Geology Reference
In-Depth Information
14.1.4 Mantle Upwelling Beneath Eastern Atlantic
and Western and Central Europe
A detailed seismic tomography of the upper mantle below the eastern Atlantic
volcanic province, the western Mediterranean and the central European rift valley
region was made by Hoernle et al. (1995). They established that the eastern Atlantic
volcanic province forms an elongated belt of islands and seamounts, which parallels
the coast of north-west Africa and Liberian peninsula. This province extends for
approximately 2,500 km towards north
northeast from the Saharan seamounts and
the Canary Islands in the south to Madeira Island in the centre to the Biscay abyssal
plain in the north. Subaerial volcanism in the Canary and Madeira Islands began in
the early Miocene, but submarine volcanism might have started 60 Ma ago.
According to them the central European volcanic province extends from France
through southwest Poland to Hungary. The province includes the Massif Central
volcanic province of France, where volcanism took place during 0 and 20 Ma and
35
-
65 Ma ago. There is a systematic record of recent volcanism in Rhenish massif
(Eifel) and Rhine Graben in Germany (0
-
20 Ma),
in Lower Silesia, Poland
-
(15
14 Ma) and in the western Pannoian basin in Czechoslovakia and Hungary
(Eocene-Miocene, and 1
-
12 Ma). According to Hoernle et al. (1995) most of the
volcanism in the central Europe is related to a NNE-trending rift belt formed in the
early Cenozoic Era. This continental rift belt includes the Rhone, Limagne, Bresse,
Rhine, Ruhr and Leine Grabens. They think that in contrast to other central European
volcanism, the Pannonian basin volcanism was associated with back-arc spreading.
They further suggested that the Western Mediterranean volcanic province
comprises the Roman province of Italy (Quaternary), eastern Sicily (Late Creta-
ceous
-
Pleistocene). They
observed that each of these volcanic region is underlain by continental crust, which
has been undergoing extension as evidenced by intensive block faulting and rift
zone.
On the basis of seismo-tomographic study they established that there is a low S-
wave velocity anomaly (LVA) with a width of about 2,500 km to NNE direction
and elongated about 4,000 km in the ESE direction, which underlies the eastern
Atlantic, northern Africa, western Mediterranean and central Europe. The LVA
zone in this model is a planar feature with a NNE strike and westward dip.
According to Hoernle et al. (1995) the local S-wave velocity model shows the
presence of a LVA zone at depths shallower than 200 km beneath western and
central Europe and the Mediterranean segment. Local P-wave velocity model also
indicates the presence of LVA at depths of 150
-
Quaternary) and Sardinia and Corsica (Oligocene
-
250 km beneath the same region.
They interpreted this low velocity zone to be a relatively hot (possibly volatile-
enriched) region of mantle upwelling. The LVA zone could be a single feature or
may re
-
ect an averaging of spatially isolated low velocity region such as cluster of
plumes. The local S-wave models however, shows the LVA to be continuous and
does not show any evidence of deep roots of the LVA beneath central Europe or the
western Mediterranean region in agreement with general global model.
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