1

CHAPTER 3: RESULTS

3.1SITE 1

Four samples from this site were stepwise AF demagnetized (see location map, Figure 5) and Kirschvink analysis was performed on the acquired data. Of the four samples analyzed, only samples 4.6.00-1a1 and 4.6.00-2a2 had lines of best fit that did not significantly bypass the origin. The remanence carried by sample 4.6.00-5a3 was quite unstable, indicated by significant scattering in the data, and no useable direction could be obtained. The results of the Kirschvink analysis for Site 1 are tabulated in Table 2. The error column gives the maximum angular deviation (MAD).

Samples 26.8.99-3 to 10, analyzed by Caines (2000), were collected from Site 7 near Site 1 (see Figure 5). These samples are now thought to be from the west limb of a small anticline whose east limb yielded the Site 1 samples 4.6.00-1 to 5. Unfortunately, the strike and dip of Site 7 is uncertain, hence the samples collected from this site could not be used for this study.

Table 2Site 1 results for samples passing Kirschvink analysis

In-situ (degrees) / Tilt corrected (degrees) / Error
(degrees)
Sample / Declination / Inclination / Declination / Inclination
4.6.00-1a2 / 179.5 / 55.2 / 156.3 / 19.2 / 4.9
4.6.00-2a1 / 186.4 / 71.2 / 147.2 / 33.3 / 5.0

3.2SITE 2

Three samples from this site (Figure 5) were stepwise AF demagnetized and Kirschvink analysis was performed on the acquired data. All samples from this site yielded lines of best fit that did not significantly bypass the origin. Samples 4.6.00-7a1 and 4.6.00-9a1 both exhibited a stable remanence with separable high and low coercivity components. The presence of a curving trend on both Zijderveld and stereo plots for sample 4.6.00-10a1 indicates two components of remanence with overlapping coercivity spectra (Figure 8). The results from this site are tabulated in Table 3.

Table 3Site 2 results for samples passing Kirschvink analysis

In-situ (degrees) / Tilt corrected (degrees) / Error
(degrees)
Sample / Declination / Inclination / Declination / Inclination
4.6.00-7a1 / 190.7 / 58 / 183.4 / 38 / 7.7
4.6.00-9a1 / 151.9 / 80 / 163.3 / 59.4 / 11.4
4.6.00-10a1 / 87.6 / 86.8 / 160.2 / 68.2 / 2.2

3.3SITE 3

Five samples from this site (Figure 5) were stepwise AF demagnetized and Kirschvink analysis was performed on the acquired data. Of these five samples, 4.6.00-11a1, 4.6.00-12a2, and 4.6.00-14a1 had lines of best fit that did not significantly bypass the origin. The stability of the remanence carried by these samples was somewhat varied. Although sample 4.6.00-11a1 exhibited a significant amount of scatter, the low and high coercivity remanence components could be resolved. The remanence carried by sample 4.6.00-12a1 exhibited some instability at fields less than 200 Oe but became quite stable

at higher field strengths; only one directional component was clearly defined for this sample. Sample 4.6.00-14a1 exhibited very little scatter in its data and showed well defined low and high coercivity components. The results from this site are tabulated in Table 4.

Table 4Site 3 results for samples passing Kirschvink analysis

In-situ (degrees) / Tilt corrected (degrees) / Error
(degrees)
Sample / Declination / Inclination / Declination / Inclination
4.6.00-11a1 / 134.4 / 59.3 / 155.5 / 46.6 / 7.6
4.6.00-12a2 / 156.4 / 42.2 / 164.8 / 25.1 / 7.4
4.6.00-14a1 / 131 / 37.8 / 142.8 / 27.2 / 3.4

3.4SITE 4

Six samples from this site (Figure 5) were stepwise AF demagnetized and Kirschvink analysis was performed on the acquired data. From these six samples, only 5.6.00-1a1 and 5.6.00-6a had lines of best fit that did not significantly bypass the origin. The remanence for both samples appears very stable with a small soft component that was removed by fields of approximately 100 Oe. The remaining samples, 5.6.00-2a2, 5.6.00-3a4, 5.6.00-4a2, and 5.6.00-5a1, all exhibit a remarkably similar behavior during demagnetization. Their remanence is very stable, remains in a tight cluster at approximately the same location on all stereo plots, and doesn’t seem to demagnetize appreciably beyond fields of 250 Oe. It is likely that these samples contain a high coercivity mineral such as hematite that could not be fully demagnetized with the alternating fields used. There was a stable component for these samples from 100 Oe to

350 Oe, illustrated in Figure 9, which did not significantly bypass the origin except for sample 5.6.00-3a4. The results of the Kirschvink analysis from this site can be found in Table 5.

Table 5Site 4 results for samples passing Kirschvink analysis

In-situ (degrees) / Tilt Corrected (degrees) / Error
(degrees)
Sample / Declination / Inclination / Declination / Inclination
5.6.00-1a1 / 170.1 / 72.3 / 165.8 / 20 / 7.4
5.6.00-2a2 / 112.7 / 82.7 / 157.2 / 33.2 / 2.7
5.6.00-4a2 / 163.7 / 66.2 / 164.0 / 14.2 / 6.3
5.6.00-5a1 / 152.4 / 82.9 / 162.4 / 30.9 / 5.0
5.6.00-6a / 123.6 / 74.4 / 152.8 / 25.6 / 3.1

3.5SITE 5

Five samples from this site (Figure 5) were stepwise AF demagnetized and Kirschvink analysis was performed on the acquired data. All of these samples yielded lines of best fit that did not significantly bypass the origin. As well, all specimens from this site were almost completely demagnetized by fields of 500 Oe and exhibited a stable remanence with little directional scatter. As indicated by the presence of curving data trends on stereographic and Zijderveld plots, samples 5.6.00-8a1 and 5.6.00-10a1 appear to contain components with overlapping coercivity spectra. A summary of the results from this site can be found in Table 6.

Table 6Site 5 results for samples passing Kirschvink analysis

In-situ (degrees) / Tilt corrected (degrees) / Error
(degrees)
Sample / Inclination / Declination / Inclination / Declination
5.6.00-7a2 / 154.6 / 77.8 / 159.2 / 41.9 / 0.8
5.6.00-8a1 / 135.1 / 67.5 / 149.4 / 33 / 2
5.6.00-9a1 / 137.8 / 64.4 / 149.7 / 29.7 / 2.1
5.6.00-10a1 / 169.2 / 76.4 / 163.5 / 40.5 / 2.4
5.6.00-11a1 / 160.7 / 82.2 / 161 / 46.2 / 1.9

3.6SITE 6

Five samples from this site were stepwise AF demagnetized and Kirschvink analysis was performed on the acquired results. Again, all samples had lines of best fit that did not significantly bypass the origin with most samples being fully demagnetized by fields of 800 Oe. The observed remanence was slightly unstable, giving rise to some directional scatter. A summary of the results from this site can be found in Table 7.

Table 7Site 6 results for samples passing Kirschvink analysis

In-situ (degrees) / Tilt corrected (degrees) / Error
(degrees)
Sample / Declination / Inclination / Inclination / Declination
5.6.00-13a1 / 160.1 / 51.9 / 177.4 / 23.7 / 6.4
5.6.00-14a2 / 153.5 / 58.6 / 177.5 / 31.4 / 7
5.6.00-15a2 / 149.3 / 59.8 / 176.3 / 33.6 / 12.1
5.6.00-16a2 / 159.9 / 52.7 / 177.8 / 24.6 / 9.7
5.6.0017a / 151.1 / 51.9 / 172.2 / 26.5 / 8

3.7RESULTS FROM PREVIOUS WORK

A paleomagnetic study of two sites within the Lac Matapédia basalts was reported by Caines (2000). Data acquired from Site #1 of Caines’ report, near Site 7 of the current study, cannot be used for the reasons outlined in section 3.1. Site #2 of Caines’ report, identified as Site 8 of the current study, showed promising results in that five of the six samples from that site passed Kirschvink analysis. This data has been included in Table 8.

Table 8Site mean directions obtained using Fisher statistics

Site / Declination / Incliniation / 95 / k / N
1 / in-situ
tilt corrected / 182.0
152.0 / 63.2
26.3 / - / 49.7 / 2
2 / in-situ
tilt corrected / 176.7
172.1 / 76.6
55.7 / 26.8 / 22.5 / 3
3 / in-situ
tilt corrected / 141.0
147.8 / 47.0
43.9 / 23.1 / 29.4 / 3
4 / in-situ
tilt corrected / 150.4
160.6 / 76.6
24.9 / 8.7 / 78.0 / 5
5 / in-situ
tilt corrected / 147.0
156.1 / 74.1
38.4 / 8.1 / 90.7 / 5
6 / in-situ
tilt corrected / 152.9
175.7 / 56.1
29.5 / 4.4 / 308.4 / 5
8 / in-situ
tilt corrected / 130.8
138.7 / 65.8
22.3 / 13.4 / 33.6 / 5

3.8SITE MEAN REMANENCE DIRECTIONS

The characteristic remanence directions listed in tables 2 to 7 were averaged for each site using Fisher statistics. The mean inclination, declination, and statistical parameters, 95and k, for each site are listed in Table 8. Only sites 4, 5, 6, and 8 have 95less than 15. Data from other sites are considered too scattered to be reliable and will not be discussed further.

3.9RESULTS OF LASER ABLATION ICP-MS AGE DATING

The Lac Matapédia basalts sit within the St. Anne River Nappe, a transported terrane. The basalts are intercalated with sandstones and are thought to have formed on the margin of Laurentia. In order to test whether the sandstones are of Laurentian origin, a detrital zircon study was undertaken. Dr. Richard Cox collected zircons from a sandstone sample obtained from a unit interbedded with the Lac Matapédia basalt flows. Pb207-Pb206 age dating of these zircons yielded ages characteristic of Laurentia (Table 9)

Table 9Ages obtained from detrital zircons

Age (Ma) / 1 sigma / Source area
3031.7 / 70.1 / Superior/Nain Provinces
1175.5 / 21.9 / Grenville Province
1406.8 / 56.8 / Pinwarian Orogenesis
2872.8 / 30.3 / Superior Province
1354.3 / 13.6 / Nain Plutonic Suite
1374.4 / 37.2 / Nain Plutonic Suite
1488.9 / 29.1 / Pinwarian Orogenesis

Hence, the detritus that formed this sandstone unit likely was derived from Laurentia. As a result, the Lac Matapédia basalts likely formed on or near the Laurentian margin and the paleomagnetic results obtained from this study will be characteristic of Laurentia. Due to time constraints, it was not possible to obtain an age for the Lac Matapédia basalts.