Microstructure and seismic properties of amphibole-rich rocks from the deep crust in southern Tibet

Wang, Xiong; Zhang, Junfeng; Tommasi, Andréa; Jing, Zhi-Cheng; Yuan, Maoshan

doi:10.1016/j.tecto.2021.228869

Cited by 11 publications

(10 citation statements)

References 63 publications

(110 reference statements)

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“…Type II of amphibole was also observed under simple shear experimental samples (Kim & Jung, 2019; Ko & Jung, 2015). Type III was less discussed than type I, which has the girdles of (010) poles and [001] axes parallel to the shear plane (XY‐plane) (Elyaszadeh et al., 2018; Ji et al., 2013; Okudaira et al., 2015; Soret et al., 2019; Wang et al., 2021). Type IV has girdles of (100), (010), and (110) poles normal to the shear direction (Kim & Jung, 2019), which is commonly related to rigid body rotation without evidence for crystal plastic deformation (Berger & Stünitz, 1996; Díaz Aspiroz et al., 2007; Imon et al., 2004; Ji et al., 2013; Kanagawa et al., 2008).…”

Section: Introductionmentioning

confidence: 99%

“…Amphibole and micas (e.g., biotite and muscovite) are likely to be the principal contributors to seismic anisotropy of the deeper continental crust due to their strong single crystal seismic anisotropy and strong CPO strength developed (Dempsey et al., 2011; Han & Jung, 2021; Ji et al., 2013, 2015; Lloyd et al., 2009; Mahan, 2006; Tatham et al., 2008). Studies of naturally deformed amphibole‐containing samples have also shown that the modal composition of amphibole, deformation strength, magmatic flow, and partial melting can have significant impacts on seismic anisotropy (Kang & Jung, 2019; Shao et al., 2021; Tatham et al., 2008; Wang et al., 2021).…”

Section: Introductionmentioning

confidence: 99%

“…Studies also suggest that amphibole grains in polyphase metamorphic rocks acts as rigid inclusions, the development of CPOs is controlled by rotating and fracturing (e.g., Berger & Stünitz, 1996; Brodie & Rutter, 1985; Díaz Aspiroz et al., 2007; Imon et al., 2004; Kim & Jung, 2019; Nyman et al., 1992; Shelley, 1994), and dissolution‐precipitation during deformation without significant strain accumulation (Giuntoli et al., 2018; Imon et al., 2002; Stokes et al., 2012) at temperature conditions below 650–700°C. CPOs of amphibole can also develop during the crystallization of magmas when the magmatic flow is controlled by a large‐scale (tectonic) stress field (e.g., Nicolas, 1992; Vauchez et al., 2019; Wang et al., 2021). What's more, there were studies reporting that amphibole CPOs can be formed owing to topotaxial growth (Giuntoli et al., 2018; Lee & Jung, 2021; Padrón‐Navarta et al., 2008).…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Development of Amphibole Crystal Preferred Orientations (CPOs) and Their Effects on Seismic Anisotropy in Deformed Amphibolites

Liu

Cao

2023

JGR Solid Earth

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Crystal preferred orientations and seismic anisotropy of amphibole play a crucial role in fingerprinting the rheological and physical properties of the deep crust. This study presents typical naturally deformed (banded, mylonitic, and ultramylonitic) amphibolites from the Ailao Shan‐Red River shear zone (ASRR‐SZ), southwestern China. In the banded amphibolite, coarse amphibole grains are highly elongated by dislocation creep and develop type I fabric of amphibole. In the mylonitic amphibolite, amphibole grains are characterized by porphyroclasts with core‐mantle structure and fine‐grained amphiboles in the matrix. Subgrain rotation recrystallization dominantly contribute to the grain size reduction process and display type III fabric of amphibole. In the ultramylonitic amphibolite, the fine‐grained amphiboles are mainly deformed by mechanical rotation of prismatic grains and develop type IV amphibole fabric. The seismic anisotropies are calculated from crystal preferred orientation (CPO) of naturally deformed amphiboles and model fabric. They both display that the transition of amphibole fabric from type III through type I to type IV also comes along with the transition of AVp patterns from Vp(X) ∼ Vp(Y) > Vp(Z) through Vp(X) > Vp(Y) > Vp(Z) to Vp(X) > Vp(Y) ∼ Vp(Z). Under the same texture strength, the strongest seismic anisotropy (both AVp and Max. AVs) occurs in the type III fabric of amphibole, the weakest seismic anisotropy is related to type IV fabric and a medium seismic anisotropy in type I fabric. This work indicates that the CPO types of amphiboles need be carefully considered in interpreting observed seismic anisotropy at the deep crustal level.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Development of Amphibole Crystal Preferred Orientations (CPOs) and Their Effects on Seismic Anisotropy in Deformed Amphibolites

Liu

Cao

2023

JGR Solid Earth

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“…The present and previous experimental data indicate that amphibole tends to develop strong CPO in response to deformation (Figure S5 in Supporting Information ; Ko & Jung, 2015) and may therefore play a critical role in the formation of strong seismic anisotropy in the deep crust. The presence of plagioclase, pyroxene, and garnet dilutes the seismic anisotropy induced by amphibole CPO (X. Wang et al., 2021). Thus observation of a strong crustal anisotropy implies both coherent deformation and large contents of amphibole (or biotite) over length scales of tens of km in the deep crust (Li et al., 2020; Lloyd et al., 2009).…”

Section: Discussionmentioning

confidence: 99%

Experimental Evidence for a Weak Calcic‐Amphibole‐Rich Deep Crust in Orogens

Wang

Zhang

Tommasi

et al. 2023

Geophysical Research Letters

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Amphibole‐rich rocks constitute significant components of the mid‐ to lower continental crust, particularly in active orogens characterized with thick and hot crusts. Nevertheless, experimental data on their viscosity remain scarce. We conducted axial compression deformation experiments on synthetic amphibolites under temperature and pressure conditions resembling deep sections of overthickened crust. A novel flow law for a calcic‐amphibole‐rich rock (80% amphibole +20% garnet) in the dislocation creep regime is derived from these experiments. Contrary to common assumptions, our results reveal that calcic‐amphibolite is 1‐2 orders of magnitude weaker than plagioclase‐rich amphibolite, granulite, or gabbro. A calcic‐amphibole‐rich, low viscosity deep crust may not only support the “channel flow” model proposed for the Tibetan Plateau but also explain the observed high crustal seismic anisotropy in the region.

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“…The plastic deformation of amphibole by dislocation glide has been reported in both naturally deformed amphiboles and experimental research [27,[33][34][35]. The LPO of amphibole can be produced by a variety of deformation mechanisms, such as rigid body rotation [29,36,37], cataclastic flow [26,28], diffusional creep (dissolution-precipitation creep) [28,38,39], and dislocation creep [27,29]. However, studies of the relationship between the LPO of amphibole and the activated slip system of amphibole are still very limited [27].…”

Section: Introductionmentioning

confidence: 99%

Dislocation Creep of Olivine and Amphibole in Amphibole Peridotites from Åheim, Norway

et al. 2021

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Amphibole peridotite samples from Åheim, Norway, were analyzed to understand the deformation mechanism and microstructural evolution of olivine and amphibole through the Scandian Orogeny and subsequent exhumation process. Three Åheim amphibole peridotite samples were selected for detailed microstructural analysis. The Åheim amphibole peridotites exhibit porphyroclastic texture, abundant subgrain boundaries in olivine, and the evidence of localized shear deformation in the tremolite-rich layer. Two different types of olivine lattice preferred orientations (LPOs) were observed: B- and A-type LPOs. Electron backscatter diffraction (EBSD) mapping and transmission electron microscopy (TEM) observations revealed that most subgrain boundaries in olivine consist of dislocations with a (001)[100] slip system. The subgrain boundaries in olivine may have resulted from the deformation of olivine with moderate water content. In addition, TEM observations using a thickness-fringe method showed that the free dislocations of olivine with the (010)[100] slip system were dominant in the peridotites. Our data suggest that the subgrain boundaries and free dislocations in olivine represent a product of later-stage deformation associated with the exhumation process. EBSD mapping of the tremolite-rich layer revealed intracrystalline plasticity in amphibole, which can be interpreted as the activation of the (100)[001] slip system.

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Microstructure and seismic properties of amphibole-rich rocks from the deep crust in southern Tibet

Cited by 11 publications

References 63 publications

Development of Amphibole Crystal Preferred Orientations (CPOs) and Their Effects on Seismic Anisotropy in Deformed Amphibolites

Development of Amphibole Crystal Preferred Orientations (CPOs) and Their Effects on Seismic Anisotropy in Deformed Amphibolites

Experimental Evidence for a Weak Calcic‐Amphibole‐Rich Deep Crust in Orogens

Dislocation Creep of Olivine and Amphibole in Amphibole Peridotites from Åheim, Norway

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