Andreas Kronz | Georg-August-Universität Göttingen (original) (raw)

Papers by Andreas Kronz

Shiveluch volcano located in northern Kamchatka erupted mainly high-Mg andesites during Holocene ... more Shiveluch volcano located in northern Kamchatka erupted mainly high-Mg andesites during Holocene times. However, tephrochronologists found two Holocene tephra layers that are unusual for this volcano: a high-Mg middle-K basalts with an age of 7600 yr BP and high-Mg high-K basalt with an age of 3600 yr BP [Volynets et al, 1997]. The proximal outcrops for these two tephra deposits were discovered just recently [Churikova et al., 2010; Gorbach & Portnyagin, 2011]. Our study of olivines from the high-Mg basalts documents unusual Mg-Fe zonation [Gordeychik et al., 2016]: Inner cores of olivines from both eruptions show Fo87-92, falling to the rim to Fo75-85. In the outer cores of both basalt tephra, forsterite decreases linearly abruptly changing to a steeper gradient towards the rim. Electron microprobe element maps reveal the complex and highly unusual zoning features of these olivines. The inner cores of the olivines of 7600 yr BP tephra have bell-shaped distributions for forsterite and nickel. The maximum forsterite in their core can be up to Fo92, decreasing outward to the outer core to Fo86. At the same time, the trace elements in the inner core remain constant. Such element distribution is consistent with diffusion of Fe, Mg, and Ni in the initially uniform high Mg cores after the phenocrysts were changed to non-equilibrium in a less mafic melt. The shape of the inner cores suggests partial dissolution after magma mixing. The interfaces between the inner and outer cores are marked by abundant melt/fluid inclusions. The inner cores were overgrown by olivine with Fo90 when the crystals moved to the high-Mg melt. As result some olivine grains have the maximum forsterite values in the outer core. The specific feature of the olivine outer cores from basalt of the 7600 yr BP tephra eruption are concentric zones with higher values of Ca, Cr, Al, P. One of the crystals has five distinct growth zones with high Cr concentrations. The width of these zones can be only a few microns and thus such zones are often missed in typical quantitative point measurements in microprobe profiles. Inner cores of olivines from the 3600 yr BP tephra are uniform in forsterite and nickel. However, Al and Ca element distribution maps show in inner cores higher concentrations with rather smooth contours. This suggests that initially the olivines were formed from high-Al and high-Ca melt, then were dissolved and the overgrowth zonation has been smoothed out due to faster Mg-Fe diffusion. Only Ca and Al with low diffusivity were conserved. The concentric zones with higher element concentrations are not so well expressed in olivines from the 3600 yr BP tephra, but some distinct growth zones are also shown in Ca, Cr, and P. Information extraction and decoding of the elemental maps allow seeing highly complex growth-dissolutiondiffusion history of magma mixing processes prior to eruption. This research was supported by RFBR-DFG grant # 16-55-12040.

Biogeosciences, 2018

The shallow-marine benthic coralline alga Clathromorphum compactum is an important annual-to sub-... more The shallow-marine benthic coralline alga Clathromorphum compactum is an important annual-to sub-annual-resolution archive of Arctic and subarctic environmental conditions, allowing reconstructions going back > 600 years. Both Mg content, in the high-Mg calcitic cell walls, and annual algal growth increments have been used as a proxy for past temperatures and sea ice conditions. The process of calcification in coralline algae has been debated widely, with no definitive conclusion about the role of light and photosynthesis in growth and calcification. Light received by algal specimens can vary with latitude, water depth, sea ice conditions, water turbidity, and shading. Furthermore, field calibration studies of Clathromorphum sp. have yielded geographically disparate correlations between MgCO 3 and sea surface temperature. The influence of other environmental controls, such as light, on Mg uptake and calcification has received little attention. We present results from an 11-month mesocosm experiment in which 123 wildcollected C. compactum specimens were grown in conditions simulating their natural habitat. Specimens grown for periods of 1 and 2 months in complete darkness show that the typical complex of anatomy and cell wall calcification develops in new tissue without the presence of light, demonstrating that calcification is metabolically driven and not a side effect of photosynthesis. Also, we show that both light and temperature significantly affect MgCO 3 in C. compactum cell walls. For specimens grown at low temperature (2 • C), the effects of light are smaller, with a 1.4 mol % MgCO 3 increase from low-light (mean = 17 lx) to highlight conditions (mean = 450 lx). At higher (10 • C) temperature there was a 1.8 mol % MgCO 3 increase from low to high light. It is therefore concluded that site-and possibly specimen-specific temperature calibrations must be applied, to account for effects of light when generating Clathromorphum-derived temperature calibrations.

Mineralogical Magazine, 2018

ABSTRACTThe Waterberg platinum deposit is an extraordinary example of a vein-type hydrothermal qu... more ABSTRACTThe Waterberg platinum deposit is an extraordinary example of a vein-type hydrothermal quartz-hematite-PGE (platinum-group element) mineralization. This study concentrates on the geochemical character of the ores and the platinum-group mineral (PGM) assemblage by application of reflected-light and scanning electron microscopy followed by electron probe microanalysis.The PGM-bearing quartz veins show multiple banding indicating numerous pulses of fluid infiltration. Mineralization was introduced contemporaneously with the earliest generation of vein quartz and hematite. High oxygen and low sulfur fugacities of the mineralizing fluids are indicated by hematite as the predominant opaque mineral and the lack of sulfides.The ‘Waterberg type’ mineralization is characterized by unique metal proportions, namely Pt>Pd>Au, interpreted as a fingerprint to the cradle of the metals, namely rocks and ores of the Bushveld Complex, or reflecting metal fractionation during ascent of an...

PALAIOS, 2009

We present the first continuous, high-resolution record of Mg/Ca variations within an encrusting ... more We present the first continuous, high-resolution record of Mg/Ca variations within an encrusting coralline red alga, Clathromorphum nereostratum, from Amchitka Island, Aleutian Islands. Mg/Ca ratios of individual growth increments were analyzed by measuring a singlepoint, electron-microprobe transect, yielding a resolution of ϳ15 samples/year and a 65-year record (1902-1967) of variations. Results show that Mg/Ca ratios in the high-Mg calcite algal framework display pronounced annual cyclicity and archive late spring-late fall sea-surface temperatures (SST) corresponding to the main season of algal growth. Mg/Ca values correlate well to local SST, as well as to an air temperature record from the same region. High spatial correlation to large-scale SST variability in the subarctic North Pacific is observed, with patterns of strongest correlation following the direction of major oceanographic features that play a key role in the exchange of water masses between the North Pacific and the Bering Sea. Our data correlate well with a shorter Mg/Ca record from a second site, corroborating the ability of the alga to reliably record regional environmental signals. In addition, Mg/Ca ratios relate well to a 29-year ␦ 18 O time series measured on the same sample, providing additional support for the use of Mg in coralline red algae as a paleotemperature proxy that, unlike algal-␦ 18 O, is not influenced by salinity fluctuations. Moreover, electron microprobe-based analysis enables higher sampling resolution and faster analysis, thus providing a promising approach for future studies of longer C. nereostratum records and applications to other coralline species.

Palaeogeography, Palaeoclimatology, Palaeoecology, 2011

We have investigated the trace elemental composition in the skeleta of two specimens of attached-... more We have investigated the trace elemental composition in the skeleta of two specimens of attached-living coralline algae of the species Clathromorphum compactum from the North Atlantic (Newfoundland) and Clathromorphum nereostratum from the North Pacific/Bering Sea region (Amchitka Island, Aleutians). Samples were analyzed using Laser Ablation-Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) yielding for the first time continuous individual trace elemental records of up to 69years in length. The resulting ...

Ore Geology Reviews, 2006

The peraluminous Land's End granite is one of the composite plutons forming the late-Variscan Cor... more The peraluminous Land's End granite is one of the composite plutons forming the late-Variscan Cornubian batholith. The western part of the pluton hosts the Sn-Cu mineralisation of the St. Just mining district. The pluton consists of early megacrystic biotite (Mg-siderophyllite) granites and albite microgranites and younger Li-siderophyllite granites, and tourmaline granites together with fine-grained massive quartz-tourmaline rocks (MQT). Most of the granite varieties evolved by fractional crystallisation from a common crustal magmatic reservoir, apart from the albite microgranite, which has a different source. Trace element analyses of K-feldspar megacrysts in the older biotite granites made using laser ablation ICP-MS reveal that the megacrysts were derived from moderately evolved sources and now reside in separate granite sub-stages with variable degrees of fractionation, so that equilibrium between phenocrysts and host no longer persists. The younger granites show a strong in situ fractionation at the cm-to 100-m-scale, whereby boron-rich melts are concentrated in the apical parts of the individual intrusive units. Geological, textural and mineralogical data suggest that the tourmaline granites and MQT evolved mainly from fractionated Li-siderophyllite granites. Cathodoluminescence, trace element and melt inclusion studies of quartz from the MQT reveal that the MQT was formed during the transition from the magmatic to hydrothermal states from a mixture of immiscible phases. The Li-siderophyllite granites, tourmaline granites and MQT appear to be the immediate magmatic precursors from which the hydrothermal fluids responsible for the mineralisation in the St Just district originated.

Journal of Asian Earth Sciences, 2014

This study explores the potential of detrital rutile geochemistry and thermometry as a provenance... more This study explores the potential of detrital rutile geochemistry and thermometry as a provenance tracer in rocks from the Central Dabie ultrahigh-pressure metamorphic (UHPM) zone in east-central China that formed during Triassic continental collision. Trace element data of 176 detrital rutile grains selected from local river sediments and 91 rutile grains from distinct bedrocks in the Shuanghe and Bixiling areas, obtained by both electron microprobe (EMP) and in situ LA-ICP-MS analyses, suggest that geochemical compositions and thermometry of detrital rutiles are comparable to those from their potential source rocks. After certification of the Cr-Nb discrimination method for the Central Dabie UHPM zone, we show that 29% of the detrital rutiles in the Shuanghe area were derived from metamafic sources whereas in the Bixiling area that it is up to 76%. Furthermore, the proportion of distinct types of detrital rutiles combined with modal abundances of rutile in metapelites and metamafic bedrocks can be used to estimate the proportion of different source lithologies. Based on this method the proportion of mafic source rocks was estimated to $10% at Shuanghe and >60% at Bixiling, respectively, which is consistent with the proportions of eclogite (the major rutile-bearing metamafic rock) distribution in the field. Therefore, the investigation of detrital rutiles is a potential way to evaluate the proportion of metamafic rocks and even to prospect for metamafic bodies in UHPM terranes. Zr-in-rutile temperatures were calculated at different pressures and compared with temperatures derived from rock-in rutiles and garnet-clinopyroxene Fe-Mg thermometers. Temperatures calculated for detrital rutiles range from 606°C to 707°C and 566°C to 752°C in Shuanghe and Bixiling, respectively, at P = 3 GPa with an average temperatures of ca. 630°C for both areas. These temperature averages and ranges are similar to those calculated for rutiles from surrounding source rocks. Combined with comparable Zr distribution characteristics between detrital and source rock rutiles, demonstrating a close source-sediment link for rutiles from clastic and rock in UHPM terranes. Thus rutiles can be accurate tracers of source rock lithologies in sedimentary provenance studies even at a small regional scale. In Bixiling, Nb/Ta ratios of metamafic and metapelitic detrital rutiles fall between 11.0 to 27.3 and 7.7 to 20.5, respectively. In contrast, in Shuanghe, these ratios are highly variable, ranging from 10.9 to 71.0 and 7.6 to 87.1, respectively. When ignoring four outlier compositions with extremely high Nb/Ta in Shuanghe, a distinct clustering of Nb/Ta ratios in rutiles is shown: metapelitic detrital rutiles have Nb/Ta of 7-40 vs. metamafic detrital rutiles with Nb/Ta = 11-25. The Nb/ Ta characteristics in detrital rutiles from both areas may reflect the degree of fluid-rock interaction during metamorphism and/or different source lithologies. Therefore, the trace element compositions in detrital rutiles can accurately trace the lithology, proportion and fluid-rock interaction of different source rocks.

Geostandards and Geoanalytical Research, 2004

This paper reports the results from a second characterisation of the 91500 zircon, including data... more This paper reports the results from a second characterisation of the 91500 zircon, including data from electron probe microanalysis, laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS), secondary ion mass spectrometry (SIMS) and laser fluorination analyses. The focus of this initiative was to establish the suitability of this large single zircon crystal for calibrating in situ analyses of the rare earth elements and oxygen isotopes, as well as to provide working values for key geochemical systems. In addition to extensive testing of the chemical and structural homogeneity of this sample, the occurrence of banding in 91500 Cet article présente les résultats d'une nouvelle caractérisation du zircon 91500, dont des données de microanalyse par sonde électronique, d'analyse par ablation laser en couplage à un ICP-MS, d'analyse par sonde ionique (SIMS) et d'analyse par fluorination laser. Le but de cette étude était de démontrer que ce large monocristal de zircon pouvait être utilisé pour la calibration d'analyses in situ de Terres Rares et des isotopes de l'Oxygène, et en même temps de fournir des valeurs "de travail" pour un certain nombre de systèmes géochimiques cruciaux. En complément des tests systématiques d'homogénéité de l'échantillon, tant chimiquement

Geochimica et Cosmochimica Acta, 2009

The phenomenon of deficient electron microprobe analyses, with sums of analyzed constituents ofte... more The phenomenon of deficient electron microprobe analyses, with sums of analyzed constituents often below 95 wt'%, is assigned to the analysis of altered, porous minerals, With the example of three zircon populations we show that low totals are related to textural features (i,e" numerous pores of tens to hundreds of nanometers size) as well as to the chemical com position (i,e., water content well within the wt% range, which may affect partial sample degradation under the electron beam). The formation of the spongy texture is explained by the alteration of a previously radiation-damaged and, thus, volume expanded material in a fluid-driven replacement reaction. The smaller volume of the reaction product (crystalline, non vol ume-expanded zircon) accounts for the formation of numerous voids and pores, which are perfect candidates for the incor poration of water. The alteration has also resulted in uptake of non-formula elements such as AI, P, Ca, Fe, Y, and REEs whereas Si and Zr are depleted. In one case, strong uptake of non-radiogenic Pb in altered zircon was observed. Because por ous, low-total zircon has formed in secondary alteration process, its occurrence can be considered as an indicator of a sec ondary alteration history of the host rock. Low-total zircon is easily recognized by very low electron back-scatter intensities, which are closely related to the two main causes of the analytical shortfall (i.e., water content and porosity) and often lowered furthermore by the presence of light non-formula elements (especially P and Fe) up to the wt% range.

Contributions to Mineralogy and Petrology, 2011

As has been demonstrated in recent years, the heterogeneities of coeval magmas can be more succes... more As has been demonstrated in recent years, the heterogeneities of coeval magmas can be more successfully revealed by zoned megacrysts rather than by analysis of the whole rocks hosting them. Here, the geochemical heterogeneities of feldspar megacrysts from the Karkonosze granite, Poland, are investigated by LA-ICP-MS. The crystals are the product of migration and growth in regions of poorly mixed magmas. 3D-modeling of the Ba, Sr, and Rb distributions emphasizes the importance of micro-domain growth morphologies. Two models of element behavior-a relative concentration model and a composition gradient model-provide a potentially effective tool for tracking the mixing process on a microscale. Measured concentrations of elements of different mobilities do not agree with what might be expected from the mixing of two end-member magmas. If mixing was the only process occurring, linear correlations between the concentrations of any two elements should be observed; this, however, is not the case. For combinations of any two of the three elements, modeling reveals differing non-linear correlations between concentrations. The megacryst heterogeneities provide an insight into how mixing magmas are chaotically advected to growing crystals and the degree of inter-magma element exchange between the magmas. Keywords Mixing Á Element mobility Á Diffusion Á Alkali feldspar Á 3D-depiction Á Cutoff value models Á Gradient models Á Probabilistic models Á Geochemical heterogeneity Á Karkonosze granite Communicated by J. Hoefs .

Chemical Geology, 2002

The structural recovery upon heat-treatment of a highly metamict, actinide-rich zircon (U ≈ 6000 ... more The structural recovery upon heat-treatment of a highly metamict, actinide-rich zircon (U ≈ 6000 ppm) has been studied in detail by a complex of techniques including X-ray powder diffraction, Raman spectroscopy, SHRIMP ion probe, electron microprobe, transmission electron microscopy and cathodoluminescence analysis. The structural regeneration of the amorphous starting material depends on random nucleation. It starts between 800 and 950°C when amorphous ZrSiO 4 decomposes to form crystalline ZrO 2 and amorphous SiO 2. At around 1100°C, well crystallised ZrSiO 4 grows at the expense of the oxides. U has been retained in the newly grown zircon whereas Pb was evaporated during the heat-treatment. This process is in marked opposition to the reconstitution of moderately metamict minerals, which experience a gradual recovery controlled by the epitaxial growth at the crystalline-amorphous boundaries. Both of these recovery processes are not the direct inverse of metamictisation. The structural regeneration was found to be connected with a significant increase in the emission of CL. In all cases (annealing heavily damaged zircon and moderately damaged zircon and monazite) we observe that the final, well crystallised annealing products emit more intense CL than their radiation-damaged starting minerals, even though having almost identical elemental composition. Our observations are taken as evidence that the CL is not only determined by the chemical composition of the sample but is also strongly controlled by structural parameters such as crystallinity or the presence of defect centres.

AGU Spring Meeting Abstracts, May 1, 2009

Coralline red algae constitute an ideal biogenic marine climate recorder owing to their common oc... more Coralline red algae constitute an ideal biogenic marine climate recorder owing to their common occurrence in mid-to high latitude oceans and their continuous growth. Encrusting coralline red algae have great potential as paleoclimate archives because they deposit spatially fixed annual growth increments in a high Mg-calcite skeleton and can reach ages of up to several hundred years. Here we present high-resolution Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) trace elemental analyses ( ...

Geostandards and Geoanalytical Research, 2008

us to exclude any unusual thermal history or heat treatment, which could potentially have affecte... more us to exclude any unusual thermal history or heat treatment, which could potentially have affected the retention of radiogenic Pb. The oxygen isotope ratio of this zircon is 13.9‰ VSMOW suggesting a metamorphic genesis in a marble or calc-silicate skarn.

Shiveluch volcano located in northern Kamchatka erupted mainly high-Mg andesites during Holocene ... more Shiveluch volcano located in northern Kamchatka erupted mainly high-Mg andesites during Holocene times. However, tephrochronologists found two Holocene tephra layers that are unusual for this volcano: a high-Mg middle-K basalts with an age of 7600 yr BP and high-Mg high-K basalt with an age of 3600 yr BP [Volynets et al, 1997]. The proximal outcrops for these two tephra deposits were discovered just recently [Churikova et al., 2010; Gorbach & Portnyagin, 2011]. Our study of olivines from the high-Mg basalts documents unusual Mg-Fe zonation [Gordeychik et al., 2016]: Inner cores of olivines from both eruptions show Fo87-92, falling to the rim to Fo75-85. In the outer cores of both basalt tephra, forsterite decreases linearly abruptly changing to a steeper gradient towards the rim. Electron microprobe element maps reveal the complex and highly unusual zoning features of these olivines. The inner cores of the olivines of 7600 yr BP tephra have bell-shaped distributions for forsterite and nickel. The maximum forsterite in their core can be up to Fo92, decreasing outward to the outer core to Fo86. At the same time, the trace elements in the inner core remain constant. Such element distribution is consistent with diffusion of Fe, Mg, and Ni in the initially uniform high Mg cores after the phenocrysts were changed to non-equilibrium in a less mafic melt. The shape of the inner cores suggests partial dissolution after magma mixing. The interfaces between the inner and outer cores are marked by abundant melt/fluid inclusions. The inner cores were overgrown by olivine with Fo90 when the crystals moved to the high-Mg melt. As result some olivine grains have the maximum forsterite values in the outer core. The specific feature of the olivine outer cores from basalt of the 7600 yr BP tephra eruption are concentric zones with higher values of Ca, Cr, Al, P. One of the crystals has five distinct growth zones with high Cr concentrations. The width of these zones can be only a few microns and thus such zones are often missed in typical quantitative point measurements in microprobe profiles. Inner cores of olivines from the 3600 yr BP tephra are uniform in forsterite and nickel. However, Al and Ca element distribution maps show in inner cores higher concentrations with rather smooth contours. This suggests that initially the olivines were formed from high-Al and high-Ca melt, then were dissolved and the overgrowth zonation has been smoothed out due to faster Mg-Fe diffusion. Only Ca and Al with low diffusivity were conserved. The concentric zones with higher element concentrations are not so well expressed in olivines from the 3600 yr BP tephra, but some distinct growth zones are also shown in Ca, Cr, and P. Information extraction and decoding of the elemental maps allow seeing highly complex growth-dissolutiondiffusion history of magma mixing processes prior to eruption. This research was supported by RFBR-DFG grant # 16-55-12040.

Biogeosciences, 2018

The shallow-marine benthic coralline alga Clathromorphum compactum is an important annual-to sub-... more The shallow-marine benthic coralline alga Clathromorphum compactum is an important annual-to sub-annual-resolution archive of Arctic and subarctic environmental conditions, allowing reconstructions going back > 600 years. Both Mg content, in the high-Mg calcitic cell walls, and annual algal growth increments have been used as a proxy for past temperatures and sea ice conditions. The process of calcification in coralline algae has been debated widely, with no definitive conclusion about the role of light and photosynthesis in growth and calcification. Light received by algal specimens can vary with latitude, water depth, sea ice conditions, water turbidity, and shading. Furthermore, field calibration studies of Clathromorphum sp. have yielded geographically disparate correlations between MgCO 3 and sea surface temperature. The influence of other environmental controls, such as light, on Mg uptake and calcification has received little attention. We present results from an 11-month mesocosm experiment in which 123 wildcollected C. compactum specimens were grown in conditions simulating their natural habitat. Specimens grown for periods of 1 and 2 months in complete darkness show that the typical complex of anatomy and cell wall calcification develops in new tissue without the presence of light, demonstrating that calcification is metabolically driven and not a side effect of photosynthesis. Also, we show that both light and temperature significantly affect MgCO 3 in C. compactum cell walls. For specimens grown at low temperature (2 • C), the effects of light are smaller, with a 1.4 mol % MgCO 3 increase from low-light (mean = 17 lx) to highlight conditions (mean = 450 lx). At higher (10 • C) temperature there was a 1.8 mol % MgCO 3 increase from low to high light. It is therefore concluded that site-and possibly specimen-specific temperature calibrations must be applied, to account for effects of light when generating Clathromorphum-derived temperature calibrations.

Mineralogical Magazine, 2018

ABSTRACTThe Waterberg platinum deposit is an extraordinary example of a vein-type hydrothermal qu... more ABSTRACTThe Waterberg platinum deposit is an extraordinary example of a vein-type hydrothermal quartz-hematite-PGE (platinum-group element) mineralization. This study concentrates on the geochemical character of the ores and the platinum-group mineral (PGM) assemblage by application of reflected-light and scanning electron microscopy followed by electron probe microanalysis.The PGM-bearing quartz veins show multiple banding indicating numerous pulses of fluid infiltration. Mineralization was introduced contemporaneously with the earliest generation of vein quartz and hematite. High oxygen and low sulfur fugacities of the mineralizing fluids are indicated by hematite as the predominant opaque mineral and the lack of sulfides.The ‘Waterberg type’ mineralization is characterized by unique metal proportions, namely Pt>Pd>Au, interpreted as a fingerprint to the cradle of the metals, namely rocks and ores of the Bushveld Complex, or reflecting metal fractionation during ascent of an...

PALAIOS, 2009

We present the first continuous, high-resolution record of Mg/Ca variations within an encrusting ... more We present the first continuous, high-resolution record of Mg/Ca variations within an encrusting coralline red alga, Clathromorphum nereostratum, from Amchitka Island, Aleutian Islands. Mg/Ca ratios of individual growth increments were analyzed by measuring a singlepoint, electron-microprobe transect, yielding a resolution of ϳ15 samples/year and a 65-year record (1902-1967) of variations. Results show that Mg/Ca ratios in the high-Mg calcite algal framework display pronounced annual cyclicity and archive late spring-late fall sea-surface temperatures (SST) corresponding to the main season of algal growth. Mg/Ca values correlate well to local SST, as well as to an air temperature record from the same region. High spatial correlation to large-scale SST variability in the subarctic North Pacific is observed, with patterns of strongest correlation following the direction of major oceanographic features that play a key role in the exchange of water masses between the North Pacific and the Bering Sea. Our data correlate well with a shorter Mg/Ca record from a second site, corroborating the ability of the alga to reliably record regional environmental signals. In addition, Mg/Ca ratios relate well to a 29-year ␦ 18 O time series measured on the same sample, providing additional support for the use of Mg in coralline red algae as a paleotemperature proxy that, unlike algal-␦ 18 O, is not influenced by salinity fluctuations. Moreover, electron microprobe-based analysis enables higher sampling resolution and faster analysis, thus providing a promising approach for future studies of longer C. nereostratum records and applications to other coralline species.

Palaeogeography, Palaeoclimatology, Palaeoecology, 2011

We have investigated the trace elemental composition in the skeleta of two specimens of attached-... more We have investigated the trace elemental composition in the skeleta of two specimens of attached-living coralline algae of the species Clathromorphum compactum from the North Atlantic (Newfoundland) and Clathromorphum nereostratum from the North Pacific/Bering Sea region (Amchitka Island, Aleutians). Samples were analyzed using Laser Ablation-Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) yielding for the first time continuous individual trace elemental records of up to 69years in length. The resulting ...

Ore Geology Reviews, 2006

The peraluminous Land's End granite is one of the composite plutons forming the late-Variscan Cor... more The peraluminous Land's End granite is one of the composite plutons forming the late-Variscan Cornubian batholith. The western part of the pluton hosts the Sn-Cu mineralisation of the St. Just mining district. The pluton consists of early megacrystic biotite (Mg-siderophyllite) granites and albite microgranites and younger Li-siderophyllite granites, and tourmaline granites together with fine-grained massive quartz-tourmaline rocks (MQT). Most of the granite varieties evolved by fractional crystallisation from a common crustal magmatic reservoir, apart from the albite microgranite, which has a different source. Trace element analyses of K-feldspar megacrysts in the older biotite granites made using laser ablation ICP-MS reveal that the megacrysts were derived from moderately evolved sources and now reside in separate granite sub-stages with variable degrees of fractionation, so that equilibrium between phenocrysts and host no longer persists. The younger granites show a strong in situ fractionation at the cm-to 100-m-scale, whereby boron-rich melts are concentrated in the apical parts of the individual intrusive units. Geological, textural and mineralogical data suggest that the tourmaline granites and MQT evolved mainly from fractionated Li-siderophyllite granites. Cathodoluminescence, trace element and melt inclusion studies of quartz from the MQT reveal that the MQT was formed during the transition from the magmatic to hydrothermal states from a mixture of immiscible phases. The Li-siderophyllite granites, tourmaline granites and MQT appear to be the immediate magmatic precursors from which the hydrothermal fluids responsible for the mineralisation in the St Just district originated.

Journal of Asian Earth Sciences, 2014

This study explores the potential of detrital rutile geochemistry and thermometry as a provenance... more This study explores the potential of detrital rutile geochemistry and thermometry as a provenance tracer in rocks from the Central Dabie ultrahigh-pressure metamorphic (UHPM) zone in east-central China that formed during Triassic continental collision. Trace element data of 176 detrital rutile grains selected from local river sediments and 91 rutile grains from distinct bedrocks in the Shuanghe and Bixiling areas, obtained by both electron microprobe (EMP) and in situ LA-ICP-MS analyses, suggest that geochemical compositions and thermometry of detrital rutiles are comparable to those from their potential source rocks. After certification of the Cr-Nb discrimination method for the Central Dabie UHPM zone, we show that 29% of the detrital rutiles in the Shuanghe area were derived from metamafic sources whereas in the Bixiling area that it is up to 76%. Furthermore, the proportion of distinct types of detrital rutiles combined with modal abundances of rutile in metapelites and metamafic bedrocks can be used to estimate the proportion of different source lithologies. Based on this method the proportion of mafic source rocks was estimated to $10% at Shuanghe and >60% at Bixiling, respectively, which is consistent with the proportions of eclogite (the major rutile-bearing metamafic rock) distribution in the field. Therefore, the investigation of detrital rutiles is a potential way to evaluate the proportion of metamafic rocks and even to prospect for metamafic bodies in UHPM terranes. Zr-in-rutile temperatures were calculated at different pressures and compared with temperatures derived from rock-in rutiles and garnet-clinopyroxene Fe-Mg thermometers. Temperatures calculated for detrital rutiles range from 606°C to 707°C and 566°C to 752°C in Shuanghe and Bixiling, respectively, at P = 3 GPa with an average temperatures of ca. 630°C for both areas. These temperature averages and ranges are similar to those calculated for rutiles from surrounding source rocks. Combined with comparable Zr distribution characteristics between detrital and source rock rutiles, demonstrating a close source-sediment link for rutiles from clastic and rock in UHPM terranes. Thus rutiles can be accurate tracers of source rock lithologies in sedimentary provenance studies even at a small regional scale. In Bixiling, Nb/Ta ratios of metamafic and metapelitic detrital rutiles fall between 11.0 to 27.3 and 7.7 to 20.5, respectively. In contrast, in Shuanghe, these ratios are highly variable, ranging from 10.9 to 71.0 and 7.6 to 87.1, respectively. When ignoring four outlier compositions with extremely high Nb/Ta in Shuanghe, a distinct clustering of Nb/Ta ratios in rutiles is shown: metapelitic detrital rutiles have Nb/Ta of 7-40 vs. metamafic detrital rutiles with Nb/Ta = 11-25. The Nb/ Ta characteristics in detrital rutiles from both areas may reflect the degree of fluid-rock interaction during metamorphism and/or different source lithologies. Therefore, the trace element compositions in detrital rutiles can accurately trace the lithology, proportion and fluid-rock interaction of different source rocks.

Geostandards and Geoanalytical Research, 2004

This paper reports the results from a second characterisation of the 91500 zircon, including data... more This paper reports the results from a second characterisation of the 91500 zircon, including data from electron probe microanalysis, laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS), secondary ion mass spectrometry (SIMS) and laser fluorination analyses. The focus of this initiative was to establish the suitability of this large single zircon crystal for calibrating in situ analyses of the rare earth elements and oxygen isotopes, as well as to provide working values for key geochemical systems. In addition to extensive testing of the chemical and structural homogeneity of this sample, the occurrence of banding in 91500 Cet article présente les résultats d'une nouvelle caractérisation du zircon 91500, dont des données de microanalyse par sonde électronique, d'analyse par ablation laser en couplage à un ICP-MS, d'analyse par sonde ionique (SIMS) et d'analyse par fluorination laser. Le but de cette étude était de démontrer que ce large monocristal de zircon pouvait être utilisé pour la calibration d'analyses in situ de Terres Rares et des isotopes de l'Oxygène, et en même temps de fournir des valeurs "de travail" pour un certain nombre de systèmes géochimiques cruciaux. En complément des tests systématiques d'homogénéité de l'échantillon, tant chimiquement

Geochimica et Cosmochimica Acta, 2009

The phenomenon of deficient electron microprobe analyses, with sums of analyzed constituents ofte... more The phenomenon of deficient electron microprobe analyses, with sums of analyzed constituents often below 95 wt'%, is assigned to the analysis of altered, porous minerals, With the example of three zircon populations we show that low totals are related to textural features (i,e" numerous pores of tens to hundreds of nanometers size) as well as to the chemical com position (i,e., water content well within the wt% range, which may affect partial sample degradation under the electron beam). The formation of the spongy texture is explained by the alteration of a previously radiation-damaged and, thus, volume expanded material in a fluid-driven replacement reaction. The smaller volume of the reaction product (crystalline, non vol ume-expanded zircon) accounts for the formation of numerous voids and pores, which are perfect candidates for the incor poration of water. The alteration has also resulted in uptake of non-formula elements such as AI, P, Ca, Fe, Y, and REEs whereas Si and Zr are depleted. In one case, strong uptake of non-radiogenic Pb in altered zircon was observed. Because por ous, low-total zircon has formed in secondary alteration process, its occurrence can be considered as an indicator of a sec ondary alteration history of the host rock. Low-total zircon is easily recognized by very low electron back-scatter intensities, which are closely related to the two main causes of the analytical shortfall (i.e., water content and porosity) and often lowered furthermore by the presence of light non-formula elements (especially P and Fe) up to the wt% range.

Contributions to Mineralogy and Petrology, 2011

As has been demonstrated in recent years, the heterogeneities of coeval magmas can be more succes... more As has been demonstrated in recent years, the heterogeneities of coeval magmas can be more successfully revealed by zoned megacrysts rather than by analysis of the whole rocks hosting them. Here, the geochemical heterogeneities of feldspar megacrysts from the Karkonosze granite, Poland, are investigated by LA-ICP-MS. The crystals are the product of migration and growth in regions of poorly mixed magmas. 3D-modeling of the Ba, Sr, and Rb distributions emphasizes the importance of micro-domain growth morphologies. Two models of element behavior-a relative concentration model and a composition gradient model-provide a potentially effective tool for tracking the mixing process on a microscale. Measured concentrations of elements of different mobilities do not agree with what might be expected from the mixing of two end-member magmas. If mixing was the only process occurring, linear correlations between the concentrations of any two elements should be observed; this, however, is not the case. For combinations of any two of the three elements, modeling reveals differing non-linear correlations between concentrations. The megacryst heterogeneities provide an insight into how mixing magmas are chaotically advected to growing crystals and the degree of inter-magma element exchange between the magmas. Keywords Mixing Á Element mobility Á Diffusion Á Alkali feldspar Á 3D-depiction Á Cutoff value models Á Gradient models Á Probabilistic models Á Geochemical heterogeneity Á Karkonosze granite Communicated by J. Hoefs .

Chemical Geology, 2002

The structural recovery upon heat-treatment of a highly metamict, actinide-rich zircon (U ≈ 6000 ... more The structural recovery upon heat-treatment of a highly metamict, actinide-rich zircon (U ≈ 6000 ppm) has been studied in detail by a complex of techniques including X-ray powder diffraction, Raman spectroscopy, SHRIMP ion probe, electron microprobe, transmission electron microscopy and cathodoluminescence analysis. The structural regeneration of the amorphous starting material depends on random nucleation. It starts between 800 and 950°C when amorphous ZrSiO 4 decomposes to form crystalline ZrO 2 and amorphous SiO 2. At around 1100°C, well crystallised ZrSiO 4 grows at the expense of the oxides. U has been retained in the newly grown zircon whereas Pb was evaporated during the heat-treatment. This process is in marked opposition to the reconstitution of moderately metamict minerals, which experience a gradual recovery controlled by the epitaxial growth at the crystalline-amorphous boundaries. Both of these recovery processes are not the direct inverse of metamictisation. The structural regeneration was found to be connected with a significant increase in the emission of CL. In all cases (annealing heavily damaged zircon and moderately damaged zircon and monazite) we observe that the final, well crystallised annealing products emit more intense CL than their radiation-damaged starting minerals, even though having almost identical elemental composition. Our observations are taken as evidence that the CL is not only determined by the chemical composition of the sample but is also strongly controlled by structural parameters such as crystallinity or the presence of defect centres.

AGU Spring Meeting Abstracts, May 1, 2009

Coralline red algae constitute an ideal biogenic marine climate recorder owing to their common oc... more Coralline red algae constitute an ideal biogenic marine climate recorder owing to their common occurrence in mid-to high latitude oceans and their continuous growth. Encrusting coralline red algae have great potential as paleoclimate archives because they deposit spatially fixed annual growth increments in a high Mg-calcite skeleton and can reach ages of up to several hundred years. Here we present high-resolution Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) trace elemental analyses ( ...

Geostandards and Geoanalytical Research, 2008

us to exclude any unusual thermal history or heat treatment, which could potentially have affecte... more us to exclude any unusual thermal history or heat treatment, which could potentially have affected the retention of radiogenic Pb. The oxygen isotope ratio of this zircon is 13.9‰ VSMOW suggesting a metamorphic genesis in a marble or calc-silicate skarn.

The ancient rock city of Petra, which lies south of the Dead Sea in the Hashemite Kingdom of Jord... more The ancient rock city of Petra, which lies south of the Dead Sea in the Hashemite Kingdom of Jordan, displays with its unusual sandstone architecture an abundance of evidence of the Nabatean culture. Petra has gained special recognition for its around 600 hundred of rock facades carved out of the sandstone rock found there. Today, the existence of the unique rock architecture of these monuments is in danger due to the action of flash floods, decomposition, poor maintenance and lack of conservation. Within on-site work and field research in collaboration with the CARCIP (Conservation and Restoration Center in Petra), findings about the process of tafoni-weathering of the cambric sandstone by the interaction of uncontrolled flowing rainwater and salt could be gathered. A new technique for desalination by sprinkling the contaminated areas has been developed and employed. An inventory of risks, damages and needs of around one third of all monuments was done. Special attention was paid to drainage systems, static tension cracks, loose ashlars and rock slabs, rubble and dilapidation. The inspections revealed more than half of all stone facades were equipped with drainage systems. In consequence a maintenance strategy by partly repair and reactivation of the ancient drainage systems and cisterns was developed. Dry slaked lime mortars, according to the still found ancient decoration mortars on the facades were produced in historic technique. The mortar was tested in situ and by salt bursting tests. The hydraulic Ancient cistern mortar was investigated by grain size distribution, binder and aggregate relation and by using electron microprobe analysis (EMPA) to identify the source and type of hydraulic binding material.

In situ LA-ICP-MS analysis of S, Se and Te in components of chondritic meteorites provide clues t... more In situ LA-ICP-MS analysis of S, Se and Te in components of chondritic meteorites provide clues to the formation of chondritic meteorites (Funk et al., this meeting).

Two volumes presenting the results from 15 years of archaeological research on the Hermeskeil mil... more Two volumes presenting the results from 15 years of archaeological research on the Hermeskeil military camp and Titus Labienus' conquest of the Treveri in 53 and 51 BC.

Metalla Sonderheft 8, 2016

Greiff S, Kronz A, Schlütter F, Prange M (2016) (Hrsg.) Archäometrie und Denkmalpflge 2016. Jahre... more Greiff S, Kronz A, Schlütter F, Prange M (2016) (Hrsg.) Archäometrie und Denkmalpflge 2016. Jahrestagung an der Georg-August-Universität Göttingen. 28. September – 1. Oktober 2016. Metalla Sonderheft 8, 240 S.
ISSN 0947-6229

Professor Karl Hans Wedepohl, a leading geochemist of postwar Germany who, in his later life, mad... more Professor Karl Hans Wedepohl, a leading geochemist of postwar Germany who, in his later life, made significant contributions to the study of Roman and medieval glass in central Europe, died, after a short illness, on May 19, 2016, at the age of 91.