Geochemical Character of the Tonalite-Trondhjemite Suite of the Tonalite-Migmatite Complex, Deception Lake, Saskatchewan I 1 2 1 1 Chris T. Coolican , Kevin M Ansde/1 , Rob Kerrich , and Mel Stauffer Coolican, C.T., Ansdell, K.M., Kerrich, R .. and Stauffer, M. (2000): Gcm:hemical character of the tonalite-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 understand the origin and emplacement of granitoids in the Davin Lake Complex of the Tonalite-Migmatite Deception lake straddles the boundary between the Complex. Their data was interpreted to indicate that Wathaman Batholith and the Tonalite-Migmatite the pink and white granites were derived from Complex in the Trans-Hudson Orogen. The focus ofth e metasedimentary and metavolcanic sources geochemical study is the tonalite-trondhjemite suite of respectively, and that they were emplaced in a suture the Tonalite-Migmatite Complex. At outcrop scale, zone along the southeast margin of the Wathaman cross-cutting relationships indicate that multiple Batholith. In contrast, Lewry et al. ( 1981) suggested tonalite phases have been emplaced which both pre­ that the contact is a defonned intrusive relationship. and posr-date the Wathaman Batholith. Although This project was initiated to improve the understanding similarities in mineralogy hinder correlation of of the Tonalite-Migmatite Complex by mapping a individual tonalite phases beyond the outcrop scale, it transect across the contact between the Wathaman is possible to subdivide them on geochemical Batholith and the Tonalite-Migmatite Complex at characteristics. Deception Lake. Using the structural constraints, geochemical analysis of the granitoid rocks will Geochemical characteristics ofthe tonalite­ provide significant information about th e origin and trondhjemite suite include high Al contents ( 14.1 to evolution of the TMC. 18.3 wt %}, high Sr (397 to 782 ppm), very low Rb/Sr ratio (0.029 to 0.092), low Y (< 15.47 ppm), negative This report will discuss preliminary results from Nb anomaly, LREE enrichment.fractionated HREE, samples collected at Deception Lake in the summer of and slight negative or positive Eu anomaly. Based on I 999 (Coolican et al. , 1999). 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 ofh igh-Al tonalite­ 2. General Geology trondhjemite-granodiorite suites, characteristic of Deception Lake, in the northwest margin of the Trans­ Archean granitic gneiss terrains. They are interpreted Hudson Orogen, straddles the boundary between the to have crystallized from magmas derived from melting Wathaman Batholith and the Tonalite-Migmatite ofs ubducted oceanic crust. Complex (Figure 1). The TMC consists of a migmatitic supracrustal sequence that has been intruded by a tonalitic to trondhjemitic intrusive suite. The contact 1. Introduction between the WB and the TMC is marked by a zone of mainly granodioritic intrusions with increasing The fonnation of the Trans-Hudson Orogen (THO) is a pegmatitic and aplitic dikes towards the WB. The WB result of collisions between the Superior, Sask, and comprises mainly porphyritic monzogranite to Hearne cratons and juvenile terrains of the Reindeer granodiorite that crosscuts all the other intrusive rocks, Zone (Chiarenzelli et al. , 1996; Lewry and Collerson, representing the youngest intrusive unit recogni zed. 1990). Collisional processes occurring between the northern margin of the THO and the Archean Hearne Two ductile deformational events were distinguished. craton are poorly understood, and therefore more Early migmatization and deformation of the geological work is needed to unravel the history of this supracrustal rocks was followed by intrusion of the part of the Orogen. The relationships within the rocks tonalite-trondhjem ite suite and occurred during D1• The comprising the Tonalite-Migmatite Complex (TMC) dominant regional fabric, S 1, strikes southwest­ and the Wathaman Batholith (WB) are crucial to northcast and dips northwest, and is axial planar to interpreting the northern margin of the THO. minor F I folds. An Sc foliation strikes slightly oblique to S 1 and has a shallow westward dip. F2 fo lds, the Previous geochemical work by Clarke and Hendry dominant folds, are isoclinal to ti ght, recumbent to near ( 1993, 1994, 1995) in the Davin Lake area of the recumbent with hinge lines trending north-northwest to Tonalite-Migmatite Complex was undertaken 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 ofJith ogeochemical .famples (cellter of ellip.~e). north-northeast, and shallow northwest dipping axial relationships; these are highlighted by variations in planes. D~ fabrics continued to form during the defonnational fabric or grain size (Coolican et al., intrusion of the WB, which acquired weak to intense S2 1999). Generally, the older tonalite-trondhjemite foliation. Upper amphibolite grade metamorphic phases have a more intense S 1 foliation and smaller conditions were attained during 0 1 as indicated by the grain size (Figure 2), and the youngest phase is homblende-plagioclase assemblage in mafic pegmatitic tonalite. However, at outcrops with only volcanogen ic units, and folded (F 1) in situ tonalitic one tonalite phase, identification of the specific phase leucosomes in the supracrustal units. Tonalitic is impossible because of the similar lithologies of the leucosomc fo lded by F1, also indicates it was generated tonalite intrusives . This also makes it difficult to prior to the intrusion of the WB at ca. 1865 Ma (Ray extend individual phases beyond outcrop scale, and and Wanless, 1980; Van Schmus et al. , 1987; Bickford therefore it is li kely that more than three tonalite et al. , 1990; Meyer et al. , 1992). In addition, fol iated phases are present in the study area. Geochemically, amphibolite xenolith s within the WB indicate that a the tonalites have been subdivided into four groups considerable pre-Wathaman deformational event based on their trace element compositions, as discussed occurred. in the Geochemistry section. Due to the similar lithologies of the tonalite intrusives, 3. Petrology of Intrusive Phases the following petrographic description is relative to all the tonalite phases. The tonalites are composed of a) Tonalite-Migmatite Complex qu artz (20 to 35%), plagioclase (An25•35 ; 45 to 65%), microcline (<5%), biotite (5 to 20%), and muscovite The earliest intrusive phases within the study area are (<2%); with accessory zircon, apatite and magnetite. the tonalite-trondhjemite suite of the TMC. At outcrop Alteration of plagioclase to sericite varies between scale, three phases can be distinguished by intrusive samples and ranges from slight alteration along grain Saskatchewan Geological Survey 87 oriented microcline phenocrysts up to 5 cm long; locally the phenocrysts exhibit a weak fl ow alignment. Homblende-biotite-rich mafic xenoliths are most common, but pelitic to psammopelitic and tonalitic xenoliths also occur. The g ranodiorites in the Wathaman Batholith are composed of quartz (20 to 30%), plagioclase (An2q 0 20 to 30%), microcline (35 to 45 %), biotite (5 to 15%), and muscovite (up to 2%); accessory minerals include zircon, apatite, magnetite, and chlorite. Microcline varies from tine interstitia l grains to phenocrysts several centimetres lo ng th at commonly have inclus ions of plagioclase. biotite. and/or magnetite. Carlsbad twinning is common, as is Figure 2 - Intensely foliated tonalite crosscut by a massive, microperthite. Plagioclase grains are 0.5 to 3 mm long, coarser grained phase. and commonly altered to sericite along grain boundaries and fractures. Parallel orientation of biotitc boundaries to pervas ive throughout the crystal. is well developed. Biotite grains arc 0.2 to 2 mm long, Plagioclase grains are generally subhedral with well­ and commonly have pleochroic haloes; rarely, developed twin planes, and commonly contain muscovite occurs as intergrown microcrystalline fl akes inclusions of quartz, biotite, and accessory minerals. with biotite or along grain boundaries. Some grain s are fractured or bent, and grain size ranges up to 4 mm, with some samples coarser grained th an others. Quartz grains are anhedral, commonly 4. Geochemistry fractured, and 0.1 to 2 mm wide. Microcline is generally anhedral to subhedral, and occurs either as A total of 44 whole rock samples were crushed and grains up to 3 mm wide with inclusions o r as ground in agate, and analysed for majo r elements myrmekitic intergrowths with quartz. Biotite together with Rb, Sr, Y. Zr, N b, and Ba using X-ray commonly has a strong parallel orientation and may fluorescence spectrometry (XRF) at X-ray Assay show a second oblique cleavage; however, random Laboratories (Don Mills, Ontario). Twenty of these orientation also occurs. Biotite crystals are generally samples were th en analysed at the University of less than