Geology of high- to ultrahigh-temperature granulites from central Madurai block, southern India ; with emphasis on the evolution of Grt-Opx-Crd granulite

The geology of Ganguvapatti area situated at the central Madurai block of southern India consisting of varous high-grade metamorphic rock types. This contribution briefly describes the geology, field occurrences and petrography of metamorphic rock from Ganguvarpatti area. Ganguvarpatti is known for its occurrence of sapphirine-bearing UHT granulites while the surrounding granulites are less studied. So in this contribution we have discussed the pressure-temperature stability and evolution of granulites surrounding UHT granulites. The pressure-temperature estimation of garnet-orthopyroxene-cordierite granulite resulted a near peak temperature condition of>950゜ C at a pressure between 9-10 kbar. These results are in good agreement with the stability field in the KFMASH petrogenetic frid

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

Geochronological evidence for multistage-metamorphic events in ultrahigh-temperature granulites from central Highland Complex, Sri Lanka

The ultrahigh-temperature (UHT)granulite from the central Highland Complex,Sri Lanka preserves histories of several metamorphic events.The application of geothermobarometries on sapphirine-garnet-orthopyroxene-sillimanite-quartz bearing granulites confirms that metamorphism occurred under the UHT condition. We report a middle Proterozoic age of 1478+-58 Ma from the internal isochron using a garnet core,whole rock and felsic fraction (quartz in the Sm-Nd system from the same rock samples.As this granulite preserves several stages of orthopyroxene formation,the measured isotope composition of orthopyroxene give mixed values.The reference isochron plotted with orthopyroxene and whole rock give an age of 550 Ma.The present results can be interpreted to mean that the middle Proterozoic metamorphic event could have been the thermal peak.During the uplift stage,this granulite might have remetamorphosed at younger stages along with the adjacent rocks

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

Resetting and closing codition of Rb-Sr whole-rock isochron system: some samples of metamorphic and granitic rocks from the Gondwana super-continent and Japan Arc

The closure temperature of the Rb-Sr whole-rock system for felsic rocks has been generally considered to be ca. 700゜C, but it falls to ca. 400゜C, as a result of efficient action of fluids,especially H_2O. Thus,the Rb-Sr whole-rock ages obtained by rocks collected from a single outcropto specimen-size are not always coincident with those of emplacement of granitic magma or partial melting under high grade metamorphism.Although the Rb-Sr whole-rock isochron ages of metamorphic rocks collected from a wide area have been sometimes interpreted as those of metamorphism,careful consideration for these ages is needed

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

Fluid inclusions in an osumilite-bearing granulite from Bunt Island in the Archean Napier Complex, East Antarctica: implications for a decompressional P-T path?

We report high-density CO_2-rich fluid inclusions in garnet,orthopyroxene,and quartz from an osumilite-bearing aluminous granulite from Bunt Island of the Archean Napier Complex,East Antarctica.The melting temperatures of fluids lie in the range of -56.8 to -57.8゜C being close to the triple point for pure CO_2 (-56.6゜C ). Homogenization of the CO_2,-rich fluids into the liquid phase occurs at temperatures in the range of -35.4 to 24.7゜C. This translates into CO_2 densities in the range of 0.788-1.084g/cm^3 .The estimated CO_2 ,isochore for high-density inclusions in garnet intersects the P-T trajectory of Bunt Island at around 10 kbar at 1050゜C, which corresponds to the peak metamorphic conditions of the region derived from mineral phase equilibria.We therefore infer that CO_2 ,was the dominant fluid species present during the ultrahigh-temperature metamorphism in Bunt Island.CO_2 inclusions with lower density occurring in quartz and garnet provide isochores that intersect the P-T path at <7 kbar and <950゜C indicating density reversal of originally high-density inclusions along a decompressional exhumation path of the ultrahigh-temperature rocks in the Bunt Island

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

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金沢大学大学院自然科学研究科自然計