Sm-Nd garnet and U-Pb monazite dating of high-grade metamorphism and crustal melting in the West Uusimaa area, southern Finland

The 100 km wide late Svecofennian granite-migmatite zone in southern Finland contains the Sulkava, the Turku and the West Uusimaa low-pressure, high-temperature granulite areas. In the West Uusimaa area the peak metamorphic conditions are estimated at T = 750-800°C and P = 4-5 kbars. Detailed isotopic dating of different parts of migmatites (mesosomes and leucosomes) as well garnet-orthopyroxene gneisses was undertaken by conventional analysis of U-Pb on monazite and Sm-Nd on garnet. U-Pb monazite ages show that the West Uusimaa area underwent a granulite facies metamorphism at peak conditions between 1832±2 Ma and 1816±2 Ma. The area was then cooled down to 700-600°C at 1.81-1.79 Ga according to Sm-Nd garnet-whole rock data. These results together with previous data show that all the three granulite areas in southern Finland share a coeval thermal event probably stemming from common or similar heat sources.</p

Modelling the impact of toxic and disturbance stress on white-tailed eagle (Haliaeetus albicilla) populations

Several studies have related breeding success and survival of sea eagles to toxic or non-toxic stress separately. In the present investigation, we analysed single and combined impacts of both toxic and disturbance stress on populations of white-tailed eagle (Haliaeetus albicilla), using an analytical single-species model. Chemical and eco(toxico)logical data reported from laboratory and field studies were used to parameterise and validate the model. The model was applied to assess the impact of ∑PCB, DDE and disturbance stress on the white-tailed eagle population in The Netherlands. Disturbance stress was incorporated through a 1.6% reduction in survival and a 10–50% reduction in reproduction. ∑PCB contamination from 1950 up to 1987 was found to be too high to allow the return of white-tailed eagle as a breeding species in that period. ∑PCB and population trends simulated for 2006–2050 suggest that future population growth is still reduced. Disturbance stress resulted in a reduced population development. The combination of both toxic and disturbance stress varied from a slower population development to a catastrophical reduction in population size, where the main cause was attributed to the reduction in reproduction of 50%. Application of the model was restricted by the current lack of quantitative dose–response relationships between non-toxic stress and survival and reproduction. Nevertheless, the model provides a first step towards integrating and quantifying the impacts of multiple stressors on white-tailed eagle populations

Distribution of cobalt, vanadinium and chromium between coexisting biotite and garnet in granulite facies rock samples

The distribution coefficients of cobalt, vanadium and chromium were determined in biotite-garnet pairs of granulite facies rock samples. The sample areas are Lapland, West Uusimaa and Sulkava. The distribution of cobalt between biotite and garnet is linear, KD being 1.7. The distribution points of vanadium fall close to a straight line, the slope of which is 9.8. The chromium distribution points are scattered. A relationship, however, is apparent between the chromium distribution coefficient and the atomic ratio Mg/Fe + Mg + Mn of garnet. The distribution coefficient decreases with an increase in the Mg/Mg + Fe + Mn of garnet

Tectono-metamorphic evolution and timing of the melting processes in the Svecofennian Tonalite-Trondhjemite Migmatite Belt: An example from Luopioinen, Tampere area, southern Finland

The Svecofennian Orogen is in southern Finland characterized by two major migmatite belts. These are the so-called Granite Migmatite Belt, in which Kfs-rich leucosomes predominate, and the Tonalite-Trondhjemite Migmatite Belt, which is characterized by Kfs-poor leucosomes and borders the former belt in the north. The present paper deals with selected migmatitic rocks from the latter belt. It is aimed to study the temporal and structural relationships of the different leucosome generations, and to establish the pressure-temperature-time paths of this belt. The Tonalite-Trondhjemite Migmatite Belt consists mainly of migmatitic rocks with various types of synorogenic granitoids and minor mafic and ultramafic crocks. The mesosome of the migmatites consist of garnet-sillimanite-biotite-plagioclase-cordierite-quartz assemblages with rare K-feldspar and late andalusite. The oldest leucosomes are dominated by plagioclase and quartz, and the content of K-feldspar increases in later leucosomes. Microtextural analysis in conjunction with THERMOCALC calculations and geothermometry shows that these rocks were metamorphosed at peak conditions of 700-750°C at 4-5 kbar and aH2O = 0.4-0.7. The formation of cordierite coronas around garnet and the late crystallization of andalusite suggest that the final stage of the P-T history was characterized by decompression and cooling within the andalusite stability field, estimated at 500-650°C and 3-4 kbar. Detailed isotopic dating of mesosome and leucosomes of the migmatites was undertaken by conventional U-Pb analyses on monazite and zircon, Sm-Nd analyses on garnet, and ion probe dating on zircon. The monazites are nearly concordant with an average age of 1878.5±1.5 Ma, and garnet-whole rock analyses show that the concordant leucosomes and the mesosome are coeval within error margins having ages of 1893±40 and 1871±14 Ma, respectively. However, garnet in the discordant vein leucosome provides an age of 1843±11 Ma, which is marginally younger than the age of the adjacent mesosome and the concordant leucosome (1877+18 and 1880±23 Ma, respectively) and the age of monazite. Zircons from the studied migmatites display complex zoning structures using SEM-based CL-imaging. Most grains have distinct cores, clearly remnants of original grains. The cores display various types of zoning but oscillatory zoning dominates. The cores are overgrown by one or two thin outer rims that are of two types: i) unzoned outer rim, considered as overgrowth of new zircon during a metamorphic event, and ii) weakly oscillatory zoned rim, considered as typical of magmatic recrystallization. Ion probe dating of cores yielded slightly discordant 207Pb/206Pb ages of between 2866-2002 Ma, which are interpreted as protolith age. Rims yielded two major age groups: the unzoned rims gave ages of 1872-1886 Ma, whereas the rims with oscillatory zoning yielded ages of 1951—1959 Ma. The youngest age group is consistent with the conventional Sm-Nd dating on garnet and U-Pb dating on monazite and we suggest that the migmatites were metamorphosed at granulite facies conditions at ca. 1880 Ma. The 1951-1959 Ma age group yielded by magmatic zircon rims remains difficult to interpret, but may reflect a magmatic event prior to the metamorphic one. This magmatic event might be related to the rifting of a Svecofennian protocontinent

Paleomagnetism and age relations of the rocks in the main sulphide ore belt in central Finland

Paleomagnetic data on the Main Sulphide Ore Belt in Finland are coherent but differ clearly from those obtained on the Archean basement area immediately north of it. The coherent magnetization in the Belt could have been caused by (i) axial uplift, (ii) a plate suture along the Belt or (iii) a short-time igneous pulse. The last interpretation is accepted since it agrees with the radiometric age data. Thus the paleomagnetic measurements in the area date the same thermal events as do the radiometric U-Pb age determinations, and the shape of the APW curve is thereby verified. A paleomagnetic pole determined for dykes intersecting the Archean basement block lies off the accepted APW curve which possibly need to be corrected. The magmatic pulse between 1880— 1840 Ma may have been associated with a plate collision or with a deep fluid convection producing the sulphide ore precipitation within the Belt

Neutron star parameter constraints for accretion-powered millisecond pulsars from the simulated IXPE data

We have simulated the X-ray polarization data that can be obtained with the Imaging X-ray Polarimetry Explorer, when observing accretion-powered millisecond pulsars. We estimated the necessary exposure times for SAX J1808.4-3658 in order to obtain different accuracy in the measured time-dependent Stokes profiles integrated over all energy channels. We found that the measured relative errors strongly depend on the relative configuration of the observer and the emitting hotspot. The improvement in the minimum relative error in Stokes Q and U parameters as a function of observing time t scales as 1/√ t, and it spans the range from 30-90% with a 200 ks exposure time to 20-60% with a 500 ks exposure time (in the case of data binned in 19 phase bins). The simulated data were also used to predict how accurate measurements of the geometrical parameters of the neutron star can be made when modelling only Q and U parameters, but not the flux. We found that the observer inclination and the hotspot co-latitude could be determined with better than 10° accuracy for most of the cases we considered. In addition, we show that the position of a secondary hotspot can also be constrained when the spot is not obscured by an accretion disc. These measurements can be used to further constrain the neutron star mass and radius when combined with modelling of the X-ray pulse profile