Fe–Mg–Ti domain-bearing garnet–sillimanite gneiss from Skallevikshalsen, Lützow-Holm Complex, East Antarctica: Implications for ultrahigh-temperature metamorphism

第3回極域科学シンポジウム/第32回極域地学シンポジウム 11月30日（金） 統計数理研究所 ３階セミナー

METAMORPHIC EVOLUTION OF GARNET–BIOTITE–MUSCOVITE SCHIST FROM BARRU COMPLEX IN SOUTH SULAWESI, INDONESIA

This paper explains the first report in metamorphic evolution of pelitic schist from Barru Complex in South Sulawesi, Indonesia. Garnet-biotitemuscovite schist was examined petrologically to assess the metamorphic evolution history, which has implications on tectonic condition of this region. The rock mainly composed of garnet, biotite, muscovite, epidote, quartz, rutile, hematite, and plagioclase. Inclusions in the garnet preserve records of prograde stage of this rock, which are epidote, titanite, quartz, and apatite. Garnet, biotite, muscovite, quartz, rutile, and plagioclase are concluded as equilibrium assemblages at peak P-T condition of this rock, which estimated at 501–562 ºC and 0.89–0.97 GPa. The result is still on the ranges of the estimated geothermal gradient P-T path of eclogite from Bantimala Complex. Similar geothermal gradients of metamorphisms might be indicated that these metamorphic rocks were metamorphosed on the similar tectonic environments. Keywords: Pelitic schist, Barru Complex, South Sulawesi, metamorphic evolution

Titanium behavior in quartz during retrograde hydration: Occurrence of rutile exsolution and implications for metamorphic processes in the Sør Rondane Mountains, East Antarctica

AbstractIn the central Sør Rondane Mountains, East Antarctica, orthopyroxene felsic gneiss (OPG) was converted to hornblende-biotite felsic gneiss (HBG) by hydration that accompanied the intrusion of pegmatite. The retrograde HBG contains exsolved rutile in quartz. The composition of orthopyroxene and clinopyroxene in OPG suggests a temperature of 840°C (interpreted as the near-peak temperature), and the composition of hornblende and plagioclase in HBG suggests a temperature of 670–700°C (interpreted as the temperature during hydration). Ti concentrations in quartz were measured using an electron probe micro-analyzer, and Ti-in-quartz thermometers were applied. Measured Ti concentrations were 110ppm (equivalent to 760–820°C) for homogeneous quartz from OPG and 35ppm (650–700°C) for an exsolution-free area of a quartz grain from HBG. The pre-exsolution Ti concentration in quartz from HBG was reconstructed with 100μm beam diameter and 25kV of accelerating voltage, giving 103ppm, similar to the value obtained for homogeneous quartz in OPG. The temperatures obtained using a Ti-in-quartz thermometer are consistent with those estimated using other thermometers. Although analysis of the main constitute minerals in HBG yields the conditions of hydration, the reconstructed pre-exsolution Ti content in quartz within HBG yields the pre-hydration conditions. Thus, the Ti-in-quartz thermometer is a potentially powerful tool with which to identify the peak or near-peak temperature conditions, even for retrogressed metamorphic rocks

Metamorphic Evolution of Garnet-bearing Epidote-Barroisite Schist From the Meratus Complex in South Kalimantan, Indonesia

DOI:10.17014/ijog.2.3.139-156This paper presents metamorphic evolution of metamorphic rocks from the Meratus Complex in South Kalimantan, Indonesia. Eight varieties of metamorphic rocks samples from this location, which are garnet-bearing epidote-barroisite schist, epidote-barroisite schist, glaucophane-quartz schist, garnet-muscovite schist, actinolite-talc schist, epidote schist, muscovite schist, and serpentinite, were investigated in detail its petrological and mineralogical characteristics by using polarization microscope and electron probe micro analyzer (EPMA). Furthermore, the pressure-temperature path of garnet-bearing epidote-barroisite schist was estimated by using mineral parageneses, reaction textures, and mineral chemistries to assess the metamorphic history. The primary stage of this rock might be represented by the assemblage of glaucophane + epidote + titanite ± paragonite. The assemblage yields 1.7 - 1.0 GPa in assumed temperature of 300 - 550 °C, which is interpreted as maximum pressure limit of prograde stage. The peak P-T condition estimated on the basis of the equilibrium of garnet rim, barroisite, phengite, epidote, and quartz, yields 547 - 690 °C and 1.1 - 1.5 GPa on the albite epidote amphibolite-facies that correspond to the depth of 38 - 50 km. The retrograde stage was presented by changing mineral compositions of amphiboles from the Si-rich barroisite to the actinolite, which lies near 0.5 GPa at 350 °C. It could be concluded that metamorphic rocks from the Meratus Complex experienced low-temperature and high-pressure conditions (blueschist-facies) prior to the peak metamorphism of the epidote amphibolite-facies. The subduction environments in Meratus Complex during Cretaceous should be responsible for this metamorphic condition

Structural basis for the substrate recognition of aminoglycoside 7′′-phosphotransferase-Ia from Streptomyces hygroscopicus

Hygromycin B (HygB) is one of the aminoglycoside antibiotics, and it is widely used as a reagent in molecular-biology experiments. Two kinases are known to inactivate HygB through phosphorylation: aminoglycoside 7′′-phosphotransferase-Ia [APH(7′′)-Ia] from Streptomyces hygroscopicus and aminoglycoside 4-phosphotransferase-Ia [APH(4)-Ia] from Escherichia coli. They phosphorylate the hydroxyl groups at positions 7′′ and 4 of the HygB molecule, respectively. Previously, the crystal structure of APH(4)-Ia was reported as a ternary complex with HygB and 5′-adenylyl-β,γ-imidodiphosphate (AMP-PNP). To investigate the differences in the substrate-recognition mechanism between APH(7′′)-Ia and APH(4)-Ia, the crystal structure of APH(7′′)-Ia complexed with HygB is reported. The overall structure of APH(7′′)-Ia is similar to those of other aminoglycoside phosphotransferases, including APH(4)-Ia, and consists of an N-terminal lobe (N-lobe) and a C-terminal lobe (C-lobe). The latter also comprises a core and a helical domain. Accordingly, the APH(7′′)-Ia and APH(4)-Ia structures fit globally when the structures are superposed at three catalytically important conserved residues, His, Asp and Asn, in the Brenner motif, which is conserved in aminoglycoside phosphotransferases as well as in eukaryotic protein kinases. On the other hand, the phosphorylated hydroxyl groups of HygB in both structures come close to the Asp residue, and the HygB molecules in each structure lie in opposite directions. These molecules were held by the helical domain in the C-lobe, which exhibited structural differences between the two kinases. Furthermore, based on the crystal structures of APH(7′′)-Ia and APH(4)-Ia, some mutated residues in their thermostable mutants reported previously were located at the same positions in the two enzymes

Associations of högbomite + spinel and spinel + quartz in pegmatitic magnetite megacrysts from West \nOngul Island, Lützow-Holm Complex, East Antarctica

第2回極域科学シンポジウム/第31回極域地学シンポジウム 11月17日（木） 国立極地研究所　2階大会議室前フロ

Geochemistry and geochronology of the Antananarivo and the Masora domain, eastern Madagascar

第2回極域科学シンポジウム/第31回極域地学シンポジウム 11月17日（木） 国立極地研究所　2階大会議

High-grade metamorphic rocks dredged from the Conrad Rise (research cruise KH-10-7, St. 2), the southern Indian Ocean

第2回極域科学シンポジウム/第31回極域地学シンポジウム 11月17日（木） 国立極地研究所　2階大会議