Paleomagnetism of the Davin Lake Granitoids, Rottenstone Domain, Trans-Hudson Orogen (part of NTS 640-12 and -13) 1 D. T.A. Symons 2, S.P. Radigan 2 , and M. T. Lewchuk 2 Symons, D.T.A., Radigan, S.P., and Lewchuk, M.T. (1996): Paleomagnetism of the Davin Lake Granitoids, Rottenstone Domain, Trans-Hudson Orogen (part of NTS 640·12 and ·13); in Summary of Investigations 1996, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 96-4. Paleomagnetic analysis of specimens from 22 sites in the Paleoproterozoic Davin Lake Granitoids in the Rottenstone Domain isolates one stable characteristic remanence direction that gives a pole position of 93°W, 54°N (dp=9°, dm=9°, N=21). This result indicates that the Rottenstone Domain was in a polar paleolatitude at - 1850 Ma, and separated from the Wathaman Batholith on its northwest side by the -5000 km wide Manikewan Ocean, so that this contact now marks the locati on of the main subduction-zone suture in the Trans-Hudson Orogen. Many geologists have concluded that the Archean Slave-Rae-Hearne (SRH) Craton (Figure 1) closed against the Superior Craton during the Paleoproterozoic in a transpressive, Himalayan-type orogeny to form the intervening Trans-Hudson Orogen (THO) (e.g. Gibb, 1983; Lewry, 1981 ; Stauffer, 1984; Gr een et al., 1985; Hoffman, 1988). Dunsmore and Symons (1990) showed that available paleomagnetic data, mainly from the cratons, fit such a model remarkably well. Since then, LITHOPROBE, Canada's program for research into the lower crust, has sponsored paleomagnetic studies of rock units in the THO. This research has shown that the - 1855 Ma Wathaman Batholith on the northwest side of the Rottenstone Domain was formed beside the SRH Craton in subtropical paleolatitudes (Symons, 1991 ) and that the - 1849 Ma Macoun Lake Pluton in the Lynn Lake-La Ron ge Domain on its southeast side was emplaced relatively close to the Superior Craton in polar paleolatitudes (Symons et al ., 1994). The purpose of this paleomagnetic study of the Davin La ke Granitoids was to locate the relative position of its host Rottenstone Domain at - 1855 Ma. This paper provides the details of the paleomagnetic methods and results, and a brief overview of the geote ctonic implications of the results. 1. Geology The Rottenstone Domain extends northeastwards from beneath Phanerozoic cover in central Saskatchewan and then eastwards through northern Manitoba as the South Indian Domain (Figure 1 ). Along its northwestern side is the 1855 ±6 Ma Wathaman Batholith, a -900 km long, Paleoproterozoic arc that formed along the SRH cratonic margin (Fumerton et al., 1984; Symons. 1991 ; Meyer et al., 1992). To the southeast, across th e Birch Rapids Shear Zone, is the Lynn lake-La Ronge Domain and other mainly juvenile, arc-related domains of the Paleoproterozoic THO across to the Superior Craton (Bickford et al. , 1990). The oldest rocks of the Rottenstone Domain in the study area are gneisses derived from psammitic to pelitic protoliths (Lewry et al., 1980; Johnston, 1985). They were injected by leucotonalite and trondjemite migmatites and metamorphosed to mid to upper amphi- bolite grade, as at sample sites 21 and 22. Coeval or younger, white and pink granitoids were emplaced next. The white granitoids correspond to the Davin Lake Complex of Lewry et al . (1980). They include medium- grained l eucotonalite-trondj emite gneisses. typically massive, coarse trondjemite and massive trondjemi te pegmatite from a dominantly metavolcanic protolith (Clarke and Henry, 1995). The pink granitoids corre- spond mostly to the generally massive, pink granite migmatites to massive pink pegmatites of Unit 9 of Lewry et al. (1980) that were derived from a dominantly metasedimentary protolith (Clarke and Henry, 1995). Lewry et al. (1980) consider the pink granitoids to be younger intrusions into white granitoids whereas Clarke and Henry (1995) consider them to be in fault contact . Furth er, Lewry et al. (1980) believe that the grano- diorites of the 1855 Ma Wathaman Batholith intruded the white granitoids, based on regional mapping and petrologic observations. In contrast, Clarke and Henry (1994, 1995) believe that the two units are simply in fault contact, from their more detailed mapping, petro- logic, and geochemical studies. The youngest rock in the study area is a <15 m thick, soft, jointed di abase dike that trends north-south and is poorly exposed. It predates north-south block faulting. The age of th e granitoids is in doubt. Bickford et al . (1986), using U-Pb zircon geochronology, determined an age of 1867 ±8 Ma for "coreless" zircons from a white granitoid (Figure 1 ). Zircons with visible cores and abraided zircon cores gave ages of 1885 ±15 and 1922 ±24 Ma, respecti vely, indicati ng that older rocks were remobilized to form these rocks. They also determined an age of 1867 ±8 Ma tor "corel ess" zircons from a pink granitoid. From their data, it is evident that the 1867 Ma ages may re fle ct inheritance, giving an older age than (1) Funding for th is project was provided by an NSERC LITHOPROBE re search grant ; LI THOPROBE publication number 8 15. (2) Department of Earth Sciences, Unive rsity of Windsor, Windsor. ON N98 3P4. Saskatchewan Geological Survey 111
Transcript
Paleomagnetism of the Davin Lake Granitoids, Rottenstone Domain, Trans-Hudson Orogen (part of NTS 640-12 and -13) 1
D. T.A. Symons 2, S.P. Radigan 2, and M. T. Lewchuk 2
Symons, D.T.A., Radigan, S.P., and Lewchuk, M.T. (1996): Paleomagnetism of the Davin Lake Granitoids, Rottenstone Domain, Trans-Hudson Orogen (part of NTS 640·12 and ·13); in Summary of Investigations 1996, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 96-4.
Paleomagnetic analysis of specimens from 22 sites in the Paleoproterozoic Davin Lake Granitoids in the Rottenstone Domain isolates one stable characteristic remanence direction that gives a pole position of 93°W, 54°N (dp=9°, dm=9°, N=21). This result indicates that the Rottenstone Domain was in a polar paleolatitude at - 1850 Ma, and separated from the Wathaman Batholith on its northwest side by the -5000 km wide Manikewan Ocean, so that this contact now marks the location of the main subduction-zone suture in the Trans-Hudson Orogen.
Many geologists have concluded that the Archean Slave-Rae-Hearne (SRH) Craton (Figure 1) closed against the Superior Craton during the Paleoproterozoic in a transpressive, Himalayan-type orogeny to form the intervening Trans-Hudson Orogen (THO) (e.g. Gibb, 1983; Lewry, 1981 ; Stauffer, 1984; Green et al., 1985; Hoffman, 1988). Dunsmore and Symons (1990) showed that available paleomagnetic data, mainly from the cratons, fit such a model remarkably well. Since then , LITHOPROBE, Canada's program for research into the lower crust , has sponsored paleomagnetic studies of rock units in the THO. This research has shown that the - 1855 Ma Wathaman Batholith on the northwest side of the Rottenstone Domain was formed beside the SRH Craton in subtropical paleolatitudes (Symons, 1991 ) and that the - 1849 Ma Macoun Lake Pluton in the Lynn Lake-La Ronge Domain on its southeast side was emplaced relatively close to the Superior Craton in polar paleolatitudes (Symons et al., 1994). The purpose of this paleomagnetic study of the Davin Lake Granitoids was to locate the relative position of its host Rottenstone Domain at - 1855 Ma. This paper provides the details of the paleomagnetic methods and results, and a brief overview of the geotectonic implications of the results.
1. Geology
The Rottenstone Domain extends northeastwards from beneath Phanerozoic cover in central Saskatchewan and then eastwards through northern Manitoba as the South Indian Domain (Figure 1 ). Along its northwestern side is the 1855 ±6 Ma Wathaman Batholith, a -900 km long, Paleoproterozoic arc that formed along the SRH cratonic margin (Fumerton et al., 1984; Symons. 1991 ;
Meyer et al., 1992). To the southeast, across the Birch Rapids Shear Zone, is the Lynn lake-La Ronge Domain and other mainly juvenile , arc-related domains of the Paleoproterozoic THO across to the Superior Craton (Bickford et al. , 1990).
The oldest rocks of the Rottenstone Domain in the study area are gneisses derived from psammitic to pelitic protoliths (Lewry et al., 1980; Johnston, 1985). They were injected by leucotonalite and trondjemite migmatites and metamorphosed to mid to upper amphibolite grade, as at sample sites 21 and 22. Coeval or younger, white and pink granitoids were emplaced next. The white granitoids correspond to the Davin Lake Complex of Lewry et al. (1980). They include mediumgrained leucotonalite-trondjemite gneisses. typically massive, coarse trondjemite and massive trondjemite pegmatite from a dominantly metavolcanic protolith (Clarke and Henry, 1995). The pink granitoids correspond mostly to the generally massive, pink granite migmatites to massive pink pegmatites of Unit 9 of Lewry et al. (1980) that were derived from a dominantly metasedimentary protolith (Clarke and Henry, 1995). Lewry et al. (1980) consider the pink granitoids to be younger intrusions into white granitoids whereas Clarke and Henry (1995) consider them to be in fault contact . Further, Lewry et al. (1980) believe that the granodiorites of the 1855 Ma Wathaman Batholith intruded the white granitoids, based on regional mapping and petrologic observations. In contrast, Clarke and Henry (1994, 1995) believe that the two units are simply in fault contact, from their more detailed mapping, petrologic, and geochemical studies. The youngest rock in the study area is a <15 m thick, soft, jointed diabase dike that trends north-south and is poorly exposed. It predates north-south block faulting.
The age of the granitoids is in doubt. Bickford et al. (1986), using U-Pb zircon geochronology, determined an age of 1867 ±8 Ma for "coreless" zircons from a white granitoid (Figure 1 ). Zircons with visible cores and abraided zircon cores gave ages of 1885 ±15 and 1922 ±24 Ma, respectively, indicating that older rocks were remobilized to form these rocks. They also determined an age of 1867 ±8 Ma tor "coreless" zircons from a pink granitoid. From their data, it is evident that the 1867 Ma ages may re flect inheritance, giving an older age than
(1) Funding for this project was provided by an NSERC LITHOPROBE research grant; LITHOPROBE publication number 8 15. (2) Department of Earth Sciences, University of Windsor, Windsor. ON N98 3P4.
Figure 1 - Location map showing major tectonic elements and site locations wi th geology from Lewry et al. (1980) and Johnston (1985); BRSZ, Birch Rapids shear zone; C-SBZ. Churchill-Superior boundary zone; and HB, Hanson Lake Block.
112 Summary of Investigations 1996
reality, if the "coreless" zircons do in fact have cores that are not visible. This possibility is consistent with a Rb-Sr isochron age of 1801 ±25 Ma determined by Clarke and Henry (1995) using samples from both the white and pink granitoids. In addition Meyer et al. (1992) have summarized the U-Pb zircon data for the Wathaman Batholith, and they range from 1865 to 1850 Ma near the study area with an average of 1855 ±6 Ma.
2. Experimental Methods
The Davin Lake area was sampled at nine sites in white granitoids, 11 in pink granitoids and two in adjacent migmatite (Figure 1 ). Four or five cores, oriented by sun compass, were drilled at each site and then sliced to give two or three specimens, yielding 196 specimens in all (Table 1 ). Each specimen's natural remanent magnetization (NRM) was measured with an automated CTF-cryogenic magnetometer inside a shielded room . Next its low-field susceptibility was measured, showing nearly half the specimens contained pyrrhotite (Stupavsky and Symons, 1992). Two specimens per site were alternating field (AF) demagnet-
Table 1 - Site mean remanence directions.
Number o f Site, Specimens Unit u d g e N R D"
1, p 0 0 0 7 7 0 208.9
2, W 0 0 0 9 9 0 244.8
3, W 0 0 0 9 9 0 277.2
4,W 0 0 5 4 1 187.5
5, W 3 1 0 3 3 0 36.5
6, W 0 0 0 11 11 0 187.6
7, W 1 1 0 7 6 181.6
8, p 0 2 0 6 5 323.8
9, p 2 0 0 5 3 2 49.7
10, P 0 0 2 2 2 2 1.3
11, P 0 0 0 9 9 0 60.5
12, P 0 0 0 14 14 0 82.1
13, P 0 0 4 4 0 151 .9
14, P 0 0 9 9 0 29.7
15, P 0 2 0 6 3 3 320.3
16, P 0 0 6 6 0 16.7
17, P 1 3 0 5 5 0 133.5
18, W 0 0 4 8 9 3 131.8
19, W 0 0 2 8 10 0 274.3
20, W 0 0 0 13 13 0 110.6
21, M 0 0 0 7 7 0 85. l
22, M 0 0 8 8 0 148.2
Notes:
ized in 12 steps to 120 mT, and two more thermally demagnetized in 12 or 15 steps to 600° or 690°C. The remaining specimens were AF and/or thermally demagnetized, mostly in 20 mT steps above 20 mT or in 20° to 30°C increments above 500°C to define their characteristic remanent magnetizations (ChRM). Specimens with evident pyrrhotite were AF step demagnetized and then thermally demagnetized at 280° and 320°C. Saturation isothermal remanent magnetization (SIAM) tests were run on 12 typical specimens of various lithologies to better characterize their magnetic mineralogy by pulse magnetizing them in eight steps to 900 mT and then AF demagnetizing them in five step to 50 mT. ChRM directions were defined using visual vector component plots (Zijderveld, 1967) and the principal component method of Kirschvink (1980). Their means were calculated using Fisher (1953) statistics.
3. Results
White granitoid specimens have weak NAM intensities that are mostly in the 10·4 Alm range whereas pink granitoid specimens are variable, ranging from 10-4 to 1 oo Alm, but both react similarly to demagnetization.
Mean Demagnetizing Direction Range
1· Cl95 0 k mT ·c
70.3 15.9 15.4 10-120 325-500
54.2 7.8 44.8 20-120 280-550
76.1 4.7 120.2 20- 120 275-500
85.0 21.9 13.1 20- 120 275-350
81. 1 15.8 61.7 20-120 275-565
79.3 8.5 29.7 20- 120 272-565
78.7 14.9 17.4 20-60 325-500
82.3 8.4 64.0 20-100 200·550
70.1 8.8 76.8 20-120 200-565
84.5 9.8 89.8 20-30 200-565
76.5 9.0 33.4 20-80 200-580
77.2 5. 1 62. 1 20-120 200-600
80.9 17.2 29.5 20-120
85.7 5.7 81 .6 20-120 200-600
87.0 11.0 38. 1 20-120 275-580
77.6 7.2 88.9 20-60 200-565
64.0 17.0 21.1 20-80 200-565
85.2 13.5 11.3 20-40 200-320
87.7 14.1 12.7 20-120 300-600
86.4 6.4 43.0 20-120 200-525
79.5 10.1 36.8 20-120 300-550
76.6 14.3 16.0 20-50 450-525
Units: M. migmatite; P, pink granitoid; and W, white granitoid. Specimens: u, unstable; d, divergent endpoint; g, used remagnetiza-tion great-circle ; e, used endpoint; N , used normal-polarity vector; and R, used reversed-polarity vector. Vector: 0 °, declination, degrees; 1°, inclination, degrees; cx95 °, radius of 95 percent confidence, degrees; and k, precision parameter (Fisher, 1953); Range: mT, alternating-field coercivity, millitesla; and °C. unblocking temperature, degrees Celcius.
Saskatchewan Geological Survey 113
Typically a viscous remanence , directed steeply down to the north, is removed between the NAM and 20 mT or 250°C steps that appears to record the present Earth's magnetic field direction. On AF demagnetization, the ChRM is typically defined over a broad coercivity range from 20 mT up to >100 mT, isolating both steeply down or up directions in all rock types (Figure 2). Thermal demagnetization shows that this ChRM is unblocked in the diagnostic pyrrhotite range from 250° to 320°C and/or magnetite range from 500° to 585°C (Figure 3). Consistent ChRM directions were not found in the hematite range from 600° to 675°C, perhaps recording the conversion of iron from sulphide to oxide form in the oven. SIAM testing shows rapid acquisition curves typical of magnetite, slower curves typical of pyrrhotite, and one curve typical of hematite, and demagnetization curves indicative of single domain, pseudosingle domain, and multidomain behaviour with some contrasts between rock types (Figure 4). Nearly all specimens retain ChRM endpoint vectors with mean angular deviation values of <<15° (Kirschvink, 1980), with few deviating from its site population (Table 1 ). In a few cases, remagnetization circles were also used to determine a site mean. Individual sites are reasonably well clustered with an average radius of 95% confidence (ag5) of 10.4°.
4. Statistical Analysis
The removed vector was determined for 53 normal and nine reversed polarity specimens in the pyrrhotite temperature range, and tor 32 normal and seven reversed specimens in the magnetite temperature range. Their mean directions and dispersions are indistinguishable at the 95% confidence level (Table 2; McElhinny, 1964; McFadden and Lowes, 1981). This implies that both minerals acquired their ChRM at the same time, implying rapid cooling through both unblocking temperature ranges in a few million years.
When the site mean ChRM directions are plotted (Figure Sa), it is evident that site 2 is deviant. It is excluded from further discussion. The F test of McElhinny (1964) shows that the white and pink granitoid populations have dispersions that are different at the 95% confidence level, giving a k ratio of 2.57 that exceeds the comparison statistic of 2.22. Using the dissimilar dispersion test of McFadden and Lowes (1981), the observed statistic of 0.0980 is very much less than the 95% confidence statistic of 0.1927. Thus both can be drawn from a single population and, therefore, can be validly combined (Figure 5b). The two migmatite site mean directions fall within this population, and so are included also (Figure Sa, Table 2). The fact that white and pink granitoids yield the same ChRM direction indicates that : 1) they are coeval, implying the Ch RM is primary and 2) no differential tilt has occurred between them, implying that the granitoid terrane has behaved as a single tectonic block.
Well-defined, antiparallel reversed directions are found at three white granitoid and three pink granitoid sites (Figures 2c, 3e and d; Table 1 ). This suggests that cooling of the Davin Lake Granitoids took a sufficiently long
114
. -·-· ---- --·----·-----··-·-"·----
a W,U
0.8
NRM
E. D
b W, U
E. D
c N, U
0.8
S,O
FigCJre 2 - Orthogonal alternating field step demagnetization diagrams for example specimens from sites 14(a), 20(b), and 9(c) with natural remanent magnetization intensities (Jo) of 282, 3.92 and 40.9 x t0-3 Alm, respecti vely. Cirdes and triangles show projections on the horizontal (N, £, S, W) and vertical (U, D) planes, respectively. The axial CJnit is the Jo valCJe. Treatment steps are shown in mi/lites/a.
period of time , probably ~5 Ma, to record at least one reversal of the Earth's magnetic field which, in tum, is additional evidence that the granitoids retain a primary ChRM. The pole position for the Davin Lake Granitoids is located at 93.2°W, 54.0°N (dp=9.3°, dm::9.3°, N=21) (Figure 6) .
5. Discussion
The Davin Lake Granitoids were emplaced when the Rottenstone Domain was located at a high to polar paleolatitude (Figure 6). Its pole is similar to coeval poles from rock units to the southeast, including the - 1850 Ma Baldock Batholith in the South Indian Domain, the 1849 Ma Macoun Lake Pluton of the Lynn Lake-La Ronge Domain, the 1844 Ma Hanson Lake Pluton in the Hanson Lake Block, and the 1851 Ma Reynard Lake Pluton of the Flin Flon Domain in the THO, and the 1850 Ma Sudbury Irruptive Complex in the Superior Craton (Morris, 1984; Gala et al. , 1994; Symons et aL, 1994; Symons, 1995; Symons et al., 1996). Thus these terranes were within - 2000 km of each other at - 1855 Ma. In contrast, coeval poles from rock units in terranes to the northwest give subtropical paleolatitudes, including the bounding 1855 Ma Wathaman Batholith , gabbros in the pericratonic Peter Lake Domain, and the - 1860 Ma average of five poles for the SRH Craton (Symons, 1991, 1994). To accommodate the difference between the pole positions, the Manikewan Ocean must have been about 5000 km wide between the Rottenstone Domain and the Watha man Batholith , and the contact between them must represent a major geotectonic boundary.
This boundary, or Manikewan suture, is deemed to be the site of subduction of most of the Manikewan Ocean basin and to have a significant, sin istral, strike-slip
SCJmmary of Investigations 1996
a W. U
275
0.8
NRM E. D
b w.u
E. D
525
350
275
c N, U
0.8
NRM S. D
:·OLP .M. :·Ocs.M. ~-Ou Jo Jo Jo
0 0 0 O T 600 0 T 600 0 T 600
e f w.u N, U
N
E, D S, D
d W, U
E,D
~-0~.M. Jo
0 O T 600
g W, U
E,D
~-O~ M
Jo
0
~-O~ M Jo
0
:_·Ocs:M Jl
0 O T 600 O T 600 O T 600
Figure 3 - Orthogonal thermal step demagnetization diagrams for example specimens from sites 4 (a), 6 (b), 12 (c), 21 (d), 16 (e), 9 (f), and 15 (g) with Jo values of 0.523, 0.733, 1.36, 2 1.2, 191, 97.2. and 95.5 x 1Cf3 Alm, respectively. Conventions as in Figure 2 except some treatment steps shown in degrees Celsius. The plots in the middle show the change in the J/Jo ratio as a function of temperature (T) wi th bars showing the diagnostic unblocking temperature range for pyrrhotite (P) and magnetite (M) where the ratio drops more rapidly.
Saskatchewan Geological Survey 115
1.0
J J900
0.5
0.0
0
1.0
0
1.0
3
6 19
0.5 9
white 20 granitoids
\MD ........ 18
.......... -0.0 300
Hdc 600 900 0
Hat 50
1.0
pink granitoids 8 and migmatites
300 H 600 de
900 0 50
Figure 4 · Saturation isothermal remanent magnetization (S/RM) curves for representative specimens identified by site number, showing direct fie ld (DC) acquisition up to 900 mT and subsequent alternating field (AF) demagnetization. Shown are typical curves for single, pseudosingle, and multidomain magnetite (SD, PSD, MD) and for coarse- and fine-grained hematite (CH, FH).
Table 2 - Unit mean remanence directions.
Number of Mean Direction Unit Spec. Sites oo 10 <Xg50 k
Notes: 1) 53 normal and 19 reversed polarity specimens; 2) 32 normal and 7 reversed polarity specimens; 3) deviant site 2 excluded; 4) pole position: longitude, 93.2 °W; latitude 54.0°N; oval of 95 percent confidence, dp=9.3°, dm=9.3° (Fisher, 1953); other conventions as in Table 1.
116
component from transpressive oblique collision. Thus, our result supports Clarke and Henry {1995) who proposed that the Wathaman Balholith-Rottenstone Domain boundary is a fault contact. They also interpreted petrological observations and geochemical data, including major, trace and rare earth element analyses and strontium and neodymium isotopic analyses, to show that the boundary marks a subduction zone. Thomas (1992) has shown that there are significant changes in the aeromagnetic and gravity signatures at the boundary that are consistent with the presence of a suture. The reflection seismic data for LITHOPROBE line S2b along Provincial road 905 through the study area (Hajnal et al., 1995) show reflectors in the La Range and Rottenstone domains that dip under the Wathaman Batholith, fitting a northwesterly subduction model. Finally, the initial interpretation for magnetotelluric data acquired along line S2b by Ferguson and Jones (1995) show a dramatic contrast in resistivity as well as a northwest sense of dip for the Rottenstone and La Ronge domains under the batholith. The geotectonic analysis of the poles from within the THO on the southeastern side of the Manikewan suture is fess certain at this time. To bring the Davin Lake pole into agreement with the Macoun Lake Pluton's pole, for example, requires the Davin Lake Granitoids to be corrected for a 7° southeastdown tilt about a horizontal N35°E axis parallel to the trend of the Rottenstone and La Range domains (Figure 6). This correction swings the Davin Lake pole to an appropriate position near the 1849 Ma Macoun Lake pole. A southeastward tilt is suggested by the distribution of petrologic phases in the Davin Lake area, with higher-level granitic phases exposed on the southeastern side and lower-level granodioritic phases exposed on the northwestern side (Figure 1 ). A more likely alternative is that the Davin Lake Granitoids have not been tilted but rather that the Macoun Lake Pluton has been tilted to the northwest. Symons et al . (1994) cite several lines of evidence that favour this alternative. Also, the close agreement of the
Summary of Investigations 1996
0 0
+ +
+ + . 270 + + . • 1't .. :.
::. + + <® + + 90
+ • pink 01 allitoids • white gra11110,cts • migmatite ... overall mean
+
180
Figure 5 - Equal-area lower hemisphere stereograms showing: a) the site mean directions and b} the unit mean directions with their cones of 95% confidence.
Figure 6 - Plot of pole positions. Pole positions with subtropical paleolatitudes for the 1855 Ma Wathaman Batholith (WB), -1869 Ma gabbros of the Peter Lake domain (PD), and - 1855 Ma composite from six studies for the Archean S/ave-Rae-Heame craton (SRH) that contrast with poles with polar paleo/atitudes for the Davin Lake complex (DL) and - 1850 Ma Baldock Batholith (BB) of the Rottenstone--South Indian domain, 1850 Ma Reynard Lake pluton of the Flin Flan domain (RE), 1849 Ma Macoun Lake pluton of the La Range domain (MC), 1844 Ma Hanson Lake pluton of the Hanson Lake block (HB), and the 1850 Ma Sudbury Intrusive Complex of the Archean Superior craton (SI). The circular standard deviation limits are shown about the poles, and their references are cited in the text. The triangle shows the location of the Davin Lake's (DL) pole after correction for a l°SE tilt suggested by its petrologic phases. Alternatively, the Macoun Lake (MC) pole moves back beside the uncorrected DL pole if evidence for its NW tilt is true; SUP. Superior Craton; and THO, TransHudson Orogen.
Saskatchewan Geological Survey
Davin Lake pole with the apparently coeval Baldock Batholith pole from the same domain, suggests that neither pluton incorporates significant tilt and that the swing from a northeast-southwest trend to an east-west trend in the THO is a primary arc featu re on the southeastern side of the suture rather than a later deformation feature .
6. Conclusions
The main conclusion of this study is that the contact between the Wathaman Batholith and the Rottenstone Domain is the major structural feature in the THO. It is named the Manikewan suture and defines either side of an - 5000 km wide ocean at - 1855 Ma with closure thereafter. More detailed mapping, geochemical affinity testing, and radiometric age dating on either side of the suture are required to evaluate this hypothesis. It is unclear whether the Davin Lake Granitoids and host Rottenstone Domain should be considered a tilted terrane or translated terrane. These options need to be constrained by further paleomagnetic, geobarometric, and seismic work.
7. Acknowledgments
The authors thank: Wes Borowsky and the staff of Davin Lake Lodge for logistical help in the field and Brock Symons for specimen preparation.
8. References Bickford, M.E., Van Schmus, W.R., Macdonald, A., Lewry,
J.F .. and Pearson, J.G. (1986): U-Pb zircon geochronology project for the Trans-Hudson: Current sampling and recent results: in Summary of Investigations 1986, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 86-4, p101-107 .
Bickford , M.E., Collerson, K. D., Lewry, J.F., Van Schmus, W.R. , and Chiarenzelli, J.R. (1990): Proterozoic collision in the Trans-Hudson Orogen, Saskatchewan; Geol., v18, p14-18.
Clarke, D.S. and Henry, A.S. (1994): Petrochemical and structural evidence for the origin of granitoid rocks in the Rottenstone Domain; in Hajnal, Z. and Lewry, J. (eds.). LITHOPROBE, Trans-Hudson Orogen Transect, Rep. 38, p188-195.
----·- (1995): Petrogenetic and tecton ic significance of migmatites and granites in the Davin Lake area of the Rottenstone Domain; in Hajnal, Z. and Lewry, J. (eds.), LITHOPROBE, Trans-Hudson Orogen Transect, Rep. 48, p104·11 0.
Dunsmore, D.J. and Symons, D.T.A. (1990): Paleomagnetism of the Lynn Lake gabbros in the Trans-Hudson Orogen and closure of the Superior and Slave cratons; in Lewry. J.F. and Stauffer, M.A. (eds.), The Early Proterozoic TransHudson Orogen of North America, Geo!. Assoc. Can., Spec. Rep. 37, p215-228.
Ferguson, I. and Jones, A. (1995): Electromagnetic measurements on the Trans-Hudson Orogen transect: in Hajnal, Z. and Lewry, J. (eds.), LITHOPROBE, Trans-Hudson Orogen Transect. Rep. 48, pl 62-1 69.
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Fisher, A.A. (1953}: Dispersion on a sphere; Proc. Roy. Soc. London, Series A. v217, p295-305.
Fumerton, S.l., Stauffer, M.A., and Lewry, J.F. (1984): The Wathaman Batholith: Largest known Precambrian pluton; Can. J. Earth. Sci., v21, p1082·1097.
Gala, M.G .. Symons, D.T.A .. and Palmer, H.C. (1994): Paleomagnetism and geotectonic implications of the Hanson Lake Pluton, Hanson Lake Block, Trans-Hudson Orogen; in Summary of Investigations 1994, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 94-4, p116·122.
Green, A.G., Hajnal, Z., and Weber, W. (1985): An evolutionary model ot the western Churchill Province and western margin of the Superior Province in Canada and the northcentral United States; Tectonophysics. v16, p281-322.
Gibb, R. (1983): Model tor suturing the Superior and Churchill plates: An example of double indentation tectonics; Geol., v11, p413·417.
Hajnal, Z., White, D.J., and Lewry, J.F. (1995): 1994 reflection data acquisition program Trans-Hudson Orogen transect; In Ha)nal, Z. and Lewry, J. (eds.), LITHOPROBE, TransHudson Orogen Transect, Rep. 48, pl-14.
Hoffman, P.F. (1988): United plates of America, the birth of a craton, Early Proterozoic assembly and growth of Laurentia; Annu. Rev. Earth Planet. Sci., v16, p543-603.
Johnston . W.G.Q. (1985): Geology of the Wathaman Lake (east) area; Sask. Energy Mines. Open File Rep. 85·1, 65p.
Kirschvink, J.O. (1980): The least-squares line and plane and the analysis of paleomagnetic data; Geophys. J. Roy. Astr. Soc., v62, p699-718.
Lewry, J.F. (1981): Lower Proterozoic arc-microconlinent collisional tectonics in the western Churchill Province; Nature, v294, p69-72.
Lewry, J.F .. Curry, D., and Roberts, K. (1980): Geology of an area around Ghana Lake; Sask. Dep. Miner. Resour., Rep. 191, 29p.
McElhinny, M.W. (1964): Statistical significance of the fold test in palaeomagnetism; Geophys. J. Roy. Astr. Soc., vs. p338-340.
McFadden, P.L. and Lowes, F.J. (1981): The discrimination of mean directions drawn from Fisher distributions; Geophys. J. Roy. Astr. Soc., v67, p19-33.
118
Meyer, M.T., Bickford, M.E., and Lewry, J.F. (1992): The Wathaman Batholith: An Early Proterozoic continental arc in the Trans-Hudson orogenic belt, Canada; Geol. Soc. Amer. Bull ., v104, p1073·1 085.
Morris, W.A. (1984): Paleomagnetic constraints on the magnetic, tectonic, and metamorphic evolution of the Sudbury Basin region; Ont. Geol. Surv. , Spec. Vol. 1, p411-427.
Stauffer, M.R. (1984): Manikewan: An Early Proterozoic ocean in central Canada, its igneous history and orogenic closure; Precamb. Resear., v25, p257-281.
Stupavsky, M. and Symons, D.T.A. (1992): Predictive test ing for pyrrhotite in paleomagnetic specimens using magnetic susceptibility in 0.1-1.0 mT fields; EOS, v73, p98.
Symons, D.T.A. (1991 ): Paleomagnetism of the Proterozoic Wathaman Batholith and the suturing of the Trans-Hudson Orogen in Saskatchewan; Can. J. Earth Sci. , v28, p1931· 1938.
_ ____ (1994): Geotectonics of the Peter Lake Domain in the Proterozoic Trans-Hudson orogenic belt of Saskatchewan, Canada, from paleomagnetism; Precamb. Resear., v69, pl 1-24.
_ _ _ _ _ (1995): Paleomagnetism of the 1851 Ma Reynard Lake Pluton. Flin Flon Domain, Trans-Hudson Orogen: Geotectonic implications; in Summary of Investigations 1995, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 95-4, p137-144.
Symons. D.T.A., Lohnes. C.A., and Lewchuk, M.T. (1994): Geotectonlcs of the Lynn Lake-la Range arc in the TransHudson Orogen from paleomagnetism of the Paleoproterozoic Macou n Lake Pluton; in Summary of Investigations 1994, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 94-4, pl 23-131.
Symons, D.T.A .. Lewchuk, M.T., and Harris, M.J. (1996): Paleomagnetism of the Paleoproterozoic Baldock Batholith (NTS 648-14); Mani!. Energy Mines, Rep. of Activities 1996.
Thomas, M.D. (1992): Potential contributions of gravity and magnetic data analysis to the Trans-Hudson Orogen transect; in Hajnal, Z. and Lewry, J. (eds.). LITHOPROBE, Trans-Hudson Orogen Transect, Rep. 26, p73·74.
Zijderveld, D.A. {1967): A.C. demagnetization of rocks: Analysis of results; in Collinson, D.W., Creer, K.M., and Runcorn, S.K. (eds.), Methods in Paleomagnetism, Elsevier, Amsterdam, p254-286.
