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Field Guide
Geology of the Southern Alps: Intro - 1
SOUTHERN ALPS: GEOLOGY
Introduction to the Geology of the Southern Alps
The Alps are a complex mountain region formed
from the collision of two continents (Europe to the North
and Adria, a “promo­ntory” of the African continent, to
the South) which were previously separated by a narrow
ocean (Fig. 1). The formation of the Alps can be divided
in four stages (Fig. 2).
1) Jurassic to Cretaceous: phase of ocean spreading
Before this initial stage, the continents were all joined
in a supercontinent named Pangea. Forces from the interior
of the Earth determined the break-up of Pangea and oceans
began to form which progressively pushed the continents
apart. The first ocean to open was the Central Atlantic,
separating Africa from North America and Europe.
At this stage, the area where the Alps would form
was occupied by a small northern extension of the Central
Atlantic, named Ligurian-Piedmont Ocean (Fig. 2, top),
and Europe and Adria were still separated by this narrow
but actively spreading ocean basin.
Europe
North
America
2) Cretaceous to Eocene: phase of oceanic subduction
An important tectonic change occurred in the Cretaceous. The opening of the South Atlantic caused a counterclockwise rotation of the African continent (Fig. 1). This
new direction of movement pushed Adria against Europe.
As a result, the Ligurian-Piedmont Ocean started to shrink
and its oceanic crust was progressively subducted under
the Adria plate (Fig. 2, center). The Ligurian-Piedmont
Ocean is therefore a lost ocean, which was created and then
consumed as plates moved around. The only remnants and
traces of its existence are slivers of oceanic crusts found
at the core of the Alps, caught between two colliding continents (Figs. 3, 4).
3) Eocene to Oligocene: phase of continental collision
In the final part of the Eocene, the Ligurian-Piedmont
Ocean was almost completely consumed and Europe and
Adria collided. The margins of the two continents started
to deform and thicken along the suture zone. The European
Ligurian-Piedmont
Ocean
Adria
Africa
A
C
B
European and American crust
Faults
Oceanic crust
Subduction zone
African crust
Mid-ocean ridge
Direction of extension
Trace of future rifting
Fig. 1: The formation of the Alps is related to the collision of Adria (a promontory of Africa) against Europe. This diagram illus­trates
the larger tectonic movements which controlled the genesis of the Alps: a) Permian-Triassic: the continents are still joined, forming
the supercontinent Pangea. However, incipient rifting is going to separate them in different blocks; b) Jurassic-Cretaceous: the Central
Atlantic has opened, separating Africa from North America and Europe. The north­eastern extension of the Atlantic is the LigurianPiedmont Ocean, where the Alps will form; c) Cre­taceous: opening of the South Atlantic causes Africa to rotate counter­clockwise.
This rotation forces Adria to collide with Europe. The Ligurian-Piedmont Ocean is pinched between the two plates and is progressively
consumed in subduction. Drawn after Lemoine et al. (1987).­
©2014 Geoscience Research Institute
Geology of the Southern Alps: Intro - 2
2014 Field Conference
N
S
Europe
Ligurian-Piedmont Ocean
Africa (Adria)
Oceanic crust and mantle
Rocks of the subduction complex
European crust and mantle
African crust and mantle
Direction of plate movement
Magmatic intrusions
Fig. 2: Sketch showing the progressive development of the Alps, from top to bottom. Phase 1: The expanding Ligurian-Piedmont
Ocean separates the European and African plates. Phase 2: Rotation of the African continent (see Fig. 1) generates compression and
triggers subduction of the oceanic crust. Rocks get caught in the subduction zone and form a subduction prism. Phase 3: The two
continents collide, interrupting the subduction process and determining the rupture of the subducted slab. Magma rises through the
window created by the slab break-off. Notice how slivers of oceanic crust remain trapped within the subduction complex. Phase 4:
At an advanced stage of continental collision, the crust of the African block starts to be deformed by south-verging thrusts. Drawn in
part after Bosellini (1996).­
©2014 Geoscience Research Institute
Field Guide
NW
Geology of the Southern Alps: Intro - 3
NORTHERN ALPS
Periadriatic
Lineament
SE
SOUTHERN ALPS
Dolomites
Prealps
Po Plain
km
10
20
rocks of the Ligurian-Piedmont Ocean involved in subduction
crust of the Ligurian-Piedmont Ocean
granitic intrusions
basin infill of Alps-derived sediment on European plate
rocks of the African margin involved in subduction and collision
basin infill of Alps-derived
sediment on African plate
crustal rocks of the European margin
crustal rocks of the African margin
basement rocks of the European plate
basement rocks of the African plate
Fig. 3: Geologic profile across the Alps (approximate trace of profile is shown in Fig. 4). The profile illustrates how thrusts in the
mountain belt are oriented in opposing directions. Note how the European plate is subducted under the African (Adria) plate, as shown
by the dip of basement rocks on the European block. Note how remnants of a lost ocean (the Ligurian-Piedmont Ocean) have been
preserved at the core of the chain, in the suture zone. The Periadriatic Lineament is an important fault which separates areas of the
chain with different tectonic history. This lineament was also the zone where magma intrusions were emplaced during the Eocene–
Oligocene phase of continental collision. Figure drawn after Dal Piaz (1990) and Castellarin et al. (1998).­
plate was overridden by the Adria plate. In this early phase
of collision, thrusts and deformation were mostly directed
towards the North. The change from subduction to collision also resulted in the break off of the subducted slab and
emplacement of magmas (Fig. 2, center). These granitic
rocks are examples of Cenozoic (and therefore relatively
recent) magma intrusions.
4) Miocene to present: phase of collision with thrusts in opposite directions
tinued to be affected by north-directed thrusts. However,
from the Miocene, the margin of the Adria plate, which
had not been compressed before, began to be affected by
south-directed thrusts (Fig. 2, bottom). The Alps can therefore be divided in two realms, the one with north-directed
thrusts (Alps sensu strictu) and that with south-directed
thrusts (Southern Alps) separated by an important tectonic
lineament named Periadriatic Lineament (Figs. 3, 4). The
Dolomites and the Prealps contouring the Po Plain are all
part of the Southern Alps.
As collision progressed, deformation spread to the
interior of the two continents. The European plate con-
GERMANY
SWITZERLAND
F R A N C E
A U S T R I A
PL
I T A L Y
Po Plain
Ap
Adriatic Sea
enn
Tyrrhenian Sea
ine
s
basin infill of Alps-derived sediment on European plate
crustal rocks of the European margin
basement rocks of the European plate
0
50
100
150
200 Kilometres
rocks of the Ligurian-Piedmont Ocean involved in subduction
basin infill of Alps-derived
sediment on African plate
crust of the Ligurian-Piedmont Ocean
crustal and basement rocks
of the African margin
rocks of the African margin involved in subduction and collision
Fig. 4: Left: Tectonic map of the Alps (from Dal Piaz et al., 2003). Black lines indicate main faults and thrusts (tic marks are placed on
block which has been thrust over). The Periadriatic Lineament (PL) separating Northern from Southern Alps is also indicated (thick
black line). The red line shows the trace of the profile of Fig. 3. On the right, geographic view of the area covered in the tectonic map,
given for reference.­
©2014 Geoscience Research Institute
Geology of the Southern Alps: Intro - 4
2014 Field Conference
Questions for reflection
1) The plate movements which generated the Alps are an example of the dynamicity of the Earth, with
oceans and mountain chains being formed and consumed. Most creationists prefer to ascribe tectonic
movements to catastrophic disruption during the flood. A negative theological connotation is often attributed to a dynamic Earth, possibly reflecting classic Greek philosophy which proposed a dualism
between divine/immutable and earthly/ever-changing.
In the light of processes observed on other planetary bodies, would you be comfortable with a view of
a dynamic Earth before creation week? What about after creation and before the fall? What questions
on natural disasters caused by geologic processes are related to the dynamic Earth scenario?
2) Plate tectonics is an example of a large-scale process which entails numerous transformations and
redistributions of the minerals and elements constituting the Earth. While intelligent design seems selfevident in biological organisms, is it possible to recognize a design signature also in geologic processes
such as plate tectonics?
3) Think of the magnitude of the forces involved in the collision between two continents. Where does the
energy driving this process come from? What does this tell us about the power of the Creator?
©2014 Geoscience Research Institute