<P> Detailed Nd isotopic mapping in the southwestern
Grenville Province between North Bay, Ontario, and
Temiscaming, Quebec has revealed the precise trend of the
proposed Penokean-aged suture discovered during reconnaissance
isotopic mapping by Dickin and McNutt (1989). </p> <p> Lithotectonic domains proposed by Easton (1989} for the
greater North Bay area are cross-cut by the suture. As
presently located, the Tilden-Tomiko domain boundary effects
no apparent offset of the suture which would be expected
during low angle differential Grenville thrusting. Although
a lack of apparent offset suggests these domains are not
significant Grenville structures a definitive answer must
await more precise mapping of their boundaries. There appears
to be some potential for unravelling aspects of Grenville
tectonism through such cross-cutting relationships. </p> <p> In the North Bay-Temiscaming area the full model age
transition from ca 1.90 Ga to ca 2.70 Ga is negotiated in
stepwise fashion through metasediments of intermediate Nd
model age spanning an area from a few kilometers to a few tens
of kilometers in width. This suggests the suture boundary is
better described as a suture zone. Presently two groups of
intermediate aged metasediments are recognized (1} a 2.00-2.39
Ga group and ( 2) a 2. 40-2.60 Ga group. These age groups correspond to rocks of two different lithologies separated
along strike of the suture in the Temiscaming and North Bay
areas respectively. Although the ages of metasediments
comprising the suture zone more or less spans the entire
interval between 1.90 and 2.70 Ga, there is no well defined
transect wherein the whole range of intermediate aged crust
is recorded within a single rock type. Therefore a
'splitting' rather than 'lumping' approach is deemed justified
for the intermediate aged crust until provenance studies
using zircons can be undertaken to show in a definitive manner
whether or not the two groups are related in a genetic sense. </p> <p> The absence of plutonism with crystallization ages
between 2.00 and 2.60 Ga in the North Bay-Temiscaming area
suggests that metasediments of the suture zone acquired their
model age from sedimentological mixing between crust of
Archean (ca 2.70 Ga) and Proterozoic (ca 1.90 Ga) provenance.
The arrangement of mixed provenance metasediments coincident
with the suture suggests a genetic relationship. It is
proposed that the mixed provenance metasediments are part of
a foreland basin assemblage which formed in response to downloading
of the cratonal edge by the combined effect of an
overriding island arc and the attempted subduction of the
Superior craton. </p> <p> Major element analyses show that mixed provenance and
arc derived sediments of the proposed foreland basin display
a wide range in their maturity. This is consistent with the foreland basin environment where sediments can be reworked to
varying degrees in response to tectonically controlled local
sea level fluctuations. Contrasting the dynamic environment
of the foreland basin the belt of Archean crust north of the
suture with model ages of ca 2.72 Ga shows a very restricted
range of reworking implying a uniform depositionary
environment e.g., deep water passive margin. </p> <p> North of the field area a lobe of Archean crust extends
into the Grenville Province, anchored by the Pontiac Group on
the northern margin of the Grenville Front (GF), and
consisting in part of the parautocthonous Red Cedar Lake
Gneiss south of the GF. The full expression of the Archean
lobe within the Grenville Province and north of the North Bay Temiscaming
field area is unknown, however, preliminary
results from Nd isotopic mapping suggest that Archean crust
between the suture and the Grenville Front Tectonic Zone
(GFTZ) may be part of, or, derived from this Archean
parautocthonous lobe. Archean provenance crust north of the
field area defines a relatively homogeneous belt of crust with
ca 2.72 Ga model ages and a whole rock Sm-Nd isochron age of
2.77 Ga. This is in sharp contrast to the heterogeneity of
model ages displayed by Archean crust further west, between
the suture (French River area) and the Grenville Front near
Sudbury, Ontario (Dickin et al., 1989). Here, the Archean
foreland may owe its peculiar heterogeneity to mixing between
2. 72 Ga crust and 2. 4 Ga Huronian volcanics andjor 1. 7 Ga Kilarnian juvenile crust (Dickin et al., 1990). Evidence for
the presence of these crustal endmembers in the North Bay Temiscaming
area is lacking. </p> <p> Finally, the presence of a suture zone consisting of
mixed provenance metasediments is the best evidence yet in
support of the suture hypothesis explanation for the model
age transition as opposed to juxtaposition of two crustal age
domains by Grenville thrusting. </p> / Thesis / Bachelor of Science (BSc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/19357 |
| Date | 04 1900 |
| Creators | Holmden, Christopher |
| Contributors | Dickin, A. P., Geology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
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