-This 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.

This contribution reports the metamorphic evolution of the high-pressure metamorphic rocks from the Bantimala Complex, South Sulawesi, Indonesia. Barroisite-bearing and barroisite-free eclogites were examined to assess their metamorphic evolutions, which have implications regarding the tectonic conditions in this region. The eclogites mainly consist of garnet, omphacite, phengite, rutile, and epidote, with or without barroisite. The variations in mineral assemblages are interpreted to depend upon local changes in the bulk chemical composition. The barroisite-bearing eclogites contain two types of euhedral garnet: coarse-(1-1.5 mm) and finegrained (<0.5 mm). Mineral inclusions in the coarse-grained garnet core and mantle show epidote + titanite and glaucophane + epidote assemblages, that stabilized at 0.9-1.5 GPa and 350-550°C within epidote blueschist-facies conditions. Mineral chemistry and chemical-mapping analyses indicate that both fine-grained garnet and the rim of coarse-grained garnet formed at peak P-T conditions, which were estimated as 2.3-2.7 GPa at 615-680°C based on the garnet-omphacite-phengite-quartz equilibrium. Peak P-T conditions for barroisitefree eclogite were similar (2.5-2.7 GPa at 650-690°C) to those for barroisite-bearing eclogite. Actinolite rims overgrowing matrix sodic-calcic amphiboles attest to retrogression at P < 0.5 GPa and T < 350°C in a clockwise P-T path. The very low geothermal gradient experienced during the prograde path (~5°C/km) likely suggests the subduction of an old and cold oceanic crust. The low geothermal gradient on the retrograde path suggests decompressional cooling during exhumation, possibly favored by a serpentinite-dominated matrix within a subduction channel environment.

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Geomorphology is a landform that extends on the surface of the earth as a result of interactions between endogenous and exogenous processes. Landform classification based on morphometry, morphogenesis, and morphoarengement. Kebumen has attractive geological diversity. The potential of iron sand spread out as beach sand deposits. This research conducted to map landforms, including south coast region and analyze the distribution of iron sand sediment. The study used DEMNAS image analysis, a 1: 20, 000 scale with Arc-GIS software. Variables analysis includes elevation, aspect, roughness, hill shade, river pattern, and hill roughness accompanied by a field survey. Resistivity survey on old beach deposits morphology (2 locations) and young beach deposits (2 locations) to obtain data on the potential of iron sand. Measurement using OYO Model 2, McOHM Resitivimeter, Schlumberger configuration, and geophysical modelling using Res-2Din software. The landform in Kebumen consists of 33 units as structural, denudational, dissolving, fluvial, and coastal landforms. The Coastal Sediment landscape consists of 3 units, in the form of young coastal sediment, old coastal sediment, and fluvio marine sediment. The potential of iron sand is founded in young coastal sediment (M5) is about 764, 77 Ha, and old coastal sediment (M4) about 590, 84 Ha. Mineral compositions are olivine, pyroxene, hornblende, biotite, and impurities as quartz, plagioclase, orthoclase, rutile and calcite minerals. Coastal sand sediment in the Old Sediment is found 30-60 m depth with overburden up to 4 m. The potential of beach sand about 406, 686, 300 m3 similar with 1, 037, 050, 065 tons, total Fe estimated about 629, 696, 799 tons.

DOI:10.17014/ijog.7.3.225-239Garnet amphibolites, which suggest medium-pressure/high-temperature (MP/HT), are widely recognized in Luk Ulo Complex, Central Java. Their occurrences associated with high-pressure/low-temperature (HP/LT; eclogite, blueschist) metamorphic rocks in the Luk Ulo Complex will provide important constraint on the geodynamic model of Central Indonesian Accretionary Collision Complex (CIACC). This study aimed to estimates P-T metamorphic condition of garnet amphibolite from Luk Ulo Complex by using mineral parageneses, thermodynamic data, and NCKFMASHO pseudosection. Prograde stage assemblages represented by inclusions in the garnet, which are garnet core, zoisite, titanite, apatite, and quartz. Mineral coexistences at the peak P-T condition are garnet rim, magnesio-hornblende, zoisite, titanite, quartz, albite, and phengite. The retrograde stage represented by secondary minerals fill the crack in the garnet and other minerals, which are chlorite and quartz. P-T metamorphic condition of garnet amphibolite can only be interpreted from the peak metamorphic stage. The temperature of the garnet amphibolite is estimated using the garnet-amphibole and garnet-phengite geothermometers. Meanwhile, the pressure condition is estimated from phengite geobarometer. The results were compared to the stability and compositions of the phases in NCKFMASHO pseudosection in order to constrain the peak P-T metamorphic conditions. It is concluded that the peak P-T metamorphic condition for garnet amphibolite is 0.9 - 1.4 GPa and 558 - 606 ºC. The estimated peak P-T metamorphic temperature is higher compared to the previously published gradient geothermal of eclogite and tourmaline-eclogite in the Luk Ulo Complex. The MP/HT (amphibolite) and HP/LT (blueschist and eclogite) metamorphic rocks could have similar metamorphic ages if both footwall and hanging wall had initially very high thermal gradients and the rate of subduction was very slow (10 km/Ma or less).

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No abstract