Quartz preferred orientation in naturally deformed mylonitic rocks (Montalto shear zone–Italy): a comparison of results by different techniques, their advantages and limitations

Fazio, Eugenio; Punturo, Rosalda; Cirrincione, Rosolino; Kern, H.; Pezzino, Antonino; Wenk, Hans‐Rudolf; Goswami, Sumit; Mamtani, Manish A.

doi:10.1007/s00531-016-1424-y

Cited by 23 publications

(10 citation statements)

References 79 publications

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“…We need to involve detailed microstructural work and high-resolution techniques to constrain intrinsic and extrinsic factors [21] such as temperature, pressure, mineralogy, deformation mechanisms and timing. Many works confirm the importance of a multidisciplinary approach to study shear zones [4,7,9,18,[22][23][24][25][26]. In this view, field observations, geochronological data, deformation microstructures and the vorticity of the flow and finite strain measurements are necessary.…”

Section: Introductionmentioning

confidence: 97%

Kinematics and Timing Constraints in a Transpressive Tectonic Regime: The Example of the Posada-Asinara Shear Zone (NE Sardinia, Italy)

et al. 2020

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Detailed geological field mapping, integrated with meso- and microstructural investigations, kinematic of the flow and finite strain analyses, combined with geochronology, are fundamental tools to obtain information on the temperature–deformation–timing path of crystalline rocks and shear zone. The Posada-Asinara shear zone (PASZ) in northern Sardinia (Italy) is a steeply dipping km-thick transpressive shear zone. In the study area, located in the Baronie region (NE Sardinia), the presence of mylonites within the PASZ, affecting high- and medium-grade metamorphic rocks, provides an opportunity to quantify finite strain and kinematic vorticity. The main structures of the study area are controlled by a D2 deformation phase, linked to the PASZ activity, in which the strain is partitioned into folds and shear zone domains. Applying two independent vorticity methods, we detected an important variation in the percentage of pure shear and simple shear along the deformation gradient, that increases from south to north. We constrained, for the first time in this sector, the timing of the transpressive deformation by U–(Th)–Pb analysis on monazite. Results indicate that the shear zone has been active at ~325–300 Ma in a transpressive setting, in agreement with the ages of the other dextral transpressive shear zones in the southern Variscan belt.

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Section: Introductionmentioning

confidence: 97%

Kinematics and Timing Constraints in a Transpressive Tectonic Regime: The Example of the Posada-Asinara Shear Zone (NE Sardinia, Italy)

et al. 2020

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“…As was mentioned earlier, a range of methods were used to investigate quartz textures, ranging from optical methods [148,149], conventional X-ray diffraction [19,65], synchrotron X-ray diffraction [150,151], neutron diffraction (ranging from monochromatic [149,152] to time-of-flight [49]), and electron backscatter diffraction (EBSD) [79,143,144,146]. Results from different methods were compared [25,49,63,149,153,154]. Optical methods are limited to record c-axis orientations, EBSD records textures on surfaces, neutron diffraction probes large volumes of samples.…”

Section: Comparison Of Methods Of Texture Measurementsmentioning

confidence: 99%

“…Many samples with D-type fabrics underwent recrystallization and display equiaxed grain shapes. A transition from a Z-maximum (Type A) to a YZ girdle (Type B) was documented in Montalto/Italy quartzites [63] as well as in Mt. Isa/Australia gneisses [64].…”

Section: Quartz Texture Typesmentioning

confidence: 99%

Preferred Orientation of Quartz in Metamorphic Rocks from the Bergell Alps

Wenk

Vogel

et al. 2019

Minerals

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Crystal preferred orientation of 47 samples of quartzite and eight samples of associated marbles from the Bergell Alps have been analyzed with time-of-flight neutron diffraction and EBSD. The results show a clear distinction of texture types for quartzites transformed from Triassic sandstones and quartz layers in gneiss. Textures of Triassic quartzites are overall weak and display a maximum of c-axes perpendicular to the foliation or a crossed girdle perpendicular to the lineation. Pole figures for positive rhombs {10 1 ¯ 1} show a maximum perpendicular to the foliation and negative rhombs {01 1 ¯ 1} generally display a minimum. Based on polycrystal plasticity models this texture type can be attributed to a combination of basal and rhombohedral slip. Asymmetry of the distributions is attributed to simple shear and local strain heterogeneities. The relatively weak texture is partially caused by muscovite limiting dislocation motion and grain growth, as well as adjacent layers of marble that accommodate significant strain. Most quartz layers in gneiss, including mylonites, display a texture with a-axes parallel to the lineation and a c-axis maximum in the intermediate fabric direction. This texture type can be attributed to dominant prismatic slip. Many samples are recrystallized and recrystallization appears to strengthen the deformation texture. The study shows good agreement of neutron diffraction and EBSD. Neutron diffraction data average over larger volumes and maximum pole densities are generally lower and more representative for the bulk material. With EBSD the microstructure and mechanical twinning can be quantified.

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“…Well constrained Alpine shear zones are long known in the Aspromonte Massif and Peloritani Mountains from the southern Calabria-Peloritani Orogen (CPO; e.g., [1,2,[26][27][28][29][30][31][32][33][34][35]). Here, Alpine tectonics locally reworked Mesozoic sedimentary rocks, as well as portions of Variscan and older basements, hampering the reconstruction of the pre-Alpine tectono-metamorphic evolution.…”

Section: Introductionmentioning

confidence: 99%

Submagmatic to Solid-State Deformation Microstructures Recorded in Cooling Granitoids during Exhumation of Late-Variscan Crust in North-Eastern Sicily

Fazio¹,

Fiannacca²,

Russo³

et al. 2020

Geosciences

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Late-Variscan granitoid rocks of trondhjemitic and granitic composition, intruded in migmatitic paragneisses in the north-eastern Peloritani Mountains (southern Italy) at ~310 Ma and ~300 Ma, respectively, exhibit a range of deformation microstructures developed under a shear regime at decreasing temperatures. Non-coaxial deformation is documented by sigmoidal feldspar porphyroclasts, mica fish, and asymmetric boudins affecting tiny andalusite crystals. Late-Variscan shearing during granitoid cooling is constrained by largely represented chessboard patterns in quartz and, especially, submagmatic fractures in plagioclase, indicating deformation at high-temperature conditions (T > 650 °C), in the presence of melt. Submagmatic deformation was extensively superseded by deformation at lower temperatures. Examples of solid state-high temperature deformation-related microstructures (T > 450 °C) include feldspar bulging, quartz grain boundary migration, and subgrain rotation recrystallization. Finally, low temperature subsolidus microstructures (T < 450 °C) consist of quartz bulging, mica kinks, and feldspar twinning and bending. A complete sequence of deformation, operating from submagmatic to low-temperature subsolidus conditions is recorded in both the older and younger granitoids, suggesting a duration of ~20 Ma for shear zone activity during post-collisional exhumation of the Variscan middle crust in southernmost Italy.

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Quartz preferred orientation in naturally deformed mylonitic rocks (Montalto shear zone–Italy): a comparison of results by different techniques, their advantages and limitations

Cited by 23 publications

References 79 publications

Kinematics and Timing Constraints in a Transpressive Tectonic Regime: The Example of the Posada-Asinara Shear Zone (NE Sardinia, Italy)

Kinematics and Timing Constraints in a Transpressive Tectonic Regime: The Example of the Posada-Asinara Shear Zone (NE Sardinia, Italy)

Preferred Orientation of Quartz in Metamorphic Rocks from the Bergell Alps

Submagmatic to Solid-State Deformation Microstructures Recorded in Cooling Granitoids during Exhumation of Late-Variscan Crust in North-Eastern Sicily

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