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

Neptunium(V) transport in granitic rock : A laboratory scale study on the influence of bentonite colloids

In the present study neptunium(V) uptake by crystalline granitic rock (Kuru Grey granite) and the role of stable and mobile bentonite colloids (MX-80) on the migration of neptunium(V) was investigated. Two different experimental setups were utilized, batch-type experiments under stagnant conditions and column experiments under flowing water conditions. The uptake of 10(-6) M neptunium(V) by 40 g/L crushed granite in 10 mM NaClO4 was found to be pH-dependent, whereas neptunium(V) uptake by MX-80 bentonite colloids (0.08-0.8 g/L) was pH-independent up to a pH-value of approximately 11. Column experiments were conducted in the presence and absence of colloids at two pH values (pH = 8 and 10) and two flow rates (0.3 and 0.8 mL/h) in 10 mM NaClO4. The injected neptunium(V) concentration was 2x10(-4) M and the colloid concentration ranged from 0.08 to 0.32 g/L. The properties of the flow field in the columns were investigated with a conservative chloride tracer, at the same two flow rates of 0.8 and 0.3 mL/h. The resulting breakthrough curves were modeled using the analytical solution of advection-matrix diffusion equation. A tailing of neptunium(V) breakthrough curves in comparison to the conservative tracer was observed, which could be explained by a slightly higher retardation of neptunium(V) in the column caused by sorption on the granite. The sorption was in general lower at pH 8 than at pH 10. In addition, the tailing was almost identical in the absence and presence of MX-80 bentonite colloids, implying that the influence of colloids on the neptunium(V) mobility is almost negligible.Peer reviewe

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

Paleoproterozoic metamorphism and deformation in Central Lapland, Finland

Three main ductile deformations, D1-D3, and contemporaneous and later shear zones account for most structures in Central Lapland. The oldest tectono-metamorphic feature is the bedding-parallel, mostly microscopic S1, overprinted by the main foliation S2, which is the most prominent structural feature seen in almost all rock types throughout the study area. Subhorizontal S2 is an axial plane foliation to tight or isoclinal, inclined to recumbent F2 folds. Kinematic indicators in the central and southern parts of the study area indicate a northward transport direction, but close to the S and SW border the Lapland Granulite Belt it may be of opposite direction. F3 folds deform the D2 structures. F3 folding show an extreme variety regarding the fold vergence with N-vergent folds in south, SW-W-vergent folds in north and E-vergent folds in west close to the Kolari shear system. Apparently, the F3 folding seems to be associated with complex tectonic movement directions, from S to N direction in the south, from NE to SW in the north and northeast part, and from W to E in the western part of the study area. Several metamorphic zones have been mapped in the area. These are I) granulite facies migmatitic amphibolites south of the granulite complex (including the so called Tanaelv belt next to the granulites); II) high pressure mid-amphibolite facies rocks south of Zone I, characterised by garnet-kyanite-biotite-muscovite assemblages with local migmatisation in metapelites, garnet-hornblende-plagioclase assemblages in mafic rocks, local cordierite-orthoamphibole rocks intercalated with mafic volcanics; III) low-pressure mid-amphibolite facies rocks south of Zone II, garnet-andalusite-staurolite- chlorite-muscovite assemblages with retrograde chloritoid and kyanite in metapelites, hornblende-plagioclase-quartz±garnet in metabasites; IV) greenschist facies rocks of the Central Lapland Greenstone Belt, fine-grained white mica-chlorite-biotite-albite-quartz in metapelites, actinolite-albite-chlorite-epidote-carbonate in metabasites; V) prograde metamorphism south of Zone IV from lower amphibolite facies (andalusite-kyanite- staurolite-muscovite-chlorite±chloritoid schists, V.1-2) to mid-amphibolite facies (kyanite-andalusite-staurolite-biotite-muscovite gneisses, V.3) and upper amphibolite facies garnet-sillimanite-biotite gneisses (V.5); VI) amphibolite facies pluton-derived metamorphism related with heat flow from central and western Lapland granitoids, where Zone VI.2 represents both andalusite and sillimanite-present, and Zone VI.3 only sillimanite-present, andalusite absent gneisses. Pelitic rocks exhibit decompressional PT paths where andalusite grade metamorphism was preceded by higher pressure. Metamorphism was partly related with tectonic thickening during overthrusting of the Lapland Granulite Belt to the south, but the present metamorphic structure may record later, postmetamorphic faulting and folding events.</p

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 (ε=+2.2) and the trondhjemite sample an age of 1867±4Ma (ε=+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.</p

LITHOSPHERE 2021: ELEVENTH SYMPOSIUM ON STRUCTURE, COMPOSITION AND EVOLUTION OF THE LITHOSPHERE: PROGRAMME AND EXTENDED ABSTRACTS

The Central Svecofennian Arc Complex (CSAC) and the Southern Svecofennian Arc Complex (SSAC) showdifferent ages of peak metamorphism: ~1.88 Ga in the CSAC and ~1.83 Ga in the SSAC. In the present project we study the age of the metamorphism in SW Finland. We have collected two samples. Of these the Eurajoki leucosome zircons were > 1.92 Ga, i.e.,inherited, but monazites show two populations: ~1.83 Ga and ~1.7 Ga. The zircons from the Rauma leucosome yielded two populations: ~1.86 Ga and ~1.83 Ga. The monazites show ages of ~1.83 Ga and ~1.7 Ga. We interpret that the ~1.86 Ga zircons represent the older metamorphism and the 1.83 Ga zircon and monazite group to represent the younger metamorphism. The 1.7 Ga group is unusual and needs further investigation.</p

Efficiency of siRNA delivery by lipid nanoparticles is limited by endocytic recycling

Despite substantial efforts to understand the interactions between nanoparticles and cells, the cellular processes that determine the efficiency of intracellular drug delivery remain largely unclear. Here we examined cellular uptake of siRNA delivered in lipid nanoparticles (LNPs) using cellular trafficking probes in combination with automated high-throughput confocal microscopy as well as defined perturbations of cellular pathways paired with systems biology approaches to uncover protein-protein and protein-small molecule interactions. We show that multiple cell signaling effectors are required for initial cellular entry of LNPs through macropinocytosis, including proton pumps, mTOR, and cathepsins. SiRNA delivery is substantially reduced as ≅70% of the internalized siRNA undergoes exocytosis through egress of LNPs from late endosomes/lysosomes. Niemann Pick type C1 (NPC1) is shown to be an important regulator of the major recycling pathways of LNP-delivered siRNAs. NPC1-deficient cells show enhanced cellular retention of LNPs inside late endosomes/lysosomes and increased gene silencing of the target gene. Our data suggests that siRNA delivery efficiency might be improved by designing delivery vehicles that can escape the recycling pathways