Kurt Krenn

TiO2 exsolution from garnet by open-system precipitation: evidence from crystallographic and shape preferred orientation of rutile inclusions

We investigated rutile needles with a clear shape preferred orientation in garnet from (ultra) high-pressure metapelites from the Kimi Complex of the Greek Rhodope by electron microprobe, electron backscatter diffraction and TEM techniques. A definite though complex crystallographic orientation relationship between the garnet host and rutile was identified in that Rt[001] is either parallel to Grt<111> or describes cones with opening angle 27.6° around Grt<111>. Each Rt[001] small circle representing a cone on the pole figure displays six maxima in the density plots. This evidence together with microchemical observations in TEM, when compared to various possible mechanisms of formation, corroborates a precipitate origin. A review of exchange vectors for Ti substitution in garnet indicates that rutile formation from garnet cannot occur in a closed system. It requires that components are exchanged between the garnet interior and the rock matrix by solid-state diffusion, a process we refer to as “open-system precipitation” (OSP). The kinetically most feasible reaction of this type will dominate the overall process. The perhaps most efficient reaction involves internal oxidation of Fe2+ to Fe3+ and transfer from the dodecahedral to the octahedral site just vacated by

Room temperature synthesis of CuInS2 nanocrystals

{\text{Ti}}^{ 4+ }: 6\,{\text{M}}^{ 2+ }_{ 3} {\text{TiAl}}\left[ {{\text{AlSi}}_{ 2} } \right]{\text{O}}_{ 1 2} + 6\,{\text{M}}^{ 2+ }_{ 2, 5} {\text{TiAlSi}}_{ 3} {\text{O}}_{ 1 2} = 10\,{\text{M}}^{ 2+ }_{ 3.0} {\text{Al}}_{ 1. 8} {\text{Fe}}_{0. 2} {\text{Si}}_{ 3} {\text{O}}_{ 1 2} + {\text{M}}^{2+} + 2 {\text{e}}^{-} + 1 2\,{\text{TiO}}_{ 2} .

Re-equilibration of a high-pressure metamorphic fluid: evidence from tourmaline-, apatite- and quartz-hosted fluid inclusions in an Eoalpine eclogite from the Eastern Alps

OSP is likely to occur at conditions where the transition of natural systems to open-system behaviour becomes apparent, as in the granulite and high-temperature eclogite facies.

Microtextures and fluid inclusions from vein minerals hosted in the Pillow Lavas of the Troodos supra-subduction zone

This paper describes the first findings of pumpellyite in fine-grained ductile deformed metapelites of the Schneeberg Complex as an indicator for high pressure-low temperature metamorphism. Microscopic observations of oriented samples indicate that pumpellyite is always associated with biotite and texturally arranged within arrays of early schistosities (S-C-textures and fold hinge areas). Post-deformational growth of pumpellyite is not observed. Textural, microprobe and Raman spectroscopic data of pumpellyite are compared with subduction related pumpellyite from New Caledonia and Afghanistan and point to a geodynamic setting of mineral growth during convergence and subduction within the Austroalpine continental crust.

Deciphering Magmatic and Metasomatic Processes Recorded by Fluid Inclusions and Apatite within the Cu–Ni±PGE-Sulfide Mineralized Bathtub Intrusion of the Duluth Complex, NE Minnesota, USA

Herein, we investigate a synthetic approach to prepare copper indium sulfide nanocrystals at room temperature. The nanocrystals have a chalcopyrite crystal structure, a diameter of approximately 3 nm and are well soluble in organic solvents like toluene or chloroform. The synthesis is performed by dissolving metal xanthates as precursors together with oleylamine in toluene followed by stirring for several hours at room temperature leading to nanocrystals stabilized with oleylamine ligands. The nanoparticles are characterized in terms of inner structure by X-ray diffraction, transmission electron microscopy, Raman-, absorption- and photoluminescence spectroscopy. Their formation process is investigated by small angle X-ray scattering, UV-Vis absorption spectroscopy and NMR spectroscopy. The formation of the copper indium sulfide nanocrystals proceeds via a chemical reaction of the amine with the thiocarbonyl functionality of the xanthate. The presented method exemplifies a synthesis strategy, which can be easily expanded to other metal sulfide nanocrystals.

A zircon study from the Rhodope metamorphic complex, N-Greece: Time record of a multistage evolution

Abstract In this study, we present new data from microthermometry of fluid inclusions entrapped in hydrothermal veins along the Cocos Ridge from the IODP Expedition 344 Site U1414. The results of our study concern a primary task of IODP Expedition 344 to evaluate fluid/rock interaction linked with the tectonic evolution of the incoming Cocos Plate from the Early Miocene up to recent times. Aqueous, low saline fluids are concentrated within veins from both the Cocos Ridge basalt and the overlying lithified sediments of Unit III. Mineralization and crosscutting relationships give constraints for different vein generations. Isochores from primary, reequilibrated, and secondary fluid inclusions crossed with litho/hydrostatic pressures indicate an anticlockwise PT evolution during vein precipitation and modification by isobaric heating and subsequent cooling at pressures between ∼210 and 350 bar. Internal over and underpressures in the inclusions enabled decrepitation and reequilibration of early inclusions but also modification of vein generations in the Cocos Ridge basalt and in the lithified sediments. We propose that lithification of the sediments was accompanied with a first stage of vein development (VU1 and VC1) that resulted from Galapagos hotspot activity in the Middle Miocene. Heat advection, either related to the Cocos‐Nazca spreading center or to hotspot activity closer to the Middle America Trench, led to subsequent vein modification (VC2, VU2/3) related to isobaric heating. The latest mineralization (VC3, VU3) within aragonite and calcite veins and some vesicles of the Cocos Ridge basalt occurred during crustal cooling up to recent times. Fluid inclusion analyses and published isotope data show evidence for communication with deeper sourced, high‐temperature hydrothermal fluids within the Cocos Plate. The fluid source of the hydrothermal veins reflects aqueous low saline pore water mixed with invaded seawater.

Tectonometamorphic evolution of the Rhodope orogen

Fluid inclusions in tourmaline, apatite and quartz from an eclogite of the Polinik Complex, as part of the Koralpe-Wolz high-pressure (H P ) nappe system (Eastern Alps), have been investigated. All three minerals are interpreted as part of the eclogite- to post-eclogite-facies mineral assemblage which formed during Cretaceous Eoalpine metamorphism at ~ 20 kbar and ~ 650°C. Tourmaline, apatite and quartz contain two types of fluid inclusions: (1) a fluid in the system of H 2 O–NaCl–CaCl 2 –CO 2 –CH 4 –N 2 system, and (2) a fluid in the system of H 2 O–NaCl–CaCl 2 ± MgCl 2 system. Type (1) dominates in tourmaline, and type (2) in apatite and quartz. Fluid inclusions of type (1) occur individually and as clusters. In addition to isolated inclusions, type (2)-inclusions also arranged along intragranular/transgranular fluid inclusion planes – but not at grain contacts. The clear distinction in their textural occurrence enables the reconstruction of the H P fluid evolution from a supposed precursor fluid to stages of retrogression accompanied with re-equilibration and preferential loss of the aqueous fluid phase along a proposed exhumation path. Calculated fluid densities of type (1) indicate conditions that reach 14 kbar in tourmaline and 12 kbar in quartz when linked with peak temperatures of ~ 650°C. Conditions are interpreted as minimum conditions during formation of the host minerals. Fluid-inclusion densities from the studied aqueous system type (2) are coherent in the studied host minerals and reach pressures of about 8–10 kbar. A possible reason for the differences in estimated pressure between type (1) and type (2) is, beside textural arguments, the preferred loss of water during recrystallization of the studied minerals at post-peak stages. This hypothesis is supported by the same fluid chemistry of the aqueous phase (H 2 O–NaCl–CaCl 2 ± MgCl 2 ) in type (1)- and type (2)-inclusions. Additionally, different wetting behaviour of fluids containing dominantly polar [type (1)] and non-polar [type (2)] species promoted recrystallization, especially in quartz, and led to widespread decrepitation of large fluid inclusions in quartz during decompression. Hence, the fluid evolution documented in the Polinik eclogites can be reconstructed through effects of physical and chemical changes of the host minerals after peak metamorphism.

Fluid entrapment and reequilibration during subduction and exhumation: A case study from the high-grade Nestos shear zone, Central Rhodope, Greece

This study deals with microtextures and fluid inclusions from veins and vesicles hosted in the Troodos Pillow Lavas that enable a conclusive model for vein formation during the post-magmatic stage of the Troodos supra-subduction zone. Three different types of veins from the Upper and Lower Pillow Lavas are distinguished and imply different modes of fracturing, fluid flow, and precipitation. (1) Syntaxial calcite-, quartz-, and zeolite-bearing veins are interpreted as mineralized extension fractures that were pervaded by seawater. This advective fluid flow in an open system changed later into a closed system characterized by geochemical self-organization. (2) Blocky and (3) antitaxial fibrous calcite veins are associated with host rock brecciation due to hydrofracturing and diffusion-crystallization processes, respectively. Based on aqueous fluid inclusion chemistry with seawater salinities in all studied vein types, the representative fluid isochores crossed with minimum hydrostatic pressure conditions yield vein mineral precipitation temperatures between 180 and 210 °C at 250 bar, independently of the Pillow Lava units. This points to a heat source for the circulating seawater and implies that vein and vesicle minerals precipitated shortly after pillow lava crystallization under dominant isobaric cooling conditions. Compared to previous suggestions derived from secondary mineral parageneses, significant higher temperatures of vein formation in the Troodos Pillow Lavas are proposed. LITHOSPHERE; v. 10; no. 4; p. 566–578 | Published online 6 June 2018 https://doi.org/10.1130/L696.1