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- Green, Paul F., et al.
(författare)
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The post-Caledonian thermo-tectonic evolution of Fennoscandia
- 2022
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Ingår i: Gondwana Research. - : Elsevier. - 1342-937X .- 1878-0571. ; 107, s. 201-234
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of Fennoscandia following the early Devonian collapse of the Caledonian mountains is a matter of debate, due largely to the scarcity of post-Caledonian cover rocks. The preserved geological record therefore provides only partial documentation of the geological evolution. A more complete understanding is obtained by also considering evidence of rocks that were formerly present but have since been removed. We report apatite fission track data and associated thermal history constraints in 331 samples of Precambrian basement, younger sedimentary cover, Paleozoic and Mesozoic igneous rocks from outcrops and boreholes (up to 6 km depth) across Fennoscandia, which define thirteen phases of cooling (each representing kilometre-scale exhumation) over the last 1100 Myr. Key post-Caledonian episodes began in the intervals 311–307 Ma (late Carboniferous), 245–244 Ma (Middle Triassic), 170–167 Ma (Middle Jurassic), 102–92 Ma (mid-Cretaceous) and 23–21 Ma (early Miocene). These episodes, varying in magnitude, are recognised across Fennoscandia, and their effects are documented in the stratigraphic record and as prominent regional peneplains. The results define a history involving repeated episodes of regional burial and exhumation. Major offsets in Mesozoic paleotemperatures over short distances define kilometre-scale differential vertical displacements, emphasising the tectonic nature of the history. Results from Finland record the same events recognised in Norway and Sweden (though less pronounced), and are not consistent with long-term cratonic stability. The lack of preserved Phanerozoic sedimentary cover in Finland is interpreted to be due to complete removal during multiple episodes of denudation. In southern Norway and Sweden, early Miocene exhumation led to creation of a peneplain, which in Pliocene times was uplifted and dissected, producing the modern landscape. Post-Caledonian exhumation episodes defined here are broadly synchronous with similar events in Greenland, the British Isles and North America. Far-field transmission of plate-tectonic stress and/or mantle processes may explain the vertical movements described here.
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| 4. |
- Kukkonen, Ilmo T., et al.
(författare)
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Postglacial Faults in Fennoscandia: Targets for scientific drilling
- 2010
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Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 132:1, s. 71-81
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Tidskriftsartikel (refereegranskat)abstract
- During the last stages of the Weichselian glaciation (ca. 9,000-15,000 years B.P.), reduced ice loads and glacially affected stress fields resulted in active faulting in Fennoscandia with fault scarps up to 160 km long and up to 30m high. These postglacial (PG) faults are usually SE dipping, SW-NE oriented thrusts, and represent reactivated, pre-existing crustal discontinuities. Postglacial faulting indicates that the glacio-isostatic compensation is not only a gradual viscoelastic phenomenon, but also includes unexpected violent earthquakes, suggestively larger than other known earthquakes in stable continental regions. We explore here possibilities and benefits for investigating, via scientific drilling, the characteristics of postglacial faults in northern Fennoscandia, including their structure and rock properties, present and past seismic activity and state of stress, as well as hydrogeology and associated deep biosphere. The research is anticipated to advance science in neotectonics, hydrogeology and deep biosphere studies, and provide important information for nuclear waste disposal, petroleum exploration on the Norwegian continental shelf and studies of mineral resources in PG fault areas.
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- Sharma, Prabhakar, et al.
(författare)
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Analysis of 6‑year fluid electric conductivity logs to evaluate the hydraulic structure of the deep drill hole at Outokumpu, Finland
- 2016
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Ingår i: International journal of earth sciences. - : Springer Science and Business Media LLC. - 1437-3254 .- 1437-3262. ; 105:5, s. 1549-1562
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Tidskriftsartikel (refereegranskat)abstract
- Over the last two decades, the flowing fluid electric conductivity (FFEC) logging method has been applied in boreholes in the well-testing mode to evaluate the transmissivity, hydraulic head, and formation water electrical conductivity as a function of depth with a resolution of about 10–20 cm. FFEC profiles along the borehole are obtained under both shut-in and pumping conditions in a logging procedure that lasts only 3 or 4 days. A method for analyzing these FFEC logs has been developed and successfully employed to obtain formation parameters in a number of field studies. The present paper concerns the analysis of a unique set of FFEC logs that were taken from a deep borehole reaching down to 2.5 km at Outokumpu, Finland, over a 6-year time period. The borehole intersects paleoproterozoic metasedimentary, granitoid, and ophiolite- derived rocks. After the well was drilled, completed, and cleaned up, FFEC logs were obtained after 7, 433, 597, 948, and 2036 days. In analyzing these five profiles, we discovered the need to account for salinity diffusion from water in the formation to the borehole. Analysis results include the identification of 15 hydraulically conducting zones along the borehole, the calculation of flow rates associated with these 15 zones, as well as the estimation of the variation of formation water electrical conductivity as a function of depth. The calculated flow rates were used to obtain the tentative hydraulic conductivity values at these 15 depth levels.
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