Articles de revues : « Ultramafic rock »

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Jahidin, LO Ngkoimani, LM Iradat Salihin, Hasria, Erzam S. Hasan, Irfan Ido et Suryawan Asfar. « Analysis of Ultramafic Rocks Weathering Level in Konawe Regency, Southeast Sulawesi, Indonesia Using the Magnetic Susceptibility Parameter ». Journal of Geoscience, Engineering, Environment, and Technology 5, n^o 2 (24 juin 2020) : 73–81. http://dx.doi.org/10.25299/jgeet.2020.5.2.4247.

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The Konawe region is part of the Sulawesi Southeast Arm ophiolite belt where ultramafic rocks are exposed in the form of dunite and peridotite. The formation of nickel deposits is closely related to the weathering process of ultramafic rocks as a source rock. Ultramafic rocks exposed to the surface will experience weathering which is influenced by many factors, including in the form of climate change, topography, and existing geological structures. The weathering process in the source rock can influence variations in chemical elements and magnetic properties in laterite soil profiles. For example, the chemical weathering might affect magnetic mineralogy and the physical weathering could affect granulometry as well as the quantity of magnetic minerals in the soil. Condition of weathering of ultramafic rocks (initial, moderate and advanced) can affect nickel content in laterite sediments. The weathering profile study of serpentine mineral is an indication of the lateralization process that occurs in ultramafic rocks and is carried out through petrographic analysis of thin cuts and polish cuts. Determination of weathering level like this is based on the level of weathering of the mineral serpentine. In this study, the determination of the weathering level of ultramafic rocks (initial, moderate, and continued) uses magnetic susceptibility parameter. A total of 232 ultramafic rock core samples obtained from 34 hand samples were taken from different places and weathered levels were analyzed. The results of the research have shown that the magnetic susceptibility of ultramafic rocks in the study area varies, from 580 x 10-6 SI to 4.724 x 10-6 SI. Based on the value of magnetic susceptibility, magnetic minerals contained in ultramafic rock samples are hematite and geotite minerals. This means that the weathering level of ultramafic rock samples is the continued weathering level. The level of continued weathering that occurs in ultramafic rocks in the study area produces nickel laterite deposits with a nickel content of 1.65 - 2.40% in the saprolite zone, 0.42% in the saprock zone, and 0.20 - 0.51% in the basic rock zone (bedrock).

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Guice, George L., Michael R. Ackerson, Robert M. Holder, Freya R. George, Joseph F. Browning-Hanson, Jerry L. Burgess, Dionysis I. Foustoukos, Naomi A. Becker, Wendy R. Nelson et Daniel R. Viete. « Suprasubduction zone ophiolite fragments in the central Appalachian orogen : Evidence for mantle and Moho in the Baltimore Mafic Complex (Maryland, USA) ». Geosphere 17, n^o 2 (5 février 2021) : 561–81. http://dx.doi.org/10.1130/ges02289.1.

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Abstract Suprasubduction zone (SSZ) ophiolites of the northern Appalachians (eastern North America) have provided key constraints on the fundamental tectonic processes responsible for the evolution of the Appalachian orogen. The central and southern Appalachians, which extend from southern New York to Alabama (USA), also contain numerous ultramafic-mafic bodies that have been interpreted as ophiolite fragments; however, this interpretation is a matter of debate, with the origin(s) of such occurrences also attributed to layered intrusions. These disparate proposed origins, alongside the range of possible magmatic affinities, have varied potential implications for the magmatic and tectonic evolution of the central and southern Appalachian orogen and its relationship with the northern Appalachian orogen. We present the results of field observations, petrography, bulk-rock geochemistry, and spinel mineral chemistry for ultramafic portions of the Baltimore Mafic Complex, which refers to a series of ultramafic-mafic bodies that are discontinuously exposed in Maryland and southern Pennsylvania (USA). Our data indicate that the Baltimore Mafic Complex comprises SSZ ophiolite fragments. The Soldiers Delight Ultramafite displays geochemical characteristics—including highly depleted bulk-rock trace element patterns and high Cr# of spinel—characteristic of subduction-related mantle peridotites and serpentinites. The Hollofield Ultramafite likely represents the “layered ultramafics” that form the Moho. Interpretation of the Baltimore Mafic Complex as an Iapetus Ocean–derived SSZ ophiolite in the central Appalachian orogen raises the possibility that a broadly coeval suite of ophiolites is preserved along thousands of kilometers of orogenic strike.

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Hasria, Erzam S. Hasan, Deniyatno, L. M. Iradat Salihin et Asdiwan. « Characteristics of Ultramafic Igneous Rock Ofiolite Complex in Asera District, North Konawe Regency Southeast Sulawesi Province ». Journal of Geoscience, Engineering, Environment, and Technology 5, n^o 3 (18 août 2020) : 121–26. http://dx.doi.org/10.25299/jgeet.2020.5.3.4113.

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The research area is located in Asera District, North Konawe Regency, Southeast Sulawesi Province which has ultramafic rock lithology. The purpose of this study is to determine the characteristics of ultramafic igneous rocks using petrographic and geochemical analysis. Petrographic analysis aims to determine the types and abundance of minerals present so that rock types can be determined based on the classification of Travis (1955) and Streckeisen (1976). The geochemical analysis aims to determine the oxide/major element so that it can determine the type of magma based on the AFM classification according to Irvine and Baragar (1971) and the origin of the magma / original rock formation environment based on Pearce (1977). Petrographic analysis results showed that ultramafic rocks in the study area consisted of 2 types of rocks namely peridotite consisting of wherlit and lherzoite and serpentinite. The results of geochemical analysis indicate that the type of magma in the study area is thoellitic series and the origin of the magma/rock formation environment comes from the expansion of the oceanic floor or mid oceanig ridge (MOR) which is ultramafic.

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Edgar, A. D., L. A. Pizzolato et G. M. Butler. « Petrology of the ultramafic lamprophyre and associated rocks at Coral Rapids, Abitibi River, Ontario ». Canadian Journal of Earth Sciences 31, n^o 8 (1 août 1994) : 1325–34. http://dx.doi.org/10.1139/e94-115.

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An ultramafic lamprophyre sill and dikes, and an olivine–melilite-rich dike rock intrude Lower to Middle Devonian sediments and low- to high-grade Archean metamorphic rocks on the west bank of the Abitibi River, Coral Rapids, Ontario. Although previously considered to be kimberlitic, all these rocks contain olivine + clinopyroxene + phlogopite ± melilite, and hence are ultramafic alkaline rocks. The ultramafic lamprophyre can be distinguished from the dike by its lower SiO2, Na2O, Al2O3, and higher MgO and FeO. In contrast the olivine–melilite dike rock has a more uniform composition, characteristically contains melilite, and has higher Cr and Ni contents. Enriched light rare earth element (LREE) chondrite-normalized patterns are similar for all rocks.Olivine, clinopyroxene, and phlogopite have Mg# (Mg# = 100 Mg/(Mg + Fe) mol) typical of minerals in primitive alkaline rocks. Melilite composition is similar to that of igneous melilites. Phlogopites in all rock types are enriched in Ba and F and the degree of enrichment is distinct for each rock type. Accessory minerals include apatite, carbonates, chlorite, sericite, and sodalite (only in the olivine–melilite-bearing rock).The mineralogy and chemistry of the Coral Rapids rocks suggest that they are derived from a primitive olivine melilitite magma that may have evolved by fractionation of small amounts of olivine and clinopyroxene to form these alkaline ultramafic magmas.Xenoliths in the ultramafic lamprophyre sill and in lesser abundance in the olivine–melilite dike rock include olivine, phlogopite, and clinopyroxene-rich mantle-derived assemblages. The similarity between these xenoliths and their host rocks at Coral Rapids and those from southwest Uganda and West Eifel, Germany, suggests that the Coral Rapids rocks may be derived from magmas that originated from metasomatized mantle sources.

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ZINCHUK, NIKOLAY. « Specific features of petrographic study of kimberlite ». Domestic geology, n^o 6 (10 janvier 2023) : 34–49. http://dx.doi.org/10.47765/0869-7175-2022-10033.

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Based on the analysis of specific actual and analytical material capabilities and perspectives of petrographic and petrological investigations of kimberlite rocks are indicated. Kimberlite is a volcanic igneous rock, undersaturated by silica, enriched in volatiles of peralkaline ultramafic hybrid formations, containing mantle and crust material in varying quantities and ratios. Mantle material in kimberlite is represented by xenoliths of ultramafic, alkali-rich mafic-ultramafic rocks and xeno-minerals from them.

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Hasria, Febiyanti, Masri, Ali Okto, Erzam S. Hasan, La Hamimu, Sawaludin, La Ode Muhammad Iradat Salihin et Wahab. « Serpentinization Study On Ultramafic Rock at Morombo Area, Lasolo Islands District, North Konawe Regency, Southeast Sulawesi, Indonesia ». Journal of Geoscience, Engineering, Environment, and Technology 7, n^o 1 (30 mars 2022) : 15–20. http://dx.doi.org/10.25299/jgeet.2022.7.1.6643.

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The research is in Morombo area, North Konawe Regency, Southeast Sulawesi. The purpose of this study was to determine the characteristics of serpentinized ultramafic rock and serpentine paragenesis. Research was conducted using field observations and laboratory analysis consisting of petrographic and geochemical analysis in the form of X-Ray Fluorosence (XRF). Petrographic analysis was carried out to identify the mineral content and textures in the rock and to determine the percentage of serpentine mineral presence. Both of these rocks are petrographically dominated by primary minerals olivine and clinopyroxine and secondary minerals namely lizardite, chrysotile, antiorite and opaque minerals. The XRF analysis was to determine the elements of Ni, Fe, Co, MgO, SiO2, CaO, Al2O3 and P in ultramafic rocks. The results of petrographic analysis show that serpentinized ultramafic rocks in the study area consist of serpentinized dunite and serpentinized peridotite. The formation of clay minerals in rocks does not occur because of the low serpentinization process in the rock. The results of XRF analysis showed that all samples in the bedrock showed Ni content above 0.2%. This is caused by the enrichment of Ni which is interpreted as a result of the serpentinization process along with the formation of lizardite in the rock. The serpentinization sub-processes in the study area comprised by hydration, serpentine recrystallization, and deserpentinization. Serpentine paragenesis is formed from the mid-oceanic ridge ocean floor, the orogenic phase to weathering. Substitution of Mg by Ni in ultramafic rocks will produce Ni-Serpentin. It is estimated that in the research area lizardite and chrysotile lizardite and chrysotile are the causes of Ni enrichment in bedrocks. The serpentinization characteristics of ultramafic rocks in the study area show a low to moderate level of serpentinization.

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Erskine, Bradley G. « Geologic Investigations for Compliance with the CARB Asbestos ATCM ». Environmental and Engineering Geoscience 26, n^o 1 (20 février 2020) : 99–106. http://dx.doi.org/10.2113/eeg-2290.

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ABSTRACT The California Air Resources Board Airborne Toxic Control Measure for Construction, Grading, Quarrying, and Surface Mining Operations (ATCM) provides requirements for the evaluation for naturally occurring asbestos (NOA) on a construction site. There are two compliance triggers: (1) a determination that the site is located within a geographic ultramafic rock unit, defined as a geographic area designated as an ultramafic rock on referenced maps, and (2) the presence of NOA, serpentinite, or ultramafic rock. The California Geological Survey requires that NOA evaluations be conducted by a licensed professional geologist. However, under the ATCM, a professional geologist is required only when a property owner wishes to demonstrate that a geographic ultramafic rock unit is not actually represented by ultramafic rocks. The professional geologist who must advise whether the ATCM applies at a construction site is therefore placed in a precarious position. Does a limited desktop review of geologic maps meet any standard of practice? If the ATCM is triggered by the presence of asbestos, is the geologist negligent if no evaluation is recommended or conducted? Could geologic units be pre-screened for asbestos potential? Using case studies and geologic data in the city of San Francisco and East Bay, this presentation reviews these issues and provides a context for the geologist to conduct the appropriate level of investigation for compliance with the ATCM.

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RAJAKARUNA, Nishanta, Kerry KNUDSEN, Alan M. FRYDAY, Ryan E. O'DELL, Nathaniel POPE, Fred C. OLDAY et Suzie WOOLHOUSE. « Investigation of the importance of rock chemistry for saxicolous lichen communities of the New Idria serpentinite mass, San Benito County, California, USA ». Lichenologist 44, n^o 5 (24 août 2012) : 695–714. http://dx.doi.org/10.1017/s0024282912000205.

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AbstractAlthough several lichen inventories exist for European ultramafic sites, only four surveys of serpentine lichens for North America have been published to date. Of those, only one has been conducted in California. We conducted a survey of saxicolous lichens from ultramafic rocks (including nephrite, partially serpentinized peridotite, and serpentinite) and non-ultramafic rocks (including silica-carbonate, shale, and sandstone) at the New Idria serpentinite mass, San Benito County, California. X-ray Fluorescence Analysis of the rocks from which the lichens were collected revealed significant elemental differences between the ultramafic and non-ultramafic rocks for 26 of the 32 major and trace elements analyzed. We identified a total of 119 species of lichenized and lichenicolous fungi; 60 species were restricted to ultramafic substrata, 19 to silica-carbonate, and 15 to shale and sandstone. Only 4 species were shared in common. A permutational multivariate analysis of variance (perMANOVA) test revealed significant differences in lichen assemblages between ultramafic and non-ultramafic rocks at the species level but not at the generic level, with species richness (alpha-diversity) significantly greater at the ultramafic sites. We suggest that, although differences in geochemistry clearly influence the lichen community composition, other factors, especially substratum age and the physical characteristics of the rock, are of equal, if not greater, importance. Of all the species collected, six, Buellia aethalea, B. ocellata, Caloplaca oblongula, Rhizocarpon saurinum, Thelocarpon laureri, and Trapelia obtegens, are reported new to California, along with an apparently previously undescribed Solenopsora sp. The rest of the species encountered are relatively frequent in the lichen flora of southern and central California, except Aspicilia praecrenata, a rare California endemic that we collected on both ultramafic and non-ultramafic rocks.

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Martins, Vanessa, Douglas Ramos Guelfi Silva, Giuliano Marchi, Maurício Cunha Almeida Leite, Éder de Souza Martins, Ana Stella Freire Gonçalves et Luiz Roberto Guimarães Guilherme. « EFFECT OF ALTERNATIVE MULTINUTRIENT SOURCES ON SOIL CHEMICAL PROPERTIES ». Revista Brasileira de Ciência do Solo 39, n^o 1 (février 2015) : 194–204. http://dx.doi.org/10.1590/01000683rbcs20150587.

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The current high price of potassium chloride and the dependence of Brazil on imported materials to supply the domestic demand call for studies evaluating the efficiency of alternative sources of nutrients. The aim of this work was to evaluate the effect of silicate rock powder and a manganese mining by-product, and secondary materials originated from these two materials, on soil chemical properties and on brachiaria production. This greenhouse experiment was conducted in pots with 5 kg of soil (Latossolo Vermelho-Amarelo distrófico - Oxisol). The alternative nutrient sources were: verdete, verdete treated with NH4OH, phonolite, ultramafic rock, mining waste and the proportion of 75 % of these K fertilizers and 25 % lime. Mixtures containing 25 % of lime were heated at 800 ºC for 1 h. These sources were applied at rates of 0, 150, 300, 450 and 600 kg ha-1 K2O, and incubated for 45 days. The mixtures of heated silicate rocks with lime promoted higher increases in soil pH in decreasing order: ultramafic rock>verdete>phonolite>mining waste. Applying the mining waste-lime mixture increased soil exchangeable K, and available P when ultramafic rock was incorporated. When ultramafic rock was applied, the release of Ca2+ increased significantly. Mining subproduct released the highest amount of Zn2+ and Mn2+ to the soil. The application of alternative sources of K, with variable chemical composition, altered the nutrient availability and soil chemical properties, improving mainly plant development and K plant uptake, and are important nutrient sources.

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Σερέλης, Κ., Ε. Γκάρτζος et Π. Τσαουσίδου. « STUDY OF THE WALL ROCK ALTERATION OCCURRING IN ULTRAM A F I C ROCKS HOSTING MAGNESITE DEPOSITS, EVIA, GREECE »,. Bulletin of the Geological Society of Greece 36, n^o 1 (1 janvier 2004) : 377. http://dx.doi.org/10.12681/bgsg.16688.

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Three different kinds of alteration processes occur in the studied ultramafic host rocks of the magnesite deposits of N. Evia. In chronological order: Pre-magnesite event (serpentinization), syngenetic brown alteration and weathering. This paper concerns the syngenetic wall rock alteration of the ultramafic host rocks. Two types of wall rock alteration were distinguished. The first one named type (B-i) concerns cases of brown alteration accompanying thin to medium size veins of magnesite. Alteration is restricted in thin (a few cm to 20 cm) vein-parallel bands occurring on both sides of the vein. Alteration increases gradually towards the edges of the vein. The altered band consists mainly of abundant dolomite and/or quartz. The second type (B2) concerns argillic alteration of large ultramafic masses in areas with intense magnesite mineralization and can be observed along the walls of the open pit mines. Secondary vermiculite has been formed in this case. Both types are related to the genesis of the magnesite deposits

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Emmanuel Franck Gouedji, Gnamba, Zie Ouattara, Clement Odon N CHO, Sangah Mita-Roland Cardioula, Marc-Antoine Audet, Bouake Bakayoko, Yacouba Coulibaly, Moro Olivier Boffoue et Christian Picard. « PETROGRAPHY AND HYDROTHERMAL ALTERATION OF ULTRAMAFIC BED-ROCKS OF SOUTH SIPILOU : IMPLICATION IN THE LATERITIC NICKEL MINERALIZATION (DEPARTMENT OF SIPILOU, WESTERN IVORY COAST) ». International Journal of Advanced Research 10, n^o 10 (31 octobre 2022) : 1050–61. http://dx.doi.org/10.21474/ijar01/15580.

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South Sipilou is an area containing lateritic nickel mineralization that developed on ultramafic rocks in the department of Sipilou-Biankouma in western Ivory Coast. The objective of this study was to characterize the petrography and hydrothermal alterations affecting these ultramafic bed-rocks and to understand their involvement in lateritic nickel mineralization. Then to compare them to the ultramafic rocks already characterized in the department of Sipilou-Biankouma. Thus, the macroscopic characterization of these rocks was carried out in the field. Then, microscopic observations on the petrography and the hydrothermal alterations were made on these rocks after the preparation of thin sections in the laboratory.The results indicated that the lithologies of the ultramafic bed-rocks of South Sipilou consist of strongly serpentinized dunites, more or less harzburgitic lherzolites and olivine orthopyroxenites. Their petrographic characteristics showed a similarity with the ultramafic bed-rocks of the nickel-bearing lateritic mineralization of North Biankouma, North Sipilou and differences with those of Samapleu, Yepleu, in the department of Sipilou-Biankouma. Also, the main hydrothermal alterations of the ultramafic rocks of South Sipilou are composed of silicification, carbonation and serpentinization. Only serpentinizationcontributed to the concentration of nickel in the bed-rock and within the lateritic profile.

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Burns, Laurel E. « The Border Ranges ultramafic and mafic complex, south-central Alaska : cumulate fractionates of island-arc volcanics ». Canadian Journal of Earth Sciences 22, n^o 7 (1 juillet 1985) : 1020–38. http://dx.doi.org/10.1139/e85-106.

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A discontinuous, elongate zone of mafic and ultramafic plutonic rock crops out in south-central Alaska for a distance of more than 1000 km. Intermediate- and detailed-scale geologic mapping, petrographic study, and compositional data suggest that the plutonic rocks are compositionally, petrologically, and mineralogically distinct from rocks in mid-ocean ridge and back-arc basin ophiolites. The mafic and ultramafic rocks instead represent part of the plutonic core of an intraoceanic island arc.The mafic–ultramafic zone, referred to as the Border Ranges ultramafic and mafic complex (BRUMC), is composed of ultramafic cumulates, gabbronorite cumulates, and massive gabbronorites. A very minor amount of tectonized ultramafic rock of mantle origin is present in the southern part of the BRUMC. A thick sequence of andesitic volcanic rocks, the Talkeetna Formation of Early Jurassic age, lies to the north of and structurally above the mafic–ultramafic zone. Voluminous calcalkaline plutons composed of quartz diorite, tonalite, and minor granodiorite intrude both the mafic plutonic complexes and the andesitic volcanic rocks.The cumulate ultramafic sections are largely composed of dunite ± chromite, wehrlite, clinopyroxenite, and websterite and are characterized by a wide range of Mg–Fe silicate compositions (Fo90–81; En45–50, Fs1–7, Wo45–49; En88–82, Fs11–17), chrome-rich spinels, and a lack of plagioclase. The gabbroic sections are composed of gabbronorites with up to 10–15% magnetite ± ilmenite. Hornblende, if present, is a very minor phase in most gabbroic rocks. The coexisting mineral compositions seen in the gabbroic rocks of the BRUMC (relatively iron-rich pyroxene—Fs6–13, En45–40; En81–63 —and calcic plagioclase An75–100) and their association with magnetite are common in plutonic xenoliths in island-arc rocks.The mineralogy and composition of the gabbroic rocks in the BRUMC are consistent with the fractional crystallization products predicted to be associated with the formation of andesite from a basaltic magma. Consideration of additional data, including detailed and regional field mapping of the plutonic and volcanic rocks and geochronology of the BRUMC and the nearby Talkeetna arc volcanic rocks, strongly suggests that the BRUMC represents relatively deep fractional crystallization products of magmas that produced the Talkeetna Formation volcanic rocks. Field relationships also indicate that intrusion of quartz diorites, tonalites, and granodiorites of batholithic proportions occurred slightly later than formation of the BRUMC.

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Fedortchouk, Yana, et William LeBarge. « Sources of placer platinum in Yukon : provenance study from detrital minerals ». Canadian Journal of Earth Sciences 45, n^o 8 (août 2008) : 879–96. http://dx.doi.org/10.1139/e08-032.

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Source rocks for the platinum group minerals (PGM), historically reported in a number of Yukon placers, remain either unknown or poorly understood. A study of heavy-mineral samples from five creeks draining bedrock in west and central Yukon was undertaken to confirm the presence of placer platinum, to determine which mafic–ultramafic rock is the source of PGM in Kluane area, southern Yukon, and to explain platinum occurrences in Canadian and Florence creeks, central Yukon, where no known mafic–ultramafic rocks are present. Diverse composition of chromian spinel and clinopyroxenes from three creeks in the Kluane area indicate several sources of ultramafic rocks, including fragments of Alpine-type peridotites formed in back-arc basin and mid-ocean-ridge settings, and a source rock for zoned zinc-rich chromites of unknown origin. The Kluane ultramafic sills are the most likely source of PGM in this area. The heavy-mineral sample from Canadian Creek returned one PGM grain, no chromite, and abundant ilmenite and titanomagnetite. A group of chromium-rich magnesian ilmenites (∼4 wt.% MgO) closely match the composition of ilmenites from continental mafic intrusions produced during continental rift magmatism. This supports the continental rifting event recently proposed for this part of Yukon and indicates the economic potential of the Canadian Creek platinum occurrence. Composition of spinel from Florence Creek sample indicates an Alaskan-type intrusion as the source of PGM.

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Salisbury, Matthew H., et Nikolas I. Christensen. « Olivine fabrics in the Bay of Islands Ophiolite : implications for oceanic mantle structure and anisotropy ». Canadian Journal of Earth Sciences 22, n^o 12 (1 décembre 1985) : 1757–66. http://dx.doi.org/10.1139/e85-186.

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Petrofabric analysis of oriented ultramafic and mafic rock samples from six traverses representing all four massifs of the Bay of Islands ophiolite complex, Newfoundland, indicate that the ultramafic rocks are tectonites displaying fabrics consistent with high-temperature plastic flow on the olivine (010) [100] and (0kl) [100] slip systems. The fabric orientation is uniform in three of the four massifs but varies between massifs, suggesting differential rotation before or during emplacement. Within North Arm Mountain, the olivine a axes are aligned approximately perpendicular to the sheeted dikes in both the ultramafic tectonites and the overlying gabbroic tectonites. In Blow Me Down Mountain, the olivine a axes in the gabbros are perpendicular to the dikes, but they are parallel to them in the ultramafic rocks. It is concluded that the ultramafic rocks on Blow Me Down Mountain were rotated 90° during emplacement or that local decoupling and rotation occurred between the crust and upper mantle prior to emplacement. Within the Lewis Hills, the olivine fabrics rotate and weaken near the shear zone in the center of the massif. A second deformation, perhaps associated with low-temperature plastic flow, appears to have obliterated the fabric patterns still observed in the ultramafic rocks to the east.

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Arafin, Sayyadul, et Ram N. Singh. « Thermal and Transport Properties of Mafic and Ultramafic Rocks of Oman Ophiolite ». Sultan Qaboos University Journal for Science [SQUJS] 21, n^o 1 (1 novembre 2016) : 69. http://dx.doi.org/10.24200/squjs.vol21iss1pp69-81.

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Thermal and other physical properties of rocks and minerals are of considerable significance for deriving mineralogical and compositional models of the Earth's mantle. We have determined these properties for the mafic rock such as gabbro and ultramafic rock like harzburgite of the Oman ophiolite suite by utilizing the Debye characteristic property ,Θ-

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Petrounias, Petros, Panagiota P. Giannakopoulou, Aikaterini Rogkala, Alkiviadis Sideridis, Petros Koutsovitis, Paraskevi Lampropoulou, Nikolaos Koukouzas, Panagiotis Pomonis et Konstantin Hatzipanagiotou. « Influence of Petrogenesis on the Engineering Properties of Ultramafic Aggregates and on Their Suitability in Concrete ». Applied Sciences 12, n^o 8 (14 avril 2022) : 3990. http://dx.doi.org/10.3390/app12083990.

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This study focuses on the use of petrology as a useful tool in construction applications (i.e., concrete). More specifically, this study investigates how the petrogenetic characteristics of ultramafic rocks derived from ophiolite complexes (Veria–Naousa, Gerania) can act as a key tool for the prediction of the final behaviour of ultramafic aggregates as concrete aggregates. For this reason, their petrographic, chemical and mineralogical characteristics were examined and correlated with their engineering properties for evaluating their suitability as concrete aggregates. This study had come up, for the first time, that the genesis environment of the ultramafic rocks is the determinant factor for their physico-mechanical characteristics. Their suitability is relevant to the impact of their mineralogical and structural characteristics both from the two different ophiolite complexes (Veria–Naousa and Gerania). Except serpentinization, the basic alteration process-index of ultramafic rocks, there are also other chemical indices which can be used for ultramafic rocks that may determine their properties. In this context the term ‘fertility rate’ (FR) was introduced which may characterize ultramafic rocks as fertile or not. Furthermore, the Ultramafic Rock Health Index (U.R.H.I.) as well as the Normalized U.R.H.I. (U.R.H.I.N) was also introduced and correlated with the engineering properties of the investigated aggregate rocks. The last index aims to assess and quantify the overall health conditions, encompassing the two major modifying factors that include removal of primary mineral phases, as well as the extent of serpentinization. The main conclusion of this paper is that the genesis environment of the ultramafic rocks is the critical factor that determines their mineralogical, petrographic and chemical characteristics which consequently determines the basic engineering properties of rocks that determine their suitability or not as concrete aggregates.

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Pedro, Jorge, António A. Araújo, Patrícia Moita, Massimo Beltrame, Luis Lopes, António Chambel, Edgar Berrezueta et Júlio Carneiro. « Mineral Carbonation of CO2 in Mafic Plutonic Rocks, I—Screening Criteria and Application to a Case Study in Southwest Portugal ». Applied Sciences 10, n^o 14 (16 juillet 2020) : 4879. http://dx.doi.org/10.3390/app10144879.

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This article describes the screening, ranking and characterization of ultramafic and mafic rocks in southern Portugal for mineral carbonation as an alternative to conventional CO2 storage in sedimentary rocks. A set of criteria including mineralogy, structure, surface area, distance to CO2 sources, expected volume, and socioeconomic conditions was applied to screen ultramafic and mafic rock massifs in the Alentejo region, southern Portugal. Ranking of the massifs indicated that the plutonic massifs of Sines and of Torrão‒Odivelas were the most promising. A characterization was made of the Sines massif, a subvolcanic massif composed mostly of gabbros and diorites, located immediately adjacent to the CO2 sources and outcropping along 300 km2 onshore and offshore. These studies confirmed that these rock samples exhibited the appropriate mineralogical and geochemical features, but also indicated that the secondary porosity provided by the fracture patterns was very small.

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Zhao, Xiaoyan, Kunpeng Li, Dian Xiao et Xun Li. « Experimental Study of the Mechanism of Acid Rain-Gabbro Interaction ». E3S Web of Conferences 98 (2019) : 01053. http://dx.doi.org/10.1051/e3sconf/20199801053.

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As a common natural disaster, acid rain could not only cause serious environmental pollution, but also endanger the engineering properties of rock due to water-rock interactions. The failure of slopes of mafic igneous or ultramafic igneous rock is not unusual in areas affected by acid rain, but the specific mechanism of instability remains to be studied. In this study, fresh gabbro samples were processed, and a simulated acid rain treatment of pH 3.0 in the laboratory was carried out. Then the shear strength parameters were evaluated on samples before and after the acid rain test. Finally, the samples were analyzed by X-ray Diffraction (XRD), Polarizing Microscope and Scanning Electron Microscope (SEM) to analyze the mechanism of acid rain-gabbro interaction. Overall, this study provided useful insights toward the evaluation of engineering properties of mafic igneous and ultramafic igneous rocks in acid rain area.

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Dyer, Richard D., et Peter J. Barnett. « Multimedia exploration strategies for PGEs : insights from the Surficial Geochemistry Case Studies Project, Lake Nipigon Region Geoscience Initiative, northwestern Ontario ». Canadian Journal of Earth Sciences 44, n^o 8 (1 août 2007) : 1169–202. http://dx.doi.org/10.1139/e07-031.

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The Surficial Geochemistry Case Studies Project in the Lake Nipigon region involved detailed Quaternary mapping and multimedia geochemical sampling within five case study areas. Two of these areas, Lac des Iles and Tib Lake, contain known platinum group element (PGE) mineralization. The other three case study areas feature drainage catchments with lakes that contain anomalous levels of PGEs in bottom sediment. Surficial media sampled included till, soils, stream sediment, lake sediment, peat, surface water, and groundwater. Over Archean terrain, such as at Lac des Iles and Tib Lake, there is excellent geochemical contrast between the PGE prospective rock type (mafic to ultramafic intrusive) and the surrounding rock type (e.g., granitoid rocks). This geochemical contrast is mirrored in the geochemistry of most surficial media sampled during this project. Over the Nipigon Embayment, the geochemical contrast between mafic and ultramafic rocks (e.g., Seagull-type intrusions) and the surrounding diabase sill rocks is inherently weaker due to the relatively high background levels for copper, palladium, and gold in the Nipigon diabase sills. However, the results of stream-water geochemistry over the Seagull and Disraeli ultramafic intrusions highlight their unique geochemical footprint on the surficial landscape, in particular with respect to Cr, Mg, and Ni, compared with the surrounding Nipigon diabase. In addition, lake sediments underlain by the Seagull, Disraeli, and Hele intrusions have distinctly elevated Cr concentrations and Gd/Yb ratios compared with the surrounding areas underlain by Nipigon diabase sills or Sibley Group rocks. Therefore, exploration value can be maximized over the Nipigon Embayment by exploiting these geochemical contrasts in surficial media to discriminate between ultramafic rocks and the surrounding Nipigon diabase sills. The results of this study highlight the importance of chromium concentrations in surficial media as a diagnostic feature for the presence of ultramafic rocks, regardless of their age or location. In general, a cost-effective exploration strategy for PGE mineralization includes targeting the associated metals (Cr, Ni) within drift deposits (C-horizon till) and drainage media (stream sediment, lake sediment) to vector to prospective mafic–ultramafic intrusive rocks, prior to detailed (property scale) follow-up, involving the determination of base metals and PGEs within soil, till, stream sediment, and peat samples. Relative to the metals copper, nickel, and chromium (ppm levels), the PGEs have significantly lower initial concentrations (ppb levels), are less mobile in the surficial environment, have significantly shorter glacial dispersion trains, and are less reliably determined at the laboratory.

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Nomuulin, Amarbayar, Noriyoshi Tsuchiya, Otgonbayar Dandar, Atsushi Okamoto, Masaoki Uno, Undarmaa Batsaikhan et Jiajie Wang. « Multi-stage serpentinization of ultramafic rocks in the Manlay Ophiolite, southern Mongolia ». Mongolian Geoscientist 26, n^o 53 (30 décembre 2021) : 1–17. http://dx.doi.org/10.5564/mgs.v26i53.1787.

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Serpentinization of ultramafic rocks in ophiolites is key to understanding the global cycle of elements and changes in the physical properties of lithospheric mantle. Mongolia, a central part of the Central Asian Orogenic Belt (CAOB), contains numerous ophiolite complexes, but the metamorphism of ultramafic rocks in these ophiolites has been little studied. Here we present the results of our study of the serpentinization of an ultramafic body in the Manlay Ophiolite, southern Mongolia. The ultramafic rocks were completely serpentinized, and no relics of olivine or orthopyroxene were found. The composition of Cr-spinels [Mg# = Mg/(Mg + Fe2+) = 0.54 and Cr# = Cr/(Cr + Al) = 0.56] and the bulk rock chemistry (Mg/Si = 1.21–1.24 and Al/Si < 0.018) of the serpentinites indicate their origin from a fore-arc setting. Lizardite occurs in the cores and rims of mesh texture (Mg# = 0.97) and chrysotile is found in various occurrences, including in bastite (Mg# = 0.95), mesh cores (Mg# = 0.92), mesh rims (Mg# = 0.96), and later-stage large veins (Mg# = 0.94). The presence of lizardite and chrysotile and the absence of antigorite suggests low-temperature serpentinization (<300 °C). The lack of brucite in the serpentinites implies infiltration of the ultramafic rocks of the Manlay Ophiolite by Si-rich fluids. Based on microtextures and mineral chemistry, the serpentinization of the ultramafic rocks in the Manlay Ophiolite took place in three stages: (1) replacement of olivine by lizardite, (2) chrysotile formation (bastite) after orthopyroxene and as a replacement of relics of olivine, and (3) the development of veins of chrysotile that cut across all previous textures. The complex texture of the serpentinites in the Manlay Ophiolite indicates multiple stages of fluid infiltration into the ultramafic parts of these ophiolites in southern Mongolia and the CAOB.

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Mohanty, William K., Animesh Mandal, S. P. Sharma, Saibal Gupta et Surajit Misra. « Integrated geological and geophysical studies for delineation of chromite deposits : A case study from Tangarparha, Orissa, India ». GEOPHYSICS 76, n^o 5 (septembre 2011) : B173—B185. http://dx.doi.org/10.1190/geo2010-0255.1.

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In Orissa, India, chromite deposits occur in a NE-SW trending belt as discontinuous pods associated with tectonically deformed and metamorphosed ultramafic rocks. Geological mapping and detailed geophysical survey (including gravity, magnetic, electrical, and electromagnetic methods) for exploring chromite were conducted in a [Formula: see text] area at Tangarparha, located within the belt. Lithologies include sheared granite, quartzofeldspathic gneiss, and mafic/ultramafic rocks. The calculated Bouguer anomaly map shows a distinct positive anomaly (up to 16 mGal) in the northern part of the area, indicating the existence of a very high density rock in the subsurface. The trend-surface analysis technique was applied to the gravity and magnetic data for regional-residual separation. The 2D and 2.5D forward modelings of the residual gravity anomaly suggest the presence of lithologies with densities higher than mafic/ultramafic rocks in the subsurface. Chromite fragments recovered from pits within the soil cover around the location indicate that the very high density material is likely to be chromite. Correlation of magnetic and gravity anomalies further emphasizes this possibility. The results of very low frequency (VLF) and DC-resistivity surveys reveal that the suspected chromite deposit is about 250–300 m long in a south-north direction, and 300–350 m wide in the east-west direction. The estimated depth of the deposit varies from 35–100 m. VLF and DC-resistivity methods suggest that chromite occurs in the form of a small disseminated body within a mafic/ultramafic rock matrix. The ambiguity of interpretation is reduced by systematic integration of complementary geophysical methods, compared to that from any single geophysical technique.

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Guice, George, Iain McDonald, Hannah Hughes, Denis Schlatter, Kathryn Goodenough, John MacDonald et John Faithfull. « Assessing the Validity of Negative High Field Strength-Element Anomalies as a Proxy for Archaean Subduction : Evidence from the Ben Strome Complex, NW Scotland ». Geosciences 8, n^o 9 (8 septembre 2018) : 338. http://dx.doi.org/10.3390/geosciences8090338.

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The relative depletion of high field strength elements (HFSE), such as Nb, Ta and Ti, on normalised trace-element plots is a geochemical proxy routinely used to fingerprint magmatic processes linked to Phanerozoic subduction. This proxy has increasingly been applied to ultramafic-mafic units in Archaean cratons, but as these assemblages have commonly been affected by high-grade metamorphism and hydrothermal alteration/metasomatism, the likelihood of element mobility is high relative to Phanerozoic examples. To assess the validity of HFSE anomalies as a reliable proxy for Archaean subduction, we here investigate their origin in ultramafic rocks from the Ben Strome Complex, which is a 7 km2 ultramafic-mafic complex in the Lewisian Gneiss Complex of NW Scotland. Recently interpreted as a deformed layered intrusion, the Ben Strome Complex has been subject to multiple phases of high-grade metamorphism, including separate granulite- and amphibolite-facies deformation events. Additional to bulk-rock geochemistry, we present detailed petrography, and major- and trace-element mineral chemistry for 35 ultramafic samples, of which 15 display negative HFSE anomalies. Our data indicate that the magnitude of HFSE anomalies in the Ben Strome Complex are correlated with light rare earth-element (LREE) enrichment likely generated during interaction with H2O and CO2-rich hydrothermal fluids associated with amphibolitisation, rather than primary magmatic (subduction-related) processes. Consequently, we consider bulk-rock HFSE anomalies alone to be an unreliable proxy for Archaean subduction in Archaean terranes that have experienced multiple phases of high-grade metamorphism, with a comprehensive assessment of element mobility and petrography a minimum requirement prior to assigning geodynamic interpretations to bulk-rock geochemical data.

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Irzon, Ronaldo, et Baharuddin Abdullah. « Geochemistry of Ophiolite Complex in North Konawe, Southeast Sulawesi ». EKSPLORIUM 37, n^o 2 (19 décembre 2016) : 101. http://dx.doi.org/10.17146/eksplorium.2016.37.2.2868.

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ABSTRACTSoutheast Sulawesi is crosscutted by Lasolo Fault into two geological provinces: Tinondo and Hialu. Tinondo Geological Province is occupied largely by Ophiolite Complex in the northern part of Southeast Arm of Sulawesi. No study was conducted in relation to the geochemistry composition of Ophiolite Complex in North Konawe Regency. The aim of this study is to describe the ultramafic rock of the Ophiolite Complex in North Konawe Regency using field, geochemical, and petrographical analysis. Megascopically, the selected nine samples are described as greyish to blackish and fine to medium grains ultramafic rocks, which consist of pyroxene and olivine. Microscope, X-Ray Fluorescence (XRF), and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) devices were used to obtain both petrography and geochemistry data. Major oxides data confirm that the selected samples are classified into ultramafic rocks as SiO2, MgO, and Fe2O3T are the most abundant oxides. The studied samples presumably came from arc tholeiitic environment tectonic setting. Ultramafic rocks often contain promising economic metals whereas the average numbers of Ni, Mn, Cr, and Co of this study are 2,675; 1,074; 2,386; and 117 ppm respectively. The rocks are generally enriched in high field strength elements whilst rare earth elements value are low, ranging from 2.11 to 7.10 ppm. Microscopically, samples can be classified into three groups: olivine-hornblende pyroxenite, lherzolite, and olivine websterite. Geochemical data describes more about the discriminant analysis of the groups. ABSTRAKWilayah Sulawesi Tenggara dipotong oleh Sesar Lasolo yang membagi daerah ini menjadi dua lajur: Tinondo dan Hialu. Lajur Tinondo diisi sebagian besar oleh Komplek Ophiolit, yang berada di bagian utara dari Lengan Tenggara Sulawesi. Belum ada studi yang terfokus kepada kandungan geokimia Komplek Ophiolit tersebut di wilayah Kabupaten Konawe Utara.Studi ini bertujuan untuk mempelajari karakter batuan ultramafik dari Komplek Ophiolit di Kabupaten Konawe Utara melalui kegiatan lapangan, analisis geokimia, dan analisis petrografi. Secara megaskopis, sembilan contoh batuan terpilih teridentifikasi sebagai batuan ultramafik berwarna kelabu hingga hitam, berukuran butir sedang hingga halus, dan mengandung piroksen maupun olivine. Perangkat mikroskop, X-Ray Fluorescence (XRF), dan Inductively Coupled Plasma Mass Spectrometry (ICP-MS) dimanfaatkan untuk memperoleh data geokimia maupun mikroskopis. Data oksida utama mengklasifikasikan contoh terpilih ke dalam batuan utramafik dengan SiO2, MgO, dan Fe2O3T sebagai oksida dengan kelimpahan tertinggi. Contoh terpilih mungkin terbentuk pada lingkungan busur tektonik tholeitik. Batuan ultramafik sering mengandung logam ekonomis dengan kadar rata-rata Ni, Mn, Cr, dan Co pada studi ini adalah: 2.675, 1.074, 2.386, dan 117 ppm secara berurutan. Batuan telah mengalami pengayaan unsur high field strength elements meskipun dengan kadar unsur tanah jarang yang rendah, berkisar dari 2,11 hingga 7,10 ppm. Secara petrografi, batuan terpilih dapat dibagi menjadi tiga kelompok: olivine-hornblende pyroxenite, lherzolite, and olivine websterite. Data geokimia menjelaskan lebih lanjut mengenai perbedaan dari kelompok-kelompok tersebut.

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Zozulya, Dmitry R., Kåre Kullerud, Enrico Ribacki, Uwe Altenberger, Masafumi Sudo et Yevgeny E. Savchenko. « The Newly Discovered Neoproterozoic Aillikite Occurrence in Vinoren (Southern Norway) : Age, Geodynamic Position and Mineralogical Evidence of Diamond-Bearing Mantle Source ». Minerals 10, n^o 11 (18 novembre 2020) : 1029. http://dx.doi.org/10.3390/min10111029.

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During the period 750–600 Ma ago, prior to the final break-up of the supercontinent Rodinia, the crust of both the North American Craton and Baltica was intruded by significant amounts of rift-related magmas originating from the mantle. In the Proterozoic crust of Southern Norway, the 580 Ma old Fen carbonatite-ultramafic complex is a representative of this type of rocks. In this paper, we report the occurrence of an ultramafic lamprophyre dyke which possibly is linked to the Fen complex, although 40Ar/39Ar data from phenocrystic phlogopite from the dyke gave an age of 686 ± 9 Ma. The lamprophyre dyke was recently discovered in one of the Kongsberg silver mines at Vinoren, Norway. Whole rock geochemistry, geochronological and mineralogical data from the ultramafic lamprophyre dyke are presented aiming to elucidate its origin and possible geodynamic setting. From the whole-rock composition of the Vinoren dyke, the rock could be recognized as transitional between carbonatite and kimberlite-II (orangeite). From its diagnostic mineralogy, the rock is classified as aillikite. The compositions and xenocrystic nature of several of the major and accessory minerals from the Vinoren aillikite are characteristic for diamondiferous rocks (kimberlites/lamproites/UML): Phlogopite with kinoshitalite-rich rims, chromite-spinel-ulvöspinel series, Mg- and Mn-rich ilmenites, rutile and lucasite-(Ce). We suggest that the aillikite melt formed during partial melting of a MARID (mica-amphibole-rutile-ilmenite-diopside)-like source under CO2 fluxing. The pre-rifting geodynamic setting of the Vinoren aillikite before the Rodinia supercontinent breakup suggests a relatively thick SCLM (Subcontinental Lithospheric Mantle) during this stage and might indicate a diamond-bearing source for the parental melt. This is in contrast to the about 100 Ma younger Fen complex, which were derived from a thin SCLM.

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Hogarth, D. D., et J. C. Roddick. « Discovery of Martin Frobisher's Baffin Island "ore" in Ireland ». Canadian Journal of Earth Sciences 26, n^o 5 (1 mai 1989) : 1053–60. http://dx.doi.org/10.1139/e89-086.

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Five cobbles of metamorphosed ultramafic rock from the shores of southern Ireland are believed to have been derived from the ship Emanuel of Bridgwater in 1578. The Emanuel, one of Martin Frobisher's fleet, had loaded what was thought to be gold ore from three localities in southeast Baffin Island and, on the return journey, was wrecked and then beached on the western side of Smerwick Harbour, close to where the cobbles were found. One type of cobble, with brown hornblende, forsterite, and ilmenite, is similar to rock collected from Countess of Sussex mine, Baffin Island, which accounted for 25% of the Emanuel's lading and 30% of the ore mined by Frobisher in 1577 and 1578. It was Frobisher's largest mine, and the rock resembled ore stored by Frobisher in Dartford, England. The other type of cobble, composed of green hornblende, diopside, and ilmenite, could not be matched with Baffin Island or Dartford rock. K–Ar ages of the two rock types were 1810 Ma (hornblende + diopside) and 1881 Ma (hornblende + forsterite), consistent with a Hudsonian overprint on southeast Baffin Island. Hornblende-rich "ore" from Frobisher's first mine (not loaded on the Emanuel) gave a K–Ar age of 1722 Ma. The K–Ar ages and ultramafic rocks are unlike any known in Ireland.

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Asano, Kouhei, Katsuyoshi Michibayashi et Tomohiro Takebayashi. « Rheological Contrast between Quartz and Coesite Generates Strain Localization in Deeply Subducted Continental Crust ». Minerals 11, n^o 8 (4 août 2021) : 842. http://dx.doi.org/10.3390/min11080842.

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Deformation microstructures of peak metamorphic conditions in ultrahigh-pressure (UHP) metamorphic rocks constrain the rheological behavior of deeply subducted crustal material within a subduction channel. However, studies of such rocks are limited by the overprinting effects of retrograde metamorphism during exhumation. Here, we present the deformation microstructures and crystallographic-preferred orientation data of minerals in UHP rocks from the Dabie–Shan to study the rheological behavior of deeply subducted continental material under UHP conditions. The studied samples preserve deformation microstructures that formed under UHP conditions and can be distinguished into two types: high-strain mafic–ultramafic samples (eclogite and garnet-clinopyroxenite) and low-strain felsic samples (jadeite quartzite). This distinction suggests that felsic rocks are less strained than mafic–ultramafic rocks under UHP conditions. We argue that the phase transition from quartz to coesite in the felsic rocks may explain the microstructural differences between the studied mafic–ultramafic and felsic rock samples. The presence of coesite, which has a higher strength than quartz, may result in an increase in the bulk strength of felsic rocks, leading to strain localization in nearby mafic–ultramafic rocks. The formation of shear zones associated with strain localization under HP/UHP conditions can induce the detachment of subducted crustal material from subducting lithosphere, which is a prerequisite for the exhumation of UHP rocks. These findings suggest that coesite has an important influence on the rheological behavior of crustal material that is subducted to coesite-stable depths.

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Leinonen, Seppo. « Exploration for Soapstone Occurrences : Use of Bulk Chemical Analyses to Select Potential Formation Areas ». Key Engineering Materials 548 (avril 2013) : 10–19. http://dx.doi.org/10.4028/www.scientific.net/kem.548.10.

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Soapstone is a talc and carbonate containing metamorphic ultramafic rock commonly found in greenschist-amphibolite facies greenstone belts. The regional metamorphism and shear zones as pathways for CO2 containing water fluids are interpreted to have been essential to the formation of soapstone. In spite of the supposed uniform metamorphic conditions favourable to talc-carbonate soapstone, also unaltered serpentinites are usually found in the same location areas and deposits. The objective of this study is to define the bulk chemical response of ultramafic rocks to form soapstone in hydration-carbonation metamorphic processes. Thermodynamic calculations and pseudosection modelling indicate that soapstone is most likely to occur in high silica low magnesium ultramafic sequences, because they turn to talc-carbonate even with very low CO2 content of metamorphic fluids. This is a new approach to classify and locate potential deposit areas in soapstone exploration.

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Yakich, Tamara, Matthew Brzozowski, Alexey Chernishov, Giovanni Grieco, Olesya Savinova, Timofey Timkin et Alexander Marfin. « Petrological Features of the Burlakski and Nizhne-Derbinsk Mafic-Ultramafic Plutons (East Sayan Mountains, Siberia, Russia) ». Minerals 10, n^o 2 (30 janvier 2020) : 119. http://dx.doi.org/10.3390/min10020119.

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The Nizhne-Derbinsk mafic-ultramafic complex is located between the Central Asian Orogenic Belt and the Siberian Craton and, is associated with the Ballyk fault. The largest, spatially related to each other, plutons in the central part of the complex are the Burlakski and Nizhne-Derbinsk. Rocks in the main units of these plutons are divided into three groups: peridotites (ultramafic), pyroxenites (sub-ultramafic), and gabbroic rocks (mafic). The ultramafic and sub-ultramafic cumulate series are devoid of plagioclase and contain <3 vol. % chromian spinel. The Fo content of olivine in the sub-ultramafic cumulates from both plutons ranges from Fo79 to Fo86. The En content [= Mg/(Mg + Fe + Ca) × 100 atomic ratio] of clinopyroxenes and orthopyroxenes varies from 46–56, and 63–80, respectively. Plagioclase corresponds to labradorite with An contents between 55 and 57. Hornblende is compositionally similar to pargasite. The sequence of change of rock units corresponds to the paragenesis: olivine − olivine + clinopyroxene (orthopyroxene) − clinopyroxene + orthopyroxene – clinopyroxene + orthopyroxene + plagioclase – orthopyroxene. Petrographic, mineralogical, and mineral chemical features of the Burlakski and Nizhne-Derbinsk plutons suggest that the diversity of the material composition of these plutons is due to the processes of magmatic differentiation in deep-seated conditions. Estimates of crystallization pressures and temperatures of the Burlakski and Nizhne-Derbinsk plutons suggest that they crystallized at high pressures ≥ 10kb and temperatures ranging from 1000–1400 °C. Mineralogical and petrological features suggest that the mafic-ultramafic cumulates were derived from a high-Mg basaltic magma. The presence of magmatic hornblende and hydrous mineral assemblages within the ultramafic cumulates indicates that the parental melts had been enriched in dissolved volatile constituents. Taking into account the age of the gabbronorites of the Burlakski pluton (~490 ± 11.8 Ma), the magmatism likely occurred during the Ordovician collision stage of the evolution of the Central Asian Fold Belt.

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BOZKURT, ERDİN, JOHN A. WINCHESTER, MUHARREM SATıR, QUENTIN G. CROWLEY et CHRISTIAN J. OTTLEY. « The Almacık mafic-ultramafic complex : exhumed Sakarya subcrustal mantle adjacent to the İstanbul Zone, NW Turkey ». Geological Magazine 150, n^o 2 (22 octobre 2012) : 254–82. http://dx.doi.org/10.1017/s0016756812000556.

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AbstractThe Almacık Mountains in northwestern Turkey expose an upper-amphibolite-facies complex consisting of alternating ultramafic (harzburgitic and websteritic) and mafic (metagabbroic) rock types. In the eastern part of this complex are island arc meta-tholeiites and transitional to calc-alkaline metabasites that are chemically quite similar to those of the Permo-Triassic Çele mafic complex north of Bolu, and this suggests an equivalence. However, much of the section exposes structurally deeper and chemically different mafic and ultramafic rocks, which have no equivalent in the Çele mafic complex, and isotopic dating has suggested that these rocks also formed during the Permian period and underwent Triassic and Jurassic metamorphism. Furthermore, sparse inherited ages, unlike those from İstanbul Zone granitoids, suggest a link with North African-derived Armorican-type basement (and hence the Sakarya Zone), rather than Amazonia-derived Avalonian basement. Alternating mafic and ultramafic rocks suggest structural repetition, supported by the exposure of discrete high-strain zones or poorly exposed shattered rock west of each outcrop of ultramafic rocks. The high grade of metamorphism, and the absence of either extrusive lavas or sheeted dyke rocks, suggests that the Almacık complex was not an ophiolite, but formed instead as subcontinental lower crust and subjacent mantle. Dominantly calc-alkaline geochemistry suggests that it formed the basement to an active continental margin bounding the north side of the Sakarya Continent, with S-dipping subduction of Palaeotethys. The Almacık complex was uplifted as a late result of compression against the southern margin of the İstanbul Zone in the Jurassic period. Lack of coeval high-grade metamorphism in the İstanbul Zone indicates that the latter was overthrust southwards over the Sakarya margin, and that there was therefore a change of subduction polarity in the Triassic period. The evidence further casts doubt on the existence of a Mesozoic Intra-Pontide Ocean in northwestern Turkey and suggests that the latest Permian magmatism, with subsequent Triassic and Jurassic metamorphism, was instead related to the closure of the Palaeotethyan Ocean.

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Upton, B. G. J. « Gardar mantle xenoliths : Igdlutalik, South Greenland ». Rapport Grønlands Geologiske Undersøgelse 150 (1 janvier 1991) : 37–43. http://dx.doi.org/10.34194/rapggu.v150.8139.

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A dyke of presumed Gardar age on Igdlutalik island near Narsaq contains an abundance of ultramafic xenoliths. Both host rock and xenoliths have been metamorphosed and the original mineral assemblages largely replaced by tremolite, chlorite and magnetite. Textural and geochemical evidence suggests: (a) that the host rock was a part of the ultramafic lamprophyre suite known throughout the Tugtut6q-Ilimaussaq-nunataq lineament, and (b) that the xenoliths were mantle-derived peridotites (possibly garnetiferous), together with some glimmerites that may be analogues of MARID-suite xenoliths known from kimberlite occurrences.

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Ramos, Rodrigo Chaves, et Edinei Koester. « Lithogeochemistry of the meta-igneous units from Arroio Grande Ophiolitic Complex, southernmost Brazil ». Brazilian Journal of Geology 45, n^o 1 (mars 2015) : 65–78. http://dx.doi.org/10.1590/23174889201500010005.

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Ophiolites are defined as slices of genetically-related upper mantle serpentinized peridotites and oceanic crustal rocks, tectonically displaced from its primary igneous origin of formation by plate convergence and associated (meta) sedimentary rocks of marine origin. From this premise, a meta-ultramafic-mafic-sedimentary complex (Cr-rich magnesian schists - upper mantle or crustal ultramafic cumulate candidates; epidote amphibolites, metadiorites and metagabbros - oceanic crust candidates; metasedimentary schists, quartzites and marbles - marine sedimentary rocks candidates), located in southeastern Dom Feliciano Belt (southernmost Brazil), started to be interpreted as possible slices of an ophiolitic complex related to the closure of a paleo-ocean during Brasiliano/Pan-African orogenic cycle and was called Arroio Grande Ophiolitic Complex. The present research fills the lack of geochemical data from previous studies and tests the hypothesis of an oceanic setting for the meta-igneous units of this complex from a lithogeochemistry point of view. The meta-ultramafics were interpreted as peridotites (mantle or crustal cumulates) that were subsequently serpentinized (probably in the ocean floor) and posteriorly metasomatized (probably in a continental setting). The meta-mafics were interpreted as oceanic gabbros/basalts formed in a back-arc basin. The results, together with field relationships, rock associations and petrographic evidences, support an oceanic origin for the protoliths of the meta-igneous units. The hypothesis that these rocks represent metamorphosed slices of an ophiolitic complex is still the most reasonable one. This work updates the geologic knowledge of the area and supports discussions about the evolution of Dom Feliciano Belt and Western Gondwana paleocontinent.

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Canil, Dante, Stephen T. Johnston, Rameses J. D’Souza et Larry M. Heaman. « Protolith of ultramafic rocks in the Kluane Schist, Yukon, and implications for arc collisions in the northern Cordillera ». Canadian Journal of Earth Sciences 52, n^o 7 (juillet 2015) : 431–43. http://dx.doi.org/10.1139/cjes-2014-0138.

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Mafic and ultramafic rocks crop out as decimetre- to centimetre-sized bodies of talc–antigorite–olivine (±orthopyroxene) and chlorite–amphibole schists interleaved in the pelitic Kluane Schist of southwestern Yukon. The metamorphic assemblages in ultramafic rocks exposed at Doghead Point overprint two generations of cleavage and are consistent with metamorphism reaching >550 °C (talc + olivine) and >750 °C (olivine + enstatite) in the contact aureole of the Eocene Ruby Range batholith. The bulk rock major and trace element patterns in the ultramafic schists (>40 wt.% MgO, Mg/(Mg + Fe) > 0.90) are unlike residual mantle from partial melting (i.e., ophiolite, orogenic massif, abyssal ocean floor) but are similar to peridotite or pyroxenite cumulates from arc magmas. Identical trace element concentrations and patterns are observed in several late Triassic basalts, pyroxenites, and websterites occurring to the southeast in Stikinia (present coordinates). A highly discordant U–Pb zircon date for one antigorite–talc–olivine schist sample (200–210 Ma) is within the range of U–Pb zircon ages for the late Triassic Lewes River – Stuhini arc in northwestern Stikinia (200–208 Ma, 216–220 Ma). When combined with other published age information, the ultramafic rocks in the Kluane Schist are interpreted as fragments of deeper arc-related mafic and ultramafic intrusive rocks introduced to the Kluane forearc basin between 95 and 82 Ma by exhumation along shear zones in northwestern Stikinia, most likely the Wann River or Llewellyn Faults. The Kluane Schist represents a west-facing forearc basin bordered to the east by arc-parallel strike-slip fault(s) that served to exhume and imbricate large knockers into the accretionary prism.

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Silva, Douglas Ramos Guelfi, Giuliano Marchi, Carlos Roberto Spehar, Luiz Roberto Guimarães Guilherme, Thomaz Adolpho Rein, Danilo Araújo Soares et Fabrício William Ávila. « Characterization and nutrient release from silicate rocks and influence on chemical changes in soil ». Revista Brasileira de Ciência do Solo 36, n^o 3 (juin 2012) : 951–62. http://dx.doi.org/10.1590/s0100-06832012000300025.

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The expansion of Brazilian agriculture has led to a heavy dependence on imported fertilizers to ensure the supply of the growing food demand. This fact has contributed to a growing interest in alternative nutrient sources, such as ground silicate rocks. It is necessary, however, to know the potential of nutrient release and changes these materials can cause in soils. The purpose of this study was to characterize six silicate rocks and evaluate their effects on the chemical properties of treated soil, assessed by chemical extractants after greenhouse incubation. The experimental design consisted of completely randomized plots, in a 3 x 6 factorial scheme, with four replications. The factors were potassium levels (0-control: without silicate rock application; 200; 400; 600 kg ha-1 of K2O), supplied as six silicate rock types (breccia, biotite schist, ultramafic rock, phlogopite schist and two types of mining waste). The chemical, physical and mineralogical properties of the alternative rock fertilizers were characterized. Treatments were applied to a dystrophic Red-Yellow Oxisol (Ferralsol), which was incubated for 100 days, at 70 % (w/w) moisture in 3.7 kg/pots. The soil was evaluated for pH; calcium and magnesium were extracted with KCl 1 mol L-1; potassium, phosphorus and sodium by Mehlich 1; nickel, copper and zinc with DTPA; and the saturation of the cation exchange capacity was calculated for aluminum, calcium, magnesium, potassium, and sodium, and overall base saturation. The alternative fertilizers affected soil chemical properties. Ultramafic rock and Chapada mining byproduct (CMB) were the silicate rocks that most influenced soil pH, while the mining byproduct (MB) led to high K levels. Zinc availability was highest in the treatments with mining byproduct and Cu in soil fertilized with Chapada and mining byproduct.

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Lopes-Assad, Maria L., Simoni H. Avansini, Márcia M. Rosa, José R. P. de Carvalho et Sandra R. Ceccato-Antonini. « The solubilization of potassium-bearing rock powder by Aspergillus niger in small-scale batch fermentations ». Canadian Journal of Microbiology 56, n^o 7 (juillet 2010) : 598–605. http://dx.doi.org/10.1139/w10-044.

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The fungus Aspergillus niger was cultivated in culture medium with an alkaline ultramafic rock powder to evaluate the solubilization of potassium for biofertilizer production. The assays were carried out with 2 strains (CCT4355 and CCT911) in small-scale batch fermentations using 125, 500, 1000, and 2000 mL Erlenmeyer flasks, with a nominal volume of 40%, and rock powder at 0.4%, shaken at 160 r/min, incubated at 30 °C, and sampled every 7 days for 35 days. The amount of soluble K+, the pH of the culture medium, and the acidity were determined. Both strains solubilized K+ from the rock powder to the same extent (approximately 62%–70% after 35 days) in the 125 mL flasks; however, the percent solubilization decreased at higher volumetric scales. The results also indicated a difference in strain sensitivity to the increase in volumetric scales in batch fermentation. When filter-sterilized air was injected into the medium, the K+ percent solubilization obtained after 4 days of cultivation was similar to that obtained after a 28 day period. The acid production by the fungus may be a mechanism of rock solubilization, in spite of the elevation in pH values probably caused by the increasing hydrolysis of the silicates. Both strains of A. niger are recommended for solubilizing potassium from ultramafic rocks, but it is necessary to optimize the oxygen transfer, which seemed to affect the rock solubilization at higher volumetric scales.

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Mareoli, Eksel Setiawan, Riska Puspita et Ninasafitri Ninasafitri. « Karakteristik Batuan Ultrabasa Di Desa Winatu Dan Kamarora, Kabupaten Sigi, Provinsi Sulawesi Tengah ». Jurnal Teknologi Sumberdaya Mineral (JENERAL) 3, n^o 2 (21 décembre 2022) : 49. http://dx.doi.org/10.19184/jeneral.v3i2.35009.

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Ultramafic rocks are found in Sigi district in the Kamarora and Winatu areas but are not mentioned in the regional geology of the Poso sheet and the Pasangkayu sheet so that it is interesting to investigate further. Therefore, it is important to conduct this research to determine the characteristics and processes of ultramafic rock formation in the Kamarora and Winatu areas of Sigi district using the Petrographic and X-Ray Fluorescence (XRF) methods. The results of this study are based on petrographic analysis of two rock samples in Kamarora Village containing olivine (60-55%), omphasite (15-10%), enstatite (5%), serpentine (10%), garnet (15-10%) ) and chlorite (5%) with the rock name lherzolite, while one rock sample in Winatu Village contained serpentine minerals (75%), olivine (15%), omphasite (5%), enstasite (5%) with serpentine rock names. The chemical composition and percentage of each element of the samples analyzed by XRF stations ST01K, ST02K, ST01W are as follows: major element SiO2 (40 – 41.1 wt %), Al2O3 (2.90 – 19.6 wt %), Fe2O3 (7 – 9.98 wt %), MgO (17 – 33.7 wt %), CaO (11.30 – 12.4 wt %), Na2O (0.147–2.11 wt %), K2O (0.0558 – 0.234 wt %) and minor elements with a content range of TiO2 (0.104 – 0.965 wt %), MnO (0.102 – 0.145 wt%), SO3 (0.0719 – 0.259 wt %), Cl ( 0.0954 – 0.360 wt %), NiO (0.0272 – 0.307 wt %), Cr2O3 (0.111 – 0.403 wt %), Co2O3 (0.0246 wt %), WO3 (0.0563 – 0.0661 wt %). Rocks formed in the type of tholeiite magma, this type of magma has a low potassium content, usually formed in subduction and non-subduction areas. Based on the results of the plot on the Pearce et al (1976) diagram, it is known that the tectonic order of rock formation is on the ocean ridge and floor or the expansion of the ocean floor.

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Alexakis, D., et D. Gamvroula. « Arsenic, Chromium, and Other Potentially Toxic Elements in the Rocks and Sediments of Oropos-Kalamos Basin, Attica, Greece ». Applied and Environmental Soil Science 2014 (2014) : 1–8. http://dx.doi.org/10.1155/2014/718534.

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Rocks and sediments are non-anthropogenic sources of elements contamination. In this study, a series of potentially toxic elements were quantified in rocks and sediments of the Oropos-Kalamos basin. Only As, Hg, Pb, and Sb contents, in all the examined rocks and sediments, were higher than the levels given in international literature. Concentration of the elements As, Cr, Hg, Mo, Ni, and U is highly elevated in the lignite compared to crustal element averages. The enrichment of Cr and Ni in the lignite can be attributed to the known ultramafic rock masses surrounding the basin, while enrichment of As, Hg, Mo, Sb, and U is associated with the past geothermal activity of the Upper Miocene (about 15 million years ago). Nickel and Cr were transported into the lignite deposition basin by rivers and streams draining ultramafic rock bodies. The results of this study imply the natural source of Cr3+and Cr6+contamination of the Oropos-Kalamos groundwater, since high Cr contents were also recorded in the lignite (212.3 mg kg−1), chromiferous iron ore occurrences (256.6 mg kg−1), and alluvial deposits (212.5 mg kg−1), indicating Cr leaching and transportation to the depositional basin dating from the Upper Miocene age.

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Adams, Cameron, Michael Dentith et Marco Fiorentini. « Characterization of altered mafic and ultramafic rocks using portable XRF geochemistry and portable Vis-NIR spectrometry ». Geochemistry : Exploration, Environment, Analysis 21, n^o 2 (15 février 2021) : geochem2020–065. http://dx.doi.org/10.1144/geochem2020-065.

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The accurate characterization of mafic and ultramafic rocks is a challenging but necessary task given the spatial and genetic relationship of mineralization with specific lithologies (e.g. komatiite hosted nickel-sulfides preferentially associated with cumulate-rich ultramafic rocks). Rock classification is further complicated as most mafic and ultramafic rocks have undergone varying degrees of alteration. The accuracy and reproducibility of characterization can be significantly improved by using portable energy dispersive X-ray fluorescence (pXRF) chemical data with portable visible and near-infrared (pVis-NIR) mineralogical data.A new workflow using pXRF and pVis-NIR is presented and used to reliably characterize mafic and ultramafic rocks from the Yilgarn Craton, Western Australia. The workflow involves six steps:(1) Mitigate and identify compound processing and closure issues. For example, we used a pXRF with helium flush to reliably and rapidly measure light elements and mitigate closure, i.e. problems related to data failing to sum to 100%.(2) Identify and exclude geochemically heterogeneous samples. Heterogeneity may be unrelated to alteration and caused by veining or small-scale structure interleaving of different rock types. Geochemical heterogeneity was evaluated using skewness and kurtosis of SiO2 data.(3) Relate rocks from similar magmatic, weathering and alteration events. This was achieved by interpreting data grouping of Vis-NIR ferric and ferrous iron data via a 852 nm/982 nm reflectance v. 651 nm/982 nm reflectance plot and the ferrous abundance index. Unrepresentative data were omitted.(4) Correct XRF iron data, and characterize lithology and alteration. Values ascribed to regions in the TAS (total alkali silica) diagram were used to approximate FeO and Fe2O3. Subsequently, geochemical indices (e.g. Mg#) were used to characterize the alteration box plot.(5) Characterize fractionation in detail. Fractionation variation diagrams were used to interpret fractionation, e.g. MgO v. Al2O3, Ca/Al v. Al2O3, Ni/Cr v. Ni/Ti, and MgO v. Cr.(6) Identify and quantify talc alteration and serpentinization. This included the use of a new alteration plot (Mg# v. 1410 nmRAD/Albedo) to estimate serpentinization and identify relationships between serpentine, carbonate, chlorite and talc abundances.The results and observations contained in this contribution have important implications for progressive technologies such as core logging platforms that are equipped with pXRF and pVis-NIR instruments.

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Petrounias, Petros, Aikaterini Rogkala, Panagiota P. Giannakopoulou, Paraskevi Lampropoulou, Petros Koutsovitis, Nikolaos Koukouzas, Nikolaos Laskaris, Panagiotis Pomonis et Konstantin Hatzipanagiotou. « Removal of Cu (II) from Industrial Wastewater Using Mechanically Activated Serpentinite ». Energies 13, n^o 9 (3 mai 2020) : 2228. http://dx.doi.org/10.3390/en13092228.

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We investigate with this study the effectiveness of mechanically activated serpentinite in capturing Cu (II) from the multi-constituent acidic wastewater of the pit lakes of the Agios Philippos mine (Greece), proposing specific areas with serpentinites suitable for such environmental applications. For this purpose ultramafic rock samples that are characterized by variable degrees of serpentinization from ophiolitic outcrops exposed in the regions of Veria-Naousa and Edessa have been examined regarding their capacity to remove the toxic load of Cu (II) from wastewater after having been mechanically activated through a Los Angeles (LA) machine (500, 1000 and 1500 revolutions). The more serpentinized and mechanically activated samples, as they have been characterized after a combination of various mineralogical, petrographic, geochemical analyses as well as after different stresses of abrasion and attrition, seem to be more effective in Cu removal than the less serpentinized ones. Selective removal of Cu (II) in the wroewolfeite phase was obtained by using the mechanically activated highly serpentinized ultramafic rocks. Furthermore, areas with highly serpentinized ultramafic rocks defined after petrographic mapping, using GIS method, which can potentially be used as filters for the effective Cu (II) removal from industrial wastewater are suggested.

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Abbas, I. R. H., et A. Maulana. « Petrology of ultramafíc Rocks from PT. Sebuku Iron Lateritic Ore (SILO) concession area and Its Effect on Ni and Fe in Sebuku Island, South Kalimantan, Indonesia ». IOP Conference Series : Earth and Environmental Science 921, n^o 1 (1 novembre 2021) : 012057. http://dx.doi.org/10.1088/1755-1315/921/1/012057.

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Abstract Widely distribution of serpentinization rock especially ultramafic rocks in Sebuku Island, South Kalimantan, primarily in the concession area of PT. Sebuku Iron Lateritic Ore (SILO). Some representative samples were taken from the site and analyses the level of serpentinization to determine the characteristic of the rocks. The ultramafic rocks in the study area consist of peridotite with a low to high degree of serpentinization to serpentinite. The pseudomorph textures are shown like mesh, bastite, blades/flaky, hourglass, vein, and veinlet. Serpentine occurs as lizardite, chrysotile, and antigorite. Geochemical analysis like XRF (X-ray fluorescence) was used to find out the composition element. By this analysis, the wt.% of the element will be shown and determine the level of Nickel (Ni), and Iron (Fe), and the level of serpentinization also. The Serpentinization levels are affecting Ni and Fe. The higher the serpentinization level, the higher Fe (wt.%), whereas the higher level of serpentinization, the lower Ni (wt.%).

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Onggang, S., A. Maulana, Sufriadin et U. R. Irfan. « Preliminary Study of Scandium Enrichment in Lateritic Profile from Weathered Ultramafic Rock in Lapaopao Area Kolaka Regency of Southeast Sulawesi ». IOP Conference Series : Earth and Environmental Science 921, n^o 1 (1 novembre 2021) : 012040. http://dx.doi.org/10.1088/1755-1315/921/1/012040.

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Abstract Scandium is one of the rare earth elements which is currently widely used for various needs such as the aerospace industry, solid oxide fuel cells, electronics industry and in metallurgical applications. Generally, Scandium appears in small amounts so its structural role in the host minerals cannot be readily identified. Some studies reported the scandium extraction from lateritic nickel deposit where may contain considerable amount of scandium in addition to nickel and cobalt. Preliminary research of scandium enrichment has been investigated from the ultramafik rock indicates that an enrichment of scandium concentration was found in the red limonite. The aim of this study was to investigate the potentially enrichment of scandium mineral from nickel laterite in Lapaopao Area. There are a total of 38 samples from 1 (one) diamond drill holes which represent the limonite, saprolite and bedrock profiles have been collected and studied to investigate the distribution pattern of Sc grades within the lateritic profile. These samples are being analized by XRF for major and minor element and ICP-OES method for rare earth element assaying. The study has confirmed that scandium is enriched in limonite layer of weathered ultramafic laterite profile. The scandium content from the ultramafic bedrock is 15 ppm and has enriched until 81 ppm of scandium in the limonite layer.

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Dunworth, E. A., et K. Bell. « The Turiy Massif, Kola Peninsula, Russia : mineral chemistry of an ultramafic-alkaline-carbonatite intrusion ». Mineralogical Magazine 67, n^o 3 (juin 2003) : 423–51. http://dx.doi.org/10.1180/0026461036730109.

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AbstractThe Turiy Massif, on the southern coast of the Kola Peninsula, consists of five intrusive complexes containing a variety of carbonatites, phoscorites, melilitolites, ijolites and pyroxenites. Petrographic and mineralogical studies of the different rocks show that the samples are texturally heterogeneous. Minerals including apatite, garnet, magnetite, melilite, mica and pyroxene, show systematic variations in composition relating to the rock type in which they occur. Compositional similarities and/or distinct trends are seen in the mineral compositions within the each of the pyroxenite-melilitolite, and melteigite-ijolite rock series, indicating linked petrogenetic histories within each of the two series. The carbonatites from the northern complex may be related to nearby melilitolites, but the central complex carbonatites and phosocorites do not bear any mineralogical (or isotopic) similarities to any of the silicate rocks within the massif.

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Seaman, S. J., M. L. Williams, K. E. Karlstrom et P. C. Low. « Petrogenesis of the 91-Mile peridotite in the Grand Canyon : Ophiolite or deep-arc fragment ? » Geosphere 17, n^o 3 (21 avril 2021) : 786–803. http://dx.doi.org/10.1130/ges02302.1.

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Abstract Recognition of fundamental tectonic boundaries has been extremely diffi-cult in the (>1000-km-wide) Proterozoic accretionary orogen of south western North America, where the main rock types are similar over large areas, and where the region has experienced multiple postaccretionary deformation events. Discrete ultramafic bodies are present in a number of areas that may mark important boundaries, especially if they can be shown to represent tectonic fragments of ophiolite complexes. However, most ultramafic bodies are small and intensely altered, precluding petrogenetic analysis. The 91-Mile peridotite in the Grand Canyon is the largest and best preserved ultramafic body known in the southwest United States. It presents a special opportunity for tectonic analysis that may illuminate the significance of ultramafic rocks in other parts of the orogen. The 91-Mile peridotite exhibits spectacular cumulate layering. Contacts with the surrounding Vishnu Schist are interpreted to be tectonic, except along one margin, where intrusive relations have been interpreted. Assemblages include olivine, clinopyroxene, orthopyroxene, magnetite, and phlogopite, with very rare plagioclase. Textures suggest that phlogopite is the result of late intercumulus crystallization. Whole-rock compositions and especially mineral modes and compositions support derivation from an arc-related mafic magma. K-enriched subduction-related fluid in the mantle wedge is interpreted to have given rise to a K-rich, hydrous, high-pressure partial melt that produced early magnetite, Al-rich diopside, and primary phlogopite. The modes of silicate minerals, all with high Mg#, the sequence of crystallization, and the lack of early plagioclase are all consistent with crystallization at relatively high pressures. Thus, the 91-Mile peridotite body is not an ophiolite fragment that represents the closure of a former ocean basin. It does, however, mark a significant tectonic boundary where lower-crustal arc cumulates have been juxtaposed against middle-crustal schists and granitoids.

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Li, Ai, Jian Wang et Yue Song. « Petrology, mineral chemistry, and geochemistry of Late Triassic Ni–Cu ore-bearing mafic–ultramafic intrusions, Hongqiling, northeastern China : petrogenesis and tectonic implications ». Canadian Journal of Earth Sciences 56, n^o 2 (février 2019) : 111–28. http://dx.doi.org/10.1139/cjes-2018-0014.

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The Hongqiling magmatic Ni–Cu sulfide deposit, situated on the southern margin of the eastern Central Asian Orogenic Belt (CAOB), is composed of over 30 mafic–ultramafic intrusions. These ore-bearing intrusions are composed mainly of harzburgite, lherzolite, websterite, orthopyroxenite, and norite (gabbro). The constituent minerals are olivine, diopside, bronzite, calcic-hornblende, plagioclase, and spinel with orthopyroxene as a dominant mineral in these intrusions. These ore-bearing intrusions are not Alaskan-type complexes. Spinel and clinopyroxene both exhibit different chemical compositions from those in the Alaskan-type complexes. The rocks that make up the intrusions have high contents of MgO (average value = 25.20 wt.%) and low TiO2 (average value = 0.58 wt.%). The high MgO contents of the minerals and the high Mg# (71) of the calculated melt in equilibrium with olivine demonstrate that the parental magma of the Hongqiling mafic–ultramafic intrusions was a high-Mg tholeiitic magma. The Hongqiling ore-bearing mafic–ultramafic intrusions and the calculated “trapped liquids” for the olivine-orthopyroxene cumulate rocks are all enriched in large-ion lithophile elements and depleted in high field strength elements. The Ce/Pb, Ta/La, Th/Yb, and (La/Sm)PM values and the depletion of Nb and Ta suggest that the magma experienced crustal contamination. The Hongqiling ore-bearing intrusions display many similarities with mafic–ultramafic intrusions that formed in a post-collisional extensional environment in the western CAOB (e.g., Huangshanxi). Common features include their whole-rock compositions and mineral chemistry. Combined with the evolutionary history of the eastern segment of the CAOB, we believe that the Late Triassic Hongqiling mafic–ultramafic intrusions formed in a post-collisional extensional environment.

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Fan, Dongxu, Shucheng Tan, Xia Wang, Zeli Qin, Junfang Zhao, Le Yang, Wanhui Zhang et al. « Geochronology, Petrogenesis and Geodynamic Setting of the Kaimuqi Mafic–Ultramafic and Dioritic Intrusions in the Eastern Kunlun Orogen, NW China ». Minerals 13, n^o 1 (2 janvier 2023) : 73. http://dx.doi.org/10.3390/min13010073.

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The Kaimuqi area in the Eastern Kunlun Orogen (EKO) contains many lherzolite, olivine websterite, gabbro and diorite intrusions, and new zircon U‒Pb dating, Lu‒Hf isotope and whole-rock geochemical data are presented herein to further confirm the Late Triassic mafic–ultramafic magmatism with Cu–Ni mineralization and to discuss the petrogenesis and geodynamic setting. Zircon U‒Pb dating shows that the Late Triassic ages, corresponding to 220 Ma and 222 Ma, reveal the mafic–ultramafic and dioritic magmatism in Kaimuqi, respectively. Zircon from gabbro has εHf(t) values of −3.4 to −0.2, with corresponding TDM1 ages of 994–863 Ma. The mafic–ultramafic rocks generally have low SiO2, (Na2O+K2O) and TiO2 contents and high MgO contents and Mg# values. They are relatively enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and depleted in heavy REEs (HREEs) and high-field-strength elements (HFSEs), indicating that the primary magma was derived from the metasomatized lithospheric mantle. The diorites show sanukitic high-Mg andesite properties (e.g., MgO = 2.78%–3.54%, Mg# = 50–55, Cr = 49.6–60.0 ppm, Sr = 488–512 ppm, Y = 19.6–21.8 ppm, Ba = 583–722 ppm, Sr/Y = 23.5–25.4, K/Rb = 190–202 and Eu/Eu* = 0.73–0.79), with LREEs and LILEs enrichments and HREEs and HFSEs depletions. We suggest that the primary Kaimuqi diorite magma originated from enriched lithospheric mantle that was metasomatized by subduction-derived fluids and sediments. The Kaimuqi mafic–ultramafic and dioritic intrusions, with many other mafic–ultramafic and K-rich granitic/rhyolitic rocks in the EKO, formed in a dynamic extensional setting after the Palaeo-Tethys Ocean closure.

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Blanchard, J. A., R. E. Ernst et C. Samson. « Gravity and magnetic modelling of layered mafic–ultramafic intrusions in large igneous province plume centre regions : case studies from the 1.27 Ga Mackenzie, 1.38 Ga Kunene–Kibaran, 0.06 Ga Deccan, and 0.13–0.08 Ga High Arctic events ». Canadian Journal of Earth Sciences 54, n^o 3 (mars 2017) : 290–310. http://dx.doi.org/10.1139/cjes-2016-0132.

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Gravity and magnetic data from the global EGM2008 and EMAG2 datasets are used to identify geophysical anomalies in large igneous province (LIP) plume centre regions with the goal of characterizing mafic–ultramafic intrusions linked to those LIPs. Geophysical anomalies within 18 LIPs distributed globally are investigated. Four of these LIPs are selected for detailed modelling: the 1.27 Ga Mackenzie, 1.38 Ga Kunene–Kibaran, 0.06 Ga Deccan, and 0.13–0.08 Ga High Arctic LIPs. We recognize three spatial distribution types for intrusions in plume centre regions. These are (1) intrusions emplaced along a circular fault system that circumscribes the plume centre, (2) intrusions emplaced along linear rifts that, in some cases, converge towards the plume centre, and (3) single or unclassified intrusions. Modelling supports that the geophysical anomalies associated with these LIPs tend to be produced by large (radius >30 km) and deep-seated crustal intrusions, with densities consistent with mafic–ultramafic rock and magnetic susceptibilities consistent with serpentinized ultramafic rock, except within the Deccan where intrusions are smaller, mainly mafic in composition, and positioned at shallower depths in the crust.

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Kusky, Timothy M., et Peter J. Hudleston. « Growth and demise of an Archean carbonate platform, Steep Rock Lake, Ontario, Canada ». Canadian Journal of Earth Sciences 36, n^o 4 (7 avril 1999) : 565–84. http://dx.doi.org/10.1139/e98-108.

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The Steep Rock Group of northwest Ontario's Wabigoon subprovince is one of the world's thickest Archean carbonate platform successions. It was deposited unconformably over a 3001-2928 Ma gneissic terrane, and contains a remarkable group of biogenic and oolitic limestones, dolostones, micrites, and karst breccias capped by a thick paleosol developed between and over karst towers. The presence of aragonite fans, herringbone calcite, and rare gypsum molds suggests that the carbonate platform experienced at least local anaerobic and hypersaline depositional conditions. This sequence shows that a combination of chemical and biological processes was able to build a carbonate platform 500 m thick by 3 billion years ago. The carbonate platform is structurally overlain by a mixture of complexly deformed rocks of the Dismal Ashrock forming a mélange with blocks of ultramafic volcaniclastic rocks, mafic volcanics, carbonate, tonalite, lenses of Fe-ore rock, and metasedimentary rocks, in a shaly, serpentinitic, and fragmental ultramafic volcaniclastic matrix. The mélange shows evidence of polyphase deformation, with early high-strain fabrics formed at amphibolite facies, and later superimposed brittle fabrics related to the final emplacement of the mélange over the carbonate platform. An amphibolite- through greenschist-grade shear zone marks the upper contact of the mélange with overlying mafic volcanic and tuffaceous rocks of the ca. 2932 Ma Witch Bay allochthon, interpreted as a primitive island arc sequence. We suggest an evolutionary model for the area that begins with rifting of an arc sequence (Marmion Complex of the Wabigoon arc) that initiated subsidence and sedimentation on the Steep Rock platform and its correlatives that extend for a restored strike length exceeding 1000 km. Shallow water carbonate sedimentation continued until the platform was uplifted on the flanks of a flexural bulge related to the approach of the Witch Bay allochthon, representing collision of the rifted arc margin of the Wabigoon subprovince with the Witch Bay arc. Mélange of the Dismal Ashrock was formed as off-axis volcanic rocks were accreted to the base of the Witch Bay allochthon prior to its collision with the Steep Rock platform.

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Oliver, N. H. S., et T. D. Barr. « The geometry and evolution of magma pathways through migmatites of the Halls Creek Orogen, Western Australia ». Mineralogical Magazine 61, n^o 404 (février 1997) : 3–14. http://dx.doi.org/10.1180/minmag.1997.061.404.02.

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AbstractIn the Halls Creek Orogen of north-western Australia, the distance of melt migration through migmatitic metasedimentary rocks and adjacent metabasites is partly constrained by relationships of leucosomes and small mafic magma veins to rock boundaries and structural elements. Stromatic leucosomes in metasediments are cut by a network of small extensional fractures and shear zones, oriented steeply during melt migration. These shear zones allowed cm- to 10 m-scale migration of felsic magma derived by in situ anatexis. In the adjacent metabasite layers, a similar shear array allowed injection of H2O-undersaturated mafic to ultramafic magma, locally dehydrating and chemically modifying these rocks. However, these mafic to ultramafic veinlets are too mafic to be explained by in situ anatexis, necessitating an external magma source. Also, the lack of felsic veinlets cutting metabasites, and mafic veinlets cutting metasediments, requires that vertical inter-connectivity of these fracture systems was restricted. We propose along-layer migration of mafic to ultramafic magma through the metabasite, assisted by horizontal connection of the shear zones. This migration occurred independantly of metre-scale felsic magma migration in the adjacent metasediments, even though these two deformation-assisted magma migration systems may have been operating at the same time.

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Tzamos, Evangelos, Micol Bussolesi, Giovanni Grieco, Pietro Marescotti, Laura Crispini, Andreas Kasinos, Niccolò Storni, Konstantinos Simeonidis et Anastasios Zouboulis. « Mineralogy and Geochemistry of Ultramafic Rocks from Rachoni Magnesite Mine, Gerakini (Chalkidiki, Northern Greece) ». Minerals 10, n^o 11 (22 octobre 2020) : 934. http://dx.doi.org/10.3390/min10110934.

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The importance of magnesite for the EU economy and industry is very high, making the understanding of their genesis for the exploration for new deposits a priority for the raw materials scientific community. In this direction, the study of the magnesite-hosting ultramafic rocks can be proved very useful. For the present study, ultramafic rock samples were collected from the magnesite ore-hosting ophiolite of the Gerakini mining area (Chalkidiki, Greece) to investigate the consecutive alteration events of the rocks which led to the metallogenesis of the significant magnesite ores of the area. All samples were subjected to a series of analytical methods for the determination of their mineralogical and geochemical characteristics: optical microscopy, XRD, SEM, EMPA, ICP–MS/OES and CIPW normalization. The results of these analyses revealed that the ultramafic rocks of the area have not only all been subjected to serpentinization, but these rocks have also undergone carbonation, silification and clay alteration. The latter events are attributed to the circulation of CO2-rich fluids responsible for the formation of the magnesite ores and locally, the further alteration of the serpentinites into listvenites. The current mineralogy of these rocks was found to be linked to one or more alteration event that took place, thus a significant contribution to the metallo- and petrogenetic history of the Gerakini ophiolite has been made. Furthermore, for the first time in literature, Fe inclusions in olivines from Greece were reported.

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Malitch, Kreshimir N., Elena A. Belousova, William L. Griffin, Laure Martin, Inna Yu Badanina et Sergey F. Sluzhenikin. « Oxygen-Hafnium-Neodymium Isotope Constraints on the Origin of the Talnakh Ultramafic-Mafic Intrusion (Norilsk Province, Russia) ». Economic Geology 115, n^o 6 (1 septembre 2020) : 1195–212. http://dx.doi.org/10.5382/econgeo.4743.

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Abstract The ultramafic-mafic Talnakh intrusion in the Norilsk province (Russia) hosts one of the world’s major platinum group element (PGE)-Cu-Ni sulfide deposits. This study employed a multitechnique approach, including in situ Hf-O isotope analyses of zircon combined with whole-rock Nd isotope data, in order to gain new insights into genesis of the Talnakh economic intrusion. Zircons from gabbrodiorite, gabbroic rocks of the layered series, and ultramafic rocks have similar mantle-like mean δ18O values (5.39 ± 0.49‰, n = 27; 5.64 ± 0.48‰, n = 34; and 5.28 ± 0.34‰, n = 7, respectively), consistent with a mantle-derived origin for the primary magma(s) parental to the Talnakh intrusion. In contrast, a sulfide-bearing taxitic-textured troctolite from the basal part of intrusion has high δ18O (mean of 6.50‰, n = 3), indicating the possible involvement of a crustal component during the formation of sulfide-bearing taxitic-textured rocks. The Hf isotope compositions of zircon from different rocks of the Talnakh intrusion show significant variations, with ɛHf(t) values ranging from –3.2 to 9.8 for gabbrodiorite, from –4.3 to 11.6 for unmineralized layered-sequence gabbroic rocks, from 2.3 to 12 for mineralized ultramafic rocks, and from –3.5 to 8.8 for mineralized taxitic-textured rocks at the base of the intrusion. The significant range in the initial 176Hf/177Hf values is ascribed to interaction of distinct magma sources during formation of the Talnakh intrusion. These include (1) a juvenile source equivalent to the depleted mantle, (2) a subcontinental lithospheric source, and (3) a minor crustal component. Initial whole-rock Nd isotope compositions of the mineralized taxitic-textured rocks from the base of the intrusion (mean ɛNd(t) = –1.5 ± 1.8) differ from the other rocks, which have relatively restricted ranges in initial ɛNd (mean ɛNd = 0.9 ± 0.2). The major set of ɛNd values around 1.0 at Talnakh is attributed to limited crustal contamination, presumably in deep magma chambers, whereas the smaller set of negative ɛNd values in taxitic-textured rocks is consistent with greater involvement of a crustal component and reflects an interaction with the wall rocks during emplacement.

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Yan, Fangchao, Qing Liu, Quanlin Hou et Miao He. « Mineralogy, Geochemistry and Tectonic Setting of the Raobazhai Ultramafic Complex, North Dabie ». Minerals 12, n^o 3 (24 février 2022) : 286. http://dx.doi.org/10.3390/min12030286.

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The Raobazhai ultramafic complex is located in the north of the Dabie Mountains and is composed of spinel peridotites accompanied by a few lenticular mafic metamorphic rocks. The spinel peridotites are mostly harzburgite, along with minor dunite and lherzolite. This study reports the petrological, geochemical, and Re-Os isotopic data of spinel and chromite harzburgites from Raobazhai. The major and trace whole-rock geochemistry characteristics indicate that the rocks are remnants of partial melting to different degrees (6–17%). Both mineral and whole-rock geochemistry showed typical abyssal peridotite affinity. Due to the presence of water-bearing minerals, the Sr, Ba, and U were enriched, and the Nb, Zr, and Hf were depleted, which can be attributed to the strong metasomatism of the boninitic melting/fluid in the fore-arc domain. The flat distribution of platinum group elements (PGE) and the decoupling of Pt-Pd were also the result of the fore-arc melting/fluid interaction. The 187Os/188Os ratios (0.1149–0.1266) were generally lower than the recommended value of the primitive mantle and fell within the abyssal peridotite isotope range. This indicated that the Raobazhai harzburgites were likely mantle peridotites with oceanic characteristics that underwent a fore-arc boninitic melting/fluid transformation event.

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