Examples of modern orogenic belts - Introducing Tectonics, Rock Structures and Mountain Belts - page 92

through nearly 180°, describing a great
arc through eastern France and Swit-
zerland until, in the Austrian sector, it
trends roughly east-west. The chain
then divides into two branches, one
continuing down through the Dinar-
ides to Greece, and the other forming
the great arc of the Carpathians.
The northern branch of the system
includes tectonic units that are marginal
to the European plate and have been
overthrust onto the European foreland.
This branch includes the Betic Alps in
southern Spain, the Western and Eastern
Alps proper, and the Carpathians.
The 'southern' branch consists of the
coastal sector of the Atlas mountains,

the Apennines of Italy, the Southern
Alps , and the Dinarides; these are mar-
ginal to, and have been overthrust onto,
the Apulian micro-continent ( Apulia ),
which originally belonged to the African
plate. Part of the complexity of shape
is due to the fact that much of the
western Mediterranean (the Balearic
and Tyrhennian Seas), consists of
'young' ocean basins that have opened
up during the last 10 million years and
have resulted in the Italian peninsula
being rotated through nearly 90°.

history of the neighbouring plates, as
summarised in Figure 11.1. The central
Atlantic Ocean opened during the
Jurassic Period, while Europe was still
attached to America. This had the effect
of moving Africa eastwards with respect
to Europe. However, when the South
Atlantic opened in the Cretaceous, the
African plate changed direction with
respect to Europe and rotated anti-
clockwise, so as to move north, then
north-west, towards Europe. Finally,
as the North Atlantic opened during
the Tertiary, Europe moved eastwards,
rotating anti-clockwise in relation to
Africa. These movements resulted in the
following tectonic events (Figure 11.6).

Plate movements
An important reason for the complex-
ity of the Alpine belt is the movement

1. The separation of the Apulian
microplate from Africa (in the Creta-
ceous) due to the formation of the Neo-
Tethys ocean as Africa moved eastwards.

2. Closure of the Tethys Ocean , and
subduction of Tethyan crust beneath
Apulia as Africa converged on Europe.

3. Collision of Apulia with the
Pennine terrane .

4. Subduction beneath the Pennine
terrane and collision of the combined
Apulia-Pennine terranes with Europe
in the main Alpine event (Miocene).

Figure 11.6 Cartoon cross-sections showing a possible interpretation
of the evolution of the central Alps. 1. Pre-Cretaceous. 2. Mid-
Cretaceous: opening of Neo-Tethys ocean. 3. Late Cretaceous:
expansion of Neo-Tethys causes subduction of Tethyan crust
beneath Apulia and collision between the Pennine terrane and
Apulia. 4. Eocene: northward movement of Africa causes subduction
of Tethyan crust of the European plate beneath the combined
Pennine-Apulian microplate. 5. Oligocene: further northward
movement of Africa causes collision of the Pennine-Apulian
microplate with Europe. 6. Miocene: further convergence causes
backthrusting of the thickened orogen onto Apulia.