PLANAR MICROSTRUCTURES (LAMELLAR SUBGRAINS) IN FELDSPAR …

microstructures (such as PDFs) from those formed prior to impact such as exsolution lamellae, veins, cleavages, and twin planes [e.g. 2]. We investigated the microstructures of Or-rich alkali feldspar phenocrysts from granitoid rocks recovered from the peak ring of the Chicxulub impact structure during the recent IODP-ICDP Expedition 364 [3].

Charnockite microstructures: From magmatic to metamorphic

Feldspar may show Carlsbad twinning and compositional zoning in the case of plagioclase (Shelley, 1993). Charnockitic augen gneiss in southern Norway in which the augen represent K-feldspar phenocrysts (e.g.,Vernon, 1990)(Fig. 2), are an example of charnockites showing such a porphyritic texture. Further igneous microstructures include

SE - Deformation of feldspar at greenschist facies ...

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.

k feldspar microstructures - glasknak.nl

Feldspar Minerals: 2 Chemical And Textural,Feldspar Minerals: 2 Chemical and Textural Properties Physical,, Development of perthite microstructures in the Feldspar minerals - crystal structure andMicrostructures of melt-bearing regional,K-feldspar), the other two co-precipitating minerals (eg, quartz and sodic plagioclase) must have crystallized on existing residual grains …

Quartz and Feldspar Microstructures in Metamorphic Rocks

K-feldspar phenocrysts are chacracterized by zonally (crystallographically) arranged inclusions, especially of well-formed plagioclase crystals, whereas K-feldspar porphyroblasts are characterized by rounded quartz and plagioclase inclusions, either at random or arranged in trails reflecting an overgrown foliation.

Grain-size reduction of feldspars by fracturing and ...

Feldspar grain-size reduction occurred due to the fracturing of plagioclase and K-feldspar, myrmekite formation and neocrystallization of albitic plagioclase along shear fractures of K-feldspar porphyroclasts in the leucocratic granitic rocks from the Yecheon shear zone of South Korea that was deformed under a middle greenschist-facies condition.

Quartz and feldspar microstructures in metamorphic rocks ...

TY - JOUR. T1 - Quartz and feldspar microstructures in metamorphic rocks. AU - Vernon, Ron H. PY - 1999/4. Y1 - 1999/4. N2 - The shapes of quartz and feldspar grains in metamorphic rocks are among the most reliable criteria for determining parental rock-types.

Biochemical Evolution II: Origin of Life in Tubular ...

K-feldspar. A further 10% of the Itsaq rocks are granites and granitic gneisses with up to 40% K-feldspar. Water-lain vol-caniclastic rocks occur in the sequence at -3.7 Ga and perhaps as early as -3.8 Ga, and sedimentary banded iron formations Abbreviations: K-feldspar, potassium-rich alkali feldspar; SEM, scan-ning electron microscopy.

Argon diffusion domains in K-feldspar I: microstructures ...

Samples of MH-10, a K-feldspar thought to contain discrete diffusion domains for argon, have been examined by light and TEM microsopy to search for domain boudaries. We examined both unheated K-feldspar separates and samples heated in vacuum between 750 and 1150°C in order to characterize the initial microstructure as well as any changes resulting from laboratory …

(PDF) ZAGREB 2004 Microstructures in Two Alkali Feldspar ...

ZAGREB 2004 Microstructures in Two Alkali Feldspar Megacrysts from the Papuk Mt., Croatia Viktória KOVÁCS KIS1, Marija HORVAT2 and István DÓDONY1 Key words: Microstructure, Modulation, Alkali feld- in the host as porphyric (in adamellite and granodio- spar, Low microcline, Thermal history, Papuk Mt., rite), vein filling and diffuse, metasomatic K-feldspar Croatia.

Pristine microstructures in pseudotachylytes formed in dry ...

K-feldspar surrounding plagioclase indicates the direct growth of the two feldspar phases from a melt, because this spatial separation is unlikely to have originated during devitrification. A similar separation of plagioclase and K-feldspar has been observed in pseudotachylytes formed in the Adamello tonalites under shallower conditions, with K …

(PDF) Microstructures in feldspars from a major crustal ...

Large, inequant feldspar grains, both oligoclase (O) and microperthitic K-feldspar (K), which control the quartz ribbon orientation and define the foliation, are surrounded by recrystallized mantle grains. Hornblende from this sample also displays a core- and-mantle structure. Note the large quartz-subgrain-size (Q). Scale bar is 0.5 mm. P244.

Quartz and feldspar microstructures in metamorphic rocks ...

K-feldspar phenocrysts are characterized by zonally arranged inclusions, whereas K-feldspar porphyroblasts are characterized by spherical inclusions ofquartz and plagioclase, either at random or arranged in ffails that reflect an overgrown foliation Inclusions of quartz and feldspar tend to be spherical in metamorphic porphyroblasts (e.g., staurolite), even where the boundary …

Muscovite dehydration melting: Reaction mechanisms ... - Wiley

(b) In quartzofeldspathic domains, K-feldspar replaces plagioclase by K + –Na + cation exchange, while melt and intergrowths of sillimanite+quartz form in the aluminous domains. (c) At 7–8 vol.% melt generation, the system evolves from a closed to open system and all phases coarsen by up to two orders of magnitude, resulting in large K-feldspar porphyroblasts.

Correlations between microstructures, K-feldspar ...

Abstract The biotite granites in the Nigerian Younger Granites are a major source of the economic metals Sn, Nb, Zn and W. The textural variations in these rocks are considered together with the composition and structural state of the K-feldspars. The curious disparity in the degree of mineralization of these rocks of similar mineral assemblage is considered to be related to the …

Microstructures of melt-bearing regional metamorphic rocks ...

Microstructures of melt-bearing regional metamorphic rocks Author(s) ... or peritectic minerals (e.g., garnet, cordierite, orthopyroxene, K-feldspar) lining felsic "protoleucosomes"; (2) inclusion-free euhedral overgrowths of feldspar (precipitated from liquid) or peritectic minerals (e.g., garnet, cordierite, orthopyroxene, ...

Microstructures in feldspars from a major crustal thrust ...

Brittle microstructures Microfractures in zone 5 and the localized polysynthe- tic twins in K-feldspar that highlight the fractures are assumed to be a late feature imposed during uplift to higher crustal levels, resulting from either interaction with water (Tullis & Yund 1980, Tuilis 1983) or exten- sion due to unloading.

Preferred orientation distribution of shock ... - Wiley

Shocked quartz and feldspar grains commonly exhibit planar microstructures, such as planar fractures, planar deformation features, and possibly microtwins, which are considered to have formed by shock metamorphism. Their orientation and frequency are typically reported to be randomly distributed across a sample.

ALEX STREKEISEN-Alkalifeldspar-

Anorthoclase is the only alkali feldspar that is not K-feldspar. It is sodic in composition, optically triclinic and characterized by a twinning similar to microcline but on a smaller scale. The structural state which is the basis of the alkali feldspar classification, is dependent on the temperature of crystallization and subsequent cooling history.

Microstructures in Two Alkali Feldspar Megacrysts from the ...

The microstructures of alkali feldspars crystalli-sed at lower temperatures are relatively less known. TEM observations of twinning and exsolution texture in a hydrothermal and two pegmatitic microclines (TIBBALS & OLSEN, 1977) extended the study of K-feldspar microtextures below the temperature of the monoclinic–triclinic transformation.

ALEX STREKEISEN-Feldspar structure-

They are celsian (BaAl 2 Si 2 O 8) and hyalophane (compositionally between K-feldspar and celsian). They are also structurally similar to K-feldspars. These minerals are volumetrically very restricted, nowhere near as common as other feldspars. Fig.1: Feldspar classification. This diagram shows how feldspar minerals are classified on the basis ...

Microstructures

First Previous Section 1 Next Last; Undeformed Rock Microstructure . Click image to enlarge: 1. Undeformed feldspar and quartz grains – Undeformed granite from the Lucerne Pluton in coastal Maine shows euhedral crystals of plagioclase (blue, with two sets of albite twins), anhedral K-feldspar (yellow, with minor alteration showing as darker patches along cleavage planes), and …

(Energy related studies utilizing microline ...

Abstract. In our first year of the current funding cycle, we have investigated three interrelated aspects of K-feldspar thermochronology; (1) the Ar diffusion properties and microstructures of K-feldspars, (2) the thermal evolution of the Valles Caldera and (3) the continued development of microanalysis.

Argon diffusion domains in K-feldspar I: microstructures ...

Three classes of substructure are present in the K-feldspar, but only the third appears to have been affected by laboratory heating: (1) Cross-hatched extinction in light microscope is common but variably developed. TEM reveals almost no albite/pericline twinning but …

Quartz microstructures and deformation conditions in the ...

FELDSPAR MICROSTRUCTURES Not only quartz, but also feldspar microstructures vary in the shear zone. Evidence for the replacement of K‐feldspar porphyroclast by myrmekite, a plagioclase‐vermicular quartz symplectite ( Simpson 1985 ; Simpson & Wintsch 1989 ; Vernon 1992 ), is observed in the samples in which quartz shows …

Implications of mylonitic microstructures for the ...

In the mylonitic rocks, the development of fluxion banding (Sm) is remarkably influenced by the existence of K-feldspar, forming a myrmekitic intergrowth. Brittle microstructures indicative of truly cataclastic deformation are observed only in mylonitic rocks close to the MTL.

Lightning-induced high temperature and pressure ...

rounding K-feldspar host grains (Fig. 3f). Electron dispersive spectroscopy (EDS) point analyses indicate that the material along the planar structures has a plagioclase composition (Table 1). On this basis, we interpret the sets of planar features to be plagioclase exsolution lamellae in K-feldspar host grains and refer to these features