Early Proterozoic nappe formation: an example from Sodankylä, Finland, Northern Baltic Shield

2002 ◽  
Vol 139 (1) ◽  
pp. 73-87 ◽  
Author(s):  
P. M. EVINS ◽  
K. LAAJOKI
Keyword(s):  
Baltic Shield ◽  
Greenstone Belt ◽  
Metasedimentary Rocks ◽  
The North ◽  
Granulite Belt ◽  
Lapland Granulite Belt ◽  
Map Scale ◽  
The Baltic ◽  
Silicate Rocks ◽  
Central Lapland Greenstone Belt

The Central Lapland Greenstone belt comprises rift-related metavolcanic and metasedimentary rocks representing one of the largest supracrustal belts in the Baltic Shield. The Sodankylä area in the central part of the belt represents a complex thrust duplex within a nappe overlying Belomorian Archaean basement and autocthonous Luirojoki calc-silicate rocks. Here, an early D1 schistosity is axial planar to at least three coaxial generations of southward-verging, subhorizontal, E–W-plunging D1 folds associated with major southwards thrusting. D2 is represented by broad, map-scale, upright, NE-trending folds in the south and crenulations in the north. Staurolite-grade metamorphism represented by post-tectonic andalusite + staurolite + kyanite assemblages occurred after D2 folding. Later D3 deformation was limited to local NW-trending folds and sinistral faults. The internal nappe-like structure of the Central Lapland Greenstone belt suggests that it represents the foreland of a large collisional complex cored by the Lapland Granulite belt.

K-Ar dating of the Lower Palaeozoic K-bentonites from the Baltic Basin and the Baltic Shield: implications for the role of temperature and time in the illitization of smectite

Clay Minerals ◽  
2009 ◽  
Vol 44 (3) ◽  
pp. 361-387 ◽  
Author(s):  
J. Środoń ◽  
N. Clauer ◽  
W. Huff ◽  
T. Dudek ◽  
M. Banaś
Keyword(s):  
Baltic Shield ◽  
Vitrinite Reflectance ◽  
Sedimentary Cover ◽  
Source Rocks ◽  
X Ray Diffraction ◽  
Baltic Basin ◽  
The North ◽  
Lower Palaeozoic ◽  
Fission Track Ages ◽  
The Baltic

AbstractMixed-layer illite-smectite samples from the Ordovician and Silurian K-bentonites of the Baltic Basin and the Baltic Shield (Norway, Sweden, Denmark, Poland and Estonia) were dated by K-Ar on several grain fractions and were studied by X-ray diffraction (XRD), both on oriented and random preparations, in order to reveal the conditions of smectite illitization in the area. Authigenic K-feldspar was also dated. The geographic pattern of the degree of illitization (% smectite in illite-smectite measured by XRD) is consistent with other indicators of palaeotemperatures (acritarchs, conodont alteration index, vitrinite reflectance, apatite fission track ages). It reveals the highest maximum palaeotemperatures (up to at least 200ºC) along the Norwegian and the German-Polish branches of the Caledonides and the lowest palaeotemperatures (120ºC) in the central part of the studied area. The distribution of K-Ar ages is not well correlated with this pattern, revealing a zone of older ages (Lower Devonian-Lower Carboniferous) between Denmark and Estonia, and areas of younger ages (Upper Devonian to Carboniferous/Permian boundary) to the north and south of this zone. The zone of older ages is interpreted as the result of illitization induced by a thermal event in front of the Caledonian orogenic belt (migration of hot metamorphic fluids?). The areas of younger ages are considered as representing deep burial illitization under a thick Silurian-Carboniferous sedimentary cover, perhaps augmented by a tectonic load. The K-Ar dates invalidate the hypothesis of a long-lasting low-temperature illitization as the mechanism of formation of the Estonian Palaeozoic illite-smectite. The ammonium content of illite-smectite from the Baltic K-bentonites reflects the proximity of organic-rich source rocks that underwent thermal alteration at the time of illite crystallization.

Conditions and timing of metamorphism in the southern Abitibi greenstone belt, Quebec

1995 ◽  
Vol 32 (6) ◽  
pp. 787-805 ◽  
Author(s):  
W. G. Powell ◽  
D. M. Carmichael ◽  
C. J. Hodgson
Keyword(s):  
Greenstone Belt ◽  
Regional Metamorphism ◽  
Geothermal Gradient ◽  
Fault Zones ◽  
Low Grade ◽  
Metasedimentary Rocks ◽  
Abitibi Greenstone Belt ◽  
The North ◽  
Major Fault ◽  
Facies Transition

Regional metamorphism, ranging in grade from the subgreenschist-facies to the greenschist–amphibolite-facies transition, affects all Archean supracrustal rocks (>2677 Ma) in the Rouyn–Noranda area. Contact metamorphic minerals associated with the posttectonic Preissac–Lacorne batholith (2643 Ma) show no evidence of a regional retrograde event. Accordingly, the age of regional metamorphism can be bracketed between 2677 and 2643 Ma. Three reaction isograds were mapped in subgreenschist-facies metabasites, dividing the low-grade rocks into three metamorphic zones: the pumpellyite–actinolite zone, the prehnite–pumpellyite zone, and the prehnite–epidote zone. In addition, the pumpellyite–actinolite–epidote–quartz bathograd, corresponding to a pressure of approximately 200 MPa, occurs on both sides of the Porcupine–Destor fault. Low-pressure regional metamorphism is also indicated both by the occurrence of an actinolite–oligoclase zone, and the persistence of pre-regional-metamorphic andalusite. The coincidence of andalusite and the actinolite-oligoclase zone indicates that pressure was <330 MPa at the greenschist-amphibolite transition. The geothermal gradient during metamorphism was approximately 30 °C/km. Regionally, isograds dip shallowly to the north and trend subparallel to lithological and structural trends. Metamorphic minerals in metabasites define tectonic fabrics only near major fault zones and in zones of CO2 metasomatism. In biotite zone metasedimentary rocks the schistosity is defined by mica and amphibole. These textures indicate that metamorphism and fabric development were coeval. However, the actinolite–epidote isograd cuts the Porcupine–Destor fault, indicating that regional metamorphism postdates movement along this fault. The strong fabrics associated with the Porcupine–Destor and Larder Lake–Cadillac faults must have developed through a process dominated by flattening strain.

Olivine-bearing rocks of the Lapland granulite belt (Baltic Shield)

2016 ◽  
Vol 54 (11) ◽  
pp. 964-978 ◽  
Author(s):  
E. N. Terekhov ◽  
T. F. Shcherbakova ◽  
A. N. Konilov
Keyword(s):  
Baltic Shield ◽  
Granulite Belt ◽  
Lapland Granulite Belt

New data on origin and age (U-Pb, SHRIMP-II) of zircons from khondalites of the Lapland granulite belt (Baltic Shield)

2008 ◽  
Vol 423 (1) ◽  
pp. 1294-1298
Author(s):  
T. A. Myskova ◽  
V. A. Glebovitskii ◽  
R. I. Mil’kevich ◽  
N. G. Berezhnaya ◽  
S. G. Skublov ◽  
...  
Keyword(s):  
Baltic Shield ◽  
Granulite Belt ◽  
Lapland Granulite Belt
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