Muscovite Inclusions Research Articles

Кварц-кианит-мусковитовый магматический слюдит Борисовских сопок на Южном Урале

The article describes the simulation of ontogenesis of rock mineral aggregate with debatable genesis. Lenses or stokes of weakly deformed rocks are found in the South Urals in the block of kyanite-bearing stratified rocks of the Borisovskiye Sopki, the structure of which corresponds to the structures of igneous rocks. Induced surfaces of joint simultaneous growth are observed in all minerals — muscovite, kyanite, quartz, rutile, pyrite, monazite, xenotime and zircon. This is a paragenesis (eutectics). An interesting fact is that large quartz individuals are saturated with muscovite inclusions, while kyanite, synchronous with them, is free from muscovite inclusions, which is explained by repulsion in the melt-solution of minerals with equally charged surface. The mineral aggregate of the studied rocks lacks morphological signs of metasomatism (metacrystals, pseudomorphs, shadows of previous solid bodies) and recrystallization. This indicates magmatic genesis of the studied quartz-kyanite-muscovite rocks.

Additions to the composition of the ural beryls and inclusions of syngenetic minerals in them

In addition to the data of predecessors, the chemical composition of zoned or zoned-sectorial beryl crystals from pegmatites of the Mariinsky and Kvartalny deposits of the Urals emerald mines in the Central Urals, granitic pegmatite of mine no. 242 of the Ilmeny State Reserve and Svetlinsky pegmatite quarry in the South Urals is characterized using scanning electron microscopy and energy-dispersive analysis. The light peripheral zones of prism and pinacoid in crystal sections differ in variations in Al, Fe and Mg contents from the inner zones or areas. The presence of fractures and regenerated fragments of early beryl indicates synmineralization tectonics. In beryl from the Mariinsky deposit, the previously unknown syntactic ingrowths of bavenite and zones of parallel columnar aggregates of co-crystallization of beryl and bavenite, as well as late pyrite, fuorite, gismondine-Ca and tobermorite, are identifed. Beryls from mine no. 242 of the Ilmeny State Reserve are yellowish-greenish and bluish with a peripheral white zone and syntactic microingrowths of annite and syngenetic inclusions of columbite and Ta-Nb rutile. Muddy bluish-white beryl regenerated by colorless beryl from the Svetlinsky quarry hosts numerous syntactic inclusions of muscovite, gahnite, calcite, quartz and quartz-muscovite microaggregates with pyrite, chalcopyrite, sphalerite, galena, siderite, calcite, and micropores. The syntaxy of mica, quartz and gahnite with beryl is revealed for the frst time.

Distinguishing primary and secondary inclusion assemblages in Jack Hills zircons

Detrital igneous zircons from Jack Hills, Western Australia, range in age from ~3.0 to nearly 4.4Ga and contain an inclusion assemblage dominated by quartz and muscovite, cited as evidence of their derivation from peraluminous granitoids. However, some phosphate inclusions in these zircons are known to be secondary from their post-depositional U–Pb ages and manifest mineralization along cracks. We undertook a survey of mineral inclusions in 4.3–3.0Ga Jack Hills zircons with particular emphasis on their relationship to possible alteration features (e.g., cracks, disturbed internal zonation, and visual turbidity). Mineral inclusions revealed at polished surfaces show variations in modal mineralogy, mostly corresponding to their relationship with cracks. Muscovite is common both on and away from cracks, although the chemistry of muscovite inclusions shows little relationship with other potential alteration features. Inclusions filling cracks (secondary) and inclusions isolated from cracks differ in their modal mineralogy, although both suites are rich in muscovite and quartz. The higher incidence of crack-intersecting inclusions among younger zircons may reflect effects of the (generally larger) inclusion size among younger zircons. Mismatches between the isolated and crack-intersecting populations indicate selective loss of certain phases (e.g., feldspar, apatite) and over-representation of quartz and muscovite along cracks likely due to the effects of larger inclusion size and varying degrees of overpressure following zircon cooling and decompression. Inclusions not associated with cracks in magmatically zoned versus regions with disturbed zoning have similar phase proportions. This indicates only minor inclusion replacement away from cracks (i.e., the isolated assemblage is likely primary). This holds true also for inclusions within visually turbid versus clear volumes of zircon. Phase proportions within the inclusion assemblages differ with age indicating a provenance shift toward fewer mafic phases and apatite in <3.6Ga relative to Hadean granitoid sources.

Mica Inclusions inside Host Mica Grains from the Sutlej Section of the Higher Himalayan Crystallines, India-Morphology and Constrains in Genesis

Biotite and muscovite inclusions inside mica host minerals from the Sutlej section of the Higher Himalayan Crystalline were studied under an optical microscope. These inclusions formed possibly by local recrystallization of mica grains during regional prograde metamorphism, with some affected by top-to-SW shear leading to parallelogram shapes. Recrystallization may have been assisted by solution transfer along the cleavage planes of the host grains. The relative competency of deformed phyllosilicate inclusions with the same or different composition to the host depends on the size and orientation of (001) cleavage planes of the inclusions relative to the host. Shearing of mica inclusions led to their parallelogram geometries within the contained mica inclusions. Some of the sheared inclusions deflect cleavage planes in the host minerals and define flanking microstructures. Trapezoid-shaped inclusions are a new finding that deserves more attention for their genesis. These structurally anisotropic inclusions did not originate from sub-grains, secondary infillings or retrogression. These inclusions are also not related to pseudomorphism, isomorphism, folding of the bulk rock etc. Some of the inclusions formed by recrystallization of the host mineral during top-to-SW ductile shear.

Origin of garnet in aplite and pegmatite from Khajeh Morad in northeastern Iran: A major, trace element, and oxygen isotope approach

Triassic monzogranites and granodiorites of the Khajeh Morad region in northeastern Iran are cut by two types of garnet-bearing intrusive veins: (1) aplite and (2) granitic pegmatite. The former is composed of quartz, feldspar, muscovite, with minor garnet, biotite, and ilmenite. The latter contains quartz, plagioclase (± quartz and muscovite inclusions), alkali feldspar, and muscovite, with minor amounts of garnet, tourmaline, beryl, columbite, and ilmenite. Garnet in both rock types has MnO > 12 wt.% and CaO < ~ 2 wt.% with spessartine-rich cores, and a core-to-rim increase in Fe, Mg, and Ca. Garnet cores are enriched in Y, REE, Zr, Nb, Ta, Hf, and U. The Y, HREE, and Mn concentrations show strong positive correlations in both types of garnet associations and decrease from core-to-rim. These core-to-rim elemental variations can be explained by increasing fluid content and H2O activity in magma, together with decreasing Mn contents of an evolved host melt. Aplite and pegmatite garnet δ18O values are nearly identical (~ 10.3‰, n = 7, SD = 0.09) and are similar to magmatic garnets in granitoids elsewhere. On the basis of calculated δ18O values for magma (~ 12.5 and 12.6‰) and quartz (~ 13.6‰, n = 7, SD = 0.08) as well as the major and trace element characteristics, we suggest that the Khajeh Morad garnets crystallized from a variably fractionated S-type monzogranitic magma.

Petrogenetic links between lepidolite-subtype aplite-pegmatite, aplite veins and associated granites at Segura (central Portugal)

In the Segura area, Variscan S-type granites, aplite veins and lepidolite-subtype granitic aplite-pegmatite veins intruded the Cambrian schist-metagraywacke complex. The granites are syn D3. Aplite veins also intruded the granites. Two-mica granite and muscovite granite have similar ages of 311.0±0.5Ma and 312.9±2.0Ma but are not genetically related, as indicated by their geochemical characteristics and (87Sr/86Sr)311 values. They correspond to distinct pulses of magma derived by partial melting of heterogeneous metapelitic rocks. Major and trace elements suggest fractionation trends for: (a) muscovite granite and aplite veins; (b) two-mica granite and lepidolite-subtype aplite-pegmatite veins, but with a gap in most of these trends. Least square analysis for major elements, and modeling of trace elements, indicate that the aplite veins were derived from the muscovite granite magma by fractional crystallization of quartz, plagioclase, K-feldspar and ilmenite. This is supported by the similar (87Sr/86Sr)311 and δ18O values and the behavior of P2O5 in K-feldspar and albite. The decrease in (87Sr/86Sr)311 and strong increase (1.6‰) in δ18O from two-mica granite to lepidolite-subtype aplite-pegmatite veins, and the behaviors of Ca, Mn and F of hydroxylapatite indicate that these veins are not related to the two-mica granite.The occurrence of amblygonite–montebrasite, lepidolite, cassiterite, columbite-(Fe), columbite-(Mn) and microlite suggests that lepidolite-subtype granitic aplite-pegmatite veins are highly differentiated. Montebrasite shows a heterogeneous Na distribution and secondary lacroixite was identified in some montebrasite areas enriched in Na. Unusual Mn>Fe cassiterite is zoned, with the alternating darker zones being strongly pleochroic, oscillatory zoned, and containing more Nb and Ta than the lighter zones. Inclusions of muscovite, apatite, tapiolite-(Fe), ixiolite and microlite are present both in lighter and darker zones of cassiterite. It shows exsolutions of columbite-(Fe), columbite-(Mn,Fe) and columbite-(Mn), particularly in darker zones.

Metamorphic replacement of mineral inclusions in detrital zircon from Jack Hills, Australia: Implications for the Hadean Earth

The Hadean (before 4.0 Ga) crust has long been considered to comprise mainly primitive mafic and ultramafic rocks. However, mineral inclusions in detrital zircons as old as 4.4 Ga from Jack Hills, Australia, have been interpreted to be magmatic and to provide evidence for extensive granitic crust. In situ U-Pb dating of monazite and xenotime inclusions in 4.25–3.35 Ga detrital zircons from Jack Hills shows that these inclusions are not magmatic, but formed during metamorphism at either 2.68 Ga or 0.8 Ga. Monazite-xenotime thermometry of intergrowths in the inclusions and the quartz-muscovite rock matrix constrain temperatures to between 420–475 °C, corresponding with conditions during peak regional metamorphism. Petrography and U-Pb geochronology of zircon inclusions from other localities show that the replacement of primary inclusions may commence in the igneous host rock and continue through weathering, sedimentation, and diagenesis. With increasing metamorphic grade, the inclusion assemblage increasingly reflects the composition of the rock matrix. In Jack Hills, most of the inclusions have the same composition and abundances as the metamorphic matrix, consistent with their formation during metamorphism. The titanium content of quartz inclusions indicates formation temperatures of 350–490 °C, supporting a metamorphic origin. Several lines of evidence indicate that at least some of the muscovite inclusions are also secondary. The lack of apatite inclusions in zircons from Jack Hills, relative to zircon in common granitic rocks, suggests that secondary minerals may have replaced primary apatite. Thus, detrital zircon may not be impermeable to post-depositional fluids, raising doubts about the use of the mineral inclusions they contain to infer initial magma chemistry. These results call for a reassessment of the source melts of the Hadean zircons and the composition of the earliest crust.

Origin of zircon in jadeitite from the Nishisonogi metamorphic rocks, Kyushu, Japan

On the basis of internal structures, laser ablation U–Pb ages and trace element compositions, the origin of zircon in jadeitite in the Nishisonogi metamorphic rocks was examined. The zircon comprises euhedral zoned cores overgrown by euhedral rims. The cores contain inclusions of muscovite, quartz, albite and possibly K-feldspar, yield 238U–206Pb ages of 126 ± 6 Ma (±2 SD, n = 45, MSWD = 1.0), and have Th/U ratios of 0.48–1.64. The rims contain inclusions of jadeite, yield 238U–206Pb ages of 84 ± 6 Ma (±2 SD, n = 14, MSWD = 1.1), and have Th/U ratios of <0.06. The cores are richer in Y, Th, Ti and rare earth elements (REEs), but the rims are richer in Hf and U. Chondrite-normalized REE patterns of the cores indicate higher SmN/LaN ratios, lower YbN/GdN ratios and larger positive Ce anomalies compared with those of the rims. Thus, the cores and rims have different 238U–206Pb ages and trace element compositions, suggesting two stages of zircon growth. Although the 238U–206Pb ages of the rims are consistent with the reported 40Ar/39Ar spot-fusion ages of matrix muscovite in the jadeitite, the 238U–206Pb ages of the cores are older. The mineral inclusions and high Th/U ratios in the cores are best explained by crystallization from felsic magma. Therefore, the cores are considered relicts from igneous precursor rocks. The rims surrounding the inherited cores possibly precipitated from aqueous fluids during jadeitite formation. The elevated U concentrations in the rims suggest that infiltration of external fluids was responsible for the precipitation. This study provides an example of jadeitite formation by metasomatic replacement of a protolith.

Petrology and Geochronology of Granulites from the McKaskle Hills, Eastern Amery Ice Shelf, Antarctica, and Implications for the Evolution of the Prydz Belt

A combined petrological and geochronological study was carried out on mafic granulites and associated felsic gneisses from the McKaskle Hills, eastern Amery Ice Shelf, East Antarctica. Garnet-bearing mafic granulites exhibit reaction textures and exsolution textures that indicate two-stage metamorphic evolution. Thermobarometric estimates from matrix and symplectite assemblages yield peak and retrograde P^T conditions of 9 0^9 5 kbar and 880^9508C and 6 6^7 2 kbar and 700^7508C, respectively. Similar but slightly scattered peak P^Testimates of 7 9^10 1kbar and 820^9808C are obtained from the core compositions of minerals from felsic paraand orthogneisses. Evidence for the prograde history is provided by muscovite inclusions in garnet from a paragneiss. Sensitive highresolution ion microprobe U^Pb zircon dating reveals an evolutionary history for the granulites, including a mafic and felsic igneous intrusion at 1174^1019Ma, sedimentation after 932^916Ma, and a high-grade metamorphism at 533^529Ma. In contrast, Sm^Nd mineral^whole-rock dating mainly yields a single age population at 500Ma.This suggests that the McKaskle Hills form part of the Prydz Belt, and that the relatively high peak P^Tconditions and a decompression-dominated P^T path for the rocks resulted from a single Cambrian metamorphic cycle, rather than two distinct metamorphic events as formerly inferred for the granulites from Prydz Bay.The age data also indicate that the Precambrian history of the McKaskle Hills is not only distinct from that of the early Neoproterozoic terrane in the northern Prince Charles Mountains, but also different from that of other parts of the Prydz Belt. The existence of multiple basement terranes, together with considerable crustal thickening followed by tectonic uplift and unroofing indicated by the clockwise P^T^t evolution, suggests that the Prydz Belt may represent a collisional orogen that resulted in the assembly of Gondwana during the Cambrian period.

40Ar/39Ar dating of mica-bearing pyrite from thermally overprinted Archean gold deposits

Previous studies have suggested that pyrite may armor potassium-bearing mineral inclusions from alteration-induced argon loss, thus providing improved 40Ar/39Ar age results. To test this hypothesis, matrix muscovite and pyrite crystals hosting muscovite inclusions were selected from two variably overprinted Yilgarn gold deposits (Western Australia) and analyzed by combined single crystal 40Ar/39Ar laser probe and “in vacuo” crushing methods. Pyrite grains from the ca. 2.60 Ga Mount Charlotte gold deposit exhibit evidence of minor argon loss, but give concordant high-temperature ages averaging 2594 ± 8 Ma (2σ), indistinguishable from previous age estimates. Matrix mica from the ca. 2.63 Ga Kanowna Belle gold deposit yielded a discordant age spectrum with all ages younger than 2.5 Ga, indicating substantial 40Ar* loss related to Middle Proterozoic thermal overprinting. Crushing and low-temperature heating experiments on pyrite crystals from Kanowna Belle produced anomalously old apparent ages (up to 7.0 Ga); however, in contrast to the matrix mica, total-gas pyrite ages generally approach or overlap the inferred time of gold mineralization. This behavior is attributed to diffusion of 40Ar* to internal muscovite-pyrite grain boundaries in response to the Middle Proterozoic thermal event, with limited external loss of argon. It is concluded that pyrite acts as a partially closed system for argon, but that the 40Ar/39Ar pyrite dating method has the potential to see through later thermal and/or alteration events and resolve controversial aspects of ore deposit geochronology.

Alteration of Ilmenite in the Cretaceous Sandstones of Nova Scotia, Southeastern Canada

AbstractMost detrital ilmenite grains in sandstones of the Chaswood Formation are completely altered to pseudorutile, leucoxene and rutile. The textural, chemical and mineralogical changes involved in alteration were tracked using electron microprobe analyses, backscattered electron images, and elemental maps. Ilmenite grains (Ti/(Ti+Fe) ≈ 0.48) alter patchily to pseudorutile (Ti/(Ti+Fe) 0.5–0.7) with volume loss, forming a porous structure and this process continues with the development of leucoxene (Ti/(Ti+Fe) 0.7–0.9). Within the pseudorutile and leucoxene, stubby prismatic rutile crystals have been precipitated. Si and A1 occur in the altered ilmenite, either (1) inherited from original quartz and muscovite inclusions in the parent crystal or (2) as kaolinite altered from muscovite inclusions or precipitated in the pore space, under pedogenic or early diagenetic conditions. Distribution of alteration phases has been related to facies and diagenetic variations. With increasing amounts of leaching in different types of paleosols, there was increasing alteration of pseudorutile to leucoxene. In light gray mudstones and interbedded sandstones with diagenetic kaolinite that formed beneath the water table from percolating meteoric water, most leucoxene was converted to rutile. Burial diagenesis (to vitrinite reflectance values &gt;0.4%) also promoted the change from leucoxene to rutile. The alteration of ilmenite is an important source of Fe for diagenetic minerals in the Chaswood Formation and correlative offshore deltaic and marine facies of the Scotian basin.

Smectite formation produced by weathering in a coarse granite saprolite in Galicia (NW Spain)

Weathering of a calcalkaline granite was studied in the south of Galicia (NW Spain) where the average annual precipitation is 1400 mm and the average annual temperature is 12°C. The original rock contains perthitic K-feldspars, plagioclases with inclusions of muscovite and opaque minerals, quartz and chloritized biotite, with apatite, zircon, sphene and opaques as accessories. In the saprolite the structure of the rock is preserved, the plagioclases show up to grade 4 weathering and the biotites, between 2 and 3. Weathering in quartz and potassium feldspar crystals is manifested only by fracturing. Biotite changes following the parallel linear model and its weathering products are interstratified biotite–vermiculite and iron oxyhydroxides. The plagioclases change to a microgranular material by pseudomorphic transformation. This material, which substitutes the plagioclase, includes small clearly delimited units which retain zones with the optic characteristics of muscovite. X-ray diffraction analyses of microsamples show that they are formed by 1:1 diocthaedral phyllosilicate, smectite and a small quantity of mica. From these facts we concluded that smectite is formed inside the plagioclase crystals, and probably originates from the inclusions of muscovite contained in these crystals, as it is suggested by the microscopic study which shows the increase in volume which occurs when the crystals of muscovite are transformed.

Regional thermal overprinting during mesozoic rifting recorded by sphene and zircon fission track dates, central Appalachian Piedmont, U.S.A.

Weathering of a calcalkaline granite was studied in the south of Galicia (NW Spain) where the average annual precipitation is 1400 mm and the average annual temperature is 12°C. The original rock contains perthitic K-feldspars, plagioclases with inclusions of muscovite and opaque minerals, quartz and chloritized biotite, with apatite, zircon, sphene and opaques as accessories. In the saprolite the structure of the rock is preserved, the plagioclases show up to grade 4 weathering and the biotites, between 2 and 3. Weathering in quartz and potassium feldspar crystals is manifested only by fracturing. Biotite changes following the parallel linear model and its weathering products are interstratified biotite–vermiculite and iron oxyhydroxides. The plagioclases change to a microgranular material by pseudomorphic transformation. This material, which substitutes the plagioclase, includes small clearly delimited units which retain zones with the optic characteristics of muscovite. X-ray diffraction analyses of microsamples show that they are formed by 1:1 diocthaedral phyllosilicate, smectite and a small quantity of mica. From these facts we concluded that smectite is formed inside the plagioclase crystals, and probably originates from the inclusions of muscovite contained in these crystals, as it is suggested by the microscopic study which shows the increase in volume which occurs when the crystals of muscovite are transformed.

Partial interlayers in phyllosilicates studied by transmission electron microscopy

Interstratification of complete layers has long been recognized in phyllosilicates. Interlayering on a fine scale with a host containing partial layers of a second phase has only recently been recognized by using TEM. Considering similarities in structural units of phyllosilicates this type of interlayering should be expected. Alteration samples from Butte, Montana, show extensive development of partial interlayers in kaolinite, sericite, and pyrophyllite. Kaolinite found in plagioclase sites always grows from smectite and in the growth process incorporates unit cell thick lenses of the smectite. The interlayers show up as increased spacing in 001 fringes and cause considerable strain in the surrounding kaolinite structure. Pyrophyllite studied was found to have abundant interlayers and inclusions of muscovite. This muscovite was identified from diffuse 10 A reflections and microanalysis. The muscovite inclusions are usually less than 5 layers thick and extend from 50 A to 1,000 A in the ab plane. In sericite fine interlayering is subtle for the interlayers vary only slightly in unit cell size and composition from the host; however, structural changes are significant enough to cause imagable strain contrast in the host. Zones of fine interlayers are thought to mark healed subgrain boundaries which originally were zones of compositional heterogeneity.

Shape, size, and orientation of muscovite crystals in a schist of variable metamorphic grade

Measurements of muscovite crystals from a pelitic schist unit show that with an increase in metamorphic grade from the lower to the upper amphibolite facies the crystals on average become larger, more equidimensional in shape (the ratio of length to thickness decreases) and the number per unit volume of rock decreases. In the high grade rocks all sizes of crystals, including small inclusions of muscovite within porphyroblasts of plagioclase feldspar, tend to be relatively equidimensional. The change in shape is thus not simply related to the increase in average size, and the two variables must be considered as independent. Both variables reduce the surface area of the crystals relative to the volume as the metamorphic grade increases.Contrary to previous estimates of the preferred orientations of micas, small muscovite crystals from lower grade zones are more scattered in orientation than larger crystals from higher grade zones. The scatter is mainly due to the presence in the low grade rocks of short, relatively equidimensional crystals lying at high angles to the foliation.It is suggested that the textural changes reflect processes of continuous recrystallization and growth during prograde metamorphism and the development of the schistosity. Crystals may have reached an equilibrium shape, which is temperature dependent. These changes may be driven by surface energy forces, so that the total interfacial free energy of the rock tends to be minimized for any metamorphic grade.

Mica Surface Morphology Changes During Weathering

AbstractElectron microscopic observations of mica surfaces by the carbon replica technique indicate that weathering, a major process of K release in soils, proceeds at the (hkO) fracture edges and at the crystallographic dislocations distributed on the (001) cleavage faces of mica crystals. Fresh cleavage surfaces of a paragonite with muscovite inclusions show discontinuity of the layers and marginal rolling at edges of K mica cores 3 to 5µ in diameter. A closely intergrown mosaic of the two micas is indicated rather than a true solid solution of the K,Na. Much of the interlayer Na in paragonite readily exchanges for K on treatment with 1N KCl solution and the surface assumes the smoother morphological features of K mica. Fresh cleavages of muscovite and margarite show some folding and scrolling of layers at dislocation edges. Artificial laboratory weathering of biotite to vermiculite by treatment with MgCl2 produces surface morphology similar to that of natural vermiculites. Removal of K from biotite with tetraphenylboron causes the surfaces to crack open, yielding fresh (hkO) fracture edges. Weathering with NaOH or HCl produces characteristic surface changes. Treatment of biotite with HF for one minute produces humps scattered at 0.1 to 1µ intervals over the (001) cleavage surfaces. Desilication for a longer period produces characteristic etch pits and corroded surfaces with serrated edges.These surface studies provide a new model of mica weathering at (hkO) edges formed on the (001) cleavages, and shows layer flexibility on cation exchange which greatly aids in explanation of K release and fixation in soils.