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Статті в журналах з теми "A-type charnockites"
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Kilpatrick, Jonathan A., and David J. Ellis. "C-type magmas: igneous charnockites and their extrusive equivalents." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 83, no. 1-2 (1992): 155–64. http://dx.doi.org/10.1017/s0263593300007847.
Повний текст джерелаАнотація:
ABSTRACTIgneous charnockites are characterised by distinctively high abundances of K2O, TiO2, P2O5 and LIL elements and low CaO at a given SiO2 level compared to metamorphic charnockites, and I-, S- and A-type granites. They form a distinctive type of intrusive igneous rocks, the Charnockite Magma Type (CMT or C-type), which generally lack hornblende and consist of pyroxene, alkali feldspar, plagioclase, quartz, biotite, apatite, ilmenite and titanomagnetite. Although this mineral assemblage superficially resembles that of metamorphic charnockites, magmatic charnockites are characterised by inverted pigeonite, exceptionally calcic alkali feldspar, potassic plagioclase, and coexisting opaque oxides, all with crystallisation temperatures of 950-1050°C. Apatite is a ubiquitous phase which, together with the very high concentrations of Zr and TiO2 over a wide silica range, is consistent with the derivation of the Charnockite Magma Type by very high temperature partial melting and fractionation.The credibility of intrusive charnockites as a magmatic type has historically foundered because of their apparent restriction to granulite belts and the absence of any reported extrusive equivalents. We report examples of volcanic rocks, of various ages, with the same distinctive major and trace element compositions, mineral assemblages and high temperatures of crystallisation as intrusive chamockites.The Charnockite Magma Type is considered to be derived by melting of a hornblende-free or poor, LILE-enriched fertile granulite source which had not been geochemically depleted by a previous partial melting event but which was dehydrated in an earlier metamorphism. Whereas H2O-saturated melting produces migmatites or "failed" granites, and vapour-absent melting of an amphibolite can produce I-type granites, according to this model the vapour-absent melting of a hornblende-free or hornblende-poor granulite at even higher temperatures produces charnockites.
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Bhattacharya, S., S. K. Sen, and A. Acharyya. "Structural evidence supporting a remnant origin of patchy charnockites in the Chilka Lake area, India." Geological Magazine 130, no. 3 (May 1993): 363–68. http://dx.doi.org/10.1017/s0016756800020045.
Повний текст джерелаАнотація:
AbstractDark patches of charnockitic rocks characterized by orthopyroxene occur within garnetiferous granite gneisses (leptynites) in a granulite-migmatite suite around the Chilka Lake, Orissa, within the Eastern Ghats belt in the Indian Precambrian. Analysis of structures of different scales observed in this terrain establishes the presence of three phases of deformation. S1 is pervasive in the metapelitic granulites (mainlykhondalite), while in the migmatite complex composed of leptynites, charnockites and quartzofeldspathic veins, S1 is present exclusively within the charnockite lenses and bands, and shows different stages of obliteration in the associated leptynites. Thus, the charnockite patches must be earlier than the surrounding migmatitic rocks. The charnockite patches and the surrounding leptynitic gneisses are chemically quite different and the two rock types are not related by any prograde or retrograde transformation. The shapes and disposition of charnockite patches in the mixed exposures are found to be largely controlled by the third phase of folding and locally associated shearing. The kinematics of this late deformation are not favourable for fluid ingress from deeper levels.
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QIU, XIAO-FEI, XIAO-MING ZHAO, HONG-MEI YANG, SHAN-SONG LU, TUO JIANG, and NIAN-WEN WU. "Petrogenesis of the Early Palaeozoic granitoids from the Yunkai massif, South China block: implications for a tectonic transition from compression to extension during the Caledonian orogenic event." Geological Magazine 155, no. 8 (October 2, 2017): 1776–92. http://dx.doi.org/10.1017/s0016756817000796.
Повний текст джерелаАнотація:
AbstractA comprehensive geochronological and geochemical study was carried out on the gneissic monzogranites, porphyritic granodiorites and charnockites in the Gaozhou complex of the Yunkai massif in the southern part of the South China block to better understand the Early Palaeozoic tectonic regime of the South China block. Laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) U–Pb dating of zircons indicates an age of 453.2 ± 5.1 Ma to the formation of the gneissic monzogranites, whereas the porphyritic granodiorites and charnockites were generated at 437.0 ± 1.5 Ma and 435.2 ± 2.2 Ma, respectively. The gneissic monzogranites show geochemical features consistent with the high-K, calc-alkaline rock series and are strongly peraluminous. They have SiO2contents ranging from 67.75 to 69.65 wt. % and relatively low CaO contents (1.66–1.94 wt. %). Their REE patterns are fractionated with enriched LREEs and negative Eu anomalies. The samples also show enrichment in LILEs (e.g. Rb and K) and Pb, and depletion in Sr, Ba and HFSEs (e.g. Nb, Ta, Ti and P). They haveεNd(t) values of −8.2 to −7.7. Conversely, the porphyritic granodiorites and charnockites are characterized as medium-K, calc-alkaline rock series and weakly to strongly peraluminous. They exhibit pronounced depletions in HFSEs and positive Pb anomalies. Compared to the earlier gneissic monzogranites, these rocks have relatively lower SiO2(65.50–69.36 wt. %), but higher CaO contents (3.34–4.05 wt. %), and have slightly lowerεNd(t) values (−9.1 to −8.4). Petrography and geochemical compositions of the gneissic monzogranites indicate that they are S-type granite and likely formed by partial melting of Neoproterozoic to Early Palaeozoic immature metagreywackes; whereas The porphyritic granodiorites and charnockites are A-type granite and likely derived from low degrees of partial melting of the dry, granulitic residue depleted by prior extraction of granitic melt. The new data for the Caledonian granitoids in the Yunkai massif suggest that they were formed in a post-collisional tectonic setting. They represent the earliest post-collisional alkaline magmatism reported so far in the Yunkai massif, and thus indicate a tectonic regime switch, from compression to extension, as early as the Late Ordovician to Early Silurian (~450–435 Ma).
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Whitney, Philip R. "Charnockites and granites of the western Adirondacks, New York, USA: a differentiated A-type suite." Precambrian Research 57, no. 1-2 (June 1992): 1–19. http://dx.doi.org/10.1016/0301-9268(92)90092-3.
Повний текст джерела
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Sajna, S., J. K. Tomson, J. Amal Dev, Nilanjana Sorcar, and T. Vijaya Kumar. "Neoproterozoic Mafic Magmatism in Nagercoil Block, Southern India and Its Implications on the Gondwana Collisional Orogeny." Minerals 12, no. 12 (November 26, 2022): 1509. http://dx.doi.org/10.3390/min12121509.
Повний текст джерелаАнотація:
The Nagercoil block situated at the southernmost tip of India occupies a key position in the East Gondwana collisional tectonic models. The Nagercoil block is dominated by Orosirian I-type charnockite massifs that host numerous gabbroic emplacements. Our present understanding about the crustal architecture of the Nagercoil block is derived mostly from these charnockites, while detailed studies on gabbros are lacking. We present new petrology, geochemistry, and zircon U-Pb/Hf isotopic data of gabbros from the Nagercoil block to understand their petrogenesis and tectonic significance. The results reveal that these are formed by the partial melting of a subduction-modified lithospheric mantle source in a continental arc setting. Zircon U-Pb geochronology results reveal that the gabbros were emplaced between 561 and 531 Ma. Hafnium isotopic studies on zircons argue for a mid-Mesoproterozoic melting source with near-juvenile magmatic signatures. The Hf-TDM ages together with the available data from the terrane point to the involvement of the adjacent Achankovil unit as a possible melting source contributor. The genetic link between the Achankovil unit and Sri Lanka together with the remarkable similarity in ages and isotopic characteristics of mafic rocks from both these terranes point to their coeval formation during the East African Orogeny associated with the final stages of the Gondwana supercontinent assembly.
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Olabode, Oluwaseun Franklin, and Yinusa Ayodele Asiwaju-Bello. "Insights from the Engineering Geological Mapping of Four Basement Rocks Derived Soils." Sustainable Geoscience and Geotourism 2 (November 2018): 16–34. http://dx.doi.org/10.18052/www.scipress.com/sgg.2.16.
Повний текст джерелаАнотація:
Due to the rapid expansion and associated construction of civil engineering structures on the Federal University of Technology, Akure (FUTA) campus, there arose an urgent need for an engineering geological mapping of the underlying soils (residual soils). Generalized geological mapping revealed four types of basement rocks namely migmatite-gneisses, granites, quartzites and charnockites. Results from the fifty (50) soil samples from twenty-five test pits collected all over the spread of the campus coverage of 6.4 km2revealed that the campus is underlain by soils of granular and clayey composition, generally lateritic, having reddish to brownish colour. Engineering geological tests such as natural moisture content, particle size analysis, consistency limits, California bearing ratio and consolidation were carried out on the soils following standard procedures revealed that the values of natural moisture content do not generally follow a consistent pattern and varied from location to location. The grain size characteristics curve, displayed 84% and 16% subsoils are of well graded and poorly graded type respectively. The soils were grouped into CL (low plasticity), CI (medium plasticity) and CH (high plasticity) from consistency limits results. Compaction characteristics of the subsoils revealed 36% and 64% representative of fair to good and poor to very poor foundation materials respectively. Soils with settlement rates greater than 1mm/year were designated as high settlement subsoils. 72% and 28% of the subsoils fell into hard to stiff and soft categories from the shear strength characteristics respectively, and classified as c-ø soils. California Bearing Ratios values range from 10 – 70, indicating their suitability for pavement construction. Conclusively, areas underlain by migmatite-gneiss and charnockite-derived soils, and granite and quartzite-derived soils possessed low and high strength characteristics respectively which can be attributed to their textural characteristics. The subsoils of the entire campus spread are however capable of bearing very substantial loads.
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Duchesne, J. C., and E. Wilmart. "Igneous Charnockites and Related Rocks from the Bjerkreim-Sokndal Layered Intrusion (Southwest Norway): a Jotunite (Hypersthene Monzodiorite)-Derived A-type Granitoid Suite." Journal of Petrology 38, no. 3 (March 1, 1997): 337–69. http://dx.doi.org/10.1093/petroj/38.3.337.
Повний текст джерела
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Karniol, Tiago R., Rômulo Machado, and Nolan M. Dehler. "Transpressive dextral shear in the Italva-Itaperuna section, Northern State of Rio de Janeiro, Brazil." Anais da Academia Brasileira de Ciências 80, no. 3 (September 2008): 565–77. http://dx.doi.org/10.1590/s0001-37652008000300016.
Повний текст джерелаАнотація:
Structural analysis carried out on a segment of the Neoproterozoic Ribeira Belt, southeastern Brazil, show that it represents part of the transpressive dextral orogen related to the Central Mantiqueira Province. NNE-trending and steeply dipping regional mylonitic belts form anastomosed geometry, and describe a map-scale, S-C-like structure that is characterized by their deflection towards NE near the Além Paraíba Lineament. Lithological and structural control related to deformation partition were responsible for the formation of felsic mylonitic granulites with S-type granites lenses developed in ductile shear zones, alternated with less deformed intermediate to basic granulites associated with charnockites. The dextral shear sense indicators are consistent with transpressive deformation in the region and are common especially at the border of the main shear zones. The presence of S-type leucogranite may lead to variations of linear and planar relationships, which result in local extension zones. These elements are consistent with oblique continental collision considering the São Francisco Craton as a stable block.
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Ayodele, Olusiji Samuel. "Geochemical Exploration for Heavy Metals in the Stream Sediments of Okemesi-Ijero Area." Journal of Advance Research in Applied Science (ISSN: 2208-2352) 3, no. 4 (April 30, 2018): 01–29. http://dx.doi.org/10.53555/nnas.v3i4.648.
Повний текст джерелаАнотація:
The bedrocks and gold mineralization have been widely studied especially, in the southern extension of the Ilesha schist belt, but information regarding stream sediments in the area is rarely available in literature. The present study therefore, focused on stream sediments geochemical survey of Okemesi/Ijero axis within the northern extension of Ilesha schist belt using an integrated approach to elucidate the heavy metals potentials and its possible controlling environmental geological conditions. Detailed geological survey involved lithological and structural assessment of the bedrocks. Thirty-five (35) stream sediment samples were collected at a depth of 20-25cm. Major oxides of the stream sediments for major elements were determined using atomic emission spectroscopy (AES). Trace and rare earth elemental analysis was done using inductively coupled plasma mass spectrometry (ICP-MS). Data evaluation was carried out using statistical packages for software simulation. Results showed that bedrock types are quartzbiotite-schists, banded-gneiss, granite-gneiss, biotite-gneiss, calc-gneiss, porphyritic granites, charnockites, massive and schistose quartzites, mica-schists. Structural assessment of the bedrocks revealed folds, fractures and veins as products of Precambrian deformations. Sediments have relatively high concentration of heavy metals such as Mn (387-200ppm), Zn(76.5- 18.52ppm), Pb(39.81-20.23ppm), La 36.2-15.5ppm), Cu(12.68-13.65ppm). However, the folds, fractures and veins provided the groundwork for epigenetic type of mineralization in the studied area.
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Okon, Emmanuel E., Ebenezer A. Kudamnya, Kehinde D. Oyeyemi, Benjamin O. Omang, Omotayo Ojo, and Mohamed Metwaly. "Field Observations and Geophysical Research Applied to the Detection of Manganese (Mn) Deposits in the Eastern Part of Oban Massif, South-Eastern Nigeria: An Integrated Approach." Minerals 12, no. 10 (September 30, 2022): 1250. http://dx.doi.org/10.3390/min12101250.
Повний текст джерелаАнотація:
The growing need for an industrialized world, especially in Africa, cannot be feasible without adequate mineral resources. Thus, the search for more mineral deposits will continue to be necessary. An integrated approach involving geological mapping and a high-resolution geophysical (aeromagnetic) investigation was conducted to assess the manganese mineralization in parts of the Oban Massif, southeast Nigeria. The aeromagnetic data were processed using regional-residual anomaly separation techniques, first vertical derivative (1VD), analytical signals, source parameters imaging (SPI), and Euler deconvolution to better understand magnetic source distributions and their depths of occurrence. The geological investigation revealed a dominant variety of metamorphic rock types, including migmatitic (banded) gneisses hornblende granite gneisses, amphibolites, charnockites, and some quartzite ridges. Also present are some indications of pockets of dolerites. The study area also observed epithermal Mn+Fe+Qtz vein type mineralization associated with hydrothermal alteration zones whose orientation coincides with dominant structural orientation from aeromagnetic interpretation. Analysis of aeromagnetic data shows that the study area is dominated by ENE, NNE, and E-W structural directions (near-surface basement structures), with the ENE trends related to mineralization in the area. The manganese mineralization within Oban Massif is structurally controlled. The depths of the magnetic anomalies in the study area were estimated using SPI and Euler decomposition algorithms. SPI delineated the shallow, intermediate, and deep magnetic anomalies at 84–142 m, 152–200 m, and 215–656 m, respectively. Euler decomposition, however, revealed that shallow, intermediate, and deep depths occurrence of the magnetic anomalies are at 200–377 m, 393–472 m, and 499–793 m, respectively.
Дисертації з теми "A-type charnockites"
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Rowe, S. E. "Mechanism of formation and age of the Ayyarmalai A-type charnockite – granite association from the south-eastern Palghat- Cauvery Shear System, southern India." Thesis, 2010. http://hdl.handle.net/2440/104030.
Повний текст джерелаАнотація:
This item is only available electronically.The Ayyarmalai A-type charnockite and A-type alkali granite lies on the south-eastern margin of the Palghat-Cauvery Shear System and provides an example of co-magmatism that was later overprinted with granulite facies metamorphism at ~2.45-2.5Ga. The Palghat-Cauvery Shear System represents an intriguing zone with Neoproterozoic aged granulites (~800-500 Ma) to the south and Archaean granulites (~3000-2500 Ma) to the north; the origins of which are still often disputed. This study presents whole rock major and trace element compositions, mineral chemistry, pressure-temperature estimates and whole rock Sm-Nd, Rb-Sr, Pb-Pb and δ18O isotopic compositions of this A-type charnockite-granite association found at Ayyarmalai, Tamil Nadu, Southern India. The subsequent data from this study suggests that: (1) the Ayyarmalai charnockites from the Palghat-Cauvery Shear System have zircon ages that are synchronous with events in the Northern Granulite Terrain; (2) The Dharwar Craton is a strong candidate for the protolith of these rocks; (3) Evidence of a Neoproterozoic-Cambrian granulite metamorphic event (~520 Ma) appears to be absent in these rocks questioning the existence or location of a Neoproterozoic - Cambrian suture zone proposed for the Palghat-Cauvery Shear System recently. U-Pb zircon ages show zoned igneous cores ~2.65-2.68 Ga ages in both rock types defining the crystallisation age, while the large metamorphic rim overgrowths date the Archaean granulite metamorphic event at ~2.45 - 2.5 Ga. Geochemical data of the Ayyarmalai charnockites reveal a very primitive, unfractionated REE pattern with no Eu-anomaly, ferroan, high K-calc-alkaline, with moderate enrichment of LREE with respect to HREE and fall within the field of high Ba-Sr type granitoids. Extraction of Pyroxene- Hornblende rich cumulates resulted in an intermediate charnockites driving the crystallisation towards the final A-type alkali granite. The A-type alkali granites show a more fractionated REE pattern with a significant Eu-anomaly, ferroan, high-K- calc-alkaline, with enrichment of LREE and depletion in the low Ba-Sr type granitoids. εNd and Nd model ages indicate a highly evolved protolith (εNd(0) =-25.15 to -33.14) that encountered a crustal Archaean source (2.89-3.09 Ga) causing contamination as the magmas ascended. Harker diagrams, Nd data (isochron age, ~2519 Ma) and U-Pb zircon crystallisation ages suggest a co-magmatic relationship between the charnockite and alkali granite. Conventional geothermometry/barometry suggest minimum pressure-temperature conditions existed at 740 – 750°C and P=5.61 – 5.84 kbar. The data presented from this study is consistent with a magmatic origin of these charnockites favouring the early crystallisation of orthopyroxene. The correlation with the data from the Dharwar Craton suggest that the study region may have encountered Dharwar Craton on magmatic ascent causing crustal contamination
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2010
Частини книг з теми "A-type charnockites"
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Indares, Aphrodite, Abdelali Moukhsil, and Pierre-Arthur Groulier. "Geon 14 to early Geon 13 granitoid magmatism in the Grenville Province of Canada, northeastern Laurentia: Distribution, geochemical patterns, and links with an active-margin setting." In Laurentia: Turning Points in the Evolution of a Continent. Geological Society of America, 2022. http://dx.doi.org/10.1130/2022.1220(17).
Повний текст джерелаАнотація:
ABSTRACT Mesoproterozoic crust is widely exposed in the Grenville Province portion of northeastern Laurentia, where it is interpreted as an assemblage of two continental-arc segments separated by a composite arc belt (Quebecia) with island-arc remnants. A synthesis of the geologic context, types, and geochemical patterns of 1.5–1.35 Ga granitoids reveals a regional distribution in each segment, with dioritic to granitic plutonism variably associated with arc-related volcano-sedimentary belts in the south and inboard monzonitic to granitic plutonism in the north. In addition, belts of dioritic to granitic orthogneisses occupy intermediate positions in Quebecia and in the west. The inboard granites are consistently old in all segments (1.5–1.45 Ga), but the preserved volcano-sedimentary belts are older in the east and in Quebecia (1.5–1.45 Ga) and younger in the west (1.39? and 1.36 Ga), while the belts of orthogneisses show a large spread of ages at 1.45–1.37 Ga. Granitoids in the volcano-sedimentary belts and the orthogneisses include magnesian, calcic to calc-alkalic components to ferroan, alkali-calcic components. In contrast, the inboard plutons are dominantly ferroan and alkali-calcic to alkalic in the continental-arc segments, where they are locally associated with anorthosite-mangerite-charnockite-granite (AMCG) suites. Collectively, the different types of granitoid magmatism can be linked to an active margin, with subduction under northeastern Laurentia, involving arc building, arc rifting, back-arc opening and inboard extension, and amalgamation processes variably operating at different parts of the margin and at different times. In addition, the data provide a basis for comparison with other parts of the eastern to southwestern Laurentian margin in the 1.5–1.35 Ga time frame.