Zircon ages of high-grade gneisses in the Eastern Erzgebirge (Central European Variscides)—constraints on origin of the rocks and Precambrian to Ordovician magmatic events in the Variscan foldbelt     

M. Tichomirowa  H.-J. Berger  E.A. Koch  B.V. Belyatski  J. Gtze  U. Kempe  L. Nasdala  U. Schaltegger 《Lithos》2001,56(4):303-332

This study is an attempt to unravel the tectono-metamorphic history of high-grade metamorphic rocks in the Eastern Erzgebirge region. Metamorphism has strongly disturbed the primary petrological genetic characteristics of the rocks. We compare geological, geochemical, and petrological data, and zircon populations as well as isotope and geochronological data for the major gneiss units of the Eastern Erzgebirge; (1) coarse- to medium-grained “Inner Grey Gneiss”, (2) fine-grained “Outer Grey Gneiss”, and (3) “Red Gneiss”. The Inner and Outer Grey Gneiss units (MP–MT overprinted) have very similar geochemical and mineralogical compositions, but they contain different zircon populations. The Inner Grey Gneiss is found to be of primary igneous origin as documented by the presence of long-prismatic, oscillatory zoned zircons (540 Ma) and relics of granitic textures. Geochemical and isotope data classify the igneous precursor as a S-type granite. In contrast, Outer Grey Gneiss samples are free of long-prismatic zircons and contain zircons with signs of mechanical rounding through sedimentary transport. Geochemical data indicate greywackes as main previous precursor. The most euhedral zircons are zoned and document Neoproterozoic (ca. 575 Ma) source rocks eroded to form these greywackes. U–Pb-SHRIMP measurements revealed three further ancient sources, which zircons survived in both the Inner and Outer Grey Gneiss: Neoproterozoic (600–700 Ma), Paleoproterozoic (2100–2200 Ma), and Archaean (2700–2800 Ma). These results point to absence of Grenvillian type sources and derivation of the crust from the West African Craton. The granite magma of the Inner Grey Gneiss was probably derived through in situ melting of the Outer Grey Gneiss sedimentary protolith as indicated by geological relationships, similar geochemical composition, similar Nd model ages, and inherited zircon ages. Red Gneiss occurs as separate bodies within fine- and medium-grained grey gneisses of the gneiss–eclogite zone (HP–HT overprinted). In comparison to Grey Gneisses, the Red Gneiss clearly differs in geochemical composition by lower contents of refractory elements. Rocks contain long-prismatic zircons (480–500 Ma) with oscillatory zonation indicating an igneous precursor for Red Gneiss protoliths. Geochemical data display obvious characteristics of S-type granites derived through partial melting from deeper crustal source rocks. The obtained time marks of magmatic activity (ca. 575 Ma, ca. 540 Ma, ca. 500–480 Ma) of the Eastern Erzgebirge are compared with adjacent units of the Saxothuringian zone. In all these units, similar time marks and geochemical pattern of igneous rocks prove a similar tectono-metamorphic evolution during Neoproterozoic–Ordovician time.  相似文献   

Element budgets of pine stands on lignite and pyrite containing mine soils     

Martin Gast  Wolfgang Schaaf  Joerg Scherzer  Rudolf Wilden  Bernd U. Schneider  Reinhard F. Hüttl 《Journal of Geochemical Exploration》2001,73(2):196

To analyze the development of pine ecosystems on lignite and pyrite containing mine soils, four pine stands with ages of 3–35 years were investigated in a chronosequence approach. Bulk precipitation, throughfall and soil solution in depths of 20, 40, 70 and 100 cm were studied over a three-year period to determine element fluxes in these forest ecosystems on extreme acidic and saline soils.Element budgets are controlled by the processes induced by pyrite oxidation such as intensive weathering of primary minerals, precipitation and leaching of secondary phases.Despite low water fluxes, element outputs can reach extraordinary high values due to very high concentrations in the soil solution. Although element outputs decrease drastically with stand age, respectively, site age, they exceed those of comparable pine stands on non-mine sites. Nitrogen release from the lignite fraction represents a special characteristic of the examined substrates. Nitrogen losses beneath the rooted zone can be 34 kg N ha⁻¹ yr⁻¹ in 100 cm depth. Element input and output in the examined ecosystems are far from balance. Closed cycling of nutrients seems to be recognizable in the case of potassium.  相似文献   

Ice-sheet growth and high-latitudes sea-surface temperature     

A. Berger  H. Gallée  X. S. Li  A. Dutrieux  M. F. Loutre 《Climate Dynamics》1996,12(7):441-448

The response of the LLN 2-D climate model to the insolation and CO₂ forcings during the Eemian interglacial is compared to reconstructions obtained from deep-sea cores drilled in the Norwegian Sea and in the North Atlantic. Both reconstructions and modeling results show a decrease of sea-surface temperature (SST) in the higher latitudes (70–75 °N zonal belt for the model and the Norwegian Sea for the proxy records), associated with a more moderate cooling at lower latitudes (50–55 °N and North Atlantic), at the middle of isotopic substage 5e, several millenia before the beginning of continental ice-sheet growth. Such a comparison between the simulated SST and ice volume of the Northern Hemisphere has been extended to the whole last glacial-interglacial cycle. The influence of the insolation forcing on SST and the shortcomings of the model due to its zonal character are discussed. Received: 6 July 1995/Accepted: 19 December 1995  相似文献   

The mesoscale variability of nutrients and plankton as seen in a coupled model     

Wolfgang Fennel  Thomas Neumann 《Ocean Dynamics》1996,48(1):49-71

  相似文献   

The Baltic Sea in 1996 — continuation of stagnation and decreasing phosphate concentrations     

Dr.  habil. Wolfgang Matthäus  Dr.  Prof. Dietwart Nehring  Dr.  habil. Hans Ulrich Lass  Dr. Günther Nausch  Dr. Klaus Nagel  Dr. Herbert Siegel 《Ocean Dynamics》1996,48(2):161-174

  相似文献   

Guided wave propagation across sharp lateral heterogeneities: the complete wavefield at plane vertical discontinuities   总被引：2，自引：0，他引：2  

Stefan Stange  Wolfgang Friederich 《Geophysical Journal International》1992,109(1):183-190

  相似文献   

Extreme value analysis of the sea state at the “nordsee” research platform and off Hörnum/Sylt     

Ralf Berger 《Ocean Dynamics》1993,45(2):107-113

  相似文献   

Das Zirkulationstheorem von V. Bjerknes und seine Anwendung in der Ozeanographie     

Wolfgang Krau   《Ocean Dynamics》1957,10(1):13-19

Zusammenfassung Aus dem Zirkulationstheorem von V. Bjerknes wird eine Formel (Seite17, Formel (6)) für die praktische Berechnung von Meeresströmungen abgeleitet, welche über jene von B. Helland-Hansen und J.W. Sandström hinausgeht. Der neuen Formel lä\t sich der Gültigkeitsbereich der alten entnehmen, wenn man die Grö\enordnung der horizontalen Scherung sowie der Divergenzen kennt.

---

V. Bjerknes' circulation theorem and its application to oceanographic research

Summary From V. Bjerknes' circulation theorem a new formula (see page 17, (6)) is derived allowing practical computations of ocean currents to be made. The new formula surpasses that one given by B. Helland-Hansen and J. W. Sandström. The range of validity of the old formula can be deduced from the new one if the order of magnitude of horizontal shearing as well as that of the divergences are known.

---

Le théorème de circulation d'après V. Bjerknes et son application à des recherches océanographiques

Résumé On déduit du théorème de circulation d'après V. Bjerknes une nouvelle formule (voir page 17, (6)) permettant le calcul pratique des courants océaniques. Cette nouvelle formule est supérieure à celle présentée par B. Helland-Hansen et J. W. Sandström. La portée de validité de la formule antérieure se laisse dériver de la nouvelle formule lorsqu'on connaÎt l'ordre de magnitude du cisaillement horizontal et celui des divergences.

  相似文献   

Der Original-Beerbachit im Odenwald,ein Amphibolit-Hornfels in Pyroxen-Hornfelsfazies     

Siegfried Matthes  Wolfgang Schubert 《Contributions to Mineralogy and Petrology》1971,33(1):62-86

With this petrographic re-investigation of the beerbachite (Chelius, 1892) from Odenwald/Germany geochemical and phase-petrological data are given for the first time.By petrofabric relics (Fig. 7) and geochemical characteristics (Figs. 8–11) is shown that the beerbachite-xenoliths are due to blocks broken down from the surrounding amphibolite series. They are present high grade hornfelses.Beerbachite, porphyroblastic by plagioclase (here porphyroblastic beerbachite, Bbp) (Chelius' Gabbroporphyrit) (Fig. 6) frequently forms marginal zones of beerbachite blocks and is explained as beerbachite-metablastite.Phase relation (Fig. 13) and mineral reactions with increasing metamorphic grade from amphibolite to amphibolite-hornfels (containing hornblende) finally to beerbachite are demonstrated and discussed.The first step may be the mineral reaction: plag_I(An 35–40)+hbl_I+sphene= plag_II(An 50–60)+hbl_II+cpx+opx+magnetite/ilmenite+H₂O. The pyroxene-hornfels facies respectively the orthopyroxene subfacies of the K-feldspar-cordierite-hornfels facies (Winkler, 1967) is only reached with the typical assemblage: plag(An 55–70)-cpx-opx-mt/ilm±(quartz) of beerbachite.On condition that the load correspondends to 3–4 km the maximum temperatures may not have exceeded 720–750° C. This valuation would result from experimental data of Choudhuri and Winkler (1967) of the model reaction: hbl=en+di+an+H₂O, if . The natural conditions will differ from this experimental model because of resp. P _load (p. 81)The very probably required temperature for the mineral assemblage of beerbachite would still be within sub-solidus temperatures of the corresponding model system, according to Fig. 13d. Therefore, the coarse grained plagioclases of Bbp (p. 69) could not be formed from cotectic pockets, too.Finally, convergences and divergences to the beerbachite concept are discussed out of the recent literature.

---

---

Herrn Dr. E. Knauer vom hiesigen Institut danken wir sehr für die Bestimmung des Chemismus zweier Pyroxen-Paare aus Beerbachit bzw. Hornfels mit der Mikrosonde (CAMEGA MS 46), Leihgabe der Deutschen Forschungsgemeinschaft. Den Herren Prof. E. Nickel und Dr. M. Maggetti vom Mineralogischen Institut der Universität Fribourg (Schweiz) und Dr. H. D. Trochim, Mineralogisches Institut der Universität Bochum, verdanken wir Vergleichsproben oder Einsichtnahme in vorhandene Dünnschliffe.  相似文献   

Chlorit-Hornblende-Felse des Bergsträßer Odenwaldes und ihre Phasenpetrologie     

Wolfgang Schubert 《Contributions to Mineralogy and Petrology》1969,21(4):295-310

Ultrabasic metamorphic rocks with typical mineral assemblage of cummingtonitic hornblende+Mg-chlorite+talc (described byMatthes u.Okrusch, 1965, and called “hösbachit”) were found for the first time in Odenwald/Germany. Three steps of metamorphic development can be described: the primary magmatic ultrabasic rock consisted of (1) orthopyroxene (bronzite), clinopyroxene (diallage), poikilitic olivine, and some hornblende. This is indicated by textural relicts, structural and geochemical investigations. A regional metamorphic process under conditions of the staurolite-almandine-subfacies ofWinkler’s andTurner andVerhoogen’s almandine-amphibolite facies transformed this assemblage to (2): cummingtonitic hornblende I+Mg-chlorite I (clinochlore)+talc. The third step followed under more diaphthoritic conditions and brought mineral assemblage (3): tremolitic hornblende II+Mg-chlorite II (pennine)+talc.  相似文献