The nappe pile of eastern Crete

In eastern Crete four allochthonous units with different styles of deformation are piled up above the autochthonous Cherty Limestone (“Plattenkalk”). The emplacement of the nappes is discussed. Diapiric uplift of the Cycladic area was accompanied by large-scale gravity sliding in the direction towards the Aegean arc. There is no evidence from geophysical data for the existence of a subduction zone. Therefore, the transport of the eastern Cretan nappes may be better explained by gravity tectonics than by the model of plate tectonics.     

Partial fusion of basic granulites at 5 to 15 kbar: implications for the origin of TTG magmas

Partial fusion experiments with basic granulites (S6, S37) believed to represent the lower crust beneath the Eifel region (Germany) were performed at pressures from 5 to 15 kbar. Water-undersaturated experiments were carried out in the presence of 1 wt% H₂O plus 2.44 or 0.81 wt% CO₂ equivalent to mole fractions of H₂O/(H₂O + CO₂) of 0.5 and 0.75, respectively, of the volatile components added. At temperatures from 850 to 1100 °C the weight proportions of melt range from 7 to 30 %. Melt compositions change from trondhjemitic over tonalitic to dioritic with increasing degree of partial melting. Crystalline residua are plagioclase/pyroxene dominated at 5 kbar to garnet/pyroxene dominated at 15␣kbar. Dehydration melting was studied in granulite S35 similar in composition to S6. The magmatic precursors of the granulite xenoliths used in this study had geochemical characteristics of cumulate gabbro (metagabbro S37) and evolved melts (metabasalts S6, S35), respectively. Melts from granulite S37 match the major element compositions of natural trondhjemites and tonalites. At 5 kbar, their Al₂O₃ is relatively low, similar to tonalites from ophiolites. At 15 kbar, Al₂O₃ in the melts is high due to the near absence of plagioclase in the crystalline residua. The Al₂O₃ concentrations in 15 kbar melts from S6 (˜20 wt%) are higher than in natural tonalites. Depth constraints on the formation of tonalitic magmas in the continental crust are provided by REE (rare earth element) patterns of the synthetic melts calculated from the known REE abundances in metagabbro S37 and metabasalt S6 assuming batch melting and using partition coefficients from the literature. The REE patterns of tonalites from active continental margins and Archean trondhjemite-tonalite-granodiorite␣associations low in REE with La_N (chondrite normalised) from 10 to 30 and Yb_N from 1 to 2 are reproduced at pressures of 10 and 12.5 kbar from metagabbro S37 which displays a slightly L(light)REE enriched pattern with La_N = 8 and Yb_N = 3. Natural tonalites with La_N from 30 to 100 require a source richer in REE than granulite S37. At 15 kbar, H(heavy)REE_N in melts from granulite S37 are depressed below the level observed in natural tonalites due to the high proportion of garnet (>30 wt%) in the residue. Melts from metabasalt S6 (enriched in REE with La_N = 38 and Yb_N = 16) do not match the REE characteristics of natural tonalites under any conditions. Received: 1 July 1994 / Accepted: 11 September 1996     

Relations of field line resonances and upstream waves and the winter attenuation of pulsations

Using data on the occurrence frequency of geomagnetic pulsations of different periods from three observatories in Central Europe, conclusions are drawn about the occurrence of field line resonances and pulsations directly driven by upstream waves at L-values below 3. It was found that both types occur during the interval studied (first 6 months of the year 1991), but both the occurrence frequency of the two types and the characteristic period of the field line resonance change significantly as compared to other intervals. During Northern winter, pulsation activity is severely damped in solar maximum years, including the year 1991. The decrease in the activity of the pulsations is more significant at shorter periods.     

Test of IGRF (1980) main field and secular variation in Europe

The IGRF-models for the main field and the secular variation (IGRF 1980 and IGRF-SV 1980–1985) have been compared with geomagnetic ground based data for epoch 1980.5 in the GDR, and also with the secular variation at 34 European observatories. The results for the main magnetic field were much better than for IGRF 1965. With a level-error of ～ 45 nT, the IGRF 1980 included ～ 75% of the magnetic crust field. The structure of the IGRF-field is similar to that of other regional reference fields.The IGRF-SV for 1965, 1975 and 1980–1985 have been compared with analytical SV-models, based on low-degree polynomial approximations. It is shown that the main features of SV in Europe are represented correctly. The mean differences between observatory data and IGRF-SV 1980–1985 are 1.5′/a for declination, and 7 nT/a for total intensity.     

Form roughness and the absence of secondary flow in a large confluence–diffluence,Rio Paraná, Argentina

Confluence–diffluence units are key elements within many river networks, having a major impact upon the routing of flow and sediment, and hence upon channel change. Although much progress has been made in understanding river confluences, and increasing attention is being paid to bifurcations and the important role of bifurcation asymmetry, most studies have been conducted in laboratory flumes or within small rivers with width:depth (aspect) ratios less than 50. This paper presents results of a field‐based study that details the bed morphology and 3D flow structure within a very large confluence–diffluence in the Río Paraná, Argentina, with a width:depth ratio of approximately 200. Flow within the confluence–diffluence is dominated largely by the bed roughness, in the form of sand dunes; coherent, channel‐scale, secondary flow cells, that have been identified as important aspects of the flow field within smaller channels, and assumed to be present within large rivers, are generally absent in this reach. This finding has profound implications for flow mixing rates, sediment transport rates and pathways, and thus the interpretation of confluence–diffluence morphology and sedimentology. Copyright © 2006 John Wiley & Sons, Ltd.     

Chemical perturbations in the planetary boundary layer and their relevance for chemistry transport modelling

The role of perturbations of reactive trace gas concentration distributions in turbulent flows in the planetary boundary layer (PBL) is discussed. The paper focuses on disturbances with larger spatial scales. Sequential nesting of a chemical transport model is applied to assess the effect of neglecting subgrid chemical perturbations on the formation and loss of ozone, NO _x , peroxyacetyl nitrate (PAN) and HNO₃ calculated with a highly complex chemical mechanism. The results point to characteristic differences regarding the process of mixing of chemically reactive species in the PBL and lower troposphere.     

A new automated nondestructive system for high resolution multi-sensor core logging of open sediment cores

 A new system for logging the geophysical properties of marine sediment cores allows both whole cores and split cores to be measured in a nondestructive fashion. The current sensor configuration measures compressional (P) wave velocity (500 kHz), bulk density (using gamma-ray attenuation), and magnetic susceptibility at user-defined sample intervals down the core. Split-core logging gives more reliable results than whole core logging as it mostly eliminates core-slumping effects that can lead to spurious results; it also gives higher resolution magnetic susceptibility readings. Received: 16 May 1997 / Revision received: 24 October 1997