0000000000079440
AUTHOR
Thomas Wenzel
Age, geodynamic setting, and mantle enrichment processes of a K-rich intrusion from the Meissen massif (northern Bohemian massif) and implications for related occurrences from the mid-European Hercynian
The plutonic complex of the Meissen massif (northern margin of the Bohemian massif) comprises dioritic to mainly monzonitic and granitic rocks. The diorite to monzonite intrusions show major and trace element patterns typical for shoshonitic series. The chemical signatures of less crustally contaminated diorites are similar to arc-related shoshonitic rocks derived from continental lithospheric mantle (CLM) sources previously enriched by subduction of altered oceanic crust. Laser step heating 40Ar/39Ar analyses on actinolitic to edenitic amphiboles from geographically different occurrences of the monzonitic intrusion yielded concordant plateau ages as well as total gas ages ranging from 329.…
The compositional variability of eudialyte-group minerals
AbstractEudialyte-group minerals (EGM) represent the most important index minerals of persodic agpaitic systems. Results are presented here of a combined EPMA, Mössbauer spectroscopy and LA-ICP-MS study and EGM which crystallized in various fractionation stages from different parental melts and mineral assemblages in silica over- and undersaturated systems are compared. Compositional variability is closely related to texture, allowing for reconstruction of locally acting magmatic to hydrothermal processes. Early-magmatic EGM are invariably dominated by Fe whereas hydrothermal EGM can be virtually Fe-free and form pure Mn end-members. Hence the Mn/Fe ratio is the most suitable fractionation …
Contamination of mafic magma by partial melting of dolomitic xenoliths
Mg-skarns enclosed in dunite cumulates of the Neo-Proterozoic Ioko-Dovyren intrusion (northern Baikal region, Russia) can be traced to silica-poor dolomitic host rock layers. The dominant minerals of the skarns are brucite (pseudomorph after periclase), forsterite and Cr-poor spinel. Rapid heating of quartzpoor dolomitic xenoliths led to the formation of minor olivine, followed by the breakdown of dolomite to calcite and periclase. Xenoliths were partially melted upon further heating resulting in a calcite melt. This low-density melt was quantitatively squeezed out, mixed with the surrounding mafic magma and left behind periclase and olivine. This caused the crystallization of new olivine w…
The volatile inventory (F, Cl, Br, S, C) of magmatic apatite: An integrated analytical approach
Abstract Apatite is ubiquitous in a wide range of magmatic rocks and its F–Cl–Br–S systematics can be used to decipher e.g., mixing processes within a magmatic complex and may give insights into fluid un-mixing and degassing processes during the emplacement and cooling of plutonic rocks. In this study, we analyzed a F-apatite (Durango, Mexico), a Cl-apatite (Odegarden, Norway) and apatites from five plutonic samples from the alkaline Mt. Saint Hilaire Complex (Canada) by means of Electron Microprobe Analysis (EPMA), Laser Ablation ICP-MS (LA-ICP-MS), Secondary Ion Mass Spectrometry (SIMS), pyrohydrolysis combined with ion chromatography, Fourier Transformed Infrared Spectroscopy (FTIR), Ins…
The Magmatic to Hydrothermal Evolution of the Intrusive Mont Saint-Hilaire Complex: Insights into the Late-stage Evolution of Peralkaline Rocks
The Cretaceous Mont Saint-Hilaire complex (Quebec, Canada) comprises three major rock units that were emplaced in the following sequence: (I) gabbros; (II) diorites; (III) diverse partly agpaitic foid syenites. The major element compositions of the rock-forming minerals, age-corrected Nd and oxygen isotope data for mineral separates and trace element data of Fe-Mg silicates from the various lithologies imply a common source for all units. The distribution of the rare earth elements in clinopyroxene from the gabbros indicates an ocean island basalt type composition for the parental magma. Gabbros record temperatures of 1200 to 800 degrees C, variable silica activities between 0 center dot 7 …
Rare earth elements in apatite as a monitor of magmatic and metasomatic processes: The Ilímaussaq complex, South Greenland
Abstract Textural and compositional variations of apatite from the plutonic Ilimaussaq complex in South Greenland and its surrounding country rocks track magmatic and metasomatic processes. Detailed back-scattered electron (BSE) imaging reveals various types of apatite textures including (i) growth zonation (concentric, oscillatory as well as sector zonation) formed during magmatic differentiation, (ii) resorption and overgrowth textures due to fluid/melt induced metasomatic overprint of precursor apatite and (iii) replacement textures indicating the destabilization of apatite in favor of monazite. In the least evolved rocks of the Ilimaussaq complex, apatite incorporates rare earth element…
Thallium geochemistry in the metamorphic Lengenbach sulfide deposit, Switzerland: Thallium-isotope fractionation in a sulfide melt
The Lengenbach (Switzerland) Pb-As-Tl-Zn deposit was formed from a sulfide melt at about 500 °C during Alpine metamorphism, but details on its formation and especially the source of the metals are still under debate. In this study we present two sample sets to address these questions: 1. MC-ICP-MS analyses of thallium isotopes in sulfides, sulfosalts, and melt inclusions from the Alpine metamorphic Lengenbach deposit in the Binn Valley of Switzerland, the non-metamorphic Wiesloch Mississippi Valley-type deposit in Southern Germany, and the Cu- and As-rich mineralization at Pizzo Cervandone about 2 km SW of the Lengenbach deposit, which has been discussed as potential source of the Lengenbac…
Internal structures and dating of complex zircons from Meissen Massif monzonites, Saxony
Abstract U–Pb zircon ages were determined for accessory zircons from two monzonites from the Meissen Massif (Northern Bohemian Massif, Germany) by SHRIMP ion microprobe. BSE and CL imaging revealed that the monzonite zircons, showing oscillatory growth zoning, often contain inherited cores. Raman microprobe measurements showed that zoned rims (U 277–1426 ppm, Th 144–910 ppm) are slightly disordered to moderately metamict whereas cores have a wide spectrum of structural states, from well-crystallized to highly metamict. The radionuclide (U+Th) content of cores varies from a few hundred to more than 20,000 ppm. SHRIMP ion probe measurements on zoned rims, interpreted as zircon growth during c…
THE REDISTRIBUTION OF RARE-EARTH ELEMENTS IN SECONDARY MINERALS OF HYDROTHERMAL VEINS, SCHWARZWALD, SOUTHWESTERN GERMANY
Minerals of the rare-earth elements (REE) occur as supergene phases in the Schwarzwald ore district, southwestern Germany. They form by alteration of hydrothermal fluorite – barite – quartz – carbonate veins with various associations, including Cu– Pb, Pb–Zn and Co–Bi–Ag–U assemblages in sandstones, gneisses and granites. The REE minerals, including mixite-group minerals ([REE,Bi,Ca,Pb]Cu 6 (AsO 4 ,AsO 3 OH) 3 OH 6 •3H 2 O), rhabdophane and churchite (REEPO 4 •H 2 O and REEPO 4 •2H 2 O), chukhrovite (Ca 3 REEAl 2 SO 4 F 13 •10H 2 O) and bastnasite (REECO 3 F), were analyzed by electron microprobe and LA–ICP–MS. In addition, REE concentrations in secondary fluorite, calcite and Mn oxides cog…
The geochemistry of Tl and its isotopes during magmatic and hydrothermal processes: The peralkaline Ilimaussaq complex, southwest Greenland
Abstract We use thallium (Tl) concentrations, K/Rb, K/Tl and Rb/Tl ratios and Tl isotopes in minerals from the alkaline to peralkaline Ilimaussaq complex (South Greenland) to trace magmatic differentiation, crustal assimilation, magmatic degassing, ore precipitation and hydrothermal metasomatism. Closed-system magmatic differentiation is marked by a coherent decrease of K/Tl- and K/Rb-ratios, whereas crustal assimilation results in a strong Tl-enrichment, causing low K/Tl-ratios compared to K/Rb-ratios. Thallium isotopes show only slight changes during orthomagmatic differentiation and the assimilation of crustal material cannot be traced, since the isotopic composition of the average crust…
Trace element systematics of tourmaline in pegmatitic and hydrothermal systems from the Variscan Schwarzwald (Germany): The importance of major element composition, sector zoning, and fluid or melt composition
article An extensive data set on the compositional variation of tourmaline from granitic pegmatites, from migmatitic gneisses and from various types of hydrothermal veins from the Schwarzwald, Germany, is provided. The investigated tourmalines are members of the alkali and X-vacant groups representing mostly dravite- schorl solid solutions with some analyses belonging to the foitite-Mg-foitite series. Oxygen isotope data on quartz-tourmaline pairs indicate formation temperatures between 550 and 350 °C for most of the quartz-tourmaline veins. Most of the tourmalines show strong sector zonation, fractionating certain major (e.g., Na, Mg), minor (e.g., Ti, Ca) and trace elements (e.g., Sr, Pb,…