The Napier Complex in Enderby Land and western Kemp Land is a unique component of the East Antarctic Shield because it records a timeline of crustal growth from the Eo- to Neoarchean. It is mainly composed of enderbitic and charnockitic gneisses and granulites that were metamorphosed at ∼ 2.5 Ga, and locally at ∼ 2.8 Ga, under high- to ultra-high-temperature conditions. Despite generating scientific interest for several decades, the geological history of the complex has not been well constrained. In this study, samples from the Napier Mountains were selected for zircon imaging and U-Pb dating by Secondary Ion Mass Spectrometry. They record metamorphic growth, recrystallization, and modification of zircon at 2800-2770, 2740-2720, and 2490-2460 Ma. For the first time, fluid-related alteration at around 2730 Ma is evident in a granitic gneiss from Grimsley Peaks. At the similar time, dioritic gneiss was formed at Mount Marr. Tonalitic and granitic gneisses from Grimsley Peaks yield protolith crystallization ages of around 3210 and 2825 Ma, respectively. The generation of granitic gneiss was coeval with ∼ 2.8 Ga metamorphism in the area. These new data from this little-known part of the complex provide a better understanding of the crustal evolution of the Napier Complex.

Melanocratic dyke rocks were found at Skallevikshalsen and Rundvågshetta in the Lützow-Holm Complex. The rocks are commonly holocrystalline and aphyric, and consist mainly of alkali feldspar, biotite, augite, quartz, apatite, and titanite, with minor amounts of plagioclase. Almost all the mineral compositions tended to be homogeneous, whereas the composition of apatite sometimes showed intragranular heterogeneity in the F and Cl components. The melanocratic dyke rocks at Skallevikshalsen have an ultrapotassic mafic composition and resemble the compositional features of the lamproitic to minettic dyke rock previously found at Innhovde, located in the western region of the Lützow-Holm Complex. The dyke rocks at Rundvågshetta are considered to be a mixture of ultrapotassic mafic magma and high-Cl/F intermediate to felsic magma. Considering their occurrence and the results of Rb-Sr mineral dating, the time of intrusion was just after the metamorphism of the Lützow-Holm Complex, and the igneous activity was thought to have been caused by the collision between East and West Gondwana.

The Vengen Granite, one of early Paleozoic granitic rocks crops out of the southern end of the Vengen ridge, the Kanino-tsume Peak at the Main Shear Zone (MSZ) of the Sør Rondane Mountains, East Antarctica. This granite is composed of medium- to fine-grained mylonitic biotite granite and cuts the MSZ and Kanino-tsume Shear Zone. The fine-grained two-mica granitic dykes locally intrude the Vengen Granite. The two-mica granitic dykes have foliations parallel to mylonitic foliations of the Vengen Granite. The Vengen Granite is composed of plagioclase, quartz, K-feldspar, biotite, and muscovite with trace amounts of titanite, allanite, apatite, zircon and opaques as accessory minerals. The granite is geochemically characterized by a high-K content, which resembles adakitic affinity. These chemical data combined with rare earth elements and Sr-Nd isotope geochemistry suggest that the source magma of the Vengen Granite was derived from partial melting of the meta-tonalite with minor amounts of the pelitic gneisses in the SW-terrane subducted under the NE-terrane during collision of the West and East Gondwana continents.

This paper reports laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U-Pb ages of a suite of high-grade metamorphic rocks collected from Sinnan Rocks, Akebono Rock, Niban Rock, Gobanme Rock, Tenmondai Rock, Akarui Point, Cape Omega, and Oku-iwa Rock along the Prince Olav Coast, in the Lützow-Holm Complex (LHC), East Antarctica. The dating results indicate that a newly detected ∼ 990 Ma metamorphism of garnet-sillimanite-biotite gneiss from Niban Rock. A thermal event at 931.7 ± 9.8 Ma is recorded in zircon from staurolite-bearing garnet-gedrite-biotite-chlorite gneiss in Akebono Rock. The metamorphic zircon grains in other analyzed samples provide Ediacaran to Cambrian ages. Their multi-growth textures and age populations are possibly interpreted to exhibit three metamorphic stages during >600-580, 580-550, and 550-500 Ma. Combined with previous reports, the metamorphic rocks in Cape Hinode, Niban-nishi Rock of Niban Rock, and Akebono Rock might have experienced earlier high-temperature metamorphism at ∼ 990-930 Ma without younger overprinting. Extensive high-grade metamorphism during ∼ 650-500 Ma is recorded from not only the granulite-facies zone in the west of the LHC but also the amphibolite-facies zone in its east. The main metamorphic episode in the LHC is likely to be subdivided into a preceding thermal event (either independent single metamorphic event or prograde stage) at pre-580 Ma, near-peak condition stage during 580-560 Ma, and subsequent retrograde stage after 550 Ma. In regional context this indicates that the assembly at the central Gondwana started with the collision of early and late Neoproterozoic terranes prior to 580 Ma, as a part of the East Africa-Antarctic Orogeny. Subsequent collisions took place among late Neoproterozoic igneous terrane, above terranes collided at pre-580 Ma, and Neoarchean terrane, which were probably driven by the Kuunga Orogeny.

Spinel + plagioclase symplectites in pelitic metamorphic rocks have been reported from many localities. We report in detail an occurrence of this texture from Tenmondai Rock, Lützow-Holm Complex, East Antarctica. This texture is produced by the following metamorphic reaction; garnet + sillimanite = spinel + plagioclase. This can be described as the following two net-transfer reactions; 5Grs + Alm + 12Als = 3Hc + 15An, and 5Grs + Prp + 12Als = 3Spl + 15An. We propose new geobarometers (GASpP) based on these equations. For example, one of these is P = (−155790 + 587.4T + RT lnK_Fe) / 29.378, for garnet + sillimanite + spinel + plagioclase assemblage in the CFASZn-system. Where P is pressure in bar, T is temperature in K, and R represents gas constant. The equilibrium constant is, K_Fe = (a_Grs⁵ a_Alm)/(a_Hc³ a_An¹⁵). Our proposed new geobarometers are free from quartz, corundum, orthopyroxene, and cordierite within these equations. These barometers are useful to estimate pressure conditions for spinel-bearing pelitic metamorphic rocks within a wide pressure-temperature range (andalusite, kyanite, and sillimanite fields). We estimate the metamorphic pressure-temperature (P-T) conditions at Tenmondai Rock by applying the GASP, GRIPS, GRAIL, GASpP geobarometers, and the Zr-in-Rt geothermometer. The metamorphic evolution of the rocks at Tenmondai Rock is characterized by a clockwise P-T-t path. The peak P-T condition is about 820 MPa and 850 °C. Spinel + plagioclase symplectite was produced during the decompressional stage of this metamorphic evolution, at about 450 MPa and 700 °C.