Structural and metamorphic evolution of the Turku migmatite complex, southwestern Finland

The Turku migmatite complex in southwestern Finland is a representative area for the type of tectonic and metamorphic evolution seen within the Palaeoproterozoic Svecofennian Orogen in southern Finland. The orogeny can be divided into early, late and postorogenic stages. The early orogenic structural evolution of the crust is expressed by a D/D deformation recorded as bedding-parallel S mica foliation deformed by tight to isoclinal D folds with subhorizontal axial planes and a penetrative S axial plane foliation. Syntectonic ca. 1890-1870 Ma tonalites were emplaced during D as sheet intrusions. This deformation is attributed to thrust tectonics and thickening of the crust. The late orogenic structural evolution produced the main D folding, which transposed previous structures into a NE-SW trend. The doubly plunging fold axis produced dome-and-basin structures. The attitude of the F folds varies from upright or slightly overturned to locally recumbent towards the NW. Granite dikes were intruded along S axial planes. Large D fold limbs are often strongly deformed, intensively migmatized and intruded by garnet- and cordierite-bearing granites. These observations suggest that these potassium-rich granites, dated at 1840-1830 Ma, were emplaced during D. This late orogenic NW-SE crustal shortening further contributed to crustal thickening. Subvertical D shear zones that cut all previous rock types possibly controlled the emplacement of postorogenic granitoids. Steeply plunging lineations on D shear planes suggest vertical displacements during a regional uplift stage. Metamorphic grade increases from cordierite-sillimanite-K-feldspar gneisses in the northwest and from muscovite-quartz±andalusite rocks in the southeast to high-temperature granulite facies migmatites in the middle of the study area. Block movements during D caused the observed differences in metamorphic grade. Garnet and cordierite are mostly breakdown products of biotite and sillimanite and their growth is mainly syntectonic with D; they are elongated within the S plane and deformed by D folds. Leucosome veins were already produced during D, but in situ melting began during D producing granitic leucosomes with euhedral garnet and cordierite along the axial planes of F. Garnet is typically altered to cordierite and plagioclase in the presence of sillimanite, indicating decompression close to the temperature maximum. Pressure and temperature estimates from garnet and cordierite indicate that the granulites reached temperatures in excess of 800°C at approximately 6 kbar pressure while the adjacent amphibolite facies rocks crystallized at 100-150°C and 1-2 kbar lower temperatures and pressures. Therefore, the granulite areas represent the deepest structural levels in the area. Structural and metamorphic observations indicate that peak metamorphism was reached during the compressional late orogenic D stage ca. 1840-1830 Ma ago. Crustal thickening simultaneous with thinning of the mantle lithosphere may explain this kind of tectono-metamorphic evolution.</p

Svecofennian magmatic and metamorphic evolution in southwestern Finland as revealed by U-Pb zircon SIMS geochronology

Zircons from six samples collected from igneous and metamorphic rocks were dated using the NORDSIM ion microprobe, in order to investigate the tectonic evolution of the Palaeoproterozoic Svecofennian Orogen in southwestern Finland. These rocks represent pre-collisional, collisional and post-collisional stages of the orogeny. The ion microprobe results reveal two age groups of granodioritic-tonalitic rocks. The intrusions have different tectonic settings: the Orijärvi granodiorite represents pre-collisional 1.91-1.88 Ga island-arc-related magmatism and yielded an age of 1898 ± 9 Ma, whereas the collision-related Masku tonalite was dated at 1854 ± 18 Ma. The latter age accords with more accurate previous conventional zircon age data and constrains the emplacement age of collisional granitoids to ≈ 1.87 Ga. This is interpreted to reflect the collision between the Southern Svecofennian Arc Complex with the Central Svecofennian Arc complex and the formation of a suture zone between them during D2 deformation. Granulite facies metamorphism in the Turku area was dated at 1824 + 5 Ma using zircons from leucosome in the Lemu metapelite. This age constrains D3 folding related to post-collisional crustal shortening in this area. Crustal melting continued until ≈ 1.81 Ga, as indicated by the youngest leucosome zircons and metamorphic rims of enderbite zircons. New metamorphic zircon growth took place in older granitoids at granulite facies, but not at amphibolite facies. Detrital zircons with ages between 2.91 and 1.97 Ga were found in the mesosome of the Lemu metapelite and 2.64-1.93 Ga inherited cores were found in the 1.87 Ga Masku tonalite. © 2002 Elsevier Science B.V. All rights reserved.</p

Super star clusters and Supernovae in interacting LIRGs unmasked by NIR adaptive optics

We report on an on-going near-IR adaptive optics survey targeting interacting luminous IR galaxies. High-spatial resolution NIR data are crucial to enable interpretation of kinematic, dynamical and star formation (SF) properties of these very dusty objects. Whole progenitor nuclei in the interactions can be missed if only optical HST imaging is used. Here we specifically present the latest results regarding core-collapse supernovae found within the highly extincted nuclear regions of these galaxies. Direct detection and study of such highly obscured CCSNe is crucial for revising the optically-derived SN rates used for providing an independent measurement of the SF history of the Universe. We also present thus-far the first NIR luminosity functions of super star cluster (SSC) candidates. The LFs can then be used to constrain the formation and evolution of SSCs via constraints based on initial mass functions and cluster disruption models.Comment: 6 pages. To appear in proceedings of 'Galaxies and their Masks' (Namibia, April 2010), published by Springer, New York, eds. D.L. Block, K.C. Freeman, I. Puerar

QACCP Analyse in der Verarbeitung von biologischer Säuglingsnahrung

The aim of the study was to evaluate the quality influencing processing steps based on the processes of carrot baby food. Once the processing conditions were identified, the possibilities for alternative processing techniques will be explored to improve the overall product and process quality. Next to the food safety (hazard) in the food processing the quality aspect is getting more and more important and an analyse system to optimise the process needs to be established (QualityAnalysisCriticalControlPoint). Organic carrots (Daucus carota, Maestro variety) were processed in a pilot plant trail according a carrot puree process typical in baby food industry. The samples differed regarding the treatment of the raw material prior the sterilization process. Different factors affecting the process like processing time and temperature were documented. It can be concluded that the treatment of the raw material prior the sterilization process can be a critical point according to the process quality. Also great variations in inside temperature are possible among the samples going through the sterilization process. Since the process time is adjusted by the coldest sample, it is important to follow the factors affecting the heat transfer

Palaeoproterozoic adakite- and TTG-like magmatism in the Svecofennian orogen, SW Finland

The Palaeoproterozoic Svecofennian orogen in the Fennoscandian shield is an arc accretionary orogen that was formed at c. 1.92-1.86Ga. Arc accretion, magmatism and the subsequent continent-continent collision thickened the crust up to c. 70km, forming one of the thickest Palaeoproterozic orogens. At the end stage of accretionary tectonics, voluminous synorogenic magmatism occurred in southwestern Finland leading to the intrusion of intermediate to felsic plutonic rocks. Ion microprobe single zircon dating of one diorite sample yielded an age of 1872±3Ma (εNd=+2.2) and the trondhjemite sample an age of 1867±4Ma (εNd=+2.6). Inherited 2667-1965Ma cores and 1842±5Ma metamorphic rims were also found in zircons from the trondhjemite. The dioritic magmatism is mantle-derived and is slightly enriched by subduction-related processes. The felsic magmatism shows elevated Sr/Y and La/Yb ratios, which are typical for adakite- and TTG-like magmas. Their low Mg#, Ni and Cr contents argue against slab-melting and mantle-wedge contamination. We infer that the felsic magmatism was generated through crustal melting of the lower part of the previously generated volcanic-arc type crust. Based on published melting experiments and the Sr and Y contents of the felsic rocks we suggest that the melts were generated at a minimum pressure of 10kbar, with evidence of a 15kbar pressure for the highest Sr/Y trondhjemites. It is proposed that arc accretion combined with magmatic intrusions thickened the crust so that melting of the lower crust yielded adakite- and TTG-like compositions. The mafic magmatism is considered to be the heat source

Light and colour of cirrus, translucent and opaque dust in the high-latitude area of LDN 1642

We have performed a 5-colour surface photometric study of the high-galactic-latitude area of dark nebula LDN 1642. Scattered light properties are presented of diffuse, translucent and opaque dust over the range of 3500 -- 5500 A. Far infrared absolute photometry at 200 um improves the precision of and provides a zero point to the extinction. The intensity of the scattered light depends on dust column density in a characteristic way: for optically thin dust the intensity first increases linearly, then turns to a saturation value; at still larger extinctions the intensity turns down to a slow decrease. The $A_V$ value of the saturated intensity maximum shifts in a systematic way, from $A_V\approx$ 1.5 mag at 3500 A, to $\sim 3$ mag at 5500 A. The intensity curves offer a straight-forward explanation for the behaviour of the scattered-light colours. At the intensity peak the colour agrees with the integrated starlight colour, while it is bluer at the low- and redder at the high-column-density side of the peak, respectively. These colour changes are a direct consequence of the wavelength dependence of the extinction. We have compared the colours of the LDN 1642 area with other relevant observational studies: high-latitude diffuse/translucent clouds, wide-field cirrus dust; and externally illuminated AGB-star envelopes. For extragalactic low-surface-brightness sources cirrus is an unwanted foreground contaminant. Our results for cirrus colours can help to distinguish cases where a diffuse plume or stream, apparently associated with a galaxy or a group or cluster, is more likely a local cirrus structure. Keywords: ISM: dust, extinction -- ISM: clouds, individual LDN 1642 -- Galaxy: solar neighbourhood -- Astronomical instruments, methods and techniques: methods -- Physical data and processes: scatteringComment: 20 pages, 10 figures, accepted for publication in MNRAS, published as MNRAS advance article on June 27 202

Palaeoproterozoic mafic and intermediate metavolcanic rocks in the Turku area, SW Finland

Twenty two samples were analysed from mafic and intermediate volcanic rocks from the Turku area along ∼60 km long north-south geotraverse. Geographically and lithologically the samples were divided into the Pargas,Turku and Vahto groups. The Pargas and Turku groups consist of mafic units and intercalations within migmatitic gneisses. Their geochemical compositions are very similar. In average, they show quite flat REE curves and the multielement diagrams show moderate LILE enrichments, minor negative Ta-Nb anomalies and straight HFSE curves. We infer these as transitional between MORB and VAB. The Vahto group consists of thicker volcanic sequences in connection with synorogenic plutonic rocks. The data show enriched LREEs, LILEs,Th and P combined with negative Ta-Nb anomalies, i.e. the Vahto group shows subduction component. We interpret that the Vahto volcanic rocks belong to the Häme belt. The geochemical data indicate that the Pargas and Turku groups were formed in extensional, possibly back-arc or intra-arc setting while the Vahto group was formed at continental volcanic arc.</p

U-Th-Pb zircon geochronology on igneous rocks in the Toija and Salittu Formations, Orijärvi area, southwestern Finland: Constraints on the age of volcanism and metamorphism

Zircons from a felsic volcanic rock in the Toija Formation and a synvolcanic gabbro intrusion in the Salittu Formation within the Orijärvi area were dated by U-Th-Pb SIMS in order to provide depositional constraints on these formations. Zircon crystals from the felsic rock preserve a two-stage crystallisation history with zoned core domains and homogeneous rim domains. Inner domains yield a 1878 ± 4 Ma concordia age, interpreted to determine the crystallisation of this rock. Rims yield a 1815 ± 3 Ma concordia age interpreted to determine the regional metamorphism. Small rounded zircon grains from the Salittu gabbro, located within the Jyly shear zone, yield a concordia age of 1792 ± 5 Ma. We interpret the grain textures to suggest that they recrystallised from inherited zircon seeds during the heat and fluid flow into the shear zone. Although no direct ages for the Salittu Formation have been recovered, field relationships imply that it was deposited between 1878 - 1875 Ma.</p

1.90-1.88 Ga arc and back-arc basin in the Orijärvi area, SW Finland

The Orijärvi area within the Uusimaa Belt is a key area in resolving the stratigraphy and tectonic setting of the Southern Svecofennian Arc Complex in southern Finland. Based on field relationships, geochemistry and radiometric age determinations, the area can be divided into four formations. The bimodal Orijärvi formation, lowermost in stratigraphy, is exposed in an antiform containing the synvolcanic Orijärvi granodiorite in its core. Basalts have high LILE/HFSE ratios with pronounced negative Nb-Ta anomalies. The basalts in the lower part of the Orijärvi formation are geochemically less evolved than the basalts and basaltic andesites at higher levels. A rhyolite from a low stratigraphic level in the Orijärvi formation yielded a U-Pb zircon age of 1895.3±2.4 Ma. The Kisko formation stratigraphically overlies the Orijärvi formation and the compositions of the volcanic rocks range from basalts to rhyolites. These mafic and intermediate rocks also show high LILE/HFSE ratios but the total element abundances are higher and show a more pronounced LREE enrichment, compared to the Orijärvi formation, indicating an evolved magma system. A dacite from the upper part of the Kisko formation yielded a U-Pb zircon age of 1878.2±3.4 Ma. The Salittu formation probably overlies the Kisko formation. It mainly comprises picrites and tholeiitic pillow lavas with mica gneisses and minor marbles as intercalations. It differs from the underlying formations showing higher Mg, Ti and Zr contents and higher LILE/HFSE ratios. The major and trace element compositions indicate an oceanic affinity. The Toija formation evidently underlies the Salittu formation and comprises mafic pillow lavas, rhyolites, marbles, and one picritic horizon. The geochemical characteristics are transitional between the Salittu and Orijärvi/Kisko formations. All the formations contain both concordant and crosscutting intrusive rocks, some of which are comagmatic with the volcanic rocks. In tectonomagmatic discrimination diagrams the Orijärvi and Kisko formations plot in the island arc field and the Salittu formation plots in the E-MORB field. High LILE/HFSE ratios, typical of subduction-related volcanic rocks, characterize the Orijärvi and Kisko formations, whereas such a subduction component is less prominent in the Toija formation and is missing in the Salittu formation. Geochemistry and age relationships suggest that the Orijärvi formation was formed during the initial stages of volcanic arc evolution in an extensional tectonic regime, and the Kisko formation represents a mature stage of arc evolution. Subsequent extension of the island arc is manifested by the ultramafic/ mafic Salittu formation with E-MORB-like chemistry, interpreted to indicate a back-arc basin. The Toija formation might represent an initial stage of back-arc rifting.</p

Late Svecofennian shear zones in southwestern Finland

The bedrock of southwestern Finland is transected by a shear zone network with two dominant directions: ∼E-W and ∼N-S. The shear activity occurred after peak metamorphism and crustal melting at 1840-1810 Ma. The shear zones began to form as a consequence of north vergent oblique continent-continent collision and accommodated the resulting dextral transpression. The 150-200 km long ∼E-W oriented Somero and South Finland Shear Zones acted as dextral strike-slip faults, while the crustal unit between them was transported westward and deformed along the ∼N-S oriented reverse faults. The main deformation within these contractional shear zones took place at 1.81-1.79 Ga. After that, extensional faulting took place, tentatively at 1.79-1.77 Ga, 1.64-1.55 Ga and 1.26 Ga.</p