The dominant deformation microstructures of K-feldspar porphyroclasts are intragranular fractures at a high angle to the stretching lineation. The fractures are healed or sealed by polyphase aggregates of albite, K-feldspar, quartz and mica, which also occur along intragranular fractures of tourmaline and strain shadows around other porphyroclasts.
Abstract. Deformation microstructures of albitic plagioclase and K-feldspar were investigated in mylonitic pegmatites from the Austroalpine basement south of the western Tauern Window by polarized light microscopy, electron microscopy and electron backscatter diffraction to evaluate feldspar deformation mechanisms at greenschist facies conditions. The main mylonitic …
As shown in section 4.4, the granite is replete with deformation textures. Whilst microfractured K-feldspar with quartz/plagioclase crystallizing within the fractures is an indicator of melt-present deformation, textures such as myrmekite, subgrains in quartz and bulging quartz grains are indicators of solid-state deformation (see Fig. 11).
Back‐scattered SEM and conventional optical microscopy show that in both rock types, syntectonic myrmekitic intergrowths of oligoclase and quartz formed on the two sides of K‐feldspar grains that faced the local inferred incremental shortening direction for the mylonite.
Résumé (eng) Sanidine single crystals have been deformed in order to study the possible slip systems in this mineral. Runs have been performed at 700, 900 and 1,1000° C, with a confining pressure of 16 kbâr at a strain rate of 2 x 10-6 s-1 …
ABSTRACT In the Woodroffe Thrust mylonite zone, central Australia, recrystallization in plagioclase and K‐feldspar involved subgrain rotation, assisted by grain‐boundary or kink band boundary bulging...
Download scientific diagram | K-feldspar deformation microstructures (sample CT599). (a, b) Polarized light micrographs (crossed polarizers) of bent K-feldspar porphyroclast with healed ...
The replacement of K‐feldspar by plagioclase and quartz results in a volume decrease and is favoured on high normal stress sites around the grains. We suggest that the ambient temperature, pressure and chemical activities were such that the replacement reaction was favoured, but the addition of extra strain energy along the high‐pressure ...
293. 0000695. Sanidine. Keefer K D, Brown G E (1978) Crystal structure and composition of sanidine and high albite in cryptoperthitic intergrowth Note this sample of feldspar is from the Rabb Canyon pegmatite, Grant County, New Mexico, USA American Mineralogist 63 1264-1273.
Many points of evidence, especially igneous microstructures and structures resulting from solid-state deformation, indicate that K-feldspar megacrysts in deformed granites of the Papoose Flat ...
Experimental alterations of K-feldspar in distilled-deionized water at 150°, 175°, 200°, and 225°C were performed. The alteration products and dissolution mechanism of K-feldspar were examined by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), and X-ray …
The deformation temperatures, differential flow stresses, and rates of strain in the BG are elevated near the thrust zones with maximum near TT and within the BG increases from SE to NW direction towards DT. ... K-feldspar porphyroclasts are wrapped within foliations formed by highly sheared quartz ribbons along with biotites. Symmetric clasts ...
During progressive deformation in mylonitic, ductile shear zones myrmekite is commonly concentrated in shortening quarters in the rim of sigmoidal K-feldspar crystals. Simpson and Wintsch (1989) explain the asymmetric distribution of …
10%Abstract Many points of evidence, especially igneous microstructures and structures resulting from solid-state deformation, indicate that K-feldspar megacrysts in deformed granites of the Papoose Flat pluton are residual phenocrysts, not porphyroblasts.
Return to introduction. K-feldspar. Mineral structure: Framework silicate Common mineral in Granites, Gneisses. Rock-forming minerals associated with K-feldspar: Quartz, Plagioclase Structural varieties: Sanidine, Orthoclase, …
From previous optical studies on natural deformation microstructures in feldspars from gneisses and pegmatites, reported in a preceding paper, it would appear that recrystallization is a major process accompanying deformation of K feldspars under mesozonal conditions. In the present paper this process has been documented in augen gneisses from the Cammazes formation, …
Several examples of deformation-induced myrmekite have been found in two amphibolite facies mylonites derived from granitic protoliths, namely a muscovite-poor S-C mylonite and a single foliation, muscovite-poor mylonitic gneiss. ... The replacement of K-feldspar by plagioclase and quartz results in a volume decrease and is favoured on high ...
Albitisation, flame-perthite and tartan twining are common in K-feldspar at the early stage of deformation. The inferred dominant deformation mechanisms are: i) intracrystalline plasticity in quartz, ii) cataclasis with syntectonic crystallisation of very fine albite-oligoclase and micas in K-feldspar, and iii) cataclasis with precipitation of ...
Small pieces of albite in K-feldspar are called perthite, the reverse is antiperthite. By comparison, K-feldspars mix very well with Ba-feldspars. The ternary plot of possible feldspar compositions. The small black labels are old (and discouraged) feldspar names, the % shows the content of albite component (so basically the content of Na in ...
As the earth's crust is composed of 50 % feldspars, the mechanical proper¬ ties of these minerals are of interests to understand the tectonic deformation of most of the earth's crust rocks. Feldspars are low symmetry minerals — mono-clinic or triclinic — and various slip systems are expec¬ ted.
The deformation of feldspars in combination with chemical changes during metamorphism of any kind include very complicated processes that are set out in detail, for example in the excellent book by...
1978; Rubie, 1983), and that deformation may drive replacement reactions (Wintsch & Knipe, 1983). The role of deformation in the replacement of K-feldspar by mytinekite, a plagioclase-vermicular quartz symplectite, was considered first by Futterer (1894) who noted a greater development of mynnekite in deformed plutonic rocks
[1] A comparative study of the anisotropy of magnetic susceptibility (AMS) and K-feldspar phenocryst fabrics in the Land's End granite demonstrates that the AMS fabric predominantly reflects late magmatic deformation. Tensor analysis of the K-feldspar fabric shows a complex pattern, characterized by meter-scale variations in orientation, symmetry, …
Deformation-induced Pb isotope exchange between K-feldspar and whole rock in Neoarchean granitoids: Implications for assessing Proterozoic imprints Chemical Geology, 2009 Esa Heilimo
The constitutive equations for feldspar rocks are used to predict dominant deformation regimes prevailing at strain rate and temperature conditions that are expected relevant for plastic deformation in nature. In the deformation maps, strain rates cover a range from 10 −12 to 10 −16 s −1 and temperatures vary between 400 and 1100 °C.
Deformation maps rocks involves substantial alteration of the starting grain size, which is an important state variable affect- The deformation maps for feldspar delineate two ing the material constitutive behavior (e.g. Schmid et fields of dominant deformation mechanisms, grain al., 1980; ter Hegge, 2002).
The deformation microstructures of K-feldspar of dry eclogite facies shear zones in syenitic granulites are studied in detail. The eclogite facies overprint occurred syntectonically. The pyroxenes, feldspars, quartz and apatite in the shear zones recrystallized dynamically during shearing, partially changing their chemical composition.
Diffusion parameters have been estimated for K-feldspar in and adjacent to mylonite shear zones in the Wyangala Batholith. The parameters obtained suggest that deformation during mylonitisation would have caused argon systematics to reset because diffusion distances were reduced by cataclasis, deformation and/or recrystallisation.
These veins are formed under ductile deformation, restricted mainly to the porphyry and immediate wall-rock. ... Figure 05. A) Very fine-grained quartz-k-feldspar cross cutting strong secondary ...
A review of mesostructural and microstructural evidence favours the hypothesis that K-feldspar augen and megacrysts in felsic gneisses and mylonites are generally, ... A porphyroblastic origin is opposed by the typical zonal distribution of inclusions and the common evidence of plastic deformation and partial recrystallization of the augen. The ...
K-feldspar deformation microstructures (sample CT599). (a, b) Polarized light micrographs (crossed polarizers) of bent K-feldspar porphyroclast with healed microcracks at a high angle to the ...
The deformation is concentrated in the lower part of the sample, where the temperature was highest during deformation. A pink K-feldspar sample (250) deformed at 900°C, 1.5 GPa up to 25% strain (Figure 5b). Cracking is concentrated along a through-going deformation zone oriented at 50° to σ 1. Asymmetric conjugate shear cracks, which develop ...
(2019) Hentschel et al. Solid Earth. Deformation microstructures of albitic plagioclase and K-feldspar were investigated in mylonitic pegmatites from the Austroalpine basement south of the western Tauern Window by polarized light microscopy, electron microscopy and electron backscatter diffractio...
Authigenic K‐feldspar was investigated in two Albian to Turonian sections in Israel using K‐Ar and Ar‐Ar dating, X‐ray diffraction, scanning electron microscopy and chemical analysis. Both sections c...
From previous optical studies on natural deformation microstructures in feldspars from gneisses and pegmatites, reported in a preceding paper, it woul…