The timing and duration of high-temperature to ultrahigh-temperature metamorphism constrained by zircon U–Pb–Hf and trace element signatures in the Khondalite Belt, North China Craton

Self Cite

An Al-rich, quartz-absent corundum-bearing pelitic granulite is reported for the first time at the Diebusige complex in the Alxa Block in the western part of the Khondalite Belt (KB), North China Craton (NCC). A detailed petrographic study shows that a quartz-present domain occurs in porphyroblastic garnet cores from the corundum-bearing pelitic granulite, with a prograde metamorphic mineral assemblage (M 1 ) of garnet + plagioclase + quartz + biotite + spinel + rutile AE melt, and a quartz-absent domain occurs in the matrix of this rock, with a preserved peak mineral assemblage (M 2 ) of garnet + corundum + spinel + biotite + plagioclase + K-feldspar + rutile + melt and a retrograde metamorphic mineral assemblage (M 3 ) of garnet + sillimanite + corundum + biotite + plagioclase + K-feldspar AE rutile.Phase equilibrium modelling and Zr-in-rutile and ternary feldspar thermometry all reveal similar peak conditions of 890-940 C at 7.5-9.8 kbar, which indicate a high geothermal gradient of $110 C/kbar and ultrahigh-temperature (UHT) conditions. Combining this information with the detailed analysis of metamorphic zircons, we obtain the metamorphic evolution of the corundumbearing pelitic granulite. Specifically, the corundum-bearing pelitic granulite experienced granulite-facies metamorphism at $1950 Ma. Then, this rock was slowly uplifted with heating and partial melting until it achieved UHT conditions. Finally, it cooled to the solidus at $1830 Ma. Thus, we propose that the UHT metamorphic conditions of a corundum-bearing pelitic granulite from the Diebusige complex of the Alxa Block may be the result of long-term slow uplift with heating under a high geothermal gradient.

Section: Introductionsupporting

confidence: 82%

Section: Discussionmentioning

confidence: 99%

Paleoproterozoic ultrahigh‐temperature metamorphism in the Alxa Block, the Khondalite Belt, North China Craton: Petrology and phase equilibria of quartz‐absent corundum‐bearing pelitic granulites

Zou

Guo

Jiao

et al. 2022

Self Cite

“…In addition, the duration of UHT metamorphism in the Napier Complex was constrained to be ca. 135 Ma (from 2585 to 2450 Ma) (Clark et al, 2018); the metamorphism in the Paleoproterozoic Khondalite Belt of North China Craton is long‐lived, lasting for at least 100 Ma (Jiao et al, 2020; Li & Wei, 2016, 2017; Liu et al, 2014; Peng et al, 2010; Wan et al, 2013; Zhai, 2009; Zhou et al, 2017), and Korhonen, Brown, et al (2013) demonstrated that the Eastern Ghats Province along the coast of Peninsular India sustained UHT conditions ( T > 900°C) for >>50 Ma, and perhaps for as long as 200 Ma from ca. 1130 to 930 Ma, during a single tectono‐metamorphic event.…”

Section: Discussionmentioning

confidence: 99%

Ultrahigh temperature metamorphism and isobaric cooling of Neoarchean ultramafic‐mafic granulites in the southern granulite terrain, India: Phase equilibrium modelling and SHRIMP zircon U–Pb dating

Gou

Zhai

Zhang

et al. 2022

This study presents the results of petrology, SHRIMP zircon U-Pb analysis, conventional Fe-Mg geothermobarometry, REE (rare earth element)-based geothermobarometry, and phase equilibrium modelling, for newly discovered ultramafic-mafic granulites (garnet pyroxenite with minor plagioclase and garnet-bearing granulite) in the Namakkal Block of the southern granulite terrain (SGT), India. Results from this study shed light on the growth, evolution, and thermal state of lower continental crust during the Neoarchean, as a cross-section of the Archean lower continental crust is well-exposed in the SGT. SHRIMP zircon U-Pb dating of a garnet pyroxenite sample (18ID-41) yielded a weighted mean 207 Pb/ 206 Pb age of 2531 AE 6 Ma, which is the same within uncertainty as one weighted mean SHRIMP metamorphic zircon 207 Pb/ 206 Pb age of 2519 AE 9 Ma from mafic granulite sample (18ID-43). In addition, zircon U-Pb analyses also yielded an apparent 207 Pb/ 206 Pb age of 2474 AE 3 Ma (1σ) for the garnet pyroxenite, and a weighted mean 207 Pb/ 206 Pb age of 2489 AE 8 Ma for the mafic granulite. Thus, the timing of metamorphism of the ultramafic-mafic granulites was constrained to be ca. 2530-2470 Ma.The peak metamorphic phase assemblage of the garnet pyroxenite is grt-cpxpl-ilm-liq, which was modelled to be stable at 1058-1172 C/7.8-11.6 kbar, whereas the retrograde mineral assemblage of grt-cpx-hbl-pl-qz-ilm-liq occurred at 877-888 C/9.9-11 kbar. The mafic granulite was demonstrated to record similar peak and retrograde metamorphic P-T conditions to those of the garnet pyroxenite but have a relatively small P-T range of the peak mineral assemblage. The ultrahigh temperature metamorphism of these ultramafic-mafic granulites was further confirmed by the temperature results

“…In addition, HP pelitic granulites with the representative mineral assemblage garnet + kyanite + K‐feldspar, preserving a clockwise P – T path characterized by an ITD segment, have been reported from the Qianlishan–Helanshan terrane (Figure 1b; Yin et al, 2014; Yin et al, 2015; Zhou et al, 2010). Zircon and monazite record the HP and UHT metamorphic ages of ~1.95 Ga and ~1.93–1.91 Ga, respectively (e.g., Gou et al, 2019; Huang et al, 2019; Li & Wei, 2018; Peng et al, 2014; Yin et al, 2009, 2011), and record the retrograde or overprinting metamorphic (granulite facies or UHT) ages of ~1.85 Ga (Guo et al, 2012; Jiao, Fitzsimons, et al, 2020; Jiao, Guo, et al, 2020; Peng et al, 2014; Zou et al, 2022).…”

Section: Geological Settingmentioning

confidence: 99%

Paleoproterozoic ultrahigh‐temperature mafic granulites with a high‐pressure prograde path from the Alxa Block: Implications on the tectonic evolution of the Khondalite Belt, North China Craton

Zou,

Guo,

Zhang

et al. 2024

Self Cite

Ultrahigh‐temperature (UHT) granulites, a prominent feature of Paleoproterozoic orogenic belts, preserve a record of geodynamic processes during the Precambrian (Archean–Paleoproterozoic). Quantitative pressure–temperature–time (P–T–t) paths of these UHT granulites can constrain the tectonic processes and metamorphic evolution in such a tectonic regime. Here, UHT mafic granulites with a high‐pressure (HP) prograde path are first reported in the Diebusige Complex in the Alxa Block, western part of the Khondalite Belt (KB), North China Craton (NCC). The detailed petrographic studies show that two mafic granulite samples preserve corona textures around relict garnet or garnet pseudomorphs (completely replaced by plagioclase), and a third mafic granulite sample has a relatively simple mineralogy with a granoblastic‐polygonal texture. These mafic granulites have similar peak (Tmax) assemblages of clinopyroxene + orthopyroxene + plagioclase + ilmenite ± garnet ± amphibole ± quartz + melt. Phase equilibrium modelling and Ti‐in‐amphibole and rare earth element (REE)‐based thermometries all constrain similar peak conditions of ~880–950°C/~8.5–10 kbar implying an ~100°C/kbar apparent geothermal gradient for these mafic granulites. Based on the corona textures or pseudomorphs of garnet and mineral assemblages, we identified a Pmax (~14 kbar) prograde stage before the Tmax stage. Thus, a clockwise P–T path with heating and decompression followed by near‐isobaric cooling (IBC) is recorded from these UHT mafic granulites. In addition, zircon and apatite SHRIMP or LA–ICP–MS U–Pb dating yields an age interval of ~1.81–1.7 Ga, which is interpreted as representing the cooling time from ~900–800°C to ~575°C at the middle‐upper crustal levels (<25 km deep) for these mafic granulites, with an ~1.5–2.5°C/Myr cooling rate. The new P–T–t path of these rocks includes high‐pressure prograde, UHT peak, and slow cooling retrograde processes, which implicates a post‐collisional tectonic setting for UHT metamorphism in the KB and the processes of collision, exhumation, and cooling of the KB.