A gravity model of the North Eurasia crust and upper mantle: 1. Mantle and isostatic residual gravity anomalies
M. K. Kaban
Schmidt United Institute of Physics of the Earth, Russian Academy of Sciences, Moscow, Russia
Abstract
[1] A numerical density model of the North Eurasia crust is constructed and its
gravity effect is calculated. This model includes variations in the thickness
and density of the sedimentary cover and solid crust, derived from
generalization of seismic and geological data and specified on a
1o1o grid
within (30o-75o N, 14o W-195o E). Residual mantle anomalies are calculated by
removing the anomalous model field from the observed gravity field. The mantle
anomalies are reliably separated into two components accounting for the effects
of different factors: (1) The regional component does not correlate, in a first
approximation, with crustal structures and reflects large-scale structural
heterogeneities of the Eurasia lithosphere, supposedly related to its thermal
regime. Intense positive anomalies characterize northern and central Eurasia,
and negative anomalies are observed in Western Europe and Southeast Asia. The
regional component is consistent with the shear wave velocity distribution
obtained from seismic tomography data. (2) The local component of the mantle
gravity field has wavelengths shorter than 2000-2500 km and evidently correlates
with specific tectonic structures. Maximum positive anomalies with amplitudes
exceeding 100 mGal characterize some structures of the East European platform
(Baltic Shield and Voronezh Massif) and East Siberia (Tunguska syneclise). A
chain of negative mantle anomalies is clearly traced west of the Tesseyre-Tornquist
line (Pannonian basin-Rhine graben-Massif Central). In Central Asia
the most prominent zone of negative mantle anomalies is located southwest of
Lake Baikal, approximately in the Khamar-Daban Range area. These anomalies are
likely to be related to intrusion of an anomalously hot and light mantle. The
intense negative mantle anomalies observed along the eastern boundary of Eurasia
are associated with backarc seas. A new map of the isostatic gravity anomalies
is calculated throughout the territory studied. As distinct from previous
studies, real data on the crustal structure, including variations in the
thickness and density of the sedimentary cover and solid crust, were used for
its calculation. The use of these data instead of the traditional Airy scheme
has led in many cases to a revision of notions concerning the isostatic state of
the crustal structures. In particular, as compared with previous maps,
significantly reduced amplitudes of the isostatic anomalies are obtained for the
South Caspian, Tien Shan and Urals regions.
Received 10 August 2001; published 21 August 2001.
Keywords: residual gravity anomalies, density model of crust, modelling.
Citation: Kaban, M. K. (2001), A gravity model of the North Eurasia crust and upper mantle: 1. Mantle and isostatic residual gravity anomalies, Russ. J. Earth Sci., 3, No.2, 125-144, doi:10.2205/2001ES000062.