Geoscience Reference
In-Depth Information
Figure 10.27.
Locations of
the Archaean provinces of
North America and the
Trans-Hudson orogen
(THO). The orogen
extends across Hudson
Bay, Ungava and across
Greenland to
Scandinavia. Greenland
and western Scandinavia
are shown in the positions
that they would have had
prior to the opening of the
Atlantic Ocean. The box
indicates the location of
the 'Lithoprobe' work
shown in Fig. 10.28. (After
Lucas
et al
.(1993) and
Hoffman (1989).)
NAIN
RAE
Hudson
Bay
50
o
N
60 W
o
50 N
o
o
130 W
SUPERIOR
Atlantic
40
o
N
70
o
W
40
o
N
120
o
W
Archaean cratons
Palaeoproterozoic orogens
<1.8-Ga orogens
zones, which include subducted continental margins, obducted oceanic crust
and accreted juvenile arc terrains, sandwiched between Archaean cratons: the
Superior craton to the south and east and the Rae/Hearne craton to the north
and west. The four parallel zones, in order from the east, are (1) a foreland belt,
(2) a wide internal zone, (3) remnants of a magmatic arc and (4) a fold belt.
1. The narrow foreland belt (Thompson), the boundary zone along the eastern edge of the
orogen, consists of heavily reworked rocks of the Superior craton as well as sediments
associated with rifting and igneous rocks of unknown origin. At the end of the collision
the Superior craton was ultimately thrust westwards over the previously deformed
central part of the orogen.
2. The wide internal zone (Reindeer) comprises oceanic and arc volcanic and plutonic
rocks together with sediments, all thought to have been formed along a subduction zone.
This zone is structurally underlain by an Archaean micro-continent - small structural
windows expose Archaean rocks.
3. The remnants of the magmatic arc (Wathaman) are exposed as a 1.85-Ga batholith,
which is up to 100 km wide and extends some 800 km along the length of the orogen. It
represents the eroded interior of a major calc-alkaline intrusion similar to those in the
Andes. The presence of this magmatic arc along the northwest margin of the orogen
confirms that oceanic lithosphere was subducted beneath the Hearne craton.
4. Finally, the fold belt (Cree Lake) comprises deformed and metamorphosed continental
margin sediments as well as 1.8-Ga intrusions.
The North American Central Plains (NACP) conductivity anomaly, the largest
electrical conductor delineated by electromagnetic induction studies, is collinear
with the Trans-Hudson orogen and is thought to be caused by rocks within the
