Abstract We have investigated K-feldspar recrystallisation in granitoid mylonites within a ductile shear zone from the Ryoke metamorphic belt, SW Japan. Fine-grained K-feldspar (20 μm on average) occurs in the matrix and in pull-apart areas within fractured K-feldspar porphyroclasts.
Myrmekite replacing K-feldspar in perthite during Na-Ca-metasomatism, showing isolated quartz vermicules of irregular shape. Lyon Mountain granite gneiss, Ausable Forks, New York. A first variety of this type of metasomatism affects only enclaves within a granitoid. Here the influx of Na-rich fluids in the temperature range 450 °C to 650 °C ...
peralkaline-peraluminous alkali feldspar granites and is composed of K-feldspar, quartz, alkali amphibole, plagioclase, bio-tite and accessory minerals are iron oxides, monozite, zircon, apatite, and annite. This granitoid is associated with acid vol-canic and minor basic volcanic-plutonic and dykes.
Granitoid Classification Based on feldspar aluminum ratio KALSi3O8 1:1:3 Al 2O3 K O CaO Al2O3 K2O CaO Al2O3 CaO biotite muscovite cordierite andalusite garnet pyroxene hornblende biotite aegirine riebeckite arfvedsonite Peraluminous Metaluminous Peralkaline moles Na2O Na2 O K2O Na2 Alumina saturation classes based on the molar proportions of ...
When a granitoid is devoid or nearly devoid of plagioclase, the rock is referred to as alkali feldspar granite. When a granitoid contains less than 10% orthoclase, it is called tonalite; pyroxene and amphibole are common in tonalite.
A granitoid (a coarse-grained igneous rock composed mostly of quartz, K-feldspar (alkali-feldspar) and plagioclase). More specifically a rock having an alkali-feldspar/total feldspar ratio from 0.35-0.90 on the QAPF diagram and 20-60% quartz.
Feldspar is the most abundant mineral group in the Earth’s crust.There are more feldspars (60%) than all the other minerals combined in the outer (13-17) km of the crust 1.Feldspars occur in most igneous and metamorphic rocks.
aggregate and contain a granitoid phase assemblage (nanogranitoid inclusions) with quartz, K-feldspar, plagioclase, and one or two mica depending on the particular circumstances. After their experimental remelting under high-confining pressure, nanogranitoid MI can be analyzed combining several techniques (EMP, LA-ICP-MS, NanoSIMS, Raman).
(B) A relatively unstrained K-feldspar augen granitoid from the Analytical Procedures Permian belt in the western portion of the Stewart River map sheet. (C) Wounded Moose augen granite: a mylonitized example of augen granitoid with relict K-feldspar phenocrysts.
Apr 06, 2012· Highlights We focus on fine-grained K-feldspar in granitoid mylonites. Growth features of grains indicate a solution–precipitation process. Host-controlled crystallographic orientation may be related to grain growth. Water contents of fine-grained K-feldspar are low and homogeneous (250 ppm H 2 O). Aqueous fluid may be released during the solution–precipitation process.
K-feldspar megacrysts in granitoid plutons have been interpreted as either phenocrysts or porphyroblasts. Most of the microstructural, mineralogical and chemical evidence (e.g., shape, alignment ...
K-feldspar megacrysts grow to large sizes early in magma history, while the simultaneously crystallizing quartz and feldspar grains that overgrow irregular megacrysts are interpreted as due to later processes after the growth of euhedral megacrysts (Vernon and Paterson, 2008). Other evidences as the presence of K-feldspar crystals in dioritic
GRANITOID ROCKS. The rock . granite (or its volcanic equivalent rhyolite) has a limited range of composition that results in crystallization of equivalent amounts of quartz, plagioclase, and K-feldspar.
The Precambrian–Paleozoic boundary in the subsurface of southwestern Ontario commonly is characterized by secondary K-feldspar. In the weathered and altered Precambrian granitoid gneisses at the unconformity, secondary K-feldspar has replaced preexisting minerals, and also occurs as discrete crystals of adularia, overgrowths on altered minerals, and microcrystalline veinlets.
The granitoids have high-K calc-alkaline, metaluminous to weakly peraluminous composition(s). Silica contents increase and Mg, Fe, Ti, Ca, and P contents decrease from quartz monzodiorites through granodiorites to monzogranites and K-feldspar granites.
SiO2 and pegmatites bearing K-feldspar, fluorite, muscovite and gem minerals such as tourmaline, topaz, beryl etc. Quartz of gem-quality occurs in vugs and fissures of the country rock. Late stage ductile and shear fractures are commonly filled with disseminated sulphides. The pegmatites, quartz veins and the fracture and shear-controlled
monzogranites and K-feldspar granites with rare MME. The Dongjiangkou granitoid rocks are characterized by high K 2O, MgO, Rb, and Mg# values, but low TiO 2, Sc, and A/CNK (molar Al 2O 3/(CaO + Na 2O+K 2O)) values, with εHf(t) values of −18.1 to −0.4 and T DM2(Hf) values of 1141–2117 Ma. We suggest that the Dongjiangkou
K-feldspar (1– 12 mm in grain size) occurs as subhedral, most commonly rectangular, crystals, but rarely euhedral crystals are observed. Coarse patch perthite is common. K-feldspar is also very altered to sericite and clay minerals. Micrographic texture, in which quartz is intergrown in K-feldspar …
Granitoid Complexes. ... Granite that contains large K-feldspar grains of spherical shape, pink or reddish color is known as porphyritic granite and rapakivi (large rounded crystals of orthoclase/oligoclase feldspar) granite (Figs 4.12 and 4.13).
Granitoid bodies less affected by shearing contained myrmekites in two modes. They occurred along rims of alkali feldspar and perthite porphyroclasts, as well as along grain boundaries of K-feldspar clusters formed as a reaction rim between big plagioclase and quartz grains.
A granitoid is a coarse grained igneous rock composed mostly of quartz, K-feldspar (alkali-feldspar) and plagioclase), with 20-60% quartz on the QAPF diagram. It usually contains minor micas and/or amphiboles. Most commonly granite and granodiorite.
Alkali feldspar granite, some varieties of which are called 'red granite', is a felsic igneous rock and a type of granite rich in the mineral potassium feldspar (K-spar). It is a dense rock with a phaneritic texture. The abundance of K-spar gives the rock a predominant pink to reddish hue; peppered with minor amounts of …
The use of strontium isotopes to evaluate mineral weathering and identify sources of base cations in catchment waters requires an understanding of the behavior of Sr in the soil environment as a function of time. Our approach is to model the temporal evolution of 87Sr/86Sr of the cation exchange pool in a soil chronosequence developed on alluvium derived from central Sierra Nevada granitoids ...
May 19, 2015· Binary feldspar thermometry calculation indicates that perthites have formed at moderate to high temperature conditions in the Malanjkhand granitoid whereas low to moderate temperature conditions in Dongargarh granitoids during sub-solidus phase. Myrmekites is another feldspar intergrowth microtexture found in these granitoids.
COMPOSITIONAL VARIATIONS AND ABUNDANCES OF SELECTED ELEMENTS IN GRANITOID ROCKS AND CONSTITUENT MINERALS, CENTRAL SIERRA NEVADA BATHOLITH, CALIFORNIA By F. C. W. Dodge, H. T. Millard, Jr., and H. N. Elsheimer ABSTRACT Contents of several elements have been determined in 27 repre sentative granitoid samples from the central Sierra Nevada batho-
evidence for hypothesis (3) is that some vermicular quartz in K-feldspar may be relicts of replaced myrmekite, occurring as "ghost myrmekite." In these places the plagioclase of the myrmekite appears to have been replaced by K-feldspar or the myrmekite must have been formed earlier than the K-feldspar.
Petrography of an unknown granitoid body in the Blue Ridge of northwest Georgia Pearce, Darren, Columbus State University, Department of Earth and Space Science, Spring 2010 EASTERN BLUE RIDGE ALKALI FELDSPAR GRANITE This sample consists of approximately 25 - 30% subhedral to euhedral alkali feldspar, ranging from 0.25mm to 3mm in size.
Nd isotope geochemistry, augen granitoid, crustal growth, magmatism. Mid- to late Paleozoic K-feldspar augen granitoids of the Yukon-Tanana terrane, Yukon, Canada: Implications for crustal growth and tectonic evolution of the northern Cordillera Tyler W. Ruks † Stephen J. Piercey‡
In the Variscan Western Tatra granites hybridization phenomena such as mixing and mingling can be observed at the contact of mafic precursors of dioritic composition and more felsic granitic host rocks. The textural evidence of hybridization include: plagioclase–K-feldspar–sphene ocelli ...
The K-feldspar zoning is apparently produced by an abrupt increase in the Ba concentration of the nourishing melt, coupled in some instances by partial solution of K-feldspar. This increase is then followed by a more gradual growth of the K-feldspar during which the Ba concentration is depleted back to its previous concentration.
Abstract. At mid-crustal conditions, deformation of feldspar is mainly accommodated by a combination of fracturing, dissolution–precipitation, and reaction-weakening mecha-nisms. In particular, K-feldspar is reaction-weakened by the formation of strain-induced myrmekite – a ﬁne-grained sym-plectite of plagioclase and quartz. Here we use ...
Another present geochemistry of the K-feldspar megacryst granitoids, common texture is formed due to the deformation of K- which have been subsequently metamorphosed and deformed feldspar megacrysts and its orientation forming mylonitic to augen gneisses, in an attempt to …