A study on the b0 parameter and crystallinity index of K-white micas from low-grade metapelites in Deokpyeong and Miwon areas, central Ogcheon metamorphic belt, Korea
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Muscovite
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Abstract Psammitic schist, 2 types of pelitic schist (grey and porphyroblastic), and 4 types of greenschist (metavolcanic rock — light, spotted, foliated, and epidote rich) are recognisable on outcrop scale in textural zone 4 of the Otago Schist, northwest Otago, New Zealand. Thin horizons of metachert, marble, and ultramafic rock are commonly associated with greenschist. Broad units with 1 predominant rock type (greenschist, psammite, grey pelite, or porphyroblastic pelite) are mappable on a regional scale. These units also contain most or all of the above rock types and have poorly defined boundaries. The degree of original Stratigraphic continuity within and between these broad units is unknown. The studied area can be subdivided into 2 lithologic associations, the "Aspiring association" and the eastern "Wanaka association", separated by a north-trending, poorly defined but lithologically gradational boundary. The Aspiring association is made up predominantly of pelitic rock types with considerable quantities of greenschist and minor marble, chert, and ultramafic horizons. The Wanaka association consists of psammitic schist with subordinate greenschist and pelitic schist. The proportion of greenschist decreases eastwards. These "associations" represent fundamental lithologic differences within the Otago Schist belt, on a scale equivalent to the previously defined Te Anau Assemblage. Keywords: Otago Schistlithologypelitic schistgreenschistmetachertmarblepsammitic schist
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An investigation on gold occurrence in Buru island is needed to determine type of deposit in the area. This study aims to analyse mineralisation, alteration and metamorphic facies of metamorphic-hosted gold deposit in Buru area by using petrographic method, x-ray flourescense, x-ray diffraction, and polish section. The results reveral that there are two types of metamorphic rocks: schists and phyllite. Greenschist facies are charecterized by muscovite mineral, quartz, chlorite, biotite, clay mineral, and codierite. Phyllite is in the same genetic condition with schist (medium metamorphism), with formation temperature ranges from 300°C to 450°C with a pressure around 1-8 Kbar through a regional metamorphism process. Alteration in quartz veins indicated the nature of proximal zone to ore zone. Silicic alteration (quartz) is also found intensely, and it is generally associated by propylitic alteration (chlorite) and sericitic (muscovite). Mineralisation follows the direction of the distribution of quartz veins with crustiform banding texture. The quartz vein thickness is from 40 cm to 50 cm. The alteration and mineralisation occurrence of the studied area suggests epithermal gold deposits type.
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Ciletuh Complex is considered to be one among other localities (Luk Ulo, Bantimala, Meratus
Complexes) in Indonesia in which Cretaceous subduction fossil was occurred. The objective of this study
is determining the variation of metamorphic rocks in Ciletuh Complex by petrographical analysis
through their texture and mineral assemblages.
Metamorphic rocks in Ciletuh Complex were collected in Gunung Badak and Tegal Pamidangan areas.
Based on petrographical analysis, metamorphic rocks in Gunung Badak area consist of Grt-Ms-Qz
schist, Ms phyllite, quartzite and serpentinite. Meanwhile in Tegal Pamidangan area, consist of Ms-Qz
phyllite and slate. The metamorphic rocks indicate low-grade metamorphism in the greenschist-facies.
The protolith of metamorphic rocks are suggested from pelitic, ultramafic, and quartz-rich rocks.
Present study did not recognize the blueschist or eclogites-facies rocks which indicates high-pressure
and low-temperature metamorphism in the subduction system. The present of serpentinite among the
low-grade metamorphic rocks indicates that metamorphic environment still correlate with oceanic crust
environment or mantle. Low-grade metamorphic rocks might be developed on the near surface of the
subduction system.
Keywords : petrography analysis, mineral assemblages, metamorphic facies, protolith
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Amphibolite-facies Settler Schist in the southeastern Coast Mountains of British Columbia has long been correlated with Chiwaukum Schist of the Cascade metamorphic core, North Cascade Mountains, northwestern Washington. The additional correlation proposed here of Settler Schist with Darrington Phyllite and Shuksan Greenschist (and blueschist) of the Northwest Cascade System in Washington is based on along-strike near-continuity of outcrop areas, a similar protolith composition range, the same structural position relative to the Shuksan fault zone, and distinctive irregular structures in variably metamorphosed sandstone and pelite of both Darrington Phyllite and Settler Schist. If this correlation is valid, then the record of Early Cretaceous; subduction-related blueschist metamorphism of Shuksan–Darrington rocks was destroyed in Settler Schist by overprinting by early Late Cretaceous Barrovian metamorphism; only some distinctive, premetamorphic structures remain. The implication is that within the southeastern Coast Mountains, a cryptic record of subduction is overprinted by Barrovian metamorphism.
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