Optical anisotropy of coals as an indicator of tectonic deformation, Broad Top Coal Field, Pennsylvania

Levine, Jeffrey R.; Davis, A. W.

doi:10.1130/0016-7606(1984)95<100:oaocaa>2.0.co;2

Cited by 59 publications

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“…During rock deformation this geometry is modified in respect to the effective deviatoric stresses, whereby the direction of minimum reflectance aligns parallel to the direction of maximum compressional stresses. In folded sequences the maximum reflectance develops in the direction of the fold axis (Levine and Davis 1984;Kalkreuth 1991a, Langenberg et al 1998). These relationships lead to a general correspondence between the orientation of AVR principale axes and the fabric elements of sedimentary rocks, where R max and R int are oriented within and R min is normal to the bedding plane.…”

Section: Timing Of Coalificationmentioning

confidence: 95%

“…For further explanation see text Fig. 9 Diagram showing the relationship between the shape of AVR ellipsoids and the maximum anisotropy P. Evidently, the path from oblate to prolate geometry is accompanied by a reduction in total anisotropy particles is genetically and only linked to the maximum coalification process (Rouzaud and Oberlin 1983;Levine and Davis 1984). Because peak coalification in the CMB was directly related to the late-Variscan intrusion activity, the development of the tectonic increment of the measured AVR must have taken place contemporaneously.…”

Section: Timing Of Coalificationmentioning

confidence: 96%

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Coalification history of the Stephanian Ciñera-Matallana pull-apart basin, NW Spain: Combining anisotropy of vitrinite reflectance and thermal modelling

Frings

Lutz

Wall

et al. 2004

Int J Earth Sci (Geol Rundsch)

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The Stephanian Ciaeera-Matallana Basin of NW Spain comprises 1,500 m of alluvial to lacustrine coalbearing sediments, which were deposited in a late Variscan transtensional/transpressional pull-apart setting. The relationship between coalification pattern and rock deformation was evaluated by measurements of the anisotropy of vitrinite reflectance (AVR). The AVR ellipsoids reveal both pre-tectonic elements related to the bedding fabric and syn-tectonic elements related to folding, producing biaxial ellipsoid shapes with the maximum reflectance parallel to fold axes. The mean coalification gradient for the Stephanian succession is about 0.62 %Rr/km. Calculations of the mean palaeogeothermal gradient are presented on the basis of three different empirical equations. A palaeo-geothermal gradient of 85 C/km is considered the most realistic, with an overburden of about 1,000 m. 1-D numerical modelling of the burial history results in two possible scenarios, the most preferable involving a palaeo-heat flow of 150 mW/ m 2 and an overburden of ca. 1,050 m. These results indicate that maximum coalification was related to a localised but high palaeo-heat flow/-geothermal gradient. The anisotropy of vitrinite reflectance highlights the interactive and transitional nature of sedimentary compaction and rock deformation on the maturation of organic material within strike-slip fault zones.

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Section: Timing Of Coalificationmentioning

confidence: 95%

Section: Timing Of Coalificationmentioning

confidence: 96%

Coalification history of the Stephanian Ciñera-Matallana pull-apart basin, NW Spain: Combining anisotropy of vitrinite reflectance and thermal modelling

Frings

Lutz

Wall

et al. 2004

Int J Earth Sci (Geol Rundsch)

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“…Moreover, the previous research suggested that the value of VR and the qualitative change of the VRA was the sign of the tectonic environment where the TDC existed (Jiang et al, 2007;Levine and Davis, 1984;Komorek and Morga, 2007;Ross and Bustin, 1997). However, some researchers questioned this theory and considered that the shape change of the VRI probably could not reflect the deformation characteristics of the TDC, as the shape of the VRI was always elliptical before and after deformation; also, during the process of coalification, both the strata pressure and the tectonic stress could change the shape of VRI, therefore it needs to be discussed how to identify the shape change of the VRI that was controlled by the tectonic stress (Cao, 1990;Hou et al, 1995;Bustin et al, 1986;Jones et al, 1973).…”

Section: Figurementioning

confidence: 98%

“…In the regions where the attitude of coal seams is horizontal, the coal seams are influenced only by the strata pressure, which leads to uniaxial negative optical properties of vitrinite. The comparative analysis of the coal seams in different deformation degrees indicated that the optical property of vitrinite has been transformed from the uniaxial negative to biaxial positive, corresponding to the degree, from weak to intense, of TDC (Cao, 1990;Gao, 1993;Hou et al, 1995;Jiang et al, 1997;Jiang et al, 2007;Levine and Davis, 1984;Komorek and Morga, 2007;Ross and Bustin, 1997). However, during the lengthy geological evolution, the strata pressure and the tectonic stress are incongruent.…”

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confidence: 93%

The effect of different deformation mechanisms on the chemical structure of anthracite coals

Hou

et al. 2015

Sci. China Earth Sci.

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To study the effect of different deformation mechanisms on the chemical structure of anthracite coals and further understand the correlation between changed chemical structures and coal and gas outburst, ten groups of sub-high-temperature and sub-high-pressure deformation experiments were performed. All samples maintained primary structure, which were collected from the Qudi Mine in the southern Qinshui Basin of China. The samples were analyzed by ultimate analysis, Vitrinite Reflection (VR), Fourier Transform Infrared spectroscopy (FTIR), and Raman spectroscopy both before and after deformation experiments for contrasting. The results showed that the VR values of all samples after experiments were significantly higher than before experiments, which suggested that the metamorphism degree of anthracite coals was increased by deformation. The results also indicated that both temperature and strain rate had significant effects on the chemical structure of anthracite coals. At a high strain rate of 4×10 5 s 1 , the deformation of the samples was mainly brittle in which the mechanical energy was transformed mainly into frictional energy. In this situation, all samples developed several distinct fractured surfaces and the change of chemical structures was not obvious. On the contrary, with the decrease of the strain rates, the ductile deformation was dominated and the mechanical energy was mainly transformed into strain energy, resulting in the accumulation of deformation energy confessed by increasing quantity of dislocation and creep in the coal's interior nucleus. The absorption in the aromatic ring groups increased; otherwise the absorption in the aliphatic structures and ether oxygen groups decreased rapidly. During these experiments, CO was collected from two experimental samples. The number of aromatic rings and the structure defects within the two generated gas samples increased and the degree of molecular structure orders decreased. anthracite coal, deformation experiment, VR, Vitrinite Reflection Indicating surface (VRI), secondary structure defect Citation: Xu R T, Li H J, Hou Q L, et al. 2015. The effect of different deformation mechanisms on the chemical structure of anthracite coals. Science China: Earth Sciences,

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“…Microstructural observations of naturally deformed coals suggest both brittle and ductile processes forming microstructures, including various cleats and fractures of brittle deformation and flow cleavage or sheath folds by ductile deformation [3][4][5][6][7][8][9][10][11][12][13] . Recent experimental approaches reveal that temperatures, pressures and generation of gases have profound effects on the mechanical aspects of coal samples [11][12][13][14][15] .…”

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confidence: 99%

Macro- and microscopic mechanical behaviour of flow of coal samples experimentally deformed at high temperatures and pressures

Liu

Yang

2005

Chin.Sci.Bull.

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Coal samples from Qinshui basin, Shanxi, China are experimentally deformed at temperatures and confining pressures of 200 500 and 200-500 Mpa, strain rate of 0.5 10 5 /s and total strain of 10%. The vitrinite reflectance of the coal samples varies from 3.04 to 1.79. It is shown that the strengths of the deformed samples change obviously with coeval increasing temperatures and pressures (T/P). At the experimental range of T/P, the effects of increasing temperature predominate over that of increasing pressure. Microstructural analysis indicates a brittle to ductile transition under experimental T/P conditions from 200 to 300 , and 200 to 300Mpa. Brittle deformation microstructures include macroscopic fracture zones and penetrative fracture associations. Elongation, undulose or irregular extinction, deformation lamellae and dynamic recrystallization of grains are the main ductile deformation microstructures. The variation of deformation mechanisms of the experimentally deformed coal samples is related to both the components of coals and T/P conditions. At low T/P, fractures occur in both inertinite and vitrinite of the samples. At higher T/P, crystalline plastic deformations are observed in the inertinite only.

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Optical anisotropy of coals as an indicator of tectonic deformation, Broad Top Coal Field, Pennsylvania

Cited by 59 publications

References 0 publications

Coalification history of the Stephanian Ciñera-Matallana pull-apart basin, NW Spain: Combining anisotropy of vitrinite reflectance and thermal modelling

Coalification history of the Stephanian Ciñera-Matallana pull-apart basin, NW Spain: Combining anisotropy of vitrinite reflectance and thermal modelling

The effect of different deformation mechanisms on the chemical structure of anthracite coals

Macro- and microscopic mechanical behaviour of flow of coal samples experimentally deformed at high temperatures and pressures

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