The Advocate ophiolite mantle, Baie Verte, Newfoundland: regional correlations and evidence for metasomatismGeological Survey of Canada, Earth Sciences Sector, Contribution 20090211.

2010 ◽  
Vol 47 (3) ◽  
pp. 237-253 ◽  
Author(s):  
Jean H. Bédard ◽  
Monica Escayola
Keyword(s):  
Earth Sciences ◽  
Subduction Zone ◽  
Mineral Chemistry ◽  
Major Elements ◽  
Apparent Absence ◽  
Gold Exploration ◽  
Metasomatic Agent ◽  
Exploration Target ◽  
Chemical Signatures

Mantle rocks of the Advocate ophiolite near Flatwater Pond (Baie Verte, Newfoundland) are dominated by harzburgite tectonites, which are extensively converted to listvenite along the Baie Verte Road fault and represent a potential gold exploration target. Most Advocate harzburgites have forsteritic olivine (Fo90.5 to Fo93) and Cr-spinels, with Cr# (= 100Cr/(Cr + Al)) between 52 and 64 and Mg# (= 100Mg/(Mg + Fe2+)) between 56 and 68. These mineral chemical signatures, together with high whole-rock MgO (46%–48%), low Al2O3 (<1%), and TiO2 (<0.003%), imply the Advocate harzburgites are refractory residues after ca. 25%–35% melting. Cr-spinel compositions of Advocate mantle rocks overlap with Cr-spinels from the mantle rocks of the Point Rousse and Betts Cove ophiolites, with Mg# higher than those of Bay of Islands or Thetford Mines mantle Cr-spinels. Although refractory in terms of major elements and mineral chemistry, Advocate harzburgites contain high La–Ce–Pr–Pb–Nd–Sm–Zr contents suggestive of pervasive metasomatism. Similar geochemical signatures occur in all ophiolitic mantle rocks from the Baie Verte Peninsula examined so far. The enrichments are not consistent with supra-subduction zone syn-melting metasomatism as observed in other Appalachian ophiolites. The apparent absence of visible metasomatic channels in most outcrops suggests that metasomatism occurred before obduction by diffuse percolation, but the nature and origin of the metasomatic agent remain speculative. The similarities of mineral and whole-rock geochemistry imply that all mantle rocks from Baie Verte ophiolites are correlative and may represent remnants of a single obducted slab.

scholarly journals Contrasting Textural and Chemical Signatures of Chromitites in the Mesoarchaean Ulamertoq Peridotite Body, Southern West Greenland

Geosciences ◽  
2018 ◽  
Vol 8 (9) ◽  
pp. 328 ◽  
Author(s):  
Juan Guotana ◽  
Tomoaki Morishita ◽  
Ryoko Yamaguchi ◽  
Ikuya Nishio ◽  
Akihiro Tamura ◽  
...  
Keyword(s):  
Mineral Chemistry ◽  
Ultramafic Rocks ◽  
West Greenland ◽  
Temperature Conditions ◽  
Chemical Signatures ◽  
Fe Content ◽  
Compositional Zonation

Peridotites occur as lensoid bodies within the Mesoarchaean orthogneiss in the Akia terrane of Southern West Greenland. The Ulamertoq peridotite body is the largest of these peridotites hosted within the regional orthogneiss. It consists mainly of olivine, orthopyroxene, and amphibole-rich ultramafic rocks exhibiting metamorphic textural and chemical features. Chromitite layers from different localities in Ulamertoq show contrasting characteristics. In one locality, zoned chromites are hosted in orthopyroxene-amphibole peridotites. Compositional zonation in chromites is evident with decreasing Cr and Fe content from core to rim, while Al and Mg increase. Homogeneous chromites from another locality are fairly uniform and Fe-rich. The mineral chemistry of the major and accessory phases shows metamorphic signatures. Inferred temperature conditions suggest that the zoned chromites, homogeneous chromites, and their hosts are equilibrated at different metamorphic conditions. In this paper, various mechanisms during the cumulus to subsolidus stages are explored in order to understand the origin of the two contrasting types of chromites.

scholarly journals Occurrence of Graphite-Like Carbon in Podiform Chromitites of Greece and Its Genetic Significance

Minerals ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 152 ◽  
Author(s):  
Maria Economou-Eliopoulos ◽  
George Tsoupas ◽  
Vasilis Skounakis
Keyword(s):  
Subduction Zone ◽  
Mineral Chemistry ◽  
Present Contribution ◽  
Term Evolution ◽  
Wide Range ◽  
Carbon Recycling ◽  
Podiform Chromitites ◽  
Of Greece

The role of post-magmatic processes in the composition of chromitites hosted in ophiolite complexes, the origin of super-reduced phases, and factors controlling the carbon recycling in a supra-subduction zone environment are still unclear. The present contribution compiles the first scanning electron microscope/energy-dispersive (SEM/EDS) data on graphite-like amorphous carbon, with geochemical and mineral chemistry data, from chromitites of the Skyros, Othrys, Pindos, and Veria ophiolites (Greece). The aim of this study was the delineation of potential relationships between the modified composition of chromite and the role of redox conditions, during the long-term evolution of chromitites in a supra-subduction zone environment. Chromitites are characterized by a strong brittle (cataclastic) texture and the presence of phases indicative of super-reducing phases, such as Fe–Ni–Cr-alloys, awaruite (Ni3Fe), and heazlewoodite (Ni3S2). Carbon-bearing assemblages are better revealed on Au-coated unpolished sections. Graphite occurs in association with hydrous silicates (chlorite, serpentine) and Fe2+-chromite, as inclusions in chromite, filling cracks within chromite, or as nodule-like graphite aggregates. X-ray spectra of graphite–silicate aggregates showed the presence of C, Si, Mg, Al, O in variable proportions, and occasionally K and Ca. The extremely low fO2 during serpentinization facilitated the occurrence of methane in microfractures of chromitites, the precipitation of super-reducing phases (metal alloys, awaruite, heazlewoodite), and graphite. In addition, although the origin of Fe–Cu–Ni-sulfides in ultramafic parts of ophiolite complexes is still unclear, in the case of the Othrys chromitites, potential reduction-induced sulfide and/or carbon saturation may drive formation of sulfide ores and graphite-bearing chromitites. The presented data on chromitites covering a wide range in platinum-group element (PGE) content, from less than 100 ppb in the Othrys to 25 ppm ΣPGE in the Veria ores, showed similarity in the abundance of graphite-like carbon. The lack of any relationship between graphite (and probably methane) and the PGE content may be related to the occurrence of the (Ru–Os–Ir) minerals in chromitites, which occur mostly as oxides/hydroxides, and to lesser amounts of laurite, with pure Ru instead activating the stable CO2 molecule and reducing it to methane (experimental data from literature).

scholarly journals Elemental composition of ambient aerosols measured with high temporal resolution using an online XRF spectrometer

2017 ◽  
Vol 10 (6) ◽  
pp. 2061-2076 ◽  
Author(s):  
Markus Furger ◽  
María Cruz Minguillón ◽  
Varun Yadav ◽  
Jay G. Slowik ◽  
Christoph Hüglin ◽  
...  
Keyword(s):  
Data Quality ◽  
Time Resolution ◽  
Absorption Spectrometry ◽  
Major Elements ◽  
High Temporal Resolution ◽  
High Time Resolution ◽  
Ambient Aerosols ◽  
Field Campaign ◽  
Chemical Signatures ◽  
Icp Ms

Abstract. The Xact 625 Ambient Metals Monitor was tested during a 3-week field campaign at the rural, traffic-influenced site Härkingen in Switzerland during the summer of 2015. The field campaign encompassed the Swiss National Day fireworks event, providing increased concentrations and unique chemical signatures compared to non-fireworks (or background) periods. The objective was to evaluate the data quality by intercomparison with other independent measurements and test its applicability for aerosol source quantification. The Xact was configured to measure 24 elements in PM10 with 1 h time resolution. Data quality was evaluated for 10 24 h averages of Xact data by intercomparison with 24 h PM10 filter data analysed with ICP-OES for major elements, ICP-MS for trace elements, and gold amalgamation atomic absorption spectrometry for Hg. Ten elements (S, K, Ca, Ti, Mn, Fe, Cu, Zn, Ba, Pb) showed excellent correlation between the compared methods, with r2 values  ≥  0.95. However, the slopes of the regressions between Xact 625 and ICP data varied from 0.97 to 1.8 (average 1.28) and thus indicated generally higher Xact elemental concentrations than ICP for these elements. Possible reasons for these differences are discussed, but further investigations are needed. For the remaining elements no conclusions could be drawn about their quantification for various reasons, mainly detection limit issues. An indirect intercomparison of hourly values was performed for the fireworks peak, which brought good agreement of total masses when the Xact data were corrected with the regressions from the 24 h value intercomparison. The results demonstrate that multi-metal characterization at high-time-resolution capability of Xact is a valuable and practical tool for ambient monitoring.

Mineral chemistry of perpotassic lavas of the Vulsinian district, the Roman Province, Italy

1982 ◽  
Vol 46 (340) ◽  
pp. 379-386 ◽  
Author(s):  
Paul M. Holm
Keyword(s):  
Magma Mixing ◽  
Volcanic Rocks ◽  
Alkali Feldspar ◽  
Mineral Chemistry ◽  
Low Pressure ◽  
Major Elements ◽  
Crystal Fractionation ◽  
High Concentrations ◽  
Roman Province ◽  
Pressure Crystallization

SynopsisThe Vulsinian district is the largest and northernmost of the Roman Provinces. There is very little modern mineralogical data on the Italian Pliocene to Recent perpotassic alkaline volcanic rocks and this account deals with the compositions of the phenocrysts in the Vulsinian lavas.The lavas comprise two suites: a leueite-bearing undersaturated series of leucitites, leueite tephrites, leucite phonolites, and trachytes; and a subordinate hy-normative series of mainly trachytes and latites. All lavas are porphyritic with mostly 1–15 vol. % phenoerysts. No cumulates were found. Major elements, and Cr and Ni were determined in the phenocrysts by microprobe analysis and more than 20 trace elements were determined on mineral separates by PIXE.The undersaturated suite. Ubiquitous clinopyroxene phenoerysts belong to the Di-Hedss series and range from Di97 to Di46. Important amounts of Fe3+ are always present. In the mafic rocks the diopside is chromian, but Ti is low. AI mainly substitutes in the Z positions in all lavas. Only minor Na enrichment occurs with increasing total Fe (0–7 mole % acmite) and thus Ca ferri-Tschermak's component is important. In many of the maric lavas diopside mantles green cores of salite, which has a composition very like the salite of felsic lavas. Leucites contain 5–22 mole % orthoelase in solid solution, but show no systematic variation. Plagioclase, mostly An93-An72, occurs in the felsie lavas, and alkali feldspar only in some phonolites. They both have exceptionally high concentrations of Sr and Ba, with a maximum of 1.3 wt. % SrO and 5.6 wt. % BaO in hyalophanes. Olivine, Fo92-Fo66, occurs in some leucititic lavas in mostly accessory amounts. Phlognpite, magnetite and nepheline are accessory phases of the felsic lavas. Apatite only occur as micro-phenocrysts of the fclsic lavas. Haüyne in trace amounts is found in a few phonolites. Pargasitic amphibole microphenocrysts are found in one lava.In most marie members diopside ±leuctie ±olivine were liquidus phases. This study does not confirm that these rocks are related by crystal fractionation. In more felsie lavas clinopyroxene (salite-ferrosalite) and leucite are joined by: plagioclase, magnetite ±phlogopite, and Ba-rich alkali feldspar ±haüyne. The felsic rocks are thought to be related by crystal fractionation.Salitic green cores of phenocrystic pyroxene, mantled by diopside in rocks which also carry normally-zoned diopside, are relicts which provide evidence of either a relatively high PH2O, prior to the crystallization of diopside or magma mixing in the earlier life of these lavas. Pyroxene chemistry points towards low-pressure crystallization (2 kbar), generally in a dry environment.The hy-normative suite. All lavas have phenocrysts of augite, sanidine, plagioclase, magnetite, biotite, and olivine. The pyroxene is less calcic and has less alumina, but is otherwise rather similar to the salites of the undersaturated suite. Compared to the undersaturated suite, feldspars do not have high Sr and Ba, magnetite has higher TiO2 and olivine crystallized from even the felsic lavas. The pyroxenes show the signs of low-pressure crystallization.

Geochemistry, mineral chemistry and petrogenesis of a Neoproterozoic dyke swarm in the north Eastern Desert, Egypt

2006 ◽  
Vol 143 (1) ◽  
pp. 115-135 ◽  
Author(s):  
M. DAWOUD ◽  
H. A. ELIWA ◽  
G. TRAVERSA ◽  
M. S. ATTIA ◽  
T. ITAYA
Keyword(s):  
Tectonic Setting ◽  
Mineral Chemistry ◽  
Eastern Desert ◽  
Major And Trace Elements ◽  
Dyke Swarm ◽  
Mafic Dyke ◽  
Crustal Rocks ◽  
The North ◽  
Chemical Signatures ◽  
Dyke Swarms

Dyke swarms traverse Neoproterozoic rocks in the Hawashiya region in the extreme northern part of the Eastern Desert of Egypt. They are a suite of basaltic andesite and andesite mafic dykes, and dacitic and rhyolitic felsic dykes. The mafic dyke suite is more abundant in the younger granites (577 ± 6 Ma) than in the older granitoids (614 Ma), in which the felsic dykes are the most common. The dyke swarms trend predominantly NE–SW, and the felsic dyke suite is older than the mafic dyke suite. Both dyke suites are calc-alkaline (alkaline dykes are rare) and are relatively poor in TiO2 and Nb but enriched in the incompatible elements and HFSE. The felsic dyke suite is enriched in REE and is strongly LREE fractionated relative to the mafic dyke suite. Although the Hawashiya dykes were emplaced at the end of the Neoproterozoic era in an extensional tectonic setting, they have geochemical characteristics that are consistent with a subduction-related regime. These chemical signatures were inherited from the lithospheric rocks that produced their host Hawashiya granitoids. The felsic dyke suite magma may be derived from crustal rocks (essential source component) by partial melting. The mafic dyke suite magma was generated from a lithospheric mantle and has undergone fractional crystallization of plagioclase, amphibole, clinopyroxene and magnetite, as documented by major and trace elements fractionation modelling.

scholarly journals The Petrology and  Genesis of Silicic  Magmas in the  Kermadec Arc

2021 ◽  
Author(s):  
◽  
Simon James Barker
Keyword(s):  
Subduction Zone ◽  
Structural Changes ◽  
Mineral Chemistry ◽  
Silicic Magma ◽  
Small Scale ◽  
Mafic Enclaves ◽  
Compositional Range ◽  
Dominant Process ◽  
Wide Compositional Range ◽  
Silicic Magmas

<p>Recent work has shown that silicic volcanism can be abundant in intra-oceanic subduction settings, and is often associated with large explosive caldera-forming eruptions. Several major petrogenetic questions arise over the origin and eruption of large amounts of silicic magma at these relatively simple subduction settings. This study has investigated the geochemistry of pyroclasts collected from four volcanoes along the Kermadec arc, a young (<2 Myr) oceanic subduction zone in the southwest Pacific. Raoul, Macauley and a newly discovered volcano (here informally named 'New volcano') in the northern Kermadec arc, and Healy volcano in the southern Kermadec arc have all erupted dacitic to rhyolitic pumice within the last 10 kyr. For Raoul, New volcano and Healy, whole rock major element compositions fall with a limited compositional range. In contrast, pumice dredged from around Macauley caldera covers a wide compositional range indicating that there have been multiple silicic eruptions, not just the Sandy Bay Tephra exposed on Macauley Island. Distinctive crystal populations in both pumice samples and plutonic xenoliths suggest that many of the crystals did not grow in the evolved magmas, but were mixed in from other sources including gabbros and tonalites. Such open system mixing is ubiquitous in magmas from the four Kermadec volcanoes studied here. Silicic magmas, co-eruptive mafic enclaves and previously erupted basalts show sub-parallel REE patterns, and crystal composition and zonation suggests that mafic and silicic magmas have a strong genetic affiliation. Examination of whole rock, glass and mineral chemistry reveals that evolved magmas can be generated at each volcano through 60-75% crystal fractionation of a basaltic parent. These findings are not consistent with silicic magma generation via crustal anatexis, as previously suggested for the Kermadec arc. Although crystallisation is the dominant process driving melt evolution in the Kermadec volcanoes, the magmatic systems are open to contributions from both newly arriving melts and wholly crystalline plutonic bodies. Such processes occur in variable proportions between magma batches, and are largely reflected by small scale chemical variations between eruption units. Larger scale chemical trends reflect the position of the volcanoes along the arc, which in turn may reflect structural changes in the subduction zone and variations in sediment influx.</p>

scholarly journals Study of the chromite mineralization associated to ophiolites from Tinos Island, Attico-Cycladic Massif

2019 ◽  
Vol 55 (1) ◽  
pp. 185
Author(s):  
Maria Kokkaliari ◽  
Karen St. Seymour ◽  
Stylianos F. Tombros ◽  
Eleni Koutsopoulou
Keyword(s):  
Subduction Zone ◽  
Mantle Wedge ◽  
Binary Classification ◽  
Mineral Chemistry ◽  
Textural Features ◽  
Ophiolite Complex ◽  
Depleted Mantle ◽  
Back Arc ◽  
Host Rocks ◽  
Petrographic Study

This paper aims to study the chromitites, as well as their host rocks (meta-peridotites, meta-dunites and serpentinites) of the ophiolite complex of Mount Tsiknias, in Tinos Island. Recognition of their mineralogy and their textural features was carried out through detailed petrographic study. The mineral chemistry analysis contributed to the evaluation of the analyzed chromites, the chemical composition of which provides important information about the petrogenetic evolution of the chromitite ores. The chromites were in equilibrium with boninite melts derived from Supra-Subduction Zone, e.g., a depleted mantle wedge. In the binary classification diagram for spinels, the Tinos samples extend in the fields of Mg-chromite and chromite sensu strictu. In the TiO2 vs Al2O3 diagram, the chromites plot in the field of Supra-Subduction Zone (SSZ) peridotites and partly overlap the field of chromites in Back-Arc Basalts (BABB), however the same samples plot in the field of chromite of boninites. In the Al2O3 vs Cr2O3 diagram both groups of Tinos chromites plot in the field/extremity of “mantle chromites”.

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