Geochemical Character of the Tonalite-Trondhjemite Suite of the Tonalite-Migmatite Complex, Deception Lake, Saskatchewan I

Chris T. Coolican 1, Kevin M Ansde/1 2

, Rob Kerrich 1, and Mel Stauffer 1

Coolican, C.T., Ansdell , K.M., Kerrich, R .. and Stauffer, M. (2000): Gcm:hemical character of the tonal ite-trondhjemitc suite of the Tonalite-Migmatite Complex, Deception Lake, Saskatchewan; in Summary of Investigations 2000, Volume 2. Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 2000-4.2.

Abstract Deception lake straddles the boundary between the Wathaman Batholith and the Tonalite-Migmatite Complex in the Trans-Hudson Orogen. The focus of the geochemical study is the tonalite-trondhjemite suite of the Tonalite-Migmatite Complex. At outcrop scale, cross-cutting relationships indicate that multiple tonalite phases have been emplaced which both pre­and posr-date the Wathaman Batholith. Although similarities in mineralogy hinder correlation of individual tonalite phases beyond the outcrop scale, it is possible to subdivide them on geochemical characteristics.

Geochemical characteristics of the tonalite­trondhjemite suite include high Al contents ( 14.1 to 18.3 wt %}, high Sr (397 to 782 ppm), very low Rb/Sr ratio (0.029 to 0.092), low Y (< 15.47 ppm), negat ive Nb anomaly, LREE enrichment.fractionated HREE, and slight negative or positive Eu anomaly. Based on differences in the magnitude of REE fractionation and Eu, Nh, Sr, and Ti anomalies.four groups oftonalite have been distinguished Overall, these geochemical characteristics are typical of high-A l tonalite­trondhjemite-granodiorite suites, characteristic of Archean granitic gneiss terrains. They are interpreted to have crystallized from magmas derived from melting of subducted oceanic crust.

1. Introduction

The fonnation of the Trans-Hudson Orogen (THO) is a result of collisions between the Superior, Sask, and Hearne cratons and juvenile terrains of the Reindeer Zone (Chiarenzelli et al. , 1996; Lewry and Collerson, 1990). Collisional processes occurring between the northern margin of the THO and the Archean Hearne craton are poorly understood, and therefore more geological work is needed to unravel the history of this part of the Orogen. The relationships within the rocks comprising the Tonalite-Migmatite Complex (TMC) and the Wathaman Batholith (WB) are crucial to interpreting the northern margin of the THO.

Previous geochemical work by Clarke and Hendry ( 1993, 1994, 1995) in the Davin Lake area of the Tonalite-Migmatite Complex was undertaken to

understand the origin and emplacement of granitoids in the Davin Lake Complex of the Tonalite-Migmatite Complex. Their data was interpreted to indicate that the pink and white granites were derived from metasedimentary and metavolcanic sources respectively, and that they were emplaced in a suture zone along the southeast margin of the Wathaman Batholith. In contrast, Lewry et al. ( 1981) suggested that the contact is a defonned intrusive relationship. This project was initiated to improve the understanding of the Tonalite-Migmatite Complex by mapping a transect across the contact between the Wathaman Batholith and the Tonalite-Migmatite Complex at Deception Lake. Using the structural constraints, geochemical analysis of the granitoid rocks will provide significant information about the origin and evolution of the TMC.

This report will discuss preliminary results from samples collected at Deception Lake in the summer of I 999 (Coolican et al. , 1999).

2. General Geology Deception Lake, in the northwest margin of the Trans­Hudson Orogen, straddles the boundary between the Wathaman Batholith and the Tonalite-Migmatite Complex (Figure 1 ). The TMC consists of a migmatitic supracrustal sequence that has been intruded by a tonalitic to trondhjemitic intrusive suite. The contact between the WB and the TMC is marked by a zone of mainly granodioritic intrusions with increasing pegmatitic and aplitic dikes towards the WB. The WB comprises mainly porphyritic monzogranite to granodiorite that crosscuts all the other intrusive rocks, representing the youngest intrusive unit recognized.

Two ductile deformational events were d istingu ished. Early mig matization and deformation of the supracrustal rocks was followed by intrusion of the tona lite-trondhjem ite suite and occurred during D1• The dom inant regional fabric, S 1, strikes southwest­northcast and dips northwest, and is axial planar to minor F I folds. An Sc foliation strikes slightly oblique to S 1 and has a shallow westward dip. F2 folds, the dominant folds, are isoclinal to tight, recumbent to near recumbent with hinge lines trending north-northwest to

I Funded by NS ERC LITHOPROBE Special Studies Gram; LITHOPRO BE Publication # 1196. 2 Department of Geological Sciences, University of Saskatchewan, 11 4 Science Place, Saskatoon. SK S7N 5E2.

86 Summa,y of Investigations 2()()(), Volume 2

~

Wathaman Batholith granitoids

( ~) Transition Zone granitoids

Tonalite-Migmatite Complex

f.Z) Tonalite

C) Migmatitic Supracrustals

@°iI) Sample Location

Figure I - Simplified geological tnJJP of the eastern Deception Lake area showing the locations of Jithogeochemical .famples (cellter of ellip.~e).

north-northeast, and shallow northwest dipping axial planes. D~ fabrics continued to form during the intrusion of the WB, which acquired weak to intense S2 foliation. Upper amphibolite grade metamorphic conditions were attained during 0 1 as indicated by the homblende-plagioclase assemblage in mafic volcanogen ic units, and fo lded (F 1) in situ tonalitic leucosomes in the supracrustal units. Tonalitic leucosomc folded by F1, also indicates it was generated prior to the intrusion of the WB at ca. 1865 Ma (Ray and Wanless, 1980; Van Schmus et al. , 1987; Bickford et al. , 1990; Meyer et al. , 1992). In addition, fol iated amphibolite xenolith s within the WB indicate that a cons iderable pre-Wathaman deformational event occurred.

3. Petrology of Intrusive Phases

a) Tonalite-Migmatite Complex

The earliest intrusive phases within the study area are the tonalite-trondhjemite suite of the TMC. At outcrop scale, three phases can be distinguished by intrusive

Saskatchewan Geological Survey

relationships; these are highlighted by variations in defonnational fabric or grain size (Coolican et al., 1999). Generally, the older tonalite-trondhjemite phases have a more intense S 1 foliat ion and smaller grain size (Figure 2), and the youngest phase is pegmatitic tonalite. However, at outcrops with only one tonalite phase, identification of the specific phase is impossible because of the similar lithologies of the tonalite intrusives . This also makes it difficult to extend individual phases beyond outcrop scale, and therefore it is likely that more than three tonal ite phases are present in the study area. Geochemically, the tonalites have been subdivided into four groups based on their trace element compositions, as discussed in the Geochemistry section.

Due to the similar lithologies of the tonalite intrusives, the following petrographic description is relative to all the tonalite phases. The tonalites are composed of quartz (20 to 35%), plag ioclase (An25•35 ; 45 to 65%), microcline (<5%), biotite (5 to 20%), and muscovite (<2%); with accessory zircon, apatite and magnetite. Alteration of plag ioclase to sericite varies between samples and ranges from sl ight alteration along grain

87

Figure 2 - Intensely foliated tonalite crosscut by a massive, coarser grained phase.

boundaries to pervas ive throughout the crystal. Plagioclase grains are generally subhedral with well­developed twin planes, and commonly contain inclusions of quartz, biot ite, and accessory minera ls. Some grains are fractured or bent, and grain size ranges up to 4 mm, with some samples coarser grained than others. Quartz grains are anhedral, commonly fractured, and 0 . 1 to 2 mm wide. Microcline is generally anhedral to subhedral, and occurs e ither as grains up to 3 mm wide with inclusions o r as myrmekit ic intergrowths with quartz. Biotite commonly has a strong paralle l orientation and may show a second oblique c leavage; however, random orientation a lso occurs. Biotite crystals are generally less than 2 mm in size; fine-grained muscovite is along gra in boundaries of some samples.

b) Tonalite-Migmatitc Complex-Wathaman Batholith Contact Zone

At the contact between the TMC and the WB is a zone up to I km wide in which there are a variety of intrusive phases ranging from tonalitic to granodioritic in composition . These intrusions are non-porphyritic, weakly foliated, and crosscut the strong ly fo liated tonalite-trondhjem ite suite of the TMC.

The granodiorites from the contact zone are composed of quartz (20 to 30%), plagioclase (An 2o.io 45 to 55%), microcline ( 15 to 25%), and bioti te ( IO to 15%); accessory phases include zircon, apatite, and/or magnetite. The rocks are hypidiomorph ic granular, with alteration of plagioclase to sericite common, as is some degree of gra in fracturing and warping o f twin lamellae. Quartz and plagioclase grains are up to 5 mm wide, but I to 3 mm is common. Microcline occurs as small interstitial grains and/or larger gra ins up to 2 mm wide, commonly with plagioclase and b iotitc inclus ions. Biotite occurs in flakes up to 3 mm long, and exhibit e ither a moderate para llel orientation or are randomly oriented.

c) Wathaman Batholith

The Wathaman Batholith comprises massive to strongly foliated granodiorite to monzogranite. The rocks are most commonly porphyrit ic with randomly

88

oriented microcline phenocrysts up to 5 cm long; locally the phenocrysts exhibit a weak flow alignment. Homblende-biotite-rich mafic xenoliths are most common, but pe litic to psammopelitic and tonalitic xenoliths a lso occur.

The g ranodiorites in the Wathaman Batho lith a re composed of quartz (20 to 30%), plagioclase (An2q 0

20 to 30%), microcl ine (35 to 45 %), biotite (5 to 15%), and muscovite (up to 2%); accessory minerals inc lude zircon, apatite, magnetite , and chlorite . Microcline varies from tine interstitia l grains to phenocrysts several centimetres lo ng that commonly have inclus ions of plagioclase. biotite. and/or magnetite. Carlsbad twinning is common, as is microperthite. Plagioclase grains a re 0.5 to 3 mm long, and com monly a ltered to sericite a long gra in boundaries and fractures. Paralle l orientation of biotitc is well developed. Biotite gra ins arc 0.2 to 2 mm long, and commonly have pleochroic haloes; rarely, muscovite occurs as intergrown microcrystalline flakes wi th biotite or a long grain boundaries.

4 . Geochemistry

A total of 44 whole rock samples were crushed and ground in agate, and analysed for majo r elements together with Rb, Sr, Y. Zr, N b, and Ba using X-ray fluorescence spectrometry (XRF) at X-ray Assay Laboratories (Don Mills, Ontario). Twenty of these samples were then analysed at the University of Saskatchewan using inductively coupled plasma emission mass spectrometry (lCP- MS) to obtain a complete set of trace elem ent data including high field strength e lement (HFSE) and rare earth element (REE) data.

Samples from the TMC and TMC-WB contact zone were initially selected given that the fie ld relationships w ere most c learly understood. The remaining samples were selected to assure good geographic coverage of the study area, and on the basis of sample quality. Representat ive samples from the WB were collected and analysed to allow local comparison with the samples fro m the TMC and TMC-WB contact zone (Table I).

The geochemistry of the Wathaman Batholith is well documented (Fumerton et al., 1984; Halden et al .. 1990; Meyer el al., 1992), and therefore the fo llowing geochemica l discussion will focus on the tonalite­trondhjem ite suite of the TMC.

a) Major Element Geochemistry

As suggested by its name, the dominant rock type w ithin the T MC is tonalite; and trondhjemite is subordinate, although granodiorite intrusives occur in the WB-TMC contact zone. The dominantly tonalitic nature of the intrusives is illustrated on the normative Ab-An-O r ternary diagram (Figure 3) by a cluste r of samples w ithin the tonali te fiel d; this also demonstrates the similarity of the various tonali te phases within the

Summary of Investigations 2000. f'olume 2

Table I - Geochemical data of reprew11tative sample.5from the Deception Lake area. TMC. Samples from the WB plot with in the granite field, clearly separated from rocks of the TMC. Samples Wl3 WU-T MC TMCGp I TMC (ip 2 TMC Gp 3 TMC Gp 4

027 320

S i0 2 (wt'Y.,j 72.5 69.l Ti01 0 .296 0.261 Al10 1 14. 1 15.8 Fe 20 , 2.29 332 MnO 0.03 0 .05 MgO 0.66 us Cao 1.63 3.49 f-20 3.54 1.62 NaiO 4 . 15 4 .29 P,Oi O. l 0 .09 LOI 0.75 0.7 Sum 100.3 100.2

Rb (ppm) 99.87 15.08 Sr 4 12.42 399.92 Cs 0.7 0.47 Ba l 133.9 63638 Sc 5.44 8.22 v 20.6 34.84 Ta 0.42 0.35 Nh 10. 16 5.08 Zr 228.02 61.84 I Ir 6.59 3.24 Th 23 02 2.76 L 1.87 0.39 y 12.36 5.11 La 58. 76 5.56 l'c 10753 22.86 Pr 11.66 1.6 Nd 39.95 6.55 Sm 6.41 1.68 Eu 0.78 0.46 <id 4.79 1.57 Tb 0.55 0 .23 Dy 2.93 1.49 Ho 0.45 0.28 Fr I 0.75 Tm 0.13 0.12 Yb 0. 74 0.7 Lu 0. 11 0.09 J\ote:

223 294A

73.S 68.8 0 .13 1 0.284

14.6 16.2 1.27 2.93 0 0.02 0.48 1.22 2 .8 3.53 2.3 1 1.65 4.18 4.87 0.04 0.07 0 .6 06

100.3 100.3

14.59 14. 34 505 .65 425.86

0.43 0.42 2678.23 519

175 4. 18 15.89 36 O.l 0.29 3.22 8

37.79 85 1.74 2 .69

14.51 6 07 0 .66 0.4 1 3 .24 4

42. 11 18 70 114 .7 38.62

11.36 4.2 1 42.24 15.7

7 06 2.75 lJ 0.85 4.96 2.07 0.39 0.22 15 0.98 0 .19 0. 16 0.28 ()J 7 003 0.04 012 0.26 0.02 0.04

189A 1898

70.9 0.252

15.4 2.05 0.0 1 0.88 3 .73 1.1 6 4.49 0.09 11

100.3

24.77 73 1.92

0.4 716.68

2 .86 22.93

O I 3.59

54.35 1.71 0.33 0 .15 3.77 6.32

l l .05 1.26 4.99 0 .97 0.95 0.97 (Jl I 0 .6 1 0 .12 0.32 0.04 0.25 0.03

63 .7 0 .376

I 8.3 3.02 0 .03 l.33 4 .76 1.63 5.21 0 .42 1.45

100.4

32.99 782.72

0.61 847.81

5.85 37. l

0.25 7.86

47.68 2.5 0.87 0.42

15.47 10.3 24.32

2.99 13.73 3.6 I. I 3.73 0.53 3. 15 0.6 1.53 0.19 I.OS 0.12

Selected e lements for the granitoids from the TMC and WB are p lotted on Harker d iagrams (F igure 4). Tonalite samples contain a narrow range of Si02

between 65 to 75 wt %, and display a negative linear relationship with Al20,, MgO, Cao, Na,O, and TiO,. The K,0-SiO, tren-d demonstrates an -extremely narrow range of K20 in the TMC ranging from 1.5 to 2 wt %. WB monzogranites have a range of SiO, contents from 70 to 75 wt%, and can be d ist ingu ished from the tonalites by their higher K20 , and lower CaO and Na20 concentrations. Overall, the various phases of tonalite intrusions exhibit very similar major e lement composi tions.

b) T race Element Geochemis try

Ra re Earth Elements

WB. Wath.iman Batholith and WB-TMC. Watham.in Baihnlith--Tonalitc-Migmatitc Complex contact w nc .

Chondrite normalized REE patterns for the tonal ite­trondhjemite rocks of the TMC are coherent with enriched LREE. fractionated and depleted HREE, · and only slight negative or posit ive Eu anomalies. Although there are general similarities, there a re d istinct differences in the magnitude of fractionation

Anorthite

O Wathaman Batholilh A WB-Ti\lC contact zone ~ Tl\lC - Group I X TMC - Group 2 • TMC - Group 3 O TMC - Group 4 + T:\-IC - Uncertain phase

Albite Ort hocl ase Figure 3 -Ab-A 11-0r plot. Su btlivi.~ion of the TMC is based 011 trace element character, see Truce Element Geochemistry section 4b. Fields-· A, tcmalite; B, gru,rodiorite: C. atlamellite; D, tromll,jemite; and£, granite. Fields accortlillg to Barker (1979).

Saskatchewan Geological Survey

and anomalies which may be sign ificant in understanding the

origin of the gran itoids. These differences, along with field relationsh ips where possible, have been used to subdiv ide the tonalite-trondhjem ites into four groups (Figure 5).

Group l tonalites exh ibit the strongest LREE enrichment ((La/Yb),;= 105 to 265), and h ighest (Gd/Yb)" ratios (IO to 34). with slight to pronounced negat ive Eu anomalies. In add it ion, Group I tonalites have higher LREE abundances than the other groups. Group 2 tonalites have moderate LREE enrichment ((La/Yb)t,; = 50to 105),(Gd/Yb)Nvalues from6 to 15 and s lightly negative to sl ightly posit ive Eu anomalies. LR EE abundances of Group 2 are less than Group I, and higher than Group 3. Group 3 tonalitcs are less fract ionated than Group I and 2 tonalites ((La/Yb)r-; = 18 to 52; (Gd/Yb)" = 3 to 6) and all have strong positive Eu an om al ies relative to the other groups. Group 4 tonalites are the least fractionated ((La/Yb}r; =

7 to 10; (Gd/Yb)" = 3 to 4), have only sl ight negative

89

2 0

•

12

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Oo x

0

<>x

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.. +"-Jr;* +• ~-0111

1§1

+ 1t,! J'i • + + l- +),:

++ 111

0

0 0 0

fJ 00

+ 4 ... +

++-Mio + ·~·~

+

+

+

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. 5

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5

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o_ "' z

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0

x 00

0 0 x

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t-i>zt ... t .. ~· . ib·. +

t +

... +

X;+_.&t } ... , . . + +"" .. +

+ +of + 0 0

0

+ +. ,. a

... 0 'n";.&.) + • ... .1111 . ..

The four tonalite/trondhjemite groups were also plotted on primitive mantle normalized multi-element plots (Figure 7). As with the REE plots, the four groups generally have similc1 r patterns, incl uding: (I) fractionated pattern ; (2) weak to strong negative Nb, P, and Ti anomalies; and (3 ) re latively enriched Rb, Ba. K, and Sr.

Overall, Group I tonalites have elevated Ba and Th, and stronger negat ive Nb, P, and T i relative to the other three groups. Groups 3 and 4 have depleted Th contents relative to Groups I and 2, and distinct negative Th anomalies.

0 60 70 75 10 ,o 65 70 '' 80

Figure 8 shows multi-element plots for the TMC-WB contact zone and the Wathaman Batholith. These patterns are generally sim ilar to those of the TMC, displaying a negative slope, negative Nb, P and Ti anomalies, and similar e lement abundances. Th and U systemat ics are simila r to those in Groups I and 2 tonalites . Granodiorites from the TMC- WB contact zone have lower abundances in comparison to g ranodiorites from the WB.

SiO, (wt%) SiO, (wt%)

Figure 4 - Harker dit,grams for selected major elements. Symbol.r as in Figure 3.

or positive Eu anomalies and higher HREE abundances than the other groups.

As previously mentioned, three phases oftonalite were distinguished in the field, however, geochemical ana lysis ofpegmatitic tonalite, the youngest of the three phases, was not attempted due to difficulty in achieving sample homogeneity. The relative ages of the four geochemical groups can partia lly be determined based on field evidence. Intrusive relationships indicate that Group 3 tonalite is older than Group 4 , unfortunately samples comprising Group I and Group 2 are from outcrops with only one tonalite phase, and therefore the ir relative age is uncerta in .

The REE plots of two granodiorites from the TMC-WB contact zone are displayed in Figure 6a. Sample 320 has a comparatively unfractionated pattern ((La/Yb)N = 5.7) re lative to sample 478 ((La/Yb)" = 92), a lthough both samples display LREE enrichment and only slig htly negative Eu anomalies.

Figure 6b also demonstrates the REE patterns of porphyritic granodiorite from the Watharnan Batholith . The two samples have similar frac tionation trends ((La/Yb)r-; = 47 to 57) and abundances, and both samples have negative Eu anomalies.

9()

c) Petrogenetic and Tectonic Implications of Tonalitesffrondhjemites

Classification

Granito id rocks in this study have relatively high Na20 (Na:z0>3.6 ; see Figure 3). metaluminous to slightly peraluminous character (Al-saturation index 0.95 to 1.05), and < 1% normat ive corundum. These characte rist ics are typica l of I-type granitoids as defined by Chappe ll and White ( 1974) and Chappell and Stephens ( 1988).

Further, sam~les from the TMC d isp lay featu res typical of Archean high-Al trondhjemite-tonalite-dacite (TTD) (Drummond and Defant, 1990; Drummond e t al. . 1996) and TTG (trondhjemite-tona lite-granodiorite) (Martin. 1986, 1993) suites, including high A l contents ( 14. 1 to 18.3 wt %), high Sr(397 to 782 ppm), very low Rb/Sr ratio (0 .029 to 0 .092), LREE enrichment ((La/Yb):-,, cc 7 to 265) with slight Eu anomal ies, low Y (< 15.47 ppm) and negative Nb anomalies.

Granitoid Source and Petrogenetic Processes

The high Al content in the tonalite-trondhjemite su ite may have resulted from the removal of hornblende

Summary of lnwslif<al ions 2000. I ·olitme 2

1000

Group One -- JOMA

f---'-"-..~:::...::°"s:-- - - - - - - -----j·-160C - 1600 --- 223 - S42

0.1 -~ - - - - - - --- -- - - ··-- - -1000

100 --·---------t ;~Tw1 .. ~ --·-- -~-_j

'~~

·- ---- -~

JO

OIL·------- -- --~ ---- ------- -

L=~===:---=::~:-=-~ -------·----10 I __________ -~ -"----~-:~-~=--- ·-------·----==-

----- .... -----........ --.. T- ----- ----- ----o.1L _ _ _____ _ _ __ _ ___ _ _ __ __ _

La Cc P, Nd Sm Eu Gd Tb Dy llo Er 1·m Yb Lu

Figure 5 - Chondrite normalized REE plots for tonalitesltrondhjemites of the TMC.

from the melt either as a residual phase at the source, or as a fractionation product (Barker and Arth, 1976; Barker, 1979). Further, the metaluminous to slightly peraluminous character of these rocks indicates that hornblende is unlike ly to be the only refractory phase left at the source, because a basaltic parent with an exclusively homblendic refractory residue would form strongly peraluminous magmas (Holloway and Burnham, 1972; Drummond and Defant, 1990).

Saskatchewan Geological Survey

The REE plots (Figure 5) and multi-element plots (Figure 7) clearly display the geochemical signature of melts derived from oceanic crust and provide constraints on source material. Key features displayed by REE plots (Figures 5 and 7) include REE fractionation, HREE depletion, and no to minor positive or negative Eu anomalies. The enriched LREE character can be explained through partial melting of a basaltic source leaving a refractory phase assemblage with various proportions of clinopyroxene, hornblende, and garnet (Arth and Hanson, 1975; Gromet and Silver, I 987; Defant et al., 1988). The lack of a strong negative Eu anomaly may imply that little feldspar was retained at the site of partial melting, or separated from the melt via crystal fractionation. Although to a lesser extent, refractory garnet, hornblende, and pyroxene have the opposite effect of plagioclase. The combined effects result in the weak Eu anomalies in Groups l , 2, and 4, and the minor positive Eu anomaly in Group 3.

Refractory garnet can also explain the high Sr/Y ratio. Sr behaves incompatibly during high-pressure partial melting of basalt due to the instability of plagioclase; therefore, it will become concentrated in the melt (Drummond et al., 1996). Conversely, Y is strongly compatible with garnet and therefore is controlled by the presence of garnet in the residue. The combined effect of Sr concentration in the melt and Y concentration in the refractory garnet results in the high SrN ratio.

Multi-element plots (Figure 7) show clear negative Nb and Ti anomalies for all the tonalite/trondhjemites. Drummond and Defant ( I 990) postulate that retention of hornblende at the site of partial melting could account for these negative anomalies because of its strong affinity for Nb and Ti in siliceous melts. Hornblende exclu sion from the melt may also be the cause of the low to moderate K/Rb ratios because of

2 ·.::: "O

! 0.IL __ - -- - -- ·-- -------- ~ 1:000

1 -- --- . .... __ ratha~ao~/3atholith) "' 100 \ - • , • -----1 ·•- 009A l

Cl'J I ' - - ----~::::::::~ ./· ... ·-.,._ ______ - - ---- ---

10 1- - ---- -- . ""-.. -----------=--- . - -· I I-.. ____ -- -------------~ ::~::_-:

0 1 i --- - · - ----- -- - - - - - ·-L, Cc r, Nd Sm l:.u Gd Th l)y llo f r Tm Yb Lu

Figure 6 - Cho11drite normalized REE plots for the TMC­WB contact z.one and Wathaman Batholith.

9/

~ i: .. ~ .. > .:: ·s ' i: 1:1...

" Q. E .. en

10

I·---

Group a;;~ -108A J.

_____;__, ... _ :: ::; __

0.1 '----- --- - - - ---'----- ---

100

10001

100

10

GrnupT,;,J -- 294A

_ _ _ __ _,-- 652 -ij28

- - - --·--· ·-·· · ·---- --···· ·-·

· [Group Tl rcc . - OISA

- 189A - -- ----- - ~ 227

- 662 ' - 680A

~ 7408

·~1 . . . . . . j<:'~~~ Fou,l

]i·t 0~~-L··~--v--- '-.. 11·- ·-··-- ·- ---. ·. - -~

o.1L .. _ _ .. __ ___ ~ - ·- ---- .. _ __ _ o ~•n u Km u~ ~ ~P ITT b~h TITo ~Y n

Figure 7 - Primitive mantle normalized multi-element plots for tonalites/trondhjemites of the TMC. Normalizing values after Sun and McDonough (1989).

the preference of hornblende to accommodate K relative to Rb (Arth and Hanson, 1975).

Tectonic Implications

The tonalite-trondhjemite rocks of the TMC are I-type granitoids, and have a trace element profile

92

characteristic of arc environments. They display very similar characteristics to high-Al TTD granitoids that are interpreted to crystallize from magmas derived by melting of subducted oceanic crust, resulting in a hornblende eclogite residue. This conclusion has implications for the model for the tectonic evolution of the northwestern margin of the THO. Further refinement of this model will come with a better understanding of absolute age relationships.

5. Summary

I) In the Deception Lake area, the earliest intrusive phase in the Tonalite-Migmatite Complex is the tonalite-trondhjemite suite. At outcrop scale, three phases oftonalite were identified, however, the similarity of these phases make it difficult to correlate them across the area.

2) Chondrite nonnalized REE patterns for the tonalite-trondhjemite rocks of the TMC are coherent, with enriched LREE, fractionated HREE, and only slightly negative or positive Eu anomalies. These intrusive rocks were subdivided into four chemical groups based on distinct differences in magnitude of fractionation and anomalies displayed in their trace element geochemical patterns.

3) The tonalite-trondhjemite rocks of the TMC display very similar characteristics to high-Al TID/TTG described by Martin (l 986, 1993), Drummond and Defant ( 1990), and Drummond er

.. .. ·= 0.1

' WB-TMC.contact .zone( · +- 320

:§ 1000 i r:~an Bath~lithj

~ 1001---+-+-"--~ ~ ~ -

~ ~£~~:- ··- ·· I

'" ~--, ..... !· -·- · · - .. __ ~ ~ ;-

OIL ___ ___ , .. ~ .. ---·--- ·-~ C:• Rb Bo Th lJ K " b I.a Cc St Nd r Hf Zr Sin Eu Ti Th Dy Y Yb

Figure 8 - Primitive mantle normalized multi-element ptors for TMC-WB contact zone. Normalizing values after Sun and McDonough (/989).

Summary of Investigations 2000, Volume 2

al. . ( 1996 ). The rocks were formed in an arc environment, and are interpreted to have . crystallized from magmas derived by meltmg of subducted oceanic crust.

6. Acknowledgments

The project was funded by an NSERC LIT':IO~R(?BE Special Studies Grant. 1:hanks are due _to Q ianh Xie for assistance with preparation and analys ts of . . . geochemical sa1'!1plcs, an.ct ~ Jaine Novakovsk1 for thm section preparation. Log1st1cal support for field work from the Geolog ical Survey of Canada and . Saskatchewan Energy and Mines, and th~ assistance o f David Corrigan and Bill Slimmon in particular was oreatly appreciated. Thanks to Erm Chorney for her ~aluable field assistance throughout the summe~. I ~lso thank Charlie Harper and Gary Delaney for review mg the manuscr ipt.

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93

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94 Summary of Investigations 2000, l 'o/11me 2