Highly heterogeneous upper-mantle structure in Fennoscandia from finite-frequency P-body-wave tomography

Author:

Bulut N1ORCID,Thybo H123ORCID,Maupin V4ORCID

Affiliation:

1. Eurasia Institute of Earth Sciences, Istanbul Technical University, Maslak 34469, Istanbul, Turkey

2. State Key Laboratory GPMR, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China

3. Sinoprobe Laboratory, Chinese Academy of Geological Sciences, Beijing 100037, China

4. Center for Earth Evolution and Dynamics, University of Oslo, Blindern, 0316 Oslo, Norway

Abstract

SUMMARY We present a P-wave velocity model of the upper mantle, obtained from finite-frequency body-wave tomography, to analyse the relationship between deep and surface structures in Fennoscandia, one of the most studied cratons on the Earth. The large array aperture of 2000 km × 800 km allows us to image the velocity structure to 800 km depth at very high resolution. The velocity structure provides background for understanding the mechanisms responsible for the enigmatic and strongly debated high topography in the Scandinavian mountain range far from any plate boundary. Our model shows exceptionally strong velocity anomalies with changes by up to 6 per cent on a 200 km scale. We propose that a strong negative velocity anomaly down to 200 km depth along all of Norway provides isostatic support to the enigmatic topography, as we observe a linear correlation between hypsometry and uppermost mantle velocity anomalies to 150 km depth in central Fennoscandia. The model reveals a low-velocity anomaly below the mountains underlain by positive velocity anomalies, which we explain by preserved original Svecofennian and Archaean mantle below the Caledonian/Sveconorwegian deformed parts of Fennoscandia. Strong positive velocity anomalies to around 200 km depth around the southern Bothnian Bay and the Baltic Sea may be associated with pristine lithosphere of the present central and southern Fennoscandian craton that has been protected from modification since its formation. However, the Archaean domain in the north and the marginal parts of the Svecofennian domains appear to have experienced strong modification of the upper mantle. A pronounced north-dipping positive velocity anomaly in the southern Baltic Sea extends below Moho. It coincides in location and dip with a similar north-dipping structure in the crust and uppermost mantle to 80 km depth observed from high-resolution, controlled source seismic data. We interpret this feature as the image of a Palaeoproterozoic boundary that has been preserved for 1.8 Gy in the lithosphere.

Funder

DEEP

UiO

University of Oslo

National Taiwan University

Independent Research Fund Denmark

National Science Foundation of China

MOST

GPMR State Key Laboratory

Research Council of Norway

Publisher

Oxford University Press (OUP)

Subject

Geochemistry and Petrology,Geophysics

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