Mantle transect of the Karelian Craton from margin to core based on P-T data from garnet and clinopyroxene xenocrysts in kimberlites

Lehtonen, M.; O’Brien, Hugh

doi:10.17741/bgsf/81.2.001

Cited by 28 publications

(9 citation statements)

References 40 publications

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“…This interpretation conforms with a number of other studies of the Baltic Shield (cf. Artemieva & Thybo 2008 for a recent review), including studies of xenoliths from Finland (Lehtonen et al 2004;Lehtonen & O'Brien 2009). The low P velocities and even lower S velocities and associated high V P /V S ratios west of the UMVB are consistent with a relatively thin, and hence warmer and less depleted lithosphere and a clear asthenosphere low-velocity zone.…”

Section: The History and Compositional Structure Of The Main Upper-mamentioning

confidence: 91%

Upper-mantle velocities below the Scandinavian Mountains fromP- andS-wave traveltime tomography

Hejrani¹,

Balling²,

Jacobsen³

et al. 2016

Geophys. J. Int.

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The relative traveltime residuals of more than 20 000 arrival times of teleseismic P and S waves measured over a period of more than 10 yr in five separate temporary and two permanent seismic networks covering the Scandinavian (Scandes) Mountains and adjacent areas of the Baltic Shield are inverted to 3-D tomograms of P and S velocities and the V P /V S ratio. Resolution analysis documents that good 3-D resolution is available under the dense network south of 64 • latitude (Southern Scandes Mountains), and patchier, but highly useful resolution is available further north, where station coverage is more uneven. A pronounced upper-mantle velocity boundary (UMVB) that transects the study region is defined. It runs from SE Norway (east of the Oslo Graben) across the mountains to the Norwegian coast near Trondheim (around the Møre−Trøndelag Fault Complex), after which it follows closely along the coast further north. Seismic velocities in the depth interval 100−300 km change significantly across the UMVB from low relative V P and even lower relative V S on the western side, to high relative V P and even higher relative V S to the east. This main velocity boundary therefore also separates relatively high V P /V S ratio to the west and relatively low V P /V S to the east. Under the Southern Scandes Mountains (most of southern Norway), we find low relative V P , even lower relative V S and hence high V P /V S ratios. These velocities are indicative of thinner lithosphere, higher temperature and less depletion and/or fluid content in a relatively shallow asthenosphere. At first sight, this might support the idea of a mantle buoyancy source for the high topography. Under the Northern Scandes Mountains, we find the opposite situation: high relative V P , even higher relative V S and hence low V P /V S ratios, consistent with thick, dry, depleted lithosphere, similar to that in most of the Baltic Shield area. This demonstrates significant differences in upper-mantle conditions between the Southern and Northern Scandes Mountains, and it shows that upper-mantle velocity anomalies are very poor predictors of topography in this region. An important deviation from this principal pattern is found near the topographic saddle between the Southern and Northern Scandes Mountains. Centred around 64 • N, 14 • E, a zone of lower S velocity and hence higher V P /V S ratio is detected in the depth interval between 100 and 300 km. This 'Trøndelag−Jämtland mantle anomaly' (TJMA) is still interpreted as part of relatively undisturbed lithosphere of shield affinity because of high relative P velocity, but the relatively low V P /V S ratios indicate lower depletion, possibly higher fluid content, and most likely lower viscosity relative to the adjacent shield units. We suggest that this mantle anomaly may have influenced the collapse of the Caledonian Mountains, and in particular guided the location and development of the Møre−Trøndelag Fault Complex. The TJMA is therefore likely to have played an important role in the development of the 'two-d...

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Section: The History and Compositional Structure Of The Main Upper-mamentioning

confidence: 91%

Upper-mantle velocities below the Scandinavian Mountains fromP- andS-wave traveltime tomography

Hejrani¹,

Balling²,

Jacobsen³

et al. 2016

Geophys. J. Int.

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“…In the present study, a caveat to this continuum model is that the proto-aillikite magma interacted with a lesser proportion of the same or similar metasomatized SCLM component that dominates the proposed source of the olivine lamproites, despite being separated by ∼100 km. In this regard, a geothermobarometric study of garnet and clinopyroxene xenocrysts from kimberlites and olivine lamproites ( Lehtonen & O'Brien, 2009 ), suggests that the lithospheric mantle beneath Kuusamo, is indeed similar to that beneath the Lentiira-Kuhmo cluster.…”

Section: Geodynamic and Source Constraints For ∼1200 Ma Olivine Lampr...mentioning

confidence: 99%

Geodynamic and Isotopic Constraints on the Genesis of Kimberlites, Lamproites and Related Magmas From the Finnish Segment of the Karelian Craton

Dalton

Giuliani

Hergt

et al. 2022

Geochem Geophys Geosyst

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Despite the scientific and economic significance of kimberlites and related magmas, their origin is unclear. Here, we address this issue using whole‐rock and perovskite‐derived Sr‐Nd‐Hf isotopes for the three occurrences of kimberlite, lamproites and ultramafic lamprophyres (UMLs) in Finland. Mesoproterozoic olivine lamproites at Lentiira‐Kuhmo and UMLs at Kuusamo have different isotopic signatures yet were emplaced contemporaneously at 1,200 Ma in response to an extensional regime linked to the Baltica‐Laurentia breakup. The low εNd(i) and εHf(i) values of the olivine lamproites are consistent with an enriched subcontinental lithospheric mantle (SCLM) source while UML compositions are intermediate between those of typical kimberlites and lamproites and are interpreted to reflect mixing of asthenospheric melts and ∼10%–15% of melts sourced from metasomatized SCLM. The ∼750 Ma Kuusamo kimberlites, are probably linked to the mantle plume activity that initiated Rodinia's break‐up, exhibiting homogenous isotopic compositions which mirror the prominent Geodynamic and Source Constraints for ∼1,200 Ma Olivine Lamproite and Ultramafic Lamprophyre Magmatism in Eastern Finland (PREMA)‐like signature of kimberlites globally. By contrast, ∼620–585 Ma Kaavi‐Kuopio kimberlites show limited range in εNd(i) and 87Sr/86Sr(i) but have remarkably heterogeneous εHf(i) (+6.5 to −6.3) with a temporal trend toward lower εHf(i) values. While the Kuusamo kimberlites erupted during the early stage of continental break‐up, the Kaavi‐Kuopio kimberlites were emplaced when Rodinia break‐up was completed, coeval with formation of the Central Iapetus large igneous province. Magmas forming the Kaavi‐Kupio kimberlites may have formed from an upwelling mantle source similar to PREMA modified by increasing incorporation (up to 10%) of recycled crustal material through time accounting for the trend toward lower εHf(i) in these kimberlites.

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“…As an example of an area with a low level of anthropogenic seismic noise, we selected an area located in the Kuusamo Greenstone Belt (KuGB), Finland, because of numerous previous geological and geophysical studies there (Silvennoinen, 1991;Bruneton et al, 2004;Yliniemi et al, 2004;Silvennoinen and Kozlovskaya, 2007;Poli et al, 2012b;Pedersen et al, 2013;Silvennoinen et al, 2014;Tiira et al, 2014;Vinnik et al, 2014, etc.). Moreover, Weihed et al (2005) and Lehtonen and O'Brien (2009) have shown that this area is prospective for gold-and diamond deposits.…”

Section: Kuusamo Greenstone Belt Areamentioning

confidence: 99%

“…In our paper, we present details of this algorithm and illustrate its performance using passive seismic ambient noise data acquired in two areas of Fennoscandia: Pyhäsalmi mine (as an example of area with a high level of industrial noise) and the Kuusamo Greenstone Belt area (a quiet area prospective for new mining projects (Weihed et al, 2005;Lehtonen and O'Brien, 2009).…”

Section: Introductionmentioning

confidence: 99%

Improving the quality of empirical Green's functions, obtained by cross-correlation of high-frequency ambient seismic noise

et al. 2019

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Abstract. Studying the uppermost structure of the subsurface is a necessary part of solving many practical problems (exploration of minerals, groundwater studies, geoengineering, etc.). The practical application of active seismic methods for these purposes is not always possible for different reasons, such as logistical difficulties, high cost of work, and a high level of seismic and acoustic noise. That is why developing and improving passive seismic methods is one of the important problems in applied geophysics. In our study, we describe a way of improving the quality of empirical Green's functions (EGFs), evaluated from high-frequency ambient seismic noise, by using the advanced technique of cross-correlation function stacking in the time domain (in this paper we use term “high-frequency” for frequencies higher than 1 Hz). The technique is based on the global optimization algorithm, in which the optimized objective function is a signal-to-noise ratio of an EGF, retrieved at each iteration. In comparison to existing techniques, based, for example, on weight stacking of cross-correlation functions, our technique makes it possible to significantly increase the signal-to-noise ratio and, therefore, the quality of the EGFs. The technique has been tested with the field data acquired in an area with a high level of industrial noise (Pyhäsalmi Mine, Finland) and in an area with a low level of anthropogenic noise (Kuusamo Greenstone Belt, Finland). The results show that the proposed technique can be used for the extraction of EGFs from high-frequency seismic noise in practical problems of mapping of the shallow subsurface, both in areas with high and low levels of high-frequency seismic noise.

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Mantle transect of the Karelian Craton from margin to core based on P-T data from garnet and clinopyroxene xenocrysts in kimberlites

Cited by 28 publications

References 40 publications

Upper-mantle velocities below the Scandinavian Mountains fromP- andS-wave traveltime tomography

Upper-mantle velocities below the Scandinavian Mountains fromP- andS-wave traveltime tomography

Geodynamic and Isotopic Constraints on the Genesis of Kimberlites, Lamproites and Related Magmas From the Finnish Segment of the Karelian Craton

Improving the quality of empirical Green's functions, obtained by cross-correlation of high-frequency ambient seismic noise

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