Page 392 - Global Tectonics

374 CHAPTER 11

(a) Single supercontinent minimum of three supercratons, Sclavia, Superia, and
(”Kenorland solution”) Vaalbara, that display distinct amalgamation and break-
Slave
up histories (Fig. 11.21b). The Sclavia supercraton
appears to have stabilized by 2.6 Ga. Confi rmation of
these tentative groupings awaits the collection of
detailed chronostratigraphic profiles for each of the 35

Archean cratons.
Diachronous break-up of the supercratons defi ned
by Bleeker (2003) occurred during the period 2.5–2.0 Ga,
spawning the 35 or more independently drifting cratons.
Paleomagnetic evidence supports the conclusion that

significant differences in the paleolatitudes existed
between at least several of these fragments during the
Early Proterozoic (Cawood et al., 2006). Following the
break-up the cratons then appear to have amalgamated
into various supercontinents. Hoffman (1997) postu-
Superior
lated a Middle Proterozoic supercontinent called Nuna,
Kaapvaal
which Bleeker (2003) considered to represent the fi rst
(b) Several supercratons
(”supercraton solution”) true supercontinent. Zhao et al. (2002) also recognized
Sclavia that most continents contain evidence for 2.1–1.8 Ga
orogenic events (Section 11.4.3) (Fig. 11.12). They pos-
tulated that these orogens record the collisional assem-
bly of an Early–Middle Proterozoic supercontinent
called Columbia (Fig. 11.22). These studies, while still
speculative, suggest that at least one supercontinent

formed prior to the final assembly of Rodinia and after
the Archean cratons began to stabilize during the Late
Archean.

11.5.5 Gondwana–Pangea
Vaalbara Superia
assembly and dispersal
(c) Many supercratons
(”unlikely solution”)
The assembly of Gondwana began immediately follow-
ing the break-up of Rodinia in Late Proterozoic times.
According to the SWEAT hypothesis (Section 11.5.3)
West Gondwana formed when many small ocean basins
that surrounded the African and South American
cratons closed during the opening of the proto-Pacifi c
Ocean, creating the Pan-African orogens (Fig. 11.19b).
Subsequent closure of the Mozambique Ocean resulted
in the collision and amalgamation of West Gondwana
with the blocks of East Gondwana. This amalgamation
may have created a short-lived Early Cambrian super-
continent called Pannotia. The existence of this super-
continent is dependent on the time of rifting between
Fig. 11.21 Cartoons representing possible craton
Laurentia and Gondwana (Cawood et al., 2001). Models
configurations during Late Archean–Early Proterozoic

of Pannotia (Fig. 11.23a) are based mostly on geologic
times. Three well-known cratons (Slave, Superior and
evidence that Laurentia and Gondwana were attached
Kaapvaal) are shown shaded in (a). These cratons may
have been spawned by the larger supercratons shown in
(b) (after Bleeker, 2003, with permission from Elsevier).