4-dimensional geological modelling of the Skellefte district, Sweden
The Skellefte mining District is located in northern Sweden and comprises Palaeoproterozoic, metamorphosed, supracrustal rocks and associated intrusive rocks, which are all host to several ore deposits. Modelling was performed in the GoCAD software platform, using structural geology and petrology as well as magnetic, gravity, seismic, electric and electromagnetic geophysical data, in order to produce robust 3-dimensional models for the upper 3000 m of the Earth's crust in selected areas within the Skellefte District. Further interpretations from the regional structures and tectonics are providing a base for restoring the geological history of the district in time, the 4 dimension. * Corresponding author
Relationship between 1.90–1.85 Ga accretionary processes and 1.82–1.80 Ga oblique subduction at the Karelian craton margin, Fennoscandian Shield
Abstract The three main intrusive suites: early calc-alkaline, late I/A-type, and late S-type intrusive rocks in relation to the Svecokarelian orogeny (1.9–1.8 Ga) have been dated at the Archaean craton margin in the Palaeoproterozoic Skellefte district and surrounding areas in northern Sweden. In addition, new SIMS data have been obtained on a calc-alkaline intrusion for which unusually young TIMS ages existed, compared to similar calc-alkaline intrusions elsewhere in the region. Titanite and zircon from a subvolcanic intrusion affected by a major N-S trending shear zone have also been dated to constrain the last ductile deformation in the area. The 1895+14 −12 Ma zircon age for a calc-alkaline intrusion is interpreted as the crystallisation age and is significantly older than the existing 1825 Ma age on titanite from a pyroxene skarn in a marble horizon close to the contact. The latter age is instead interpreted as the age of peak metamorphism in this area. The 1798plusmn;4 Ma age for the S-type granite confirms that the S-type magmatism is largely coeval with the I/A type magmatism previously dated at 1803plusmn;6 Ma. At a larger scale, a zoned belt over 2000 km long with A/I-type magmatism in the west and S-type magmatism in the east can be inferred. Either mafic underplating or Cordilleran type settings can explain the magmatic belt, which trends oblique to the roughly NE-directed subduction that led to the accretion of volcanic arcs onto the older craton between 1.95 and 1.87 Ga. An intimate temporal relationship between the extensive 1.80 Ga magmatism and regional N-S-trending shear zones in the area is confirmed by the titanite age of c. 1.80 Ga from one such shear zone. Kinematics on this shear zone suggest E-W shortening. SIMS data from a calc-alkaline intrusion at Sikträsk indicate that the previously obtained conventional zircon ages of 1.85–1.86 Ga are actually mixed ages of 1.88 Ga magmatic zircons, and c. 1.80 to 1.82 Ga metamorphic overgrowths. This shows that the 1.80 Ga event was not only constrained to shear zones. It is argued that both the 1.80 to 1.82 Ga deformation and metamorphism discussed here is related to E-W shortening and the voluminous magmatism at 1.82–1.80 Ga. This is in contrast to the older c. 1.88 Ga deformation identified to the north and east within the Karelian craton that was related to Svecokarelian accretionary processes.
Turbulent boundary layer wall‐pressure fluctuations downstream from an abrupt change in surface roughness
Spectra of wall‐pressure fluctuations beneath a turbulent boundary layer have been investigated immediately downstream from an abrupt change in surface roughness, from slightly rough to very rough. Over the measurable frequency band (400 Hz to 7 kHz), the spectra in the first 150 mm scale on wall variables. This indicates that the motions responsible for the pressure fluctuations measured in this region are very close to the wall. Farther downstream this scaling procedure breaks down. It is suggested that the initially thin internal layer behaves independently of the flow external to it until it has grown appreciably and only then interacts with the outer boundary layer. It was found that, for all frequencies measured, the dimensional spectral level decreases initially then rises to a maximum at 250 mm from the roughness change before decreasing once more. The position of the maximum is close to where the internal layer ceases to have a distinct edge.