A prolonged crustal history from Archean through Proterozoic to Cambrian, spanning more than half of the Earth’s evolution through time is preserved in the rock record in East Antarctica. Geological field studies have been conducted in Dronning Maud Land and Enderby Land of East Antarctica as part of the scientific program of Japanese Antarctic Research Expedition (JARE). Late Neoproterozoic to Cambrian (>600-520 Ma) high-grade metamorphic terranes, developed as major orogenic belts during the Gondwana supercontinent formation, are recognized in central Dronning Maud Land, Sør Rondane Mountains, Belgica and Yamato Mountains (Yamato-Belgica Complex), Lützow-Holm Bay-Prince Olav Coast region (Lützow-Holm Complex) to western Enderby Land (Western Rayner Complex) over 2000 km from west to east along the coast-inland of the Antarctic continent. Relatively narrow and sporadic Meso-Neoproterozoic (1000-900 Ma) high-grade blocks (Hinode Block and Niban-nishi Rock - granulite-facies; Akebono Rock - amphibolite-facies) are identified in Prince Olav Coast geographically within the Lützow-Holm Complex. Archean high-grade-UHT granulites and gneisses of the Napier Complex represent the largest regional terrain covering 400 × 200 km² area in Enderby Land, along with widespread Meso-Neoproterozoic granulite-facies zone of Rayner Complex from Enderby Land through Kemp Land, McRobertson Land toward east to Prydz Bay region. Thus, the continental crustal domain investigated by the Japanese Antarctic expeditions is key in understanding the Archean-Proterozoic-Cambrian deep crustal history and processes. In this special issue we summarize the recent progress in the mineralogical, petrological, geochemical, and geochronological studies carried out in East Antarctica.

Blue-green potassic-ferro-chloro-pargasite containing up to 0.3 wt% BaO and 4.6 wt% Cl occurs together with Cl-poor cummingtonite in a mafic granulite composed mainly of olive-brown potassic-ferro-pargasite with subordinate orthopyroxene, Ba- and Cl-bearing biotite, calcic plagioclase, quartz, ilmenite, zircon, and Cl-rich fluorapatite. The mafic granulite is characterized by high bulk rock contents of large-ion lithophile elements such as K, Ba, Pb, and Rb. Mineral assemblages, compositions and textures suggest four stages of recrystallization to form and modify the potassic-ferro-pargasite. Stage 1 is the main granulite-facies metamorphism, whereas stages 2-4 correspond to local phenomena most probably caused by fluid infiltration along a fracture during cooling. Stage 2 includes biotite formation with concomitant compositional change of orthopyroxene and potassic-ferro-pargasite to more Fe-rich. Fluorapatite partially changed composition from Cl-rich to Cl-poor. Stage 3 was a more localized event including (1) increase of K, Cl, Al, and Fe and decrease of Si, Ti, and Mg in the potassic-ferro-pargasite, accompanied by the color change from olive-brown to blue-green, and (2) formation of Cl-poor cummingtonite and sodic plagioclase by replacement of preexisting potassic-ferro-pargasite. Stage 4 was a more localized phenomenon within blue-green potassic-ferro-pargasite. It may be expressed as a volatile-conserving reaction such as Cl-bearing potassic-ferro-pargasite → potassic-ferro-chloro-pargasite + Cl-poor cummingtonite. The mafic granulite appears not to have undergone partial melting even at stage 1 most probably because of the high Cl content of the dominant potassic-ferro-pargasite.

Organic carbon and carbonate carbon are two important reservoirs that control the carbon geodynamic cycle at convergent margins during plate subduction, arc magmatism, and continent building processes. The movement of carbon through different reservoirs in the Earth relating to the global tectonic activities is key in understanding the carbon geodynamic cycle. In this contribution, a comprehensive synthesis on the different types of occurrences of graphite, the purest form of carbon in continental crust, in the Lützow-Holm Complex (LHC), East Antarctica is carried out and carbon isotopic composition is used as a proxy to identify the movement of carbon during orogenesis. Graphite is an important reservoir of carbon in continental crust and occurs in a variety of rock types in the LHC. Based on the mode of occurrence they were classified into several types, disseminated flakes in gneissic rocks, coarse aggregates in leucosomes, graphite concentration in lithological contacts and as monomineralic graphite veins. Disseminated graphite in pelitic gneisses record the lowest carbon isotopic composition (δ¹³C_VPDB values between −25 to −15‰), suggesting biogenic signatures, however those in metacarbonate rocks have equilibrated with carbonate carbon during high temperature metamorphism to show heavier values (δ¹³C_VPDB values between −3 to −1‰). The carbon isotopic composition of disseminated graphite is modified during prograde metamorphism by devolatilization and also exchange of carbon isotopes with carbonate minerals. Coarse-grained graphite is observed in leucosomes in the migmatized metapelitic rocks. During the high-temperature metamorphism and partial melting of graphite-bearing rocks, graphite decomposes to form COH fluids, part of which, especially the lighter isotope-bearing fluids have escaped the system causing a shift toward heavier values (δ¹³C_VPDB values in the range between −18 to −10‰). Based on the field, textural and carbon isotope evidence a model is suggested, where biotite dehydration melting of graphite-bearing rocks caused the dissolution of pre-existing graphite formed from organic materials, and graphite was reprecipitated as coarse aggregates in leucosomes during melt crystallization and cooling. This resulted in the carbon remobilization and isotopic reorganization. Carbon isotopic composition of graphite concentrations in lithological contacts (δ¹³C_VPDB values ranging between −1.8 to −5.7‰) and monomineralic veins (δ¹³C_VPDB values between −3.5 and −6.0‰) suggest that they were precipitated from CO₂ fluids locally released through decarbonation reactions. The presence of large volume of skarn mineralization in the contact between carbonate and silicate rocks and similarities of carbon isotopic composition of graphite in contact zones and veins support a local source for CO₂ fluids rather than a mantle derived carbon-bearing fluid for vein type graphite. Thus, carbon is recycled and retained as graphite in the continental crust during high-grade metamorphism and anatexis, though its isotopic composition can be considerably modified during orogenesis. In summary, a comprehensive study of carbon isotopic composition of graphite occurrences in the LHC, East Antarctica has thus revealed that prograde metamorphism, anatexis and interaction between carbonate lithologies with silicate rocks can modify carbon isotopic composition of graphite in the continental crust. Recycling of carbon within the continental crust during orogenesis where graphite act as ‘long-term sinks’ of carbon has to be considered for envisaging realistic models on Earth’s carbon cycle.

We examined Sm-Nd isotopes of samples from the Archean tonalitic-granodioritic orthogneiss mass of Mt. Riiser-Larsen in the Napier Complex, East Antarctica. Analytical data show εNd ≈ 0 of ∼ 3.27 and ∼ 3.07 Ga at the time of protolith formation, as determined by SHRIMP zircon analyses. This differs from previously reported Sm-Nd whole-rock isotope data from the oldest tonalitic orthogneisses of Mt. Sones in the Napier Complex, which show εNd = 0 at 3.87-3.80 Ga (T_CHUR), which is coincident with ∼ 3.8 Ga from SHRIMP zircon analyses. These data suggest that the voluminous and homogeneous tonalitic-granodioritic rocks retained the εNd ≈ 0 signal throughout the protolith-metamorphic process and that the source materials of the rocks showed εNd ≈ 0 at ∼ 3.80, 3.27, and 3.07 Ga. Tonalitic-granodioritic orthogneisses from the Napier Complex may contain genetic information regarding Nd isotopic evolution from the Eoarchean to Mesoarchean.

The Napier Complex in East Antarctica has a complex thermal history, including ultra-high-temperature (UHT) metamorphism. Geochronology, trace element, and isotope geochemistry of zircon, apatite, and monazite in three felsic gneisses collected from Harvey Nunatak were studied using a sensitive high-resolution ion microprobe (SHRIMP) for the first time. Most zircons showed nebulous to fir-tree zoning, which is a common feature of zircons in granulite facies rocks, regardless of the core or rim. The U-Pb dating and rare earth element abundance of zircon indicated that zircon crystallization by regional metamorphism continued from 2567-2460 Ma, consistent with the previously proposed timing of UHT metamorphism. The zircon grains contained a large amount of Li (59-668 ppm). Li was incorporated with Cl at the interstitial sites of the zircon structure, and the zircons crystallized in melts with an abundant supply of Li and Cl. Monazite crystallized from apatite after the UHT metamorphism events of 2071 and 1799 Ma. The U-Pb system of apatite was completely disturbed by the crystallization of monazite at 1785 Ma. In addition, the U-Pb systems of apatite and monazite were disturbed at approximately 500 Ma.