Petrogenesis of the Wathaman batholith and La Ronge domain plutons in the Reindeer Lake area, Trans-Hudson Orogen, Saskatchewan

MacHattie, Trevor George (2001) Petrogenesis of the Wathaman batholith and La Ronge domain plutons in the Reindeer Lake area, Trans-Hudson Orogen, Saskatchewan. Masters thesis, Memorial University of Newfoundland.

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Abstract

The Paleoproterozoic Wathaman Batholith forms a major part of the Trans Hudson Orogen in northern Saskatchewan and Manitoba. On Reindeer Lake in Saskatchewan the batholith is 125 km wide and may continue for 800-900 km along strike. The size is comparable to Phanerozoic batholiths associated with destructive continental margins. The plutonism took place over a relatively short time interval, between 1865 and 1850 Ma. -- The batholith and satellite intrusions have been divided into 3 major zones based on modal, geochemical and Nd isotopic composition, from south to north these are the: La Ronge Domain (LRD); South Central (SCZ); and North East (NEZ). The LRD hosts satellite intrusions that are mainly metaluminous, calc-alkaline tonalites and granodiorites. εNd(t) in this zone ranges from +4.8 to -0.4. The SCZ is composed of two distinct series, a K-feldspar megacrystic granodiorite and a monzogranite series. The granodioritic series range in εNd(t) from -2.3 to -5.4; whilst the monzogranite series are characterized by εNd(t) +0.2 to -0.4. These rocks are all of high-K calc-alkaline affinity. The NEZ is composed of a K-feldspar megacrystic monzogranite and a monzonitic series, both of shoshonitic affinity. The monzogranites rocks have εNd(t) of -1.4 to -6.9, while the monzonites have εNd(t) of -0.3 to -4. -- The Wathaman Batholith had been interpreted as the root of a continental arc but was enigmatic in that it lacked co-magmatic mafic phases and was considered too homogeneous, too felsic, and too megacrystic, i.e., more like post-collisional granitoids. This study has resolved many of the uncertainties in the origin of this batholith. There is a greater diversity of rock types than previously described, and good field evidence for mingling of mafic and felsic magmas. Within a series εNd(t) is independent of rock type, and both the SC and NE zones rocks are characterized by high Sr and Ba. The petrogenesis of the batholith can be explained by mixing between 3 end-members: Archean crust; Proterozoic supra-subduction zone depleted mantle; and a late Archean enriched lithospheric mantle. Relative contributions from end-members change from south to north, with a major role for depleted, subduction zone affected mantle in the LRD; enriched mantle in the SCZ; and enriched mantle + crust in the NEZ. The batholith is interpreted to have formed in a subduction zone setting where mixing was dominantiy occurring in the asthenosphere and at the crust-mantle boundary. Upper level contamination processes can only be clearly seen in the NEZ.

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