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Therefore, pre-existing landforms and deposits in northern Finland escaped glacial erosion and are now particularly well preserved. Ribbed moraines found in the same area reflect a later west to east change in movement of the ice. During the last deglaciation , the first part of Finland to become ice-free was the southeastern coast; this occurred shortly before the Younger Dryas cold-spell 12, years before present BP.

While the ice cover continued to retreat in the southeast after Younger Dryas, retreat also occurred in the east and northeast. The retreat was fastest from the southeast resulting in the lower course of the Tornio river in northwest Finland becoming the last part of the country to be ice-free. Finally, by 10, years BP, the ice cover had all but left Finland, retreating to Sweden and Norway before fading away. As the ice sheet became thinner and retreated, the land began to rise due to post-glacial rebound. Much of Finland was under water when the ice retreated and was gradually uplifted in a process that continues today.

Mining for metals in Finland began in at the Ojamo iron mine [48] [D] but mining in the country was minimal until the s. When Outokumpu opened in it was Finland's first sulphide ore to be mined. This mine closed in Petsamo and its mines were, however, lost to the Soviet Union in as result of the Moscow Armistice. From to the number of metallic ores being mined dropped from eleven to the following four: [49].

There are some uranium resources in Finland, but to date no commercially viable deposits have been identified for exclusive mining of uranium. Most of Finland's metallic ores formed in the Paleoproterozoic during the Svecofennian orogeny or during the period of complex extensional tectonics that preceded it. Finland has a thriving quarrying industry.

Finnish dimension stone has been used historically for buildings in Helsinki and imperial Russia's Saint Petersburg and Reval. The dimension stone quarried in Finland includes granites, such as the wiborgite variety of rapakivi granite, and marble. Soapstone from Finland's schist zone is also quarried for use in ovens. From Wikipedia, the free encyclopedia. Further information: Kola Province.

See also: Vaasa granite and Jormua Ophiolite.

Precambrian Geology of Finland, Volume 14 - 1st Edition

Further information: Scandinavian Caledonides. Further information: Weichsel glaciation and post-glacial rebound. See also: Nickel deposits of Finland. These findings were first reported by Astrid Cleve in , leading to the assumption that the areas was drowned by the sea during the Eocene. However, as of , no sedimentary deposit from this time has been found and the marine fossils may have arrived much later by wind transport.

Nationalencyklopedin in Swedish. Cydonia Development. Retrieved November 30, Uppslagsverket Finland in Swedish. Precambrian Research. Earth Surface Processes and Landforms. Spain: Studentlitteratur. In Cawood, P. Earth Accretionary Systems in Space and Time. Geological Society, London, Special Publications. Earth-Science Reviews. Bibcode : ESRv Geological Survey of Finland Bulletin. Geological Survey of Finland, Special Paper. Retrieved 27 July Working Report. Russian Journal of Earth Sciences. Proceedings of the 7th International Kimberlite Conference.

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Geological Survey of Denmark and Greenland Bulletin. Retrieved 30 April Quaternary International. Palaeogeography, Palaeoclimatology, Palaeoecology. The intrusions c. The reprocessed seismic data provide evidence of up-doming of the lower crust representing the melt reservoir below the intrusions that, in turn, are observed at different depths in addition to a steep seismically transparent zone interpreted to be a discordant feeder dyke system. Relative age constraints and correlation with onshore saucer-shaped intrusions of different size suggest that they are internally connected and fed by each other from deeper to shallower levels.

We argue for a nested emplacement mechanism and against a controlling role by the overlying sedimentary basin as the saucer-shaped intrusions are emplaced in both the sedimentary rocks as well as in the underlying crystalline basement. The interplay between magma pressure and overburden pressure, as well as the, at the time, ambient stress regime, are responsible for their extensive extent and rather constant thicknesses c.

Saucer-shaped intrusions may therefore be present elsewhere in the crystalline basement to the same extent as observed in this study some of which are a significant source of raw materials. The main objective of the survey was to improve the understanding of the processes forming the continental crust and the juxtaposition of tectonic domains of different lithologies and metamorphic grades 1. A major focus was therefore on imaging the Moho and its geometry and crustal thicknesses across various tectonic domains to gain information that could indicate collision or accretion of different crustal units or micro-continents during the Paleoproterozoic-Archean eras.

This also hindered connecting the upper crust with deeper structures and past geological processes that may have affected the whole crust. The BABEL project was a significant collaborative geoscientific project in Europe seeking evidence that indicated that plate tectonic processes were active already in the Paleoproterozoic 2.

Additionally, intriguing features such as km scale dolerite intrusions in the upper crust 3 were observed and tentatively interpreted. The BABEL data are an extraordinary resource and have tremendous potential for improvements and for revising our understanding of past tectonic processes. Reprocessing of legacy seismic data has shown that it is possible to improve previous results sometimes significantly by using modern software and computing power 9 , Moreover, improving images of deeper structures should also be possible when comparing the currently used processing technology to that of the late 20 th century.

These lines were chosen due to the great interest in obtaining a better understanding of the tectonic evolution of central Fennoscandia.

key to the evolution of the Fennoscandian shield

These lines total altogether i. The signals from the reprocessed BABEL lines 1, 6, 7, B and C acquired in the Bothnian Sea penetrate Paleoproterozoic rocks, two major faults and subsidence-controlled depressions filled with Mesoproterozoic and younger sedimentary rocks. By convention the Mesoproterozoic sedimentary rocks in the Fennoscandian Shield are referred to as Jotnian sandstones Fig.

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Preservation of these sedimentary rocks is to a large part spatially related to the 1. The rapakivi magmatism is related to diapiric mantle upwelling, mafic underplating, significant crustal thinning and emplacement of the large batholiths that are present north of the Gulf of Finland on the Finnish and Russian mainland, southwestern Finland, in the Baltic and Bothnian Seas, along the coast and further inland in central Sweden Partial melting of the upper mantle is evident from mafic dykes, gabbro, and anorthosite, as well as from hybrid rocks formed by mixing of crustal and mantle derived melts.

Until the onset of the rapakivi magmatism, the Paleoproterozoic crust was uplifted and eroded close to the present-day levels 15 and the Mesoproterozoic sediments were deposited unconformably on this peneplain in alluvial, fluvial or aeolian environments. In places, these units are overlain by Neoproterozoic, possibly Ediacaran, to Lower Palaeozoic sedimentary rocks Fig.

At Lake Ladoga, sills were emplaced at 1. They intruded both the Paleoproterozoic crust, as well as the Mesoproterozoic sedimentary rocks, providing an upper age limit for deposition of the latter. Individual intrusions range in thickness from less than ten metres to about one kilometre and in the three central clusters they are mainly present as horizontal to gently dipping saucer-shaped or oval-shaped intrusions, whereas dykes dominate the clusters to the north and south Isotope signatures Hf and Nd indicate an asthenosphere source for the magma that interacted with the subcontinental lithospheric mantle upon ascent.

It has been inferred that the long-lived magmatism is related to either a mantle plume hot spot or discrete extensional events behind an active continental margin Along BABEL line 1, the CSDG intrusions generate strong, concave reflections and their presence below the Bothnian Sea is further indicated by the correlation with their occurrences at the Swedish and Finnish coasts in addition to direct observations on the sea floor Until this study, the processes producing the emplacement of these intrusions, linking shallow and deeper structures observed in the seismic data, have been left unexplained.

The improved seismic reprocessing results presented here are key in helping elucidate the intrusion process. In the reprocessed data the Moho boundary interpreted as the transition to a seismically transparent upper mantle is more distinct and new shallow features in the upper crust are observed. On the seafloor directly above this zone of transparent reflectivity there is a fault scarp Fig.

The scarp coincides with a sub-vertical dolerite intrusion, which is mapped by divers 22 and exposed on the sea floor. A footprint of the fault dyke filled is also visible in the bathymetry data as well as shipborne magnetic data 22 acquired during the same time as the seismic data were acquired. Smaller faults can also be observed in this region based on discontinuities in the sea-floor reflection.

The three sets of reflections S1—S3 project to, or near, the surface at the margins of the Meso- to Neoproterozoic sedimentary basin and form a concentric feature hence referred to as saucer-shaped , clearly observed in the sea-floor morphology Fig. We argue that these reflections are primary and not multiple of one another because at their edges they appear to be similarly or even less dipping and this cannot be the case for seismic multiples.

In addition, any multiple of these should occur at much later times. Reverberation is however possible but this did not show itself strong in our autocorrelation analysis of the stacked section. On the southern half of line 1, between CDP and , a basin Palaeozoic is observed B1 that was previously masked in the original processing. The existence of the basin is known from the work of Winterhalter 22 and Axberg 16 on shallow marine seismic data. At depth, a highly reflective lower crustal up-doming is well imaged L1 under which a clear sub-Moho reflection SM1 dipping to the south is observed.

Similarly, a sub-Moho reflection is also observed in the parallel line 6 SM2 , although deeper c. The lower crust is also reflective along line 6 and up-domed on its northernmost part L2 , as observed along line 1. Along line 7, two mainly opposite dipping reflectivity patterns are observed. On the westernmost part of the line, the dipping reflectivity e. Where lines 1 and 6 intersect line 7 Fig.

The eastern part of line 7 shows a higher crustal reflectivity even distinct ones such as R2 than the western and central parts of the line. A set of upper crustal southeast-dipping reflections is also observed on the southern part of the line R3 , where they appear to be truncated between CDP — Supplementary Fig. The saucer-shaped intrusions observed along line 1 S1, S2, S3 in Fig. The high reflectivity of the anomalies leads us to this interpretation as well, since we have a high-impedance contrasts between the intrusion and the surrounding rocks because of their density and velocity difference.

However, the process resulting in their emplacement both in the sedimentary rocks and in the crystalline basement over a lateral extension of kilometres has been a matter of debate. A general model of emplacement was proposed by Korja et al. The deepest intrusion has a diameter of c.

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The reprocessed seismic sections along with the geological observations of the intrusions on land suggest therefore a ladder-shaped emplacement scenario by a network of possibly interconnected saucer-shaped intrusions of different sizes. This interconnection model is based on connectivity between the smaller saucer-shaped intrusions on land and a weak set of reflections appearing to connect two deeper intrusions S2 and S3 reflections in the central part of the system. Roughly NE-SW intrusions are aligned along and displaced by this fault There is a bathymetric step on the sea floor, which is either the result of differential erosional or displacement during or after dyke emplacement.

Faulting was likely initiated during the rapakivi magmatism, as is the case for many other faults in the Bothnian and Baltic Seas. They have been repeatedly reactivated 15 , probably until the opening of the North Atlantic. The saucer-shaped intrusions are interpreted to result from the same process, i.

The 1. Partial melting of the middle and lower crust by heat generated from the mafic underplating produced felsic magma leaving behind a dense granulite restite Production or plumbing of the felsic melt was probably cyclic by inflation and deflation e.

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Emplacement of these magmas in the upper crust was associated with caldron subsidence that subsequently and successively was filled with Mesoproterozoic and younger sediments. The up-doming at the Moho Fig. This effect has also been observed in other regions in the world 30 , 31 , and interpreted as a layered intrusion in the lower crust in the form of individual sills that may have formed magma chambers for the volcanic activity at the surface The red dashed line in b should be seen as just a hint that there is a connection between the feeder dyke and up-doming, but without giving an exact interpretation of their locations.

Note that in 3D, only segment s of a feeding dyke is are connecting the intrusions of different levels and is are responsible for transport of melt to shallower levels. Sketch along the northern portion of line 1 is shown as an inset in d. Depth is exaggerated twice in a,b. While the Meso- to Neoproterozoic sedimentary rocks are only preserved locally, mainly in fault-controlled grabens, they probably covered large parts of the Fennoscandian Shield at the time of deposition 33 — Presently, the largest areas covered by these sedimentary rocks are in the Baltic and Bothnian Seas and Gulf of Bothnia where they are underlain to a large extent by rapakivi intrusions At least in the Baltic and Bothnian Seas these intrusions also coincide with the 1.

In agreement with Korja et al. The CSDG magma, with an asthenosphere source 21 , intruded through existing zones of weakness in the lithosphere, such as faults and shear zones that developed or were reactivated during extension related to the rapakivi magmatism. Through these zones enormous amount of melt migrated as dykes, and later as sills, at different levels in the upper crust. Thus, a network of several dyke zones originating from different parts of the underlying thermal anomaly is expected. The seismically transparent zone crosscutting reflections S1—S3 in the seismic section represents eventually such a network of dykes.

When the pressure of the overburden and magma was nearly equal, the feeder dykes e. For the larger intrusions, this occurred at the margin of the basins. Alternatively, the melt could have also used inter-basinal faults, so that they did not crosscut at the margin of the basin. These dykes were connected to and fed sills at shallower levels.

In the crystalline basement, at least three major sets of reflections representing sub-horizontal intrusions are visible in the BABEL profiles S1—S3 with their peripheral areas connected to the saucer-shaped intrusions exposed on land Fig. Dyke propagation and formation of saucer-shaped intrusions continued likely upwards through the crystalline basement to the sedimentary rocks. This upward propagation of emplacement levels was likely associated with different magmatic pulses as observed in the CSDG intrusions along the Swedish coast In this area, inflation of individual magma pulses produced gently and inward dipping dykes, which were occasionally replenished by multiple injections as shown by chilled margins.

The last magma pulse is represented by crosscutting vertical dykes We suggest that inward dipping oval-shaped intrusions along the west coast of the Bothnian Sea are related to the strong reflections observed along lines 1 and 6. These reflections show that the intrusions are located at different levels, have oval shapes of variable sizes and are connected with each other by feeder dykes Fig. The saucer-shaped intrusions at different levels are not vertically centred, suggesting that the upward propagating tip of the deeper intrusions acted as feeder dykes to relatively younger shallower dipping dykes and sills at successively higher levels.

As such, each group of saucer-shaped intrusions, including the sills, may have had separate feeder dykes that may have been tapped from the same magma chamber at the base of the lower crust that was continuously being recharged. Movements along this fault and continuous subsidence of the basin preserved these rocks offshore seen along northern portions of lines 1 and 6 , explaining why the saucer-shaped intrusions on land are mainly encountered in the crystalline basement.

The fact that the sill reflectors display a general gentle dip towards the zone of dykes and faults crosscutting transparent zone may be a further indication that the fault zone and those near the shoreline must have been active during and even after the emplacement of the sills. The saucer-shaped appearance of the intrusions is less likely to be due to post-emplacement tectonics, i.

While we could argue that the spatial relationship between the saucer-shaped intrusions and sedimentary basin s might support a generic relationship between the two, as has been suggested elsewhere 39 , 40 , several reasons led us to reject this scenario. First, the intrusions are not only confined to the sedimentary basins, on the contrary they are mainly emplaced in the crystalline basement. These inward dipping intrusions show undulated contacts as opposed to those found in the sedimentary rocks. Second, there are smaller saucer-shaped intrusions onshore that do not follow the outline of the subsided basin along seismic line 1.

Third, the 1.

Precambrian geology of Finland

Sedimentary rocks may have covered the latter at the time of the CSDG emplacement. These points suggest a multiple batch, nested, emplacement mechanism unrelated to basin formation with the intrusions connected to one another as a multi-set of 20—km wide saucer-shaped bodies at different levels in the upper crust. It is worth mentioning that the sedimentary basin could have contributed to the asthenosphere upwelling isostatically, however, the melt generated from this upwelling took the route that was mechanically easier to propagate upwards through and form the nested intrusions.

Different mechanisms have been proposed for emplacement of saucer-shaped intrusions. Whereas, Galland et al. This model is consistent with the data presented in this study, where the deeper intrusions have far larger lateral extent than the ones at shallower levels.

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The saucer-shaped intrusions are likely to have formed in sequence, from deeper to shallower levels, i. On land, the intrusions are often layered and occasionally cross-cut by steeply dipping dykes with chilled margins formed by late-stage magmas that were moving to shallower levels by transecting earlier intrusions 25 , It has been suggested that stacked saucer-shaped intrusions may form by magma that moves from deeper intrusions that become steeper as they propagate and act as feeder dykes for the shallower bodies This scenario is often depicted in a 2-dimensional schematic illustration Fig.

However, one of the characteristics of these saucer-shaped intrusions is their oval geometry in plan view.

Any feeder system generated from a deeper oval intrusion that as a whole propagates upward will less likely have an oval geometry. Such an oval dyke will break down into smaller segments as it propagates upward due to prevailing differential pressure Fig. A smaller more curved sheet-like feeding dyke leads to the formation of a more circular-shaped intrusion, or elliptical intrusion As it propagates, the active dyke-segment may become less-curved in the plan view Fig. A feeder dyke segment reaches shallower levels through melt pressure, which drops as it forms and feeds saucer-shaped intrusions.

The space it has created will be used again as a conduit for further melt injection. Therefore, pressure drops in the opposing segment of the dyke connected to the deeper intrusion results in the plumbing system becoming inactive. Saucer-shaped intrusions do not need to be continuous Fig. The intrusions found onshore west of the Bothnian Sea intersect each other, indicating an interlinking feeding system between them. They are interpreted to be smaller and emplaced at shallower levels compared to the larger intrusions depicted on the seismic profiles.

Some of these intrusions like those in South Africa are significant resources of critical raw materials such as Fe, Co, Cr and Ni. For example, the saucer-shaped intrusions of this study onshore were partly mined for their iron content in the past. For the seismic data acquisition year — , the S. Mintrop vessel from Prakla-Seismos was used. The ship towed an array of 42 airguns with a total volume of To improve spatial resolution, different shot spacings were used for different lines.

According to the available published reports 23 , excellent quality seismic data were acquired with minimum water-wave noise and noise from other ships passing by during the survey. Much of the reported issues were associated with the used equipment. For example, defective depth controller, power failures or autopop of the airgun Main acquisition parameters of the BABEL offshore reflection seismic survey — for the lines reprocessed in this study Data were recovered in standard SEGY Society of Exploration Geophysicists seismic data processing format thanks to a number of individuals who transferred them from tapes to digital disks and to standard seismic processing format.

However, not much information was available in the headers in terms of geometry and acquisition set-ups. A significant amount of time was spent to gather this information in order to use them for reprocessing of the data. For example, some of the files we had in the beginning were corrupted. The first few hundred shots seemed to be fine, but at some point, the traces had no amplitude and the header information was missing.

After we figured out that we were not able to recover this lost information, we could luckily find the complete files, redundant files saved, in between all the 87 BABEL files without clear structuring.