scholarly journals Graphitization of carbonaceous material in the Hitachi metamorphic rocks, Abukuma Plateau, Japan.

1989 ◽  
Vol 84 (3) ◽  
pp. 89-96
Author(s):  
Noriyoshi Tsuchiya ◽  
Shunichi Suzuki ◽  
Yukito Oda ◽  
Akio Iijima
Keyword(s):  
Carbonaceous Material ◽  
Metamorphic Rocks

scholarly journals Pyrite and pyrrhotite in a prograde metamorphic sequence, Hyland River region, SE Yukon: implications for orogenic gold

2021 ◽  
Author(s):  
C D W Padget ◽  
D R M Pattison ◽  
D P Moynihan ◽  
O Beyssac
Keyword(s):  
Raman Spectroscopy ◽  
Phase Equilibrium ◽  
Source Region ◽  
Carbonaceous Material ◽  
Orogenic Gold ◽  
Metamorphic Rocks ◽  
Small Interval ◽  
River Region ◽  
Gradual Release ◽  
Fluid Release

The distribution of pyrite and pyrrhotite is documented within an andalusite-sillimanite type (high-temperature, low-pressure) metasedimentary succession exposed in the Hyland River region of southeastern Yukon, Canada. The following metamorphic zones are recognized: chlorite, biotite, cordierite/staurolite (porphyroblast-in), andalusite, sillimanite, and K-feldspar + sillimanite. Pyrite occurs in the chlorite zone through the biotite zone, while pyrrhotite occurs from the chlorite zone to K-feldspar + sillimanite zone. The pyrite-pyrrhotite transition, therefore, occupies an interval in the chlorite and lower biotite zones that is terminated upgrade by a pyrite-out isograd in the upper part of the biotite zone or lowest grade part of the cordierite/staurolite zone. Pressure and temperature conditions of the rocks were estimated from phase equilibrium modelling and from Raman spectroscopy of carbonaceous material (RSCM) thermometry. Modelling indicates pressures of 3.7-4.1 kbar with temperatures of ~425 °C at the biotite isograd, 560-570 °C for chlorite-out/porphyroblast-in, ~575 °C for andalusite-in, 575-600 °C for the sillimanite isograd, and 645-660 °C at the K-feldspar + sillimanite isograd. RSCM temperatures are greater than or equal to 420 °C in the Chl zone, 500 °C at the Bt isograd, 525-550 °C for porphyroblast-in isograd, ~550 °C at the And isograd, and 580 °C at the Sil isograd. These results suggest the pyrite-pyrrhotite transition occurs from less than or equal to 420°C to ~560 °C. Thermodynamic modelling shows 0.6 wt. % H2O is released during metamorphism over the ~140 °C interval of the pyrite-pyrrhotite transition. The gradual release of fluid in the biotite zone is interpreted to have broadened the pyrite-pyrrhotite transition compared to other studies that predict a small interval of vigorous fluid release associated with volumetric chlorite consumption. Samples from the pyrite-pyrrhotite transition zone contain lower whole rock and pyrite Au values than samples from unmetamorphosed/lower rocks, suggesting that Au was removed from the rock at conditions below the pyrite-pyrrhotite transition (<420 °C). The chlorite zone and higher-grade metamorphic rocks of the Hyland River area do not appear to be a plausible source region for orogenic gold.

scholarly journals Precambrian organisms and the isotopic composition of organic remains in the Ketilidian of South-West Greenland

1967 ◽  
Vol 67 ◽  
pp. 1-41
Author(s):  
E Bondesen ◽  
K.R Pedersen ◽  
O Jørgensen
Keyword(s):  
Large Scale ◽  
Analytical Procedure ◽  
Isotope Composition ◽  
Carbonaceous Material ◽  
Metamorphic Rocks ◽  
Carbonaceous Matter ◽  
Globular Structure ◽  
South West ◽  
Absolute Age ◽  
Organic Remains

The geological setting of organic remnants from well preserved Ketilidian rocks of SW Greenland is presented. The absolute age (2000? m. y.) of the rocks is discussed and compared to that of other regions. Many types of organic remnants have been found in these low-metamorphic rocks. Most of the organic remnants are microscopic globules and fragments with cell-like structures. The type which is best preserved is a complex globular structure on about 1/2mm in diameter. This structure is established as a new monotypic form genus Vallenia erlingi (Raunsgaard Pedersen) n. gen. et sp. Stromatolithes and other macro-structures of possible organic origin are also found. A coal-graphite layer indicates that large-scale accumulation of organic matter has taken place. The organic remnants are so well preserved that it has been possible to extract small amounts of paraffines (n-C11 to n-C31 with maximum about n-C18 to n-C20) and other organic compounds. The carbon-isotope composition from carbonaceous matter and carbonates from a number of samples has been determined. The analytical procedure is described. The result of this investigation shows δ C13-values which indicate that the carbonaceous material is probably of organic origin.

Extending the applicability of the Raman carbonaceous-material geothermometer using data from contact metamorphic rocks

2010 ◽  
Vol 28 (9) ◽  
pp. 895-914 ◽  
Author(s):  
M. AOYA ◽  
Y. KOUKETSU ◽  
S. ENDO ◽  
H. SHIMIZU ◽  
T. MIZUKAMI ◽  
...  
Keyword(s):  
Carbonaceous Material ◽  
Metamorphic Rocks ◽  
Using Data

Graphitic material in fault zones: Implication for strain localization and rheological weakening

2020 ◽  
Author(s):  
Shuyun Cao ◽  
Franz Neubauer ◽  
Meixia Lv
Keyword(s):  
Strain Localization ◽  
Carbonaceous Material ◽  
Fault Zones ◽  
Graphitic Carbon ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Metamorphic Rocks ◽  
Chemical Compositions ◽  
Low Grade ◽  
High Grade

<p>Graphitic carbon exhibits a large range of structures and chemical compositions, from amorphous-like compounds to crystalline graphite. The graphitic carbon-bearing rocks are widely occurred in low- to high- grade metamorphic massif and fault zone. The carbonaceous material in the rock will gradually transform from an amorphous into an ordered crystalline structure by thermal metamorphism, which is called graphitization. The degree of graphitization is believed to be a reliable indicator of peak temperature conditions in the metamorphic rock. In many low-grade metamorphic rocks, graphitic carbon (e.g., soot, low-grade coal) is often associated with brittle fault gouge whereas in high-grade metamorphic rocks, graphitic carbon (crystalline granite) are most commonly seen in marble, schist or gneiss. In recent years, graphitic carbon-bearing rocks have been reported from natural fault zones (reviwers paper see Cao and Neubauer 2019 and references therein). The graphitic carbon grains in our samples tend to enrich in slip-surface or micro-shear zone with strain localization in fault, performed as dislocation glide of deformation. The graphite LPO shows slip system in the direction of basil <a> combined basil <a> slip and weak prism <a> slip systems, suggesting a low-temperature to a medium to high temperature deformation conditions, which is in consistent with the results of Raman Spectra of Carbonaceous material (RSCM) thermometry. We also proposed that the graphitic carbon formed in the rocks can significantly affect the mechanical properties of the fault during the process of faulting. This process can effectively cause reaction weakening and strain localization, which is thought to play an important role as solid lubrication in fault weakening.</p>

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