The Late Cretaceous Klepa basalts in Macedonia (FYROM)—Constraints on the final stage of Tethys closure in the Balkans          下载免费PDF全文

Dejan Prelević  Simon Wehrheim  Magnus Reutter  Rolf L. Romer  Blažo Boev  Milica Božović  Paul van den Bogaard  Vladica Cvetković  Stefan M. Schmid 《地学学报》2017,29(3):145-153

The waning stage(s) of the Tethyan ocean(s) in the Balkans are not well understood. Controversy centres on the origin and life‐span of the Cretaceous Sava Zone, which is allegedly a remnant of the last oceanic domain in the Balkan Peninsula, defining the youngest suture between Eurasia‐ and Adria‐derived plates. In order to investigate to what extent Late‐Cretaceous volcanism within the Sava Zone is consistent with this model we present new age data together with trace‐element and Sr–Nd–Pb isotope data for the Klepa basaltic lavas from the central Balkan Peninsula. Our new geochemical data show marked differences between the Cretaceous Klepa basalts (Sava Zone) and the rocks of other volcanic sequences from the Jurassic ophiolites of the Balkans. The Klepa basalts mostly have Sr–Nd–Pb isotopic and trace‐element signatures that resemble enriched within‐plate basalts substantially different from Jurassic ophiolite basalts with MORB, BAB and IAV affinities. Trace‐element modelling of the Klepa rocks indicates 2%–20% polybaric melting of a relatively homogeneously metasomatised mantle source that ranges in composition from garnet lherzolite to ilmenite+apatite bearing spinel–amphibole lherzolite. Thus, the residual mineralogy is characteristic of a continental rather than oceanic lithospheric mantle source, suggesting an intracontinental within‐plate origin for the Klepa basalts. Two alternative geodynamic models are internally consistent with our new findings: (1) if the Sava Zone represents remnants of the youngest Neotethyan Ocean, magmatism along this zone would be situated within the forearc region and triggered by ridge subduction; (2) if the Sava Zone delimits a diffuse tectonic boundary between Adria and Europe which had already collided in the Late Jurassic, the Klepa basalts together with a number of other magmatic centres represent volcanism related to transtensional tectonics.  相似文献   

Modelling thermal transients from magmatic underplating—an example from the Vøring margin (NE Atlantic)     

Magnus Wangen  Rolf Mjelde  Jan Inge Faleide 《Computational Geosciences》2011,15(4):771-788

The thermal impact of several kilometre-thick magmatic underplating in the lower continental crust is studied with analytical and numerical methods. Simple analytical solutions are derived for the thermal transient in the case of an infinite depth below the underplate and also for the case of a finite depth (down to the asthenosphere). It is shown that these solutions lead to simple approximations for when the transient surface heat flow is at its maximum, what the maximum is, and for how long the transient lasts. Even though these solutions assume that the underplate is emplaced instantaneously, they are useful in the interpretation of underplating over finite time spans. A numerical scheme is suggested for the modelling of underplating that handles both short time intervals as well as long intervals. The scheme treats magmatic underplating in a mass and energy conservative manner, and it is compared against the analytical solutions. Finally, the analytical and numerical results for thermal transients are applied to a transect from the Vøring margin (NE Atlantic), with respect to various degrees of early Cenozoic magmatic intrusion. It appears that more than half of the lower crustal body (LCB) in the Vøring margin must be magmatic underplating for the vitrinite reflectance to be substantially higher than for the non-magmatic case, where the LCB is assumed to comprise Caledonian crust.  相似文献   

Modeling undertow due to random waves     

Pham Thanh Nam  Hocine Oumeraci  Magnus Larson  Hans Hanson 《Ocean Dynamics》2014,64(8):1209-1219

A numerical model of undertow due to random waves is developed. The model includes three sub-models: (i) a model for multi-directional and multi-frequency random wave transformation, (ii) a surface roller evolution model, and (iii) a model for calculating the vertical distribution and the mean value of the undertow velocity. The calculation of wave trough level is performed based on a theory for the wave asymmetry. The model was successfully validated against small- and large-scale laboratory experiments. Thus, the model is expected to provide reliable input for the modeling of sediment transport and morphological change due to waves and currents.  相似文献   

Phytoplankton life cycle transformations lead to species-specific effects on sediment processes in the Baltic Sea     

Kristian Spilling  Magnus Lindstrm 《Continental Shelf Research》2008,28(17):2488-2495

In order to study the sediment response to different addition of organic matter, we added cultures of the dinoflagellates Scrippsiella hangoei and Woloszynskia halophila and the diatom Pauliella taeniata to aquaria containing natural sediment. The biomass added was 1550–3260 mg C m⁻², and in the control, no biomass was added (n=3). Oxygen profiles at the sediment–water interface and inorganic nutrients in the near bottom water were determined once a week. In the additions of P. taeniata and W. halophila the sediment quickly became anoxic, and subsequently there was a flux of >1 mmol PO₄³⁻ m⁻² d⁻¹ out of the sediment in these treatments. The majority of the released P came from P stored in the sediment and not from the organic phosphorus added. The result was very different for the S. hangoei addition. This species underwent a life cycle change to form temporary cysts. During this process there was a net uptake of nutrients. After the formation of cysts the concentration of inorganic nutrient was similar to that of the control. Cysts generally survive for long periods in the sediment (months to years) before germinating, but can also be permanently buried in the sediment. The novel idea presented here is that the phytoplankton composition may directly affect sediment processes such as oxygen consumption and phosphorus release, through species-specific life cycle changes and yields of resting stages produced prior to sedimentation. This can be an important aspect of nutrient cycling in eutrophic waters, like the Baltic Sea, where there is large year-to-year difference in the amount of resting stages settling at the sea floor, mainly due to differences in abundance of diatoms and dinoflagellates during the spring bloom. If yields of resting stages change, e.g. due to changes in the phytoplankton community, it may lead to alterations in the biogeochemical cycling of nutrients.  相似文献   

Analysis of digital elevation data for palaeosurfaces in south-western Sweden   总被引：3，自引：0，他引：3  

Magnus Johansson 《Geomorphology》1999,26(4):339

A 3873-km² large rectangular area of the Precambrian basement in south-western Sweden has been investigated regarding gross morphology of palaeosurfaces. GIS and digital elevation data were used to construct maps of relative and absolute relief and E–W trending height profiles. Three different palaeosurfaces were recognised and delimited; the very even sub-Cambrian peneplain in the east at an intermediate altitudinal position, an uplifted and broken part of the sub-Cambrian peneplain in the centre at the highest present elevation, and in the western coastal areas a joint-aligned valley landscape with high relative relief, probably an exhumed Mesozoic etch-surface. Phanerozoic faulting has dissected the different palaeosurfaces into tectonic blocks, which are shown from trend surface analysis to be tilted in different directions and to different degrees, characteristic and decisive for the morphological development.  相似文献   

Using UCODE_2005 and PHREEQC to determine thermodynamic constants from experimental data     

Skold ME  Thyne GD  McCray JE 《Ground water》2007,45(3):368-373

This article presents a method for estimating chemical thermodynamic constants from experimental data using the two computer programs UCODE_2005 and PHREEQC. As an example, the conditional stability constant for lead (Pb) complexation by a remediation agent (carboxymethyl-beta-cyclodextrin) is estimated, but the method can be applied to estimate other thermodynamic parameters such as sorption constants and degradation rate constants. Advantages of this technique include estimation of uncertainties associated with estimated parameters, evaluation of information content of observations, statistical evaluation of the appropriateness of the conceptual model, and statistical-based comparison of different models.  相似文献   

Indicators of road network vulnerability to storm-felled trees   总被引：1，自引：0，他引：1  

Rolf Nyberg  Magnus Johansson 《Natural Hazards》2013,69(1):185-199

In this paper, we exemplify the use of simple indicators of wind storm vulnerability of the road network that can be derived from existing geographic datasets. We point out the possible utilization of the datasets, applying GIS techniques, for highlighting road sections that, due to adjacency of high forest stands, are sensitive to closure by storm-felled trees. Indicators reflecting the reduced access to different areas or to the population in need of emergency aid can be derived based on the parameter tree height along roads and road network analysis. As a case in this study, the methodology is applied to elderly people (+80 years) with possible need of daily care at home following a severe storm. A comparison to the extreme 2005 storm felling in southern Sweden reveals that only limited estimates of road network disruption due to storm-felled trees are possible using the indicators, as other factors, for example, wind direction, which determine the exact impact of a particular storm are not taken into account. However, the indicators and network analysis also provide a possibility to draw attention to locations where disruptions of the road network would have significant effects on the accessibility to large surrounding areas. Potential critical road closures can be identified and preventive measures considered locally at these points.  相似文献   

The aperiodic broad-band X-ray variability of Cygnus X-3     

Magnus Axelsson  Stefan Larsson  Linnea Hjalmarsdotter 《Monthly notices of the Royal Astronomical Society》2009,394(3):1544-1550

We study the soft X-ray variability of Cygnus X-3. By combining data from the All-Sky Monitor and Proportional Counter Array instruments on the RXTE satellite with EXOSAT /Medium Energy (ME) detector observations, we are able to analyse the power density spectrum (PDS) of the source from 10⁻⁹ to 0.1 Hz, thus covering time-scales from seconds to years. As the data on the longer time-scales are unevenly sampled, we combine traditional power spectral techniques with simulations to analyse the variability in this range. The PDS at higher frequencies  (≳10⁻³ Hz)  are for the first time compared for all states of this source. We find that it is for all states well described by a power law, with index  ∼−2  in the soft states and a tendency for a less steep power law in the hard state. At longer time-scales, we study the effect of the state transitions on the PDS, and find that the variability below  ∼10⁻⁷ Hz  is dominated by the transitions. Furthermore, we find no correlation between the length of a high/soft-state episode and the time since the previous high/soft state. On intermediate time-scales, we find evidence for a break in the PDS at time-scales of the order of the orbital period. This may be interpreted as evidence for the existence of a tidal resonance in the accretion disc around the compact object, and constraining the mass ratio to   M ₂/ M ₁≲ 0.3  .  相似文献   

Chemistry, reaction mechanisms and micro-structures during retrograde metamorphism of gedrite-biotite-plagioclase bearing rocks from Bergslagen, south-central Sweden     

Embaie A. Ferrow  Magnus Ripa 《Lithos》1991,26(3-4):271-285

The Proterozoic rhyolitic volcanics constituting the foot-wall rocks in the Stollberg ore-field, Bergslagen, south-central Sweden, locally contain gedrite altered to chlorite and serpentine, biotite altered to chlorite and plagioclase altered to epidote.

The intergrowths between the host gedrite and the chlorite/serpentine inclusions are oriented with the a^* of gedrite parallel to the c^* of serpentine and chlorite. The biotite has been altered to chlorite by brucitization of both the K-interlayer and talc-like layer. In both cases the net change in volume during chloritization is small.

The assumption that Al is conserved during alteration of gedrite and biotite agrees very well with the micro-structures and orientation relations observed by transmission electron microscopy. Normalizing the chlorite to 1.00 mole, the overall chemical change that took place during the retrograde metamorphism of the Stollberg rocks can be written as: 0.84Ged+0.14Bio+0.65Mg+4.76H₂O+0.42H=1.00Chl+0.57Alb+0.72Fe+0.01Na+0.12K+0.01Ti+0.05Mn+0.95H₄SiO₄ The reaction results in ca 9% increase in volume for the solid phases. Thus, a slightly acidic Mg-rich fluid started the reaction and, upon leaving the system, the metasomatic fluid was enriched in Na, Fe, K, and Si.  相似文献   

The significance of rock structure,lithology and pre‐glacial deep weathering for the shape of intermediate‐scale glacial erosional landforms     

Mats Olvmo  Magnus Johansson 《地球表面变化过程与地形》2002,27(3):251-268

The main landforms within the glacially scoured Precambrian rocks of the Swedish west coast are closely connected to the principal structural pattern and have lately been explained as mainly a result of etch processes, probably during the Mesozoic and with a possible second period of etching during the Neogene. To explore the effect of multiple glacial erosion on the rock surfaces, an island with two different lithologies and with striae from different directions was selected for a detailed study, focusing on the shape of roches moutonnées. Air‐photo interpretation of bedrock lineaments and roches moutonnées combined with detailed field mapping and striae measurements are used to interpret the structural and lithological control on the resulting shape. The study reveals a significant difference in shape between roches moutonnées in augen‐granite and orthogneiss. Low elongated and streamlined roches moutonnées occur in the gneiss area, striated by a Late Weichselian ice flow from the NE. This ice flow is subparallel with both the local dominant trend of topographically well‐expressed joints and the schistosity of the gneiss. Frequently, there are no signs of quarrying on the lee‐sides of the gneiss roches moutonnées and hence they resemble the shape of whalebacks, or ruwares, as typically associated with the exposed basal weathering surface found in tropical areas. The granite roches moutonnées were formed by an older ice flow from the ESE, which closely followed the etched WNW–ESE joint system of the granite. Late Weichselian ice flow from the NE caused only minor changes of the landforms. On the contrary, marks of the early ESE ice flow are poorly preserved in the gneiss area, where it probably never had any large effect as the flow was perpendicular to both schistosity and structures and, accordingly, also to the pre‐glacial relief. The study demonstrates that coincidence between ice flow direction and pre‐glacially etched structures is most likely to determine the effects of glacial erosion. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献