The Cree Lake Zone in the southwestern part of the Hearne craton, reworked during the Paleoproterozoic Trans-Hudson orogeny, includes the Wollaston Group, a sequence of Paleoproterozoic metasedimentary rocks. As these rocks have been multiply deformed and metamorphosed to high-grade, a geochemical and isotopic study was initiated to see through the overprinting events to better constrain the provenance and evolution of the Wollaston Group.The Wollaston Group consists of thick sedimentary successions representing different depositional and tectonic environments that can be subdivided into two subgroups. The Lower subgroup is represented by deep-water turbidite to shallow-water marine deposits. The Upper subgroup, separated from the Lower one by a regional unconformity, comprises molasse-type assemblages ranging from talus to shallow-marine/lacustrine, with subordinate volcanogenic rocks. Major and trace element data obtained from 31 psammopelitic rocks indicate that the clastic material was derived from sources consisting of both felsic and malic material, although felsic sources are more important in the samples from the Lower subgroup. Sedimentary tectonic discrimination diagrams demonstrate that most of the Wollaston Group was deposited on an active continental margin rather than a passive margin. The epsilon(Nd) values for the Wollaston Group psammopelites, calculated at 1.92 Ga, the approximate age of the boundary between the Lower and Upper subgroups, vary from -3.4 to -6.8, which yields an approximate 70:30 mixture between juvenile Paleoproterozoic detritus and Archean detritus from the Hearne craton. A secondary source of detritus may be 1.95-2.0 Ga rocks of the Taltson Orogen, which is exposed to the west of the Archean Rae-Hearne craton.The Wollaston Group records the complete evolution of the western margin of the Trans-Hudson Orogen during the Paleoproterozoic. The rifting of an Archean continent at ca. 2.1 Ga led to the deposition of the passive margin siliciclastic sediments comprising the lowermost, but poorly preserved part of Wollaston Group. The formation of a continental arc (Rottenstone) along the Hearne margin at ca. 1.92 Ga resulted in a change in tectonic environment from a passive margin to a back-arc basin, and detritus in most of the Lower subgroup was then derived from both basement and newly formed magmatic arc. Collision with the juvenile La Ronge arc led to uplift along the Hearne margin which transformed the back-arc basin into a retroarc foreland basin at ca. 1.88 Ga. Sedimentary starvation and shallowing of the basin led to widespread accumulation of carbonate and evaporite deposits in the west, whereas rapidly uplifted orogenic belts in the east provided sources of coarse-grained elastic detritus, forming the Wollaston Upper subgroup. Closure and inversion of the sedimentary basin occurred by ca. 1.86 Ga, coincident with the emplacement of mafic to felsic intrusive rocks in the Cree Lake Zone and the emplacement of the voluminous ca. 1860 Ma Andean-type Wathaman batholith into the continental margin. Closure was manifested by the onset of foreland-directed thrusting of the Wollaston Group. (C) 2003 Elsevier Science B.V. All rights reserved.

This paper describes the geology, geochemistry, and age of two amphibolite facies volcano-plutonic assemblages in the southern Hanson Lake Block and southeastern Glennie Domain of the Paleoproterozoic Trans-Hudson Orogen of east-central Saskatchewan. The Hanson Lake assemblage comprises a mixed suite of subaqueous to subaerial dacitic to rhyolitic (ca. 1875 Ma) and intercalated minor mafic volcanic rocks, overlain by greywackes. Similarly with modern oceanic island arcs, the Hanson Lake assemblage shows evolution from primitive arc tholeiites to evolved calc-alkaline arc rocks. It is intruded by younger subvolcanic alkaline porphyries (ca. 1861 Ma), synvolcanic granitic plutons (ca. 1873 Ma), and the younger Hanson Lake Pluton (ca. 1844 Ma). Rocks of the Northern Lights assemblage are stratigraphically equivalent to the lower portion of the Hanson Lake assemblage and comprise tholeiitic arc pillowed mafic flows and felsic to intermediate volcaniclastic rocks and greywackes, which can be traced as far west as Wapawekka Lake in the south-central part of the Glennie Domain. The Hanson Lake volcanic belt, comprising the Northern Lights and Hanson Lake assemblages, shows strong lithological, geochemical, and geochronological similarities to lithotectonic assemblages of the Flin Flon Domain (Amisk Collage), suggesting that all of these areas may have been part of a more or less continuous island arc complex, extending from Snow Lake to Flin Flon, across the Sturgeon-Weir shear zone into the Hanson Lake Block and across the Tabbernor fault zone into the Glennie Domain.

Two whole-rock suites of metavolcanic rocks from separate volcanic belts of the Churchill Province in northern Saskatchewan have been dated by Rb–Sr. Samples from the Amisk Group of the Flin Flon – Snow Lake domain provide an isochron date of 1784 ± 44 Ma; suites from the Waddy Lake and Devil Lake areas of the La Ronge (–Lynn Lake) domain yield isochron dates of 1814 ± 26 and 1854 ± 100 Ma, respectively. All are regarded as minima for, but close approximations to, emplacement ages. The maximum crustal age of any suite cannot greatly exceed 1850 Ma.Previous Rb–Sr and U–Pb isotopic dates together with these new determinations confirm the contemporaneous existence of two volcanic arcs, active during the late Aphebian (1875–1784 Ma) in the Churchill Province.Low initial 87Sr/86Sr ratios (0.7017–0.7022) are consistent with a petrochemically inferred subduction-related origin for the volcanic rocks with no closed-system reworking of Archean crust, and a linear evolution of 87Sr/86Sr ratio in the magmatic-arc mantle source region from 4.55 Ga to the present.