The lower crust of SE Belarus: petrological, geophysical and geochemical constraints from xenoliths

Markwick, A. J.; Downes, Hilary; Veretennikov, N. V.

doi:10.1016/s0040-1951(01)00040-3

Cited by 24 publications

(8 citation statements)

References 41 publications

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“…Theoretical calculations of elastic properties of garnet granulite xenoliths from the Archangelsk area (NW Russia; Markwick & Downes 2000) and from the Fennoscandia–Sarmatia junction (SE Belarus; Markwick et al 2001) demonstrated that these rocks have high values of P ‐wave velocity and density under pressures and temperatures corresponding to the depth of the lower crust (6.94–7.7 km s −1 and 3.2–3.5 × 10 3 kg m −3 , respectively). The reported V p values are comparable to the high velocity for the lower crust used in the present study and also to the values derived by the seismic studies beneath the EUROBRIDGE'96 profile (Kozlovskaya et al 2002).…”

Section: Discussionmentioning

confidence: 99%

3-D density model of the crust of southern and central Finland obtained from joint interpretation of the SVEKALAPKO crustal P-wave velocity models and gravity data

Kozlovskaya

Elo

Hjelt

et al. 2004

Geophysical Journal International

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S U M M A R YThe paper presents a three-dimensional (3-D) density model of the crust of southern and central Finland. The large SVEKALAPKO seismic array experiment was carried out in this area during 1998-1999. One of the intermediate objectives of the experiment was compilation of a 3-D P-wave velocity model (V p model) of the crust to provide crustal corrections for teleseismic P-wave traveltimes. The model was constructed from the results of previous controlled-source seismic (CSS) experiments in the area and was composed of two main crustal layers, an upper crust and a high-velocity lower crust with V p > 7.0 km s −1 . The thickness of the crust in the model varies from 64 to 38 km and includes three pronounced troughs. We used this model and the results of petrophysical studies of bedrock density in Finland as a priori information to construct a 3-D density model of the crust in the SVEKALAPKO area. The initial results of gravity modelling demonstrated, however, that the model lacks information about lateral velocity variations in the upper and middle crust. To improve the fit of the model to the observed Bouguer anomaly, the model was corrected by introducing two additional layers, called the lower crust and the middle crust, with 6.8 < Vp < 7.0 km s −1 and 6.4 < Vp < 6.8 km s −1 , respectively. The depth to the upper boundaries of these layers was retrieved from the results of previous seismic profiles in the area and the values of density and velocity in the upper crust were constrained using the information on bedrock densities in Finland, the Bouguer anomaly and new data about the velocity distribution within the upper crust obtained from local event studies of the SVEKALAPKO seismic experiment. The corrected model was used as a starting model for inversion of the observed Bouguer anomaly. The resulting 3-D density model agrees well with the observed Bouguer anomaly and explains the sources of largescale Bouguer anomalies in the region. The model demonstrates that there is no correlation between the observed Bouguer anomaly and Moho depth. Rather, the Moho depressions in the region mark the boundaries of crustal blocks with different types of density distribution and are associated with the presence of additional compensating masses within the crust. The high-velocity lower crust of density 3.1-3.25 × 10 3 kg m −3 does not completely compensate the Moho depressions and the compensation is mostly a result of the presence of additional dense material in the upper and middle crust. Thus, the Moho depressions in central and southern Finland are fully compensated, or even overcompensated. On the other hand, the Moho depression in the area of the Gulf of Bothnia is compensated only in its southern part, resulting in a regional-scale minimum of the Bouguer anomaly in the northern part of the depression. The varying degree of compensation may result from variation in the origin and age of the present-day Moho boundary in the region.

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Section: Discussionmentioning

confidence: 99%

3-D density model of the crust of southern and central Finland obtained from joint interpretation of the SVEKALAPKO crustal P-wave velocity models and gravity data

Kozlovskaya

Elo

Hjelt

et al. 2004

Geophysical Journal International

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“…In addition to the author's data, Table 2 gives isotopic data for the grani toids of the Osnitsk complex and silicic extrusive rocks of the Klesov Group after [8] and xenoliths of lower crustal granulites from the Devonian diatremes pene trating the OMVPB complexes. According to Mark wick et al [25], these rocks are lower crustal analogues of the rocks of the Osnitsk complex.…”

Section: Strontium Neodymium and Hafnium Isotope Systematicsmentioning

confidence: 99%

Geochemistry of the Osnitsk-Mikashevichy volcanoplutonic complex of the Ukrainian shield

Shumlyanskyy

2014

Geochem. Int.

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This paper addresses the geochemistry of intrusive (Osinitsk complex) and volcanic (Klesov Group) rocks of the Osnitsk-Mikashevichy volcanoplutonic belt (OMVPB) of the Ukrainian shield, which is an active continental margin existing approximately 1980-2000 Ma ago. The Osnitsk complex comprises a wide range of rocks, from ultrabasics to granitoids, and the Klesov Group is dominated by extrusive rocks of basaltic and rhyolitic compositions metamorphosed under epidote amphibolite facies conditions. The Sr-Nd-Hf isotopic systematics (εSr 1990 from -4 to +10, εNd 1990 from -0.6 to +2.3, and εHf1990 from 0.1 to 1.4) indicates a juvenile source for the OMVPB rocks. Geochemical data suggest independent origin of the rocks of gabbroid (SiO 2 < 60 wt %) and granitoid (SiO 2 > 60 wt %) series. The gabbroids are subdivided into pre and post granite groups on the basis of the higher contents of incompatible trace elements and lower contents of compatible elements in the post granite rocks. The geochemical characteristics of the two groups of basic rocks indicate their formation in a convergent tectonic setting. The origin of the granitoid melts is attributed to the low degree (eutectoid) melting of basic rocks at relatively low temperatures.

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“…figr rid="f1">1). In Belarus, xenolith‐bearing lamprophyres of similar age were erupted on the NE shoulder of the Pripyat depression (Markwick et al ., 2001), and late Precambrian kimberlites in Finland also contain granulite xenoliths (Hölttä et al ., 2000).…”

Section: Petrology Of Lower Crustal Xenolithsmentioning

confidence: 99%

“…The Arkhangelsk mafic granulite xenoliths are similar in their mineralogy to those from Kola, but most are devoid of hydrous phases; however, scapolite is present (Markwick and Downes, 2000). In contrast, garnet‐bearing mafic granulite xenoliths from Belarus contain no rutile, and metasomatic amphibole is much more common (Markwick et al ., 2001). The Finnish xenoliths reported by Hölttä et al .…”

Section: Petrology Of Lower Crustal Xenolithsmentioning

confidence: 99%

“…2), all of the NE European granulite xenoliths plot in the enriched field (low 143 Nd/ 144 Nd, variable 87 Sr/ 86 Sr). Xenoliths from Arkhangelsk have slightly lower 87 Sr/ 86 Sr and higher 143 Nd/ 144 Nd ratios, whereas Belarussian samples (Markwick et al ., 2001) have isotope ratios intermediate between those of Kola and Arkhangelsk. Only Nd isotope data are available from three Finnish lower crustal xenoliths (Hölttä et al ., 2000); they resemble the values from the Arkhangelsk xenoliths ( 143 Nd/ 144 Nd= 0.5118–0.5125).…”

Section: Isotope Geochemistrymentioning

confidence: 99%

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The lower crust beneath cratonic north‐east Europe: isotopic constraints from garnet granulite xenoliths

et al. 2001

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Lower crustal garnet‐bearing mafic granulite xenoliths from beneath the cratonic areas of NE Europe (NW Russia, Belarus, Finland) have unradiogenic 143Nd/144Nd ratios that differ strongly from those of xenoliths from beneath Phanerozoic regions of the European plate and worldwide, but closely resemble xenoliths from other cratonic regions of the world. Phanerozoic lower crustal xenoliths worldwide also show a very limited range of Pb isotope compositions whereas most cratonic lower crustal xenoliths have more varied but usually unradiogenic Pb isotope compositions, plotting to the left of the Geochron. However, many of the xenoliths from beneath NE Europe plot on the right‐hand side of the Geochron and also have more radiogenic 208Pb/204Pb ratios. Thus, the lower crust of NE Europe shows characteristics of both cratonic lower crust (unradiogenic Nd isotopes) and Phanerozoic lower crust (radiogenic Pb isotopes). Its present‐day low U/Pb and Th/Pb ratios indicate that it has been depleted in heat‐producing elements, but the radiogenic Pb isotope ratios show that this depletion occurred relatively recently.

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The lower crust of SE Belarus: petrological, geophysical and geochemical constraints from xenoliths

Cited by 24 publications

References 41 publications

3-D density model of the crust of southern and central Finland obtained from joint interpretation of the SVEKALAPKO crustal P-wave velocity models and gravity data

3-D density model of the crust of southern and central Finland obtained from joint interpretation of the SVEKALAPKO crustal P-wave velocity models and gravity data

Geochemistry of the Osnitsk-Mikashevichy volcanoplutonic complex of the Ukrainian shield

The lower crust beneath cratonic north‐east Europe: isotopic constraints from garnet granulite xenoliths

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