo methods

• Published in: Mineralogy and petrology Vol. 115; no. 3; pp. 283 - 297
• Main Authors: Wang, Bin, Wei, Chun-Jing, Tian, Wei
• Format: Journal Article
• Language: English
• Published: Vienna Springer Vienna 01-06-2021; Springer Nature B.V
• Subjects: Aluminum; Biotite; Cooling; Cratons; Decompression; Earth and Environmental Science; Earth Sciences; Evolution; Feldspars; Garnet; Geochemistry; Heating; High temperature; Inorganic Chemistry; Iron; Isotopes; Lamellae; Magnesium; Magnetite; Metamorphism; Mineralogy; Monte Carlo simulation; Original Paper; Orogeny; Phase equilibria; Plagioclase; Probability theory; Sillimanite; Solidus; Spinel; Statistical methods; Temperature; Time; Ultrahigh temperature; Zircon; China; Jining complex; Spinel; Ultrahigh-temperature metamorphism; Pelitic granulite; Timescale
• ISSN: 0930-0708; 1438-1168
• DOI: 10.1007/s00710-021-00743-1

The peak temperature and timescale of ultrahigh-temperature (UHT) metamorphism are significant for understanding its thermal budget and geodynamic evolution. The spinel-bearing (sapphirine-absent) UHT granulite at the Xuwujia area in the Jining complex, North China Craton was revealed to have undergone a metamorphic evolution that involves the pre-
T
max
(maximum temperature) heating decompression to the
T
max
stage with an extreme temperature of ~1125 °C, the post-
T
max
cooling to the fluid-absent solidus (~860 °C) at 0.8–0.9 GPa, and sub-solidus decompression. The
T
max
condition was recorded by the inferred feldspar-absent peak assemblage of spinel ± garnet. The post-
T
max
cooling evolution was indicated by the sequential appearances of plagioclase, K-feldspar, sillimanite and biotite, as well as the core-to-rim ascending grossular component in garnet. Moreover, some texturally zoned spinel has exsolved lamellae of magnetite in the core and shows rim-ward increase of Mg and Al, which suggests a temperature decrease from >1100 °C in local domains isolated from quartz. Spinel with exsolved magnetite lamellae or low Al/(Al + Fe
3+
) is therefore proposed as an indicator for UHT conditions in metapelites. Probability simulation on the collected zircon ages yields a timescale of ~40 Myr (95% confidence; during 1.90–1.94 Ga) for the supra-solidus cooling stage of the UHT metamorphism in the Jining complex. This extreme UHT metamorphism has reached the rock’s dry solidus (~1125 °C) and undergone slow cooling, which is interpreted to result from a post-orogenic plume activity with sufficient advective heating from hyperthermal mafic intrusions.