Coupled petrological-geodynamical modeling of a compositionally heterogeneous mantle plume

Abstract Self-consistent geodynamic modeling that includes melting is challenging as the chemistry of the source rocks continuously changes as a result of melt extraction. Here, we describe a new method to study the interaction between physical and chemical processes in an uprising heterogeneous mantle plume by combining a geodynamic code with a thermodynamic modeling approach for magma generation and evolution. We pre-computed hundreds of phase diagrams, each of them for a different chemical system. After melt is extracted, the phase diagram with the closest bulk rock chemistry to the depleted source rock is updated locally. The petrological evolution of rocks is tracked via evolving chemi…

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.…

Numerical dating of the Eckfeld maar fossil site, Eifel, Germany: a calibration mark for the Eocene time scale.

Sediments of the Eckfeld maar (Eifel, Germany) bear a well-preserved Eocene fauna and flora. Biostratigraphically, Eckfeld corresponds to the Middle Eocene mammal reference level MP (Mammals Paleogene) 13 of the ELMA (European Land Mammal Age) Geiseltalian. In the maar crater, basalt fragments were drilled, representing explosion crater eruption products. By 40Ar/39Ar dating of the basalt, for the first time a direct numerical calibration mark for an Eocene European mammal locality has been established. The Eckfeld basalt inverse isochron date of 44.3 +/- 0.4 Ma suggests an age for the Geiseltalian/Robiacian boundary at 44 Ma and, together with the 1995 time scale of Berggren et al., a time…

Eckfeld Maar: Window into an Eocene Terrestrial Habitat in Central Europe

: To mark the occasion of the 175th anniversary of the Rheinische Naturforschende Gesellschaft in 2009 and of the centennial of the Mainz Natural History Museum in 2010, we present a short account of our present knowledge of the Eckfeld Maar after 20 years of continuous research. This paper does not attempt to include all of the detailed results on the geology of the Eckfeld site or its biota. To date, nearly 250 papers and books have been published since the start of our project An up-to-date list of these publications can be found at http://www.eckfeldermaar.de.

Students' field research extends knowledge of origin of a UNESCO World Heritage site in Germany

In 1992, as part of field-based course work with the Earth science department of the Universitat Minz, students began to investigate the structures of oil shale basins located in the Sprendlinger Horst, a horst-type block forming the northeastern shoulder of the Tertiary Upper Rhine Graben in southwestern Germany (figure 1). The Sprendlinger Horst is mainly built up by Hercynian or pre-Hercynian basement, Permian sediments, and volcanic rocks, as well as by several Tertiary alkali basalts and rare Cretaceous trachytes. In 1992, it was unknown whether the oil shale basins were of tectonic, volcanic, or even of impact origin.

Einfaches Verfahren zur Wasserbestimmung in biologischem Material

Die Wasserbestimmung beruht auf dem Prinzip der Entmischung eines Xylol-Alkohol-Wasser-Gemisches. Der Wassergehalt last sich bei konstanter Temperatur aus der verbrauchten Xylolmenge errechnen, wenn man eine bestimmte Alkoholmenge genau eingestellter Konzentration verwendet. Fur eine Bestimmung genugen 0,4 cm3 bzw. 0,4 g Untersuchungsmaterial. Die Methode weist eine Genauigkeit bis 0,3% auf.

Chemical composition of modern and fossil hippopotamid teeth and implications for paleoenvironmental reconstructions and enamel formation – Part 2: Alkaline earth elements as tracers of watershed hydrochemistry and provenance

Abstract. For reconstructing environmental change in terrestrial realms the geochemistry of fossil bioapatite in bones and teeth is among the most promising applications. This study demonstrates that alkaline earth elements in enamel of Hippopotamids, in particular Ba and Sr are tracers for water provenance and hydrochemistry. The studied specimens are molar teeth from Hippopotamids found in modern and fossil lacustrine settings of the Western Branch of the East African Rift system (Lake Kikorongo, Lake Albert, and Lake Malawi) and from modern fluvial environments of the Nile River. Concentrations in enamel vary by ca. two orders of magnitude for Ba (120–9336 μg g−1) as well as for Sr (9–21…

Chemical composition of modern and fossil Hippopotamid teeth and implications for paleoenvironmental reconstructions and enamel formation – Part 1: Major and minor element variation

Bioapatite in mammalian teeth is readily preserved in continental sediments and represents a very important archive for reconstructions of environment and climate evolution. This project provides a comprehensive data base of major, minor and trace element and isotope tracers for tooth apatite using a variety of microanalytical techniques. The aim is to identify specific sedimentary environments and to improve our understanding on the interaction between internal metabolic processes during tooth formation and external nutritional control and secondary alteration effects. Here, we use the electron microprobe to determine the major and minor element contents of fossil and modern molar enamel, …

Sources, degassing, and contamination of CO2, H2O, He, Ne, and Ar in basaltic glasses from Kolbeinsey Ridge, North Atlantic

Abstract New volatile data (CO2, H2O, He, Ne, and Ar) are presented for 24 submarine basaltic glasses from the Kolbeinsey Ridge, Tjornes Fracture Zone and Mohns Ridge, North Atlantic. Low CO2 and He contents indicate that magmas were strongly outgassed with the extent of degassing increasing toward the south, as expected from shallower ridge depths. Ne and Ar are significantly more abundant in the southernmost glasses than predicted for degassed melt. The strong atmospheric isotopic signal associated with this excess Ne and Ar suggests syn- or posteruptive contamination by air. Degassing, by itself, cannot generate the large variations in δ13C values of dissolved CO2 or coupled CO2-Ar varia…

The radiogenic isotope composition of the high-latitude North Atlantic mantle

New Sr, Nd, and Pb isotope data on North Atlantic high-latitude (about 69°30'N to 76°30'N) intraplate and ridge volcanic rocks, together with published data, are used to evaluate the mantle sources contributing to Iceland and the surrounding ridges. Considerable overlap between Icelandic lavas and depth-filtered North Atlantic mid-oceanic-ridge basalts (MORBs) in all isotope plots confirm that a MORB asthenosphere-plume mixing model can explain the ranges of isotope compositions found on Iceland. Regional isotope patterns north of lat 53°N show two distinct mantle domains. Lavas forming a low-radiogenic-Pb, high-radiogenic-Sr array occur north of central Iceland, whereas volcanic rocks form…

Architecture and tectono-stratigraphic evolution of the intramontane Baza Basin (Bétics, SE-Spain): Constraints from seismic imaging

The Baza basin is a large Neogene intramontane basin in the Bétic Cordillera of southern Spain that formed during the Tortonian (late Miocene). The Bétic Cordillera was produced by NW–SE oblique convergence between the Eurasian and African Plates. Three seismic reflection lines (each 18 km long; vibroseis method) were acquired across the Baza basin to reveal the architecture of the sedimentary infill and faulting during basin formation. We applied rather conventional CDP data processing followed by first arrival P-wave tomography to provide complementary structural information and establish velocity models for the post-stack migration. These images show a highly asymmetric structure for the…

Geodynamic Setting of the Tertiary Hocheifel Volcanism (Germany), Part II: Geochemistry and Sr, Nd and Pb Isotopic Compositions.

Major and trace element as well as isotopic compositions on 26 volcanic rocks from the Tertiary Hocheifel volcanic field and for comparison from Upper Rhine Graben occurrences (western Central European Volcanic Province) were measured in order to provide geochemical evidence for the geodynamic setting of the Tertiary Eifel volcanism. Except for a few differentiated lavas there are mainly basanitic compositions. These rocks were produced by low degree partial melting of a previously metasomatized garnet peridotite source at pressures and temperatures corresponding to depths of about 75 to 90 km. In contrast to the differentiated lavas, most of the basanites are not significantly affected by …

Volcanism on the Eggvin Bank (Central Norwegian-Greenland Sea, latitude ∼71°N): age, source, and relationship to the Iceland and putative Jan Mayen plumes

Abstract The Eggvin Bank (Central Norwegian-Greenland Sea, latitude ∼71°N) is a topographically anomalous shallow area with scattered volcanic peaks extending between the island of Jan Mayen and East Greenland and straddling the northern segment of the mid-Atlantic Kolbeinsey Ridge axis. Basalts dredged from the Eggvin Bank range from variably depleted, tholeiitic, near-axis lavas to enriched, transitional-to-alkaline, off-axis seamount lavas. In terms of normalised incompatible element patterns, the most depleted, near-axis tholeiite is similar to neighbouring Kolbeinsey Ridge basalts, whereas the off-axis, transitional-to-alkaline lavas are similar to other alkaline basalts occurring clos…

Understanding melt generation beneath the slow-spreading Kolbeinsey Ridge using 238U, 230Th, and 231Pa excesses

International audience; To examine the petrogenesis and sources of basalts from the Kolbeinsey Ridge, one of the shallowest locations along the global ridge system, we present new measurements of Nd, Sr, Hf, and Pb isotopes and U-series disequilibria on 32 axial basalts. Young Kolbeinsey basalts (full-spreading rate = 1.8 cm/yr; 67 degrees 05'-70 degrees 26'N) display ((230)Th/(238)U) 1 with ((230)Th/(238)U) from 0.95 to 1.30 and have low U (11.3-65.6 ppb) and Th (33.0 ppb-2.40 ppm) concentrations. Except for characteristic isotopic enrichment near the Jan Mayen region, the otherwise depleted Kolbeinsey basalts (e. g. (87)Sr/(86)Sr = 0.70272-0.70301, epsilon(Nd) = 8.4-10.5, epsilon(Hf) = 15…

Sr-Nd-Pb isotope ratios, geochemical compositions, and40Ar/39Ar data of lavas from San Felix Island (Southeast Pacific): Implications for magma genesis and sources

We present the first trace element and age data combined with new Sr, Nd, and Pb isotope ratios on lavas from San Felix Island in the Southeast Pacific. A 40Ar/39Ar plateau age of 421 ± 18 ka implies young intraplate volcanic activity in this region relative to the ∼22 Ma old volcanism on the neighbouring Easter seamount chain (ESC). The incompatible element compositions of the San Felix magmas are similar to those of EM1-type basalts from Gough, although the isotopic compositions differ. San Felix formed some 20 Ma after the ESC plume affected the plate in this region but no chemical signature of the ESC material is observed in the young volcanic rocks. The composition of the San Felix bas…

Geodynamic Setting of the Tertiary Hocheifel Volcanism (Germany), Part I: 40Ar/39Ar geochronology

The Eifel volcanism is part of the Cenozoic Central European Volcanic Province and is located close to the Rhine Graben which has been formed by rifting and subsidence since the Eocene. Whereas the Quaternary volcanism of the Eifel appears to be genetically related to mantle plume activity, the cause of the Tertiary volcanism of the Hocheifel volcanic field is less clear. Here, we present geochronological evidence for the geotectonic setting of the Tertiary Eifel volcanism based on 40Ar/39Ar dating of 27 samples from 25 volcanic occurrences. Included are samples from the northern Upper Rhine Graben in order to evaluate a possible relationship between Hocheifel volcanism and Rhine Graben tap…

Eine Vereineachung der Para-amino-hippur-S�urebestimmung

Temporal–spatial evolution of low-SiO2 volcanism in the Pleistocene West Eifel volcanic field (West Germany) and relationship to upwelling asthenosphere

Abstract The temporal–spatial evolution of low-SiO 2 lavas from the Pleistocene West Eifel volcanic field (Central European Volcanic Province) and linked petrogenetic variations are evaluated using 40 Ar/ 39 Ar age and geochemical data. Geochronological and petrological evidence is related to the physical structure of the previously established seismologically anomalous asthenosphere interpreted as thermally upwelling mantle (Eifel Plume). Lava flows >480 ka (Middle Pleistocene) occur exclusively in the NW of the volcanic field. After a time span of ca. 400 ka lacking significant activity, volcanism has migrated to the SE generating flows At melting depth >70 km of parental asthenospheric m…