Neoarchean ultrahigh-temperature sapphirine granulites from the Karimnagar Granulite Terrane, Southern India: Implications for hot orogen along the Eastern Dharwar Craton margin

Sundaralingam, K.; Uthup, Sam; Tsunogae, Toshiaki; Renjith, M.L.; Sahu, Munesh K.

doi:10.1016/j.lithos.2021.106537

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“…Therefore, integrated investigations on petrography, phase equilibria modelling, and geochronology of granulites are useful for constraining P–T conditions, timing of metamorphism, duration of high‐grade events, and regional correlation of orogenic belts (e.g., He et al, 2018; Kadowaki et al, 2019). Among various lithologies in granulite terranes, sapphirine‐bearing Mg–Al‐rich rocks and pelitic granulites have been the focus of many petrological investigations for the last three decades worldwide, because the rocks frequently preserve various reaction textures useful for quantitatively evaluating metamorphic P – T evolution (e.g., Kelsey, White, Holland, & Powell, 2004; Kelsey, White, & Powell, 2005; Santosh, Tsunogae, Li, & Liu, 2007; Sundaralingam, Uthup, Tsunogae, Renjith, & Sahu, 2021; Tsunogae & Santosh, 2010 and references therein).…”

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confidence: 99%

Petrology and geochronology of sapphirine‐bearing granulites from the Limpopo Complex in eastern Botswana: Implications for Palaeoproterozoic long‐lived high‐pressure/ultrahigh‐temperature metamorphism and rapid exhumation

2022

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The Limpopo Complex in southern Africa is a classic example of Neoarchean collisional orogens with a Palaeoproterozoic thermal overprint. We report new petrological, pressure–temperature (P–T), and geochronological data of sapphirine‐bearing Mg–Al‐rich and pelitic granulites from a metasupracrustal unit (the Beit Bridge Complex [BBC]) in the eastern part of Botswana to constrain its P–T–time evolution. Textural observations and phase equilibria modelling of the peak mineral assemblage of Mg–Al‐rich granulites (K‐feldspar + orthopyroxene [Opx2; Al2O3 up to 8.8 wt.%] + sillimanite [Sil2] + quartz + rutile + biotite [Bt2] + inferred melt) in the NCKFMASHTO system recorded a peak metamorphic condition of >930°C and > 10.3 kbar. A pelitic granulite recorded consistent P–T conditions of 960–980°C and > 10.3 kbar, indicating high‐pressure (HP) and ultrahigh‐temperature (UHT) metamorphism for the BBC in Botswana. Post‐peak retrograde conditions were obtained based on the stability of sapphirine + cordierite symplectite assemblage in the Mg–Al‐rich rocks (820–860°C and 6.4–7.0 kbar) and orthopyroxene [Opx3] + cordierite symplectite assemblage in the pelitic granulite (830–930°C and 4.3–5.8 kbar), indicating near‐isothermal decompression after the peak HP–UHT metamorphism along a clockwise P–T path. Similar HP–UHT metamorphism followed by a near‐isothermal decompression along a clockwise P–T path was reported from different regions of the BBC in South Africa and Zimbabwe (P > 14 kbar and ~1,000°C based on the stability fields of magnesian staurolite and sapphirine + quartz assemblage), although the peak P–T condition is slightly lower in Botswana. Monazite grains with patchy zoning show isochron ages of 2,115 ± 77 Ma for Th‐poor domains, and 2,058 ± 40 Ma and 2,033 ± 34 Ma for Th‐rich domains. Similar ages were obtained from zircon U–Pb geochronology as 2,232–2,135 Ma and 2,010 ± 19 Ma (Th/U = 0.05–0.26). The younger ages (2.0 Ga) probably indicate the timing of near‐peak high‐grade event, while the older ages might indicate a thermal event during the prograde heating stage. The P–T conditions and zircon/monazite ages suggest Palaeoproterozoic long‐lived metamorphism associated with intracontinental transpressional tectonics related to Palaeoproterozoic orogenic events around the united Zimbabwe–Kaapvaal Craton.

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