Charnockite, any member of a series of metamorphic rocks with variable chemical composition, first described from the state of Tamil Nadu in southern India and named for Job Charnock.The term is often limited to the characteristic orthopyroxene granite of the series. Detrital minerals identifi ed in thin section include plagioclase, perthite, epidote, magnetite, tourmaline, and titanite. Examine any two of rocks number 79, 81, 93, 94, or 96 in thin section. of thermally affected felsic metamorphic rock (now fine-grained hornfels) in charnockitic intruding mass. ► Microstructures can be obliterated by metamorphic recrystallisation. A set of thin section images, all at the same scale (1.5 x 1 cm) showing the range of textures to be found in metabasic eclogites from several different terranes, plus a few other associated high-pressure rock types. Melting experiments at 15, 20 and 25 kbar were performed on Archaean biotite-bearing charnockite of opx-bearing granodiorite composition, and on leucogranite. G. Skridlaite et al. ablation U -Pb ages for zircons in the charnockite. MATERIALS AND METHODS Polished thin sections were made from selected fresh surface samples taken from both Complexes. Charnockite ( /ˈtʃɑːrnəkaɪt/) is applied to any orthopyroxene-bearing quartz-feldspar rock, formed at high temperature and pressure, commonly found in granulite facies metamorphic regions, as an end-member of the charnockite series. Examine any two of rocks number 79, 81, 93, 94, or 96 in thin section. Charnockite, any member of a series of metamorphic rocks with variable chemical composition, first described from the state of Tamil Nadu in southern India and named for Job Charnock.The term is often limited to the characteristic orthopyroxene granite of the series. Thin section study of charnockite shows the presence of large euhedral orthopyroxenes developing after biotite (figure 5). Fig. Charnockite is a major phase in the southern DC, and it includes two types: the massive garnet-free (or with only rare garnet) charnockite and the gneissic garnet-bearing charnockite. Another six fresh samples (2 . Many of the minerals of these rocks are schillerized, as they contain minute platy or rod-shaped inclusions, disposed parallel to certain crystallographic planes or axes. Perthitic exsolution lamellae of albite in microcline. Comments are closed. Practice Problems AS Level Physics. ... Detrital minerals identifi ed in thin section include plagioclase, perthite, epidote, magnetite, tourmaline, and titanite. Rock (Geology) Petrology; Geology; Rocks; Nature; Documents Similar To Plutonic Metamorphism. The unusual feature of this rock is that it contains Fayalite, an iron rich olivine. Carousel Previous Carousel Next. Microphotograph of the Lz1/795 core showing thermally affected host Fig. Alex Strekeisen - I vetrini della mia fantasia. Fact sheet. To link to this object, paste this link in email, IM or document To embed this object, paste this HTML in website. the quartz is blue and opalescent, the feldspar has a milky shimmer like moonshine, the hypersthene has a bronzy metalloidal gleam. Whole-rock geochemical data (and CL imaging of thin sections) suggests that the extreme variation in K and Na and an increase in Al in the hydrothermally altered rocks can be explained by alkali exchange in feldspar or the addition of feldspar during fluid alteration (Figs. Additional images . Myrmekitic granulite/charnockite. A thin section image showing microcline grain in a coarse-grained sandstone from Estonia. It occurs as idioblastic, subidioblastic to highly irregular porphyroblastic grains (Figures 4a, 4b and 4k). The sample is a metasediment of the khondalite suite, lacking the sillimanite found in `definitive' khondalite. Actinolite - Ca 2 (Mg,Fe 2+) 5 [Si 8 O 22](OH,F) 2 Named in 1794 by Richard Kirwan from the Greek "aktina" for "ray" and "lithos" for "stone" in allusion to the fibrous nature of the original specimens. Microscope. Prior to dating, all samples were examined carefully in thin section under the petrographic microscope. It is inferred that initially the rock was a hyper-sthene-garnet-bearing charnockite with few or no hydrous phases, but a subsequent hydration event This will be handed in at the beginning of the lab 10. Orthopyroxene grains are weakly to strongly pleochroic in nature, where X =pink, Y =greenish yellow, Z =green and the absorption fonTIula is X < Y < Z. Dolomite (thin section) View Description. Prepare a labeled sketch of two thin sections, being sure to labe l the sketch with magnification and either CN or PP. 6A, 6B). The study area is located at the western boundary of the Nain Plutonic Suite and focuses on the Pearly Gates anorthosite pluton (PGA) and the adjacent composite body of mangerite and jotunite called the Tessiarsuyungoakh intrusion (TI). Charnockite series of India, although considered as igneous origin may also be included in this category as there is an ample evidence for metamorphism. Download: … Copyright © 2012 Production and hosting by Elsevier B.V. https://doi.org/10.1016/j.gsf.2012.05.004. Usually they appear to be segregated as isolated patches floating in a matrix of quartz and feldspar. Molybdenite (MoS 2) is a principal source of molybdenum.It is a sulfide mineral (molybdenum sulfide). granite gneiss, granite and charnockite were prepared for thin section study. [2], The charnockite series includes rocks of many different types, some being felsic and rich in quartz and microcline, others mafic and full of pyroxene and olivine, while there are also intermediate varieties corresponding mineralogically to norites, quartz-norites and diorites. The dark-colored garnet-free charnockite is massive and petrographically homogeneous with little gneissosity and can be represented by sample 635IN1 (Fig. However, it contains 20 to 45% K-feldspar, which is generally not twinned in thin section. Uploaded by. There have also been, of course, earth movements acting on the solid rock at a later time and injection of dikes both parallel to and across the primary foliation. Since the classical work of Sir Thomas Holland at the beginning of this century on the charnockite series in Peninsular India there have appeared numerous papers describing rocks from all over the world which have been claimed to belong to this series. ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. Charnockite microstructures: From magmatic to metamorphic. ... Myrmekitic granulite/charnockite. Microphotograph of Bilwinowo (1305 m) thin section showing position rock (hornfels), charnockite with layers of fine-grained chilled margin rock. The modal analysis of six important rocks of the study area have been studied and their chemical constituents (average) of the rocks were derived from modal analysis and C.I.P.W. 8b). Practice Problems AS Level Physics - Free download as PDF File (.pdf), Text File (.txt) or read online for free. A quartz-poor (less than 20%) member of the charnockite series, characterized by the presence of microperthite. Width of view 3 mm. 2) The intrusion and crystallization of the TI composite body at ca. Microcracks observed on the entire surface of the thin section. The relict character of hypersthene grains sug-gests some element of retrogression in the sample. A commercial variety called green ubatuba is found in Brazil.[5]. kdelfino23. Charnockite phenomena; Fluid-rock interaction in… Granulites of the Lewisian… Eclogite petrography. This will be handed in at the beginning of the lab 10. A log a H2O – T diagram shows that the charnockite domain in the thin-section (LLC-1/2) is stable at similar conditions observed for enderbitic domain if we use the LLC-1/4 (granitic) composition (Fig. The northern portion of the outcrop belt includes melange zone IV of the Mine Run complex of Pavlides (1989; 1990). Microphotograph of Bilwinowo (1305 m) thin section showing position rock (hornfels), charnockite with layers of fine-grained chilled margin rock. Although they are certainly for the most part igneous gneisses (or orthogneisses), rocks occur along with them, such as marbles, scapolite limestones, and corundum rocks, which were probably of sedimentary origin. Most experiments were conducted with oxalic acid (OA) to provide 2 wt % H 2 O and ∼3 wt % CO 2, but several fluid-absent runs with charnockite were also made. It may also contain sillimanite and graphite. 31, Issue. It is borrowed from the German word Gneis, formerly also spelled Gneiss, which is probably derived from the Middle High German noun gneist "spark" (so called because the rock glitters). In thin section, euhedral or subhedral pyroxene grains define an anastomosing spaced foliation that wraps around ellipsoidal plagioclase porphyroclasts ... ing of charnockite with enderbite, thereby leading to petrographic confusion and erroneous interpretations of charnockite formation. 1981; Naha and Srinivasan 1996;D’Cruz et al. In thin section under plane polarised light, cordierite grains are colourless to very pale blue mostly with no pleochrosim, though grain mounts in R.I. liquid (1.53) are distinctly pleochroic. Uploaded by. Charnockite occurs all over the world, most often in deeply eroded Precambrian basement rock complexes. Home Rocks and Minerals Dolomite (thin section) Reference URL Share . [3] In this rock the dark patches (up to 2 cm across) are rectangles and lozenges which mimic the crystal habit of staurolite. The relict character of hypersthene grains sug-gests some element of retrogression in the sample. Orthopyroxene grains are weakly to strongly pleochroic in nature, where X =pink, Y =greenish yellow, Z =green and Examples of how to use “petrographic” in a sentence from the Cambridge Dictionary Labs orthopyroxene-granite), but specific names are in widespread use such as norite, mangerite, enderbite, jotunite, farsundite, opdalite and charnockite (in the strict sense); equivalents of gabbro, monzonite, tonalite, monzodiorite, monzogranite, granodiorite and granite. The charnockites are widely distributed in the southern hemisphere. in thin section. This is not a granite as it does not contain much, if any, quartz. Longitudinal sections (parallel to the c axis) are roughly rectangular and show only one cleavage trace. The alkali feldspars in the group are generally perthites, with intergrowths of albite and orthoclase or microcline. In thin sections, we observed some acessary minerals in the granite, including titanite, epidote, magnetite, zircon and miner apatite. Composition. Composition. A close-up (C) shows at least two sets (arrows) of PDFs. The word metamorphism comes from ancient Greek words for … Lithic fragments include dacite tuff, gabbro, and monocrystalline quartz with zircon and biotite inclusions (Evans, 1984). Commonly found as plates or scales similar to the micas. Rock fabric is gradational from granofels to mylonite gneiss. The assemblage is connected by origin, the differentiation of the same parent magma. Norite is a gabbro containing orthopyroxene instead of the usual clinopyroxene. Includes dusky-green, mesocratic, coarse- to very-coarse-grained, equigranular to porphyritic, massive to vaguely foliated pyroxene-bearing granite to granodiorite; contains clinopyroxene and orthopyroxene, intermediate-composition plagioclase, potassium feldspar, and blue quartz. We use cookies to help provide and enhance our service and tailor content and ads. Similar to the charnockite and metagabbro, no evidence of partial melting, such as migmatization, ... Polished thin sections were prepared from all 550 samples and first examined on the petrographic microscope using both transmitted and reflected light. 2000;Chettyet al. Charnockite is the major rock which is mostly composed of Quartz, feldspar and hypersthene. Click the microscope button to view a thin section for this sample. This is a thin section of a Syenite from the Ragunda Massif in Sweden, known for it's rapakivi textured granite rocks. The monazite occurs as inclusions in biotite. It is characterized by cross-hatched (tartan) twinning in crossed polars. In thin section they are intergrowths of orthopyroxene with cordierite. Geological setting The BSZ and SASZ, with dextral sense of movement (Nair et al. We inter-pret the 926 Ma mode to represent thin section (nonthe age of the Woodbury event. It is of wide distribution and great importance in India, Ceylon, Madagascar and Africa. 2003;Jainet al. this is generally most uncommon in this type of rock. The charnockite suite or series is a particularly widespread form of granofels.Granofels are one of the few non-foliated rocks to form under relatively high temperatures and pressures. Charnockite occurs all over the world, most often in deeply eroded Precambrian basement rock complexes. Home Rocks and Minerals Dolomite (thin section) Reference URL Share . The analysis was conducted with a 15Kv accelerating voltage, 20nA beam current and a 10um beam … _____ , colorless and transparent in thin section, but frequently pale blue in the hand specimens, is the principal feldspathoid mineral in addition to nepheline. in thin section. This rock has a granular texture which suggests a secondary heating period. This combination is generated only deep in the crust by tectonic forces that operate on a grand scale, so granofels is a product of regional, rather than contact, metamorphism. Start slideshow. Charnockite is applied to any orthopyroxene-bearing quartz-feldspar rock, formed at high temperature and pressure, commonly found in granulite facies metamorphic regions, as an end-member of the charnockite series. Very often the different rock types occur in close association as one set forms bands alternating with another set, or veins traversing it, and where one facies appears the others also usually are found. Names are generally descriptive; they allow the user to searranite' as well as more specific names such as 'breccia'. variability is shown even in the scale of a thin section. ► Igneous and metamorphic charnockites can be identified by typical microstructures. While the granulite facies metamorphism is dated as 2.5 Ga (billion years ago) in Nilgiris, Shevaroys, Madras (Chennai) regions, the granulite facies event transforming the granitic gneisses into charnockite in the southern part of the South Indian granulite terrain is dated as 550 Ma (million years ago). Charnockite (Proterozoic Y) at surface, covers 10 % of this area. Orthopyroxenes are generally fresh, pleochroic from pale pink to green. Rocks of the charnockite series may be named by adding orthopyroxene to the normal igneous nomenclature (e.g. Granofels are one of the few non-foliated rocks to form under relatively high temperatures and pressures. Minerals in Thin Section _3. Charnockites sensu lato (charnockite-enderbite series) are lower crustal felsic rocks typically characterised by the presence of anhydrous minerals including orthopyroxene and garnet. Augen gneiss The word gneiss has been used in English since at least 1757. ... Minerals in Thin Section _3. In outcrop, the rock is easily confused with the brown sugar-coloured phases of the pPina1 enderbite. 3) The intrusion of anorthosite at 1355 +/- 1 Ma into the TI. Siurartuuq Suite 1 (nAsir1): Banded Charnockite. All charnockites were once thought to be igneous, but it is now recognized that many are metamorphic, because, despite the high temperatures and pressures, the original protolith never actually melted. ... Banding is produced by the presence of thin bands of ferromagnesian minerals and 10-25% of beige to pinkish 2 mm to 2 cm bands in diffuse contact with a fine-grained charnockitic matrix. [1], Charnockite (porphyritic quartz mangerite), sold as "Nara Brown Granite", quarried in southern Quebec. Download: … A thin section from the dike one milenortheast of Batchellerville shows: 60 per cent lath-shaped plagio-clase (andesine to labradorite) ; 25 per cent hypersthene (faintlypleochroic) ; 10 per cent biotite (much changed to chlorite) ; and 5per cent magnetite (much changed to leucoxene). They, or rocks very similar to them, also occur in Norway, France, Sweden, Germany, Scotland and North America, though in these countries they have been mostly described as pyroxene granulites, pyroxene gneisses, anorthosites, or other names. Solid-solution phases from the charnockite and proximal gneiss were generally unzoned, suggesting that chemical equilibrium has been established throughout the scale of the thin section. A metamorphic rock used to be some other type of rock, but it was changed inside the Earth to become a new type of rock. The paragenesis of garnet in charnockite, enderbite, and related granulites. cone The only obvious deformation is limited to planar frac-tures in quartz (Fig. Under thin section, these are shows as Gibbsite, Diaspore, Cliachite, Goethite and feldspar mineral assemblages. Charnockite often shows an unequal distribution of minerals that tend to form monomineralic centimetric clusters. 1360 Ma. / Gondwana Research 14 (2008) 663–674 667 they display triple junctions between biotite and opaques or orthopyroxene. It was named by geologist T. H. Holland in 1893 after the tombstone of Job Charnock, in St John's Church in Calcutta, India, which is made of this rock. These include representative samples from the Varberg charnockite overall (including the Varberg fortress and town, Getterön, Apelviken, and Trönningenäs charnockite bodies), the Torpa granite, charnockite inliers in the Torpa granite, and a pegmatite segregation associated with the VTCGA to the south of the Apelviken charnockite. Thin leucocratic quartz and plagioclase-bearing acid veins in these rocks may be related to a period of migmatization preceding the formation of charnockite. Here are thin section images and gigapans by Ron Schott. Chlorite #2 thin section (hFOV 2mm) GET 360° LIVE INTERACTION. Khondalite is quartz–manganese-rich garnet–rhodonite schist. The analysis was carried out in the Department of Geology and Mineral Science, University of Ilorin, Nigeria. Map . Click the microscope button to view a thin section for this sample. Monviso, Western Alps, metagabbro. The term charnockite in this sense is consequently not the name of a rock, but of an assemblage of rock types. They are typically of Proterozoic age. Extremely iron-rich olivine is rare, but is present in some nepheline syenite. The residual Bauxite directly overlies the charnockite group of rocks (Rao & P. S. 1979). Prepare a labeled sketch of two thin sections, being sure to labe l the sketch with magnification and either CN or PP. Microscope . « New weapon in my arsenal How to remove dust from macro photos » Articles. This is a Jotunite, a member of the Charnockite series of rocks. Occasionally pyroxenes show alteration to a brownish red or pale green mineral which often follows grain boundaries or cleavage planes. Copyright © 2021 Elsevier B.V. or its licensors or contributors. The monazite occurs as inclusions in biotite. By continuing you agree to the use of cookies. It is formed mostly from the granite clan of rocks, or occasionally from thoroughly reconstituted clays and shales. Molybdenite occurs in hydrothermal vein deposits and as disseminated grains in rocks which have been attacked by hydrothermal fluids (porphyry moly and copper deposits). The thin section is approximately 40 m thick. but the term khondalite is also used to describe other rocks of similar composition found elsewhere in India as well as in Burma, Sri Lanka and the Inner Mongolia region of China.. They either represent dry (H2O-poor) felsic magmas that are emplaced in the lower crust or granitic intrusions that have been dehydrated during a subsequent granulite facies metamorphic event. Click the microscope button to view a thin section for this sample. Relief: Moderate positive Habit/Form: Commonly as columnar, bladed, or acicular crystals elongate parallel to the c axis. A section of the crystal (dashed circled) has been broken and rotated. Khondalite is found in the Eastern Ghats between Vijayawada and Cuttack in India. Khondalite is found in the Eastern Ghats between Vijayawada and Cuttack in India. 4) and feldspar grains close to the upper cone surface and planar fluid inclusion trails 4. Chlorite PPL properties. The banded structure which these rocks commonly present in the field is only in a small measure due to plastic deformation, but is to a large extent original, and has been produced by flow in a viscous crystallizing intrusive magma, together with differentiation or segregation of the mass into bands of different chemical and mineralogical composition. Relief: Low-Moderate positive Habit/Form: Rare crystals are tabular parallel to (001) with a roughly hexagonal outline. Identify the major minerals, and write a concise description of the petrography of the rock. Add tags Comment Rate. For both magmatic charnockites and dehydrated granites, subsequent fluid-mineral interaction at intergrain boundaries during retrogradation are documented by microstructures including K-feldspar microveins and myrmekites. Refers to any word or phrase that appears in the individual rock names. This is a thin section of a rare and ancient rock from Norway, sent to me by a valued customer, to whom I am most grateful. [1], The charnockite suite or series is a particularly widespread form of granofels. For exam preparations Chapter 1. Mineralogical Magazine and Journal of the Mineralogical Society, Vol. Near shear the quartz grains are also seen. And where orthopyroxene is modally high, they define a crude foliation. It may also contain sillimanite and graphite. Quartzo feldspathic rocks Granulite & Leptynite Pyroxene igneous rocks for example Charnockite is believed to have acquired their distinctive character by this metamorphism. niccilo. Under crossed nicols, cordierite grains are but the term khondalite is also used to describe other rocks of similar composition found elsewhere in India as well as in Burma, Sri Lanka and the Inner Mongolia region of China.. Geological Sciences, (2013) Norite (Charnockite) Norway Thin Section Microscope Slide. They indicate that a large quantity of low-H2O activity salt-rich brines, were present (together with CO2 under immiscible conditions) in the lower crust. ► Charnockites may be affected by high-temperature metasomatism. ... selected for preparation of micro sections for mineral identification studies. Basal sections are diamond shaped and show the typical amphibole cleavage. In India they form the Nilgiri Hills, the Shevaroys, the Biligirirangan Hills[4] and part of the Western Ghats, extending southward to Kanyakumari and reappearing in Sri Lanka. In thin section (no picture) they are spinel + cordierite nodules. 238, p. 565. Charnockites sensu lato (charnockite-enderbite series) are lower crustal felsic rocks typically characterised by the presence of anhydrous minerals including orthopyroxene and garnet. Basalt Composition of the Earth's Crust Limestone Minerals Gabbro Rock types Arkose Sandstone Types of lava flows Chert What is sand made of Gneiss What is black sand Porphyry Sand types Conglomerate Oolite Olivine Igneous rocks … ... “ Notes on the staining of potash feldspar with sodium cobaltinitrite in thin section ”, Amer. A special feature, recurring in many members of the group, is the presence of a strongly pleochroic, reddish or green orthopyroxene (formerly known as hypersthene). Thin sections from each sample were first examined using the petrographic microscope. Bled structural and petrofrabric (selected thin section scale) analyses. Khondalite is quartz–manganese-rich garnet–rhodonite schist. The reflection of light from the surfaces of these inclusions gives the minerals often a peculiar appearance, e.g. Darwin wrote: “Primitive greenstone gradually passing into gneiss.” This granulite/charnockite contains orthopyroxene (hypersthene) associated with untwinned plagioclase feldspar and considerable biotite. In the vicinity of adjacent charnockite, anhedral actinolitic amphibole pseudomorphs after pyroxene or rims thoroughly uralitized relict pyroxene. The collected charnockite sample of Vadikovil Village shows different types of microstructures in thin section. Reddish-brown to black triclinic aenigmatite occurs also in these rocks. Traces of muscovite, zircon, magnetite, pyrite, chalcopyrite and pyrrhotite are also visible in polished thin section. 2. Charnockite and enderbite with all kinds of intermediate varieties have been encountered in different parts of ... variability is shown even in the scale of a thin section. The bauxite is formed by residual weathering and lateralization of Archean charnockites. The above features suggest the genesis of Cordierite gneisses are related to the Sinistral shearing of Achankovil shear event. This is a thin section of an ancient rock from Norway. Textural and pseudosection results show that orthopyroxene (in charnockite) and orthopyroxene-clinopyroxene (in enderbite) might have crystallized at a high temperature of 850–900 … It is inferred that initially the rock was a hyper-sthene-garnet-bearing charnockite with few or no hydrous phases, but a subsequent hydration event 3 a-g). 3. This combination is generated only deep in the crust by tectonic forces that operate on a grand scale, so granofels is a product of regional, rather than contact, metamorphism. Charnockite series. The oxides and sulphides may both be found on garnet crystal margins. Charnockite is the major rock which is mostly composed of Quartz, feldspar and hypersthene. Mineral chemistry was determined with JXA JEOL- 8900L electron probe micro analyzer at the Electron Microprobe Laboratory, McGill University, and Montreal, Canada. 2003; Mukhopadhyay et al. Dolomite (thin section) View Description. However, some orthopyroxene-bearing granites with distinct igneous features exist, and these rocks also fall within the definition of charnockite. For the distal gneiss (KL1.9) grossular-poor rims were detected in some garnets, suggesting a complex pre-charnockite metamorphic history, with mineral growth during decompression. From the Cambridge … Min., 37, 337. From the Cambridge English Corpus A basinal brine origin is consistent with the temperature of precipitation and petrographic evidence for emplacement under high pressure.

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