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200 km north of Trinidade
Vitoria seamount chain, which form the Aboralhos
platform perhaps was related to the plume. The Pb-isotope ratio of these basalts are
similar to that of the Island of Trinidade. According to Morgan (1983) the present
day centre of the Trinidade hotspot perhaps were located beneath the Alto Par-
anaiba province
-
Vitoria seamount chain represented
the surface expression of the same plume that was responsible for the alkali
magmatism in the northeast margin of the Parana basin, then the width of the
hotspot track has narrowed signi
90 Ma ago. If the Trinidade
*
-
cantly with time. This view is in agreement with
the suggestion of O
Conner and Duncan (1990), who suggested additional sea-
mounts (Hotspur, Rodgers, Minerve and Almirante Saldanha) located to the north
and south of Trinidade
'
Vitoria sea mount chain, which represented the presence of
a hotspot with large diameter, when the South American continental margin passed
over the plume 50 Ma ago.
Fluid dynamic studies by Richards et al. (1989) showed that a plume generated
from the mantle at a depth does not displace the overlying mantle. It ascended
quickly until the near super
-
cial plume head attained a large amount of buoyancy.
A narrow tail is formed behind the part of the plume head and this led to rapid
ascent of hot low viscosity materials. The plume head gradually
attened and was
dissipated, but the tail possibly persisted long after this.
Various types of plume-related igneous provinces could be recognized
depending on whether the lithosphere moved over a plume head or a tail. Conti-
nental
flood basalts or oceanic plateau basalts now cover an equant area
(1,500
2,000 km across) and are considered to have been generated by melting, as
the lithosphere passed over the plume head, whereas linear belts, which formed
hotspot tracks (<300 km) were formed, whenever the overlying lithosphere passed
over the plume tail. According to Gibson et al. (1994), the 100 km wide zone of
Late Cretaceous (80 Ma) ma
-
c potassic magmatism in the Alto Paranaiba Igneous
Province may be the surface expression of a starting plume head; and the 150 km
wide Trinidade
Vitoria seamount chain was a long-lived (post 50 Ma) hotspot track
of the plume tail. No effect of melting related to the plume could be observed and
the plume might have been turned off during the early. Tertiary, when the old thick
lithosphere of the San Francisco Craton (South America) passed over it.
-
The
plume activity reemerged from beneath the westward drifting of South American
continent and became the magma source for the ocean island volcanism of the
Atlantic Ocean and the seamounts (Gibson et al. 1994).
“
”
According to Courtney and White (1986) plume-related volcanism is usually
associated with uplift, and this was probably related to (1) positive buoyancy of the
plume, (2) due to thermal expansion of the lithosphere and (3) possibly because of
magmatic underplating (Cox 1989). According to Gibson et al. the temporally and
spatially associated uplift and magmatism in the Alto Paranaiba Igneous Province
(Fig.
14.8
) were caused by the Trinidade mantle plume. Pressure estimates from a
garnet lherzolite xenolith (Leonardos et al. 1993) and analogies with experimental
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