Geology Reference
In-Depth Information
Fig. 4
North In Ouzzal Terrane:
a
Tin Tchik Tchik charnockitic
TTG (dated at 3.2
2.7 Ga);
b
Alouki Greenstone belt;
c
Alouki Al
-
Mg granulites
showing an ultrahigh temperature
paragenesis;
d
Tekhamalt
migmatitic Al
-
Fe granulites
showing a ultrahigh temperature
paragenesis;
e
Ihaouhaou
รจ
ne
carbonatitic hills;
f
In Eher
rupestral engravings
-
charnockites, and a supracrustal unit of quartzites, banded
iron formations, marbles, Al
region (Ouzegane et al.
2003
) is currently considered as one
of the most extreme in world literature (Harley
2008
; Kelsey
2008
). In the late stage of this metamorphism, carbonatitic
magmas were emplaced (Bernard-Grif
-
Mg and Al
-
Fe granulites
commonly associated with ma
c (metanorites and garnet
pyroxenites) and ultrama
c (pyroxenites, lherzolites and
harzburgites) lenses (Ouzegane et al.
2003
), greenstone belts
(Fig.
4
b
ths et al.
1988
;
Fourcade et al.
1996
, Fig.
4
e). These carbonatites exposed in
the Ihouhaouene area are special for several reasons: (i)
Archaean and Paleoproterozoic carbonatites are rare in the
world; (ii) they are the only ones that occured in such geo-
dynamic context during the decompression phase after
a prograde stage of a regional granulitic metamorphism
(Ouzegane
1987
; Fourcade et al.
1996
); and (iii) they contain
minerals, such as apatites which exceed 20 cm and are
extremely rich in rare earth elements (Ouzegane,
personal
communication
).
These geological sites mentioned above include a multi-
tude of small archaeological sites with paintings and engrav-
ings (Fig.
4
f), mostly on small Pan-African granitic massifs
exposed in the region or in alkaline orthogeneiss; workshops
for arrowheads and tumulus occur occasionally in this terrane.
d). The continental crust, represented by the gran-
ulitic unit of In Ouzzal, was formed during various orogenic
reworking events spread between 3,200 and 2,000 Ma. The
formation of a continental crust, composed of tonalites and
trondhjemites, took place between 3,200 and 2,700 Ma
(Fig.
4
a). Towards 2,650 Ma, extension-related alkali-gran-
ites were emplaced. The deposition of sediments (later to
become metasedimentary protoliths) between 2,700 and
2,650 Ma, was coeval with rifting. The youngest Archaean
igneous event at 2,500 Ma includes calc-alkaline granites
resulting from partial melting of a predominantly tonalitic
continental crust (Peucat et al.
1996
; Ouzegane et al.
2003
).
The Paleoproterozoic ultra-high temperature metamor-
phism associated with the Paleoproterozoic orogeny in this
-
