Carbonaceous Material in Some Metamorphic Rocks of New England and Other Areas

1974 ◽  
Vol 82 (1) ◽  
pp. 50-73 ◽  
Author(s):  
Edward S. Grew
Keyword(s):  
New England ◽  
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 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

The geochronology of some stratified metamorphic rocks in northeastern Massachusetts

1980 ◽  
Vol 17 (10) ◽  
pp. 1407-1416 ◽  
Author(s):  
William J. Olszewski Jr.
Keyword(s):  
New England ◽  
Source Area ◽  
Detrital Zircons ◽  
Metamorphic Rocks ◽  
Thermal Event ◽  
Northwest Africa ◽  
Major Period

Analyses of U and Pb in zircons and Rb and Sr in whole rocks have been made on stratified metamorphic rocks in northeastern Massachusetts. The Rb–Sr results show an age of about 450 Ma, which is interpreted as a resetting age. This would indicate the major period of metamorphism in the area. Zircons from the Fishbrook Gneiss give an upper intercept age of 730 ± 26 Ma, which is interpreted as the age of volcanism that produced the Fishbrook Gneiss sequence. The upper intercept of the Westboro Formation detrital zircons is 1511 ± 22 Ma and is interpreted as the age of the source for the Westboro sediments. The lower intercepts of the Fishbrook (289 Ma) and the Westboro (278 Ma) zircons suggest an episodic Pb loss correlated with the thermal event in southeastern New England recognized by other methods. The intercept ages of the Shawsheen Gneiss (2042 and 517 Ma) are more difficult to interpret, but also suggest an old source area. This source area is tentatively suggested to be northwest Africa.

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.

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