Tests of inter-hotspot motion and of hotspot motion relative to the spin axis

First, an updated Pacific paleomagnetic skewness pole for chron 32 (72 Ma) is presented. The updated paleomagnetic pole corrects for the spreading-rate dependence of anomalous skewness, a correction which hasn't been applied to Pacific skewness poles before. The presence of anomalous skewness is one of the main factors limiting the accuracy of paleomagnetic poles determined from the skewness data. Thus, successfully correcting for the anomalous skewness, as was done in this study, significantly improves the reliability of the skewness poles. The earlier assertions that the Hawaiian hotspot has shifted southward relative to the spin axis by 13° since ≈72 Ma are also confirmed. Second, updated reconstructions of the Pacific plate relative to the hotspots for the past 68 million years are presented, with the uncertainties in the reconstructions. Plate-circuit reconstructions are used to predict the tracks of some major Indo-Atlantic hotspots (Tristan da Cunha, Reunion and Iceland) from the Pacific-hotspot plate motion and the rates of relative motion between the Pacific and Indo-Atlantic hotspots are estimated. Within the uncertainties, motion between the hotspots is found insignificant for the past 48 million years. For earlier times, a systematic error in the plate circuit used to make the predictions is inferred and which may be due to unmodeled motion between East and West Antarctica. If the observed discrepancy can be shown to correspond to an error in the plate circuit, the southward motion of the Hawaiian hotspot of 13° since ≈72 Ma can likely be attributed to true polar wander. Building on the above-mentioned work, finally, for the first time, a globally self-consistent model of plate motions relative to the global hotspots for the past 48 million years is presented, and the implications of this model to the question of relative hotspot motion discussed. The provided globally self-consistent set of reconstructions can be used as a fixed frame of reference for absolute plate motions, and true polar wander, for the past 48 million years

Common Mid Point (CMP) surveying for depth calibration of ground penetrating radar data

Non peer reviewe

Metal concentrations of sediments in Vanhankaupunginlahti dam basin, river Vantaa

Non peer reviewe

COGITO-MIN seismic reflection profiling for mineral exploration in Polvijärvi, Finland

Non peer reviewe

3C Seismic Interferometry at the Polymetallic Kylylahti Deposit, Outokumpu District, Finland

Non peer reviewe

Petrophysical properties of the Kylylahti Cu-Au-Zn sulphide mineralization and its host rocks

Non peer reviewe

Seismic properties of rocks in Kylylahti Cu-Au-Zn mine

Non peer reviewe

New geophysics study programs at the University of Helsinki

Peer reviewe

Cost-effective seismic exploration: 2D reflection imaging at the Kylylahti massive sulfide deposit, Finland

We show that by using an advanced pre-stack depth imaging algorithm it is possible to retrieve meaningful and robust seismic images with sparse shot points, using only 3-4 source points per kilometer along a seismic profile. Our results encourage the use of 2D seismic reflection profiling as a reconnaissance tool for mineral exploration in areas with limited access for active seismic surveys. We used the seismic data acquired within the COGITO-MIN project comprising two approximately 6 km long seismic reflection profiles at the polymetallic Kylylahti massive sulfide mine site in eastern Finland. The 2D seismic data acquisition utilized both Vibroseis and dynamite sources with 20 m spacing and wireless receivers spaced every 10 m. For both source types, the recorded data show clear first breaks over all offsets and reflectors in the raw shot gathers. The Kylylahti area is characterized by folded and faulted, steeply dipping geological contacts and structures. We discuss post-stack and pre-stack data processing and compare time and depth imaging techniques in this geologically complex Precambrian hardrock area. The seismic reflection profiles show prominent reflectors at 4.5-8 km depth utilizing different migration routines. In the shallow subsurface, steep reflectors are imaged, and within and underneath the known Kylylahti ultramafic body reflectivity is prominent but discontinuous.Peer reviewe

New digital learning materials for teaching in geosciences

Non peer reviewe