<p> The Grenville Province represents the remains of a collisional orogeny ca. 1.2 -
1.0 Ga and contains the Central Metasedimentary Belt (CMB). Generally thought to
represent one or more accreted island arcs, the CMB is located between belts of highgrade
gneisses and contains a number of identified structural terranes. Neodymium (Nd)
model ages of the high-grade gneisses on either side of the CMB yield similar values
(~1.5 Ga) while the average model age within the CMB is usually more juvenile (<1.3
Ga). This distinction, along with observations about the geometrical shape of the juvenile
zone, has led to the creation of an alternative model for the development of the CMB in
the Grenville Province as developed by Dickin and McNutt, (2007). The new model
equates the CMB with an ensimatic rift zone with an en echelon morphology consisting
of a series of segments with NNE trends, separated by one or more horsts of older crustal
rock. The development of the CMB under these conditions implies that restricted access
to seawater may have facilitated limestone deposition prior to major biogenic influences,
and thus the morphology of the rift is defined in part by the extent of the Grenville
marble outcrops. </p> <p> The present study tests this model through the use of 80 new Nd isotope analyses to map the NW boundary of the CMB, known as the Central Metasedimentary Belt
Boundary Zone (CMBBZ), west of Bancroft, Ontario. Within this part of the CMBBZ,
the age boundary between pre-Grenvillian and juvenile gneisses is relatively sharp (1 - 4
km wide) and this age boundary makes a near 90-degree tum from a NNE trend near
Minden to an E-W trend near Haliburton. Two blocks of older material are located within
the juvenile terranes of the CMB, which are interpreted as being blocks of older crust
rifted from the walls of the older Muskoka domain to the north of the study region. These
structures are analogous to similar horsts of older crustal material found in the Afar
region of East Africa. Therefore, we suggest that the locus of the CMBBZ was
constrained by older structures, representing a transition from the side of a rift zone
segment south of Minden, to the truncated end of this rift segment between Haliburton
and Bancroft. Hence, the detailed structure of the CMBBZ in this region provides further
evidence in support of the rift zone model. </p> / Thesis / Master of Science (MSc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/21635 |
| Date | 08 1900 |
| Creators | Moretton, Katherine |
| Contributors | Dickin, Alan, Geology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
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