Elastic anisotropy of layered rocks: Ultrasonic measurements of plagioclase-biotite-muscovite (sillimanite) gneiss versus texture-based theoretical predictions (effective media modeling)

Ivankina, T. I.; Zel, I. Yu.; Lokajı́ček, T.; Kern, H.; Lobanov, K. V.; Zharikov, A. V.

doi:10.1016/j.tecto.2017.05.005

Cited by 20 publications

(6 citation statements)

References 51 publications

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“…All units in the central Adula Nappe show a top-to-the-north sense of shear (e.g., Nagel, 2008), thereby producing asymmetric quartz CPO, which in turn leads to the asymmetric V P distributions in the mica-poor orthogneisses. Both AV P as well as V P patterns are similar to those in previous studies, which either show high V P in the foliation with a maximum in the lineation direction (Ivankina et al, 2005;Ullemeyer et al, 2006;Kern et al, 2008;Zel et al, 2015;Ivankina et al, 2017;Schmidtke et al, 2021), at an angle to the lineation (Vasin et al, 2017), or elongated asymmetric maxima between the foliation normal and the foliation plane (Ullemeyer et al, 2006;Llana-Fúnez et al, 2009).…”

Section: Orthogneissessupporting

confidence: 88%

“…While experimental anisotropies are always higher than the ones modeled using CPO, the factor is variable for gneiss samples ranging from 1.3 (e.g., Vasin et al, 2017) to 6.6 (e.g., Ullemeyer et al, 2006). Considering experimental and modeled elastic anisotropy data of 18 gneiss samples from different studies, experimental anisotropy is 3 times higher than the modeled ones on average (Ivankina et al, 2005(Ivankina et al, , 2017Punturo et al, 2005;Ullemeyer et al, 2006Ullemeyer et al, , 2018Kern et al, 2008;Kern, 2009;Llana-Fúnez et al, 2009;Lokajicek et al, 2014;Zel et al, 2015;Vasin et al, 2017). V P /V S ratios of the paragneisses are determined by the volume percentage of quartz and yield values of 1.55-1.64.…”

Section: Paragneissesmentioning

confidence: 90%

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Elastic anisotropies of deformed upper crustal rocks in the Alps

et al. 2021

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Abstract. The crust within collisional orogens is very heterogeneous both in composition and grade of deformation, leading to highly variable physical properties at small scales. This causes difficulties for seismic investigations of tectonic structures at depth since the diverse and partially strong upper crustal anisotropy might overprint the signal of deeper anisotropic structures in the mantle. In this study, we characterize the range of elastic anisotropies of deformed crustal rocks in the Alps. Furthermore, we model average elastic anisotropies of these rocks and their changes with increasing depth due to the closure of microcracks. For that, pre-Alpine upper crustal rocks of the Adula Nappe in the central Alps, which were intensely deformed during the Alpine orogeny, were sampled. The two major rock types found are orthogneisses and paragneisses; however, small lenses of metabasites and marbles also occur. Crystallographic preferred orientations (CPOs) and volume fractions of minerals in the samples were measured using time-of-flight neutron diffraction. Combined with single crystal elastic anisotropies these were used to model seismic properties of the rocks. The sample set shows a wide range of different seismic velocity patterns even within the same lithology, due to the microstructural heterogeneity of the deformed crustal rocks. To approximate an average for these crustal units, we picked common CPO types of rock forming minerals within gneiss samples representing the most common lithology. These data were used to determine an average elastic anisotropy of a typical crustal rock within the Alps. Average mineral volume percentages within the gneiss samples were used for the calculation. In addition, ultrasonic anisotropy measurements of the samples at increasing confining pressures were performed. These measurements as well as the microcrack patterns determined in thin sections were used to model the closure of microcracks in the average sample at increasing depth. Microcracks are closed at approximately 740 MPa yielding average elastic anisotropies of 4 % for the average gneiss. This value is an approximation, which can be used for seismic models at a lithospheric scale. At a crustal or smaller scale, however, local variations in lithology and deformation as displayed by the range of elastic anisotropies within the sample set need to be considered. In addition, larger-scale structural anisotropies such as layering, intrusions and brittle faults have to be included in any crustal-scale seismic model.

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Section: Orthogneissessupporting

confidence: 88%

Section: Paragneissesmentioning

confidence: 90%

Elastic anisotropies of deformed upper crustal rocks in the Alps

et al. 2021

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“…We will elaborate the applicability of the model "average" rock to larger scale crustal rock units and discuss the controlling factors of the elastic anisotropy of crustal rocks. Ullemeyer et al, 2006;Kern et al 2008;Zel et al, 2015;Ivankina et al, 2017;Schmidtke et al, submitted to same issue), at an angle to the lineation (Vasin et al, 2017), or elongated asymmetric maxima between the foliation normal and the foliation plane (Ullemeyer st al., 2006;Llana-Fúnez et al, 2009). The orthogneiss sample RK15-17 measured in the lab shows high VP distributed within the foliation plane with a maximum at a slight angle to lineation direction.…”

Section: Discussionmentioning

confidence: 99%

Elastic anisotropies of deformed upper crustal rocks in the Alps

Keppler

Vasin

Lokajı́ček

et al. 2021

Preprint

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Abstract. The upper crust within collisional orogens is very heterogeneous both in composition and grade of deformation, leading to very variable physical properties at small scales. This yields difficulties for seismic investigations of tectonic structures at depth since local changes in elastic anisotropy cannot be detected. In this study, we show elastic anisotropies of the range of typical lithologies within deformed upper crustal rocks in the Alps. Furthermore, we aim to model average elastic anisotropies for these rocks and their changes with increasing depth due to the closure of microcracks. We therefore sampled rocks in the Adula Nappe of the central Alps, which is typical for upper crust in collisional orogens. The two major rock types found are orthogneisses and paragneisses, however, small lenses of metabasites and marbles also occur. Crystallographic preferred orientations (CPOs) and volume fractions of minerals in the samples were measured using time-of-flight neutron diffraction. Combined with single crystal elastic anisotropies these were used to model seismic properties of the rocks. The sample set shows a wide range of different seismic velocity patterns even within the same lithology, due to the heterogeneity of deformed upper crust. To approximate an average for these upper crustal units, we picked common CPO types of rock forming minerals within the gneiss samples, which represent the most common lithology. These data were used to determine an average elastic anisotropy of a typical upper crustal rock within the Alps. Average mineral volume percentages within the gneiss samples were used for the calculation. In addition, ultrasonic measurements of elastic anisotropies of the samples at increasing pressures were performed. These measurements, as well as the microcrack pattern determined in thin sections of the samples were used to model the closure of microcracks in the average sample at increasing depth. At ≈740 MPa microcracks are assumed to be closed yielding average elastic anisotropies of 4 % for the average gneiss. This value is an approximation, which can be helpful for seismic models at a lithospheric scale. At a crustal or smaller scale, however, it is an oversimplification and local lithological as well as deformational changes shown by the range of elastic anisotropies within the sample set have to be considered.

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“…Although the selected minerals in the three conditions are different, the diatexite's seismic properties do not vary a lot between the pre‐ and post‐melt conditions (Figure 11b). The felsic mineral dominant residuum domain has the maximum Vp oriented approximately parallel to lineation, while its minimum Vp direction is slightly inclined (∼10°) relative to the foliation, this direction is coincided with the fast biotite (010) direction (Figure ; Ivankina et al., 2017). S‐wave anisotropy's two maximum clusters are almost in symmetry by YZ plane, the Vs 1 polarization is mostly normal except in the lower part of seismic figures that are subvertical to XY plain.…”

Section: Predicted Seismic Signals Of the Lower Crust During Pre‐ Symentioning

confidence: 98%

Deformation Behavior and Inferred Seismic Properties of Tonalitic Migmatites at the Time of Pre‐melting, Partial Melting, and Post‐Solidification

Shao

Piazolo

Liu

et al. 2021

Geochem Geophys Geosyst

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As seismic data from the lower crust becomes more readily available, it is important to link seismic properties to the ongoing processes within lower crustal evolution. This includes high temperature, pre‐ and post‐migmatization solid state deformation as well as melt‐present deformation. We selected two tonalitic migmatites with variable former melt content (one metatexite and one diatexite) from the lower crustal Daqingshan area, northern North China Craton to assess the link between seismic properties and rock structure and rheology. Field observation along with microstructural features suggest that the characteristics of hornblende and plagioclase within the residuum of the metatexite can be used to derive information on the pre‐melt deformation. Residuum's plagioclase CPO (crystallographic preferred orientations) is consistent with high temperature dislocation creep as the main deformation mechanism; similarly, hornblende shows a strong CPO related to dislocation creep. During syn‐melt (melt present) conditions, phenocrysts of plagioclase in the metatexite's neosome and K‐feldspar and peritectic hornblende in the diatexite's neosome are present. The rheology of the rock was dominated by melt; hence is inferred to follow Newtonian flow. After melt crystallization deformation is minor but again dominated by dislocation creep. The seismic properties (seismic velocity, anisotropy, Vp/Vs ratio, etc.) for pre‐ and post‐melt have similar values expected values for solid mafic rocks, whilst the syn‐melt seismic velocities are generally lower and Vp/Vs ratios and seismic anisotropies are higher.

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Elastic anisotropy of layered rocks: Ultrasonic measurements of plagioclase-biotite-muscovite (sillimanite) gneiss versus texture-based theoretical predictions (effective media modeling)

Cited by 20 publications

References 51 publications

Elastic anisotropies of deformed upper crustal rocks in the Alps

Elastic anisotropies of deformed upper crustal rocks in the Alps

Elastic anisotropies of deformed upper crustal rocks in the Alps

Deformation Behavior and Inferred Seismic Properties of Tonalitic Migmatites at the Time of Pre‐melting, Partial Melting, and Post‐Solidification

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