<p> Approximately eighty new neodymium model ages were determined on grey
orthogneisses in the Mattawa region of Ontario and were used to develop a Grenvillian
tectonic model in the region. A residual-magnetic field map developed from
aeromagnetic data provides an additional constraint on the terranes mapped based on Nd-model
ages. The field area was divided into three sections: the northern section, the
Mattawa klippe, and the southern section. </p> <p> The objectives of mapping in the northern section were two-fold: 1) to map the
location of erosional remnants of the allochthon boundary thrust (ABT) and 2) to test the
hypothesis that northwestward thrusting of the ABT over the parautochthonous belt
caused decollement of a magmatically reworked Archean terrane, creating a duplex thrust
sheet and consequent northwestward thrusting of the magmatically reworked Archean
parautochthon. </p> <p> Two allochthonous units previously mapped in this region are the Lac Watson
nappe and the Lac Booth klippe. These allochthonous units, characterized by Nd-model
ages <1.8 Ga are bound by a magmatically reworked Archean terrane (referred to as the
reworked Archean parautochthon) with a Nd-model age range of 1.9-2.6 Ga. Likewise,
the perimeter of the reworked Archean parautochthon is truncated by a pristine Archean terrane which exclusively hosts Nd-model ages> 2.6 Ga, indicating that there are three
crustal stacking levels in the northern section. </p> <p> Nd-model age mapping was employed in the Mattawa klippe region with the
same objectives as in the northern section and additionally to provide constraints on the
methodology that is to be used when mapping first-order tectonic boundaries such as the
ABT. Ketchum and Davidson (2000) suggested that the ABT trended northward in this
region based on the presence of 1.16 Ga coronitic metagabbros which Ketchum (1994)
concluded were exclusively confined to the allochthonous polycyclic belt (APB). It was
detennined here that although the metagabbros are confined to allochthonous crust, based
on Nd-model ages, they are contained within an allochthonous klippe (Mattawa klippe)
overlying the reworked Archean parautochthon, that transported the coronitic
metagabbros northwestward. Therefore, this klippe represents an erosional remnant ofthe
APB but the main ABT is located further south. </p> Nd-model age mapping in the southern region identified three distinct crustal
terranes. The Mattawa fault was detennined to be a brittle fault following approximately
along a pre-Grenvillian suture. This separates the reworked Archean parautochthon from
the Paleoproterozoic parautochthon, which had a Nd-model age range from 1.8-1.9 Ga
The Paleoproterozoic parautochthon was found to be truncated by the main body of the
APB, containing Nd-model ages < 1.8 Ga. The boundary between the Paleoproterozoic
parautochthon and the APB was interpreted as the location of the main ABT. </p> <p> Based on the distnbution of Nd-model ages in the region, four distinct crustal
terranes were identified representing two thrusting events. Initially the ABT was
overthrust on the parautochthonous belt causing decollement of the reworked Archean
parautochthon. The entrainment of the reworked Archean parautochthon under the APB
generated a duplex thrust sheet, which resulted in the consequent northwestward thrusting
of the reworked Archean parautochthon over the pristine Archean terrane. Finally, the
ABT was offset by post-Grenvillian normal faulting associated with Ottawa-Bonnechere
graben. </p> / Thesis / Master of Science (MSc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/19355 |
| Date | 04 1900 |
| Creators | Herrell, Michael |
| Contributors | Dickin, Alan, Geology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
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