Henrik Blanchard - Academia.edu (original) (raw)

Papers by Henrik Blanchard

ABSTRACT In the West Eifel Vocanic field of Germany, extensive fine grained tephra beds exist. Th... more ABSTRACT In the West Eifel Vocanic field of Germany, extensive fine grained tephra beds exist. These are derived from fragmentation of Lower Devonian siltstone. Analysis of fine grain TL and the IRSL of fine-grained tephra beds from independently dated tephra layers of 11 ka and ca. 20 ka suggested that their geological luminescence was reduced to near zero residual value during the eruption. This was despite the absence of any field evidence of heating above 400°C. We examined possible resetting mechanisms and suggest that thermally assisted hydrostatic pressure can reset the latent geological TL of country rock fragments during phreato-magmatic maar eruptions. We also provide first evidence of the suitability for TL dating of such material. As anomalous fading experiments have not been completed so far, we cannot give definitive TL ages here, but as the apparent ages are underestimated as compared to the control ages, complete zeroing is inferred. However a fortuitous combination of incomplete resetting and anomalous fading, that yields the expected De, though unlikely in view of long De plateaus arguing for complete resetting, cannot be entirely ruled out.

International Journal of Earth Sciences, 2008

The Rodderberg volcanic complex (RVC) is located within the city limits of Bonn (Germany) approxi... more The Rodderberg volcanic complex (RVC) is located within the city limits of Bonn (Germany) approximately 20 km to the north of the Quaternary East Eifel Volcanic Field (EEVF). It is the product of intense phreatomagmatic volcanism forming a 90 m deep maar crater and strombolian eruptions. Deposit features indicate that the location of the vent(s) shifted from N to S during the

Chemical Geology, 2016

A specific feature of some basaltic lunar rocks is that their TiO2 contents can reach concentrati... more A specific feature of some basaltic lunar rocks is that their TiO2 contents can reach concentrations as high as 16 wt.%. The high-field strength elements (HFSE) group, which includes Ti, may provide valuable information of the processes that occurred in the lunar mantle to generate high-Ti mare basalts. To assess the effect of such high TiO2 concentrations on the partitioning of Zr, Hf, Nb, Ta, U, Th, Mo and W between major silicate and oxide phases and silicate melts, we present results from experiments at one atmosphere and 1100 °C–1305 °C, under controlled oxygen fugacity. With the exception of Nb, all DHFSEcpx/melt show a strong negative correlation with the TiO2 content of the silicate melt. Olivine/Silicate melt partition coefficients for Zr, Hf, Nb, Ta and Th decrease slightly from 0 to ca. 5 wt.% TiO2, above which they remain constant up to ca. 20 wt.% TiO2 in the silicate glass. In addition, redox sensitive elements, i.e. U, Mo, and W show clearly distinct DMsilicates/melt at different fO2, implying that these elements are relatively more compatible at reduced (ca. IW − 1.8) than at oxidized (FMQ and air) environments. Iron-rich and Mg-rich armalcolite show contrasting patterns of DMcrystal/melt, with the latter exhibiting slightly higher values of partition coefficient for all analyzed elements, except Th, which is equally incompatible in both end-members. Finally, the new dataset of DHFSEcrystal/melt was used to perform simple melting models of the lunar mantle cumulates. Results indicate that to reproduce the fractionation of W from the HFSE, as well as U and Th observed in lunar mare basalts, metal saturation and the presence of Fe–Ti oxides in the mantle sources is required.

Quaternary Geochronology, 2012

Earth and Planetary Science Letters, 2014

Quaternary Science Reviews, 2004

Quaternary International, 2014

E&G Quaternary Science Journal, 2011

Kurzfassung Der mittelpleistozäne Vulkankomplex des Rodderbergs südlich von Bonn birgt vermutlich... more Kurzfassung Der mittelpleistozäne Vulkankomplex des Rodderbergs südlich von Bonn birgt vermutlich ein höchst wertvolles Klimaarchiv von regionaler und überregionaler Bedeutung. Er sitzt der aus dem älteren Mittelpleistozän stammenden "jüngeren Hauptterrasse" des Rheins auf. Sein zentraler Krater stellt eine bis heute geschlossene Hohlform dar, die noch fast vollständig von einem Wall aus Schlacken und Tephren umgeben ist. Eine im Jahre 2000 im Krater durchgeführte 55 m tiefe Kernbohrung (Rodderberg 1) förderte fast durchgängig feinkörnige Sedimente zutage, die im oberen Teil als Lösse und Lössderivate, im unteren Teil als Seesedimente angesprochen werden. Eine vom Leibniz-Institut für Angewandte Geophysik (LIAG) im Jahre 2008 niedergebrachte 69 m tiefe Schneckenbohrung erreichte in ca. 65 m Tiefe interglaziale Torfe. Festgestein wurde bisher nicht erreicht. Eine weitere Forschungsbohrung des LIAG ist für 2011 geplant. Der vorliegende Beitrag resümiert die bisherigen Ergebnisse zur Eruptionsgeschichte des Rodderberges und zu den Untersuchungen am Kerninhalt der Bohrung Rodderberg 1, zeigt bestehende Probleme auf und versucht, Anregungen für die weiteren Untersuchungen an der geplanten neuen Forschungsbohrung sowie in ihrem Umfeld zu geben.

EG Quaternary Science Journal, 2011

Geochemical Perspectives Letters

We appreciate the comments by Yang et al. (2018) to our recent proposal (Ballhaus et al., 2017) t... more We appreciate the comments by Yang et al. (2018) to our recent proposal (Ballhaus et al., 2017) that high pressure and ultra-reduced minerals in ophiolites may form by lightning strikes. We have carried out additional experiments to address the issues raised by Yang et al. (2018). We maintain that the ultra-reduced phases in ophiolites are best explained as plasma precipitates generated by lightning strikes.

Page 1. Ancient TL Vol. 20 No 2 2002 53 The luminescence dating laboratory at the University of B... more Page 1. Ancient TL Vol. 20 No 2 2002 53 The luminescence dating laboratory at the University of Bonn: equipment and procedures B. Mauz*, T. Bode, E. Mainz, H. Blanchard, W. Hilger, R. Dikau and L. Zöller Geographisches ...

On Lanzarote (Canary Islands) soils were baked by Quaternary lava flows. This offers the possibil... more On Lanzarote (Canary Islands) soils were baked by Quaternary lava flows. This offers the possibility to date phases of eruptive activity by red thermoluminescence (RTL). We dated soil material baked by two different lava flows originating from the "Las Calderetas de Guatiza" volcanic chain in the northeast of the island by RTL. Furthermore, three samples of Helicidae-mollusk shells overlying one of the lava flows (site Mála) were dated using electron spin resonance (ESR). RTL datings were carried out using quartz grains 63-200 µm from baked material that were originally brought by eolian transport from the nearby Saharan desert. It appears that in spite of a baking temperature < 550°C the RTL-signal was sufficiently annealed and thus dating by RTL was possible. RTL ages of ca. 170 ka show good agreement with each other, however, ESR ages are up to 40 % higher than the corresponding RTL age of the lava flow in Mála. Despite this disagreement these results demonstrate that eruptive activity of the volcanic chain occurred during the Middle Pleistocene rather than during the Early Holocene/Late Pleistocene as supposed based on geomorphologic features. Furthermore, they show that 14C-ages of mollusk shells originating from Mála are underestimating volcanic activity up to a factor of 10, a problem often recorded in arid areas. These results demonstrate the value of luminescence and ESR datings on the semi arid Eastern Canary Islands. The successful dating of lava-baked soils on Lanzarote by RTL thus offers the possibility to further investigate the yet fragmentary Middle and Late Quaternary eruptive history of these islands.

EG Quaternary Science Journal, 2009

Abstract. Middle and Upper Quaternary volcanic events are often difficult to date, in particular ... more Abstract. Middle and Upper Quaternary volcanic events are often difficult to date, in particular when minerals suitable for 40Ar/39Ar-dating are missing. Here, we present first tests of a newly developed technique to use the thermoluminescence (TL) of maar tephra and crustal xenoliths for dating the eruption event. We take into consideration that resetting of the latent geological TL of country rock fragments during eruption may be incomplete. We therefore develop the “partial heat – longest plateau” (PHLP) technique to approach the inherited TL signal at eruption. This technique can overcome TL age overestimates due to incomplete zeroing, as is demonstrated for some eruptions in the Quaternary Eifel Volcanic Field, Germany, in the time range from 11 to 300 ka old. Although we avoid the often observed strong anomalous fading of volcanic feldspars and other volcanic minerals by using heated country rock xenoliths, we still face the problem of longer-term anomalous fading which may be...

Geochemical Perspectives Letters, Nov 1, 2017

Since ultra-high pressure (UHP) minerals have been discovered in ophiolites from Tibet and the Po... more Since ultra-high pressure (UHP) minerals have been discovered in ophiolites from Tibet and the Polar Urals, it is speculated that the mantle sections of ophiolites may originate deep within the mantle. The UHP minerals are frequently found together with ultra-reduced silicides, carbides, and nitrides. Consequently, it is argued that the deep mantle, or at least domains within it, must be highly reduced, so reduced that practically all transition elements at depth are present in the metallic state. We find it problematic to rewrite the history of ophiolite complexes based on these observations and suggest we should search for alternative and more realistic modes of origin. Electric discharge experiments at >6000 K reported here show that the UHP and highly reduced phase assemblages may precipitate from plasmas. We argue that the mineral assemblages may originate by lightning strikes. As such, they may not record the origin and emplacement history of the mantle lithologies within which they occur.