Structural relations between the polydeformed Flin Flon arc assemblage and Missi Group sedimentary rocks, Flin Flon area, Manitoba and Saskatchewan

Abstract

The structure of the Flin Flon area (Manitoba and Saskatchewan) has been examined through mapping of mesoscopic and macroscopic structures in both the ca. 1900 Ma Flin Flon arc assemblage volcanic basement and the unconformably overlying (or fault juxtaposed) ca. 1845 Ma Missi Group continental sedimentary cover sequence. The Flin Flon and Callinan volcanogenic massive sulphide orebodies occur within the basalt-dominated basement. The contact between the basement and the cover rocks was investigated in detail during this study. The cover sequence records three principal fold- and foliation-forming events. All deformation observed within the cover sequence is correlative with deformation observed within the volcanic basement. Significant low-angle overlap of basement on cover is attributed to development of a D1 north-verging nappe and subsequent thrust displacement on the overturned basement-cover contact. North-verging D1 structures provide evidence for a distinct post-Missi Group deformation event that preceded regional, southwestward D2 thrusting at peak metamorphic conditions across the southeastern Trans-Hudson Orogen. D2 deformation produced closed to tight, west-verging overturned folds with a well-developed axial planar cleavage and a pervasive extension lineation. D3 deformation generated open folds of the S2 and a weakly to moderately developed spaced axial planar S3 cleavage. D3 and D4 deformations produced sinistral-oblique, brittle-ductile reverse faults that offset all older features.

The Flin Flon paleosol revisited

“…Further intraoceanic amalgamation (forming the FFGC) and continental collision occurred from 1.84 to 1.80 Ga (Ansdell and Norman 1995;Norman et al 1995). This resulted in several identifiable tectonic overprints (D 3 -D 6 ) on the volcanic, successor arc plutonic, and sedimentary rocks of the central FFB (Stauffer and Mukherjee 1971;Fedorowich et al 1995;Lucas et al 1996;Gale et al 1999;Lafrance et al, in press), including thrust-stacking and folding of the internal units of the assemblages. During the final stages of continental collision between the Sask, Hearne, and Superior cratons (i.e., the Trans Hudson Orogeny), the Amisk collage was ultimately sliced up and imbricated as it was thrust onto the Sask craton, bounded by large-scale crustal detachment faults (Lucas et al 1996;Ashton et al 2005).…”

“…The arcuate outlier is a tightly folded east-striking syncline (Gale et al 1999) generated during D 4 deformation (based on temporal linkage with other structural features in the area; Lafrance et al, in press). The simplified geological map of the Missi outlier based on the work of Gale et al (1999) and Gibson et al (2013) shows the distribution of the regolith below the Missi as well as the surface axial trace of the F 4 syncline. The syncline was overprinted by later north-northwest-folding events (D 5 ), resulting in the sinuosity of the unconformity and the F 4 axial trace.…”

Integrated 3D Geological Modeling to Gain Insight in the Effects of Hydrothermal Alteration on Post-Ore Deformation Style and Strain Localization in the Flin Flon Volcanogenic Massive Sulfide Ore System

“…The 2D map pattern of NE-SW and N-S trending faults splays was previously interpreted to result from a single event of thrust faulting [23,[53][54][55]. The tightly-constrained 3D models of these faults, however, show that two distinct intersecting sets of relatively planar thrust faults are required to accommodate, in addition to the 500 m displacement of the ore horizon in westerly direction, 165-400 m of displacement of the Millrock member and the ore lenses hosted within it in a northerly direction, consistent with kinematic analysis of the D 4 faults in underground mine workings [15].…”