Komatiites in the Pacaud assemblage are Ti-depleted komatiites (TDK) with high AbO31TiOz (25-35) and low [Gd/Yb]c~ (-0.6) (CN: chondrite normalized using values from McDonough and Sun, 1995), suggesting a garnet-rich source or formation via dynamic melting similar to Gorgona komatiites (Arndt et al., 1997).
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Introduction. A large body of data exists in the literature describing chromites from ophiolites, layered intrusions, kimberlites, basalts and other provenances, but relatively few studies have looked systematically at chromite in komatiites (e.g. Zhou & Kerrich, 1992).This is the first in a series of papers which addresses the occurrence of chromite in komatiites and its …
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Komatiites are ultra-hot ultramafic lavas, largely restricted to the Archaean. They represent an extreme endmember of terrestrial magmatism and challenge our understanding …
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Komatiites and komatiitic basalts in the Abitibi greenstone belt exhibit pronounced spatial and temporal variations in major and trace element geochemistry that provide important constraints on their petrogenesis and tectonic setting. ... …
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Whole rock samples were crushed using a steel jaw crusher and small chips (3–15 mm) were then separated and washed in an ultrasonic cleaner for 10 min. Clean chips were then dried and milled using agate or mild steel mills. ... Komatiites appear further to the east, and these komatiites have been intruded by granitoids, which are in turn ...
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Komatiites are primarily extrusive volcanic rocks with high MgO contents (>18 %) that formed mainly during the Precambrian, especially during the Archean Era, and are …
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Many komatiites, including the exceptionally fresh and well exposed flows at Pyke hill in Munro township, northeastern Ontario, erupted as subaqueous lava flows 1,4.The thermal effect of seawater ...
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The komatiites that belong to the Gorgona Islands complex have been described as young komatiites (98.7 ± 7.7 to 64.4 ± 5 Ma) whose spinifex texture is composed of spicules made of olivine forsterite-type and pyroxene with high calcium content and low aluminum values.
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JOURNAL OF PETROLOGY VOLUME 41 NUMBER 3 PAGES 387–409 2000 Chromite in Komatiites, II. Modification during Greenschist to Mid-Amphibolite Facies Metamorphism STEPHEN J. BARNES CSIRO EXPLORATION ...
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Assimilation and prolonged suspension of crust-derived sulfide liquid in komatiites are essential to form Ni-rich mineralisation. Evaluating the spatial relationship between komatiite-hosted Ni mineralisation and crustal S sources may thus provide insights into mechanisms of transport, metal enrichment and deposition of assimilated sulfide liquid. This study applied …
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Many komatiites are interpreted to have ascended through continental crust and to have flowed tens of km from their eruptive sites (Lesher et al., 1984; Arndt, 1986b; Hill et al., 1995; Lesher …
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The hydrated komatiites undergo metamorphic devolatilization through a series of dehydration reactions, some of which take place at temperatures beyond the greenschist- to amphibolite-facies transition (e.g., chlorite breakdown at ~800 °C; Hartnady et al., 2022).
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477 All whole-rock powders were prepared using a ceramic jaw crusher and an agate mill. Rhenium and Os concentrations and Os isotopic compositions were obtained on 0.1–0.5 g of rock powder using a low-blank Carius tube acid-digestion method, modified from that described in Shirey & Walker (1995), the details of which are described in Lambert ...
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A broad range of primitive lavas. Mafic-ultramafic tholeiitic lavas such as basalts, picrites, and komatiites represent the deepest and hottest magmas that erupted on Earth.Three main families of komatiites are distinguished depending on their chemical composition; nicknames have been given to them according to locality of the main outcrops (): Al-depleted komatiites …
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Komatiite lavas are famous for their unique olivine spinifex and cumulate crystal textures and internal textural zonation. In komatiitic basalts, such textures can also involve pyroxene. Zone …
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Abstract. Komatiites are products of decompression melting of mantle so hot that they are almost exclusively restricted to the Archean. The high degree of partial melting ( F) and pressure ( P) required for their generation facilitates comparison between the magma composition and its mantle source.To investigate compositional variations in Archean komatiites, a global …
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The case for Ni isotopes is more complex, and fractionations have been previously thought to be small and restricted to continental weathering (Cameron and Vance, 2014; Ratié et al., 2015) or biological processes such as methanogenesis (Cameron et al., 2009).While no significant Ni isotope fractionation has been reported due to fractional crystallization or partial …
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The oxygen fugacities of nine mantle-derived komatiitic and picritic systems ranging in age from 3.55 Ga to modern day were determined using the redox-sensitive partitioning of V between liquidus olivine and komatiitic/picritic melt.
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Komatiites in the Luxi terrane have lower TiO 2 and HREE compared to others (Fig. 5, Fig. 11, Fig. 12), possibly due to higher degrees of partial melting or a more refractory mantle source, or possibly both (Polat et al., 2006). With the exception of the Barberton ADK, the depletion of komatiites' source can be seen in the steeper slopes of ...
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komatiites is metasomatic introduction or depletion of elements during metamorphic and/or hydrothermal fluid–rock interaction. In the Agnew–Wiluna greenstone belt, some portions of …
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The use of komatiites to characterize the abundance and distribution of HSE in the early mantle critically depends on developing a better understanding of the partitioning behaviors of these …
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Following the early description of komatiites from Barberton Mountainland, South Africa (Viljoen and Viljoen, 1969), these rocks were reported from different parts of the world including the greenstone belts of Canada, Africa, India and Australia.Komatiites are more common in the Archean greenstone belts and rapidly diminish in abundance by the late …
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Samples were crushed with a steel jaw crusher at the University of Western Australia to a size of 0.2–2 ... komatiites, tholeiitic basalts, and boninites. Komatiites have been subdivided into Al-undepleted (AUK, or Munro-type) and Al-depleted (ADK, or Barberton-type) varieties, and ADK into Al-depleted and Al-depleted–Ti-enriched subtypes ...
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In this paper, we report Re-Os concentrations and isotopic compositions of whole rocks and chromite separates from a suite of ca. 2.7-Ga komatiites and komatiitic basalts in the …
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Komatiites are known but knowledge about these rocks in the NCC is limited (Cheng et al., 1982). Komatiites in the eastern NCC were first reported from the Neoarchean Taishan Group in the Luxi terrane (Cheng et al., 1982). Although spinifex texture was not initially reported, subsequent studies have confirmed that komatiites in the Sujiagou ...
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komatiites are stratigraphically equivalent to those exposed in the Alexo area and in Munro Township, and are part of the spatially extensive ( 180 km 12 km) Kidd-Munro volcanic ... ceramic jaw crusher. The freshest pieces were cleaned with Milli-Q water in an ultrasonic bath for ½ h and were subsequently dried in an
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Komatiites are ultramafic volcanic rocks that occur mainly in Archean and Paleoproterozoic greenstone belts. These olivine-rich rocks are assumed to have crystallized …
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Komatiites are ultramafic volcanic rocks that occur mainly in Archean and Paleoproterozoic greenstone belts. These olivine-rich rocks are assumed to have crystallized from magmas that have about ...
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remarkably fresh, 2.7-Gyr-old komatiites have been discovered, which contain unaltered olivine crystals and small glass inclusions 1• We report ion micoprobe data for 25 trace elements from these
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Komatiites and variolitic basalts are widespread in Archean volcanic sequences. Spinifex is a spectacular bladed olivine or pyroxene texture that characterizes komatiite, a rock almost exclusively ...
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The formation of platy olivine spinifex, the texture that characterizes komatiite lavas, has long been enigmatic. A major problem is that the dendritic morphology of the olivine resembles that of crystals grown in laboratory experiments at high cooling rates (>50 C/h), but at the position where these textures form, up to several meters below the komatiite flow top, the …
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komatiites and hence promoting ore genesis (Lesher et al. 2001). However, this study questions the role of crustal ... a ceramic-faced jaw crusher. A 100–150 g aliquot of crushed sample was ground in an agate mill and was used for geochemical studies. Figure 2 (a) Simplified geological map of the Mt Keith domain, showing the location of the ...
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Textures of komatiites from the Alexo area. a A scanned thin section of a random olivine spinifex-textured lava (sample M662). Olivine crystals (in white) are randomly oriented and lie in a fine-grained matrix.b Polished slab of coarse platy olivine spinifex textured lava, sample Ax105. Large complex dendritic grains of olivine (black, serpentinized) enclose a cell within …
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shown, however, that these komatiites, like those in most other areas, erupted as lava flows. Further com-ments on the wet komatiite hypothesis have been given by Arndt et al. (1998) and Arndt (2003).
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