Regional history, lithology and structural geology of the Flin Flon greenstone belt and the broader Trans-Hudson Orogen, with special emphasis on University of Saskatchewan Flin Flon Field School map area 4 -------------------------------------------------
By: Cameron MacKay
Introduction - For the period of Sunday, August 28th – Sunday, September 4th, 2011, students from the University of Saskatchewan geological sciences department along with professors Dr. Kevin Ansdell and Dr. Kyle Larson took part in a geologic field school in and around the city of Flin Flon, Manitoba. The purpose of this field school was for students to become familiar with: i) “hard rock” field mapping techniques; ii) identification and interpretation of volcanic, plutonic and sedimentary rocks; iii) identification and analysis of fabrics resulting from deformation and metamorphism; and iv) map production, thin section and hand sample analysis and report writing. This paper outlines the regional geologic setting of the Flin Flon greenstone belt, the greater Trans-Hudson Orogen, provides a detailed thin section and hand sample description of a sample taken from a grano-diorite component of the ca. 1839 Ma boundary intrusion and provides a point form history of the geologic history of University of Saskatchewan Flin Flon Field School map area 4. Regional Geologic Setting – The Trans-Hudson Orogen (THO) is the earth’s most extensively preserved Paleoroterozoic orogenic belt (Hoffman, 1988). It is interpreted to extend southwards into the United States below the Williston basin and extends northeast into Nunavut and northern Quebec wrapping around the Archean Superior craton (Ansdell, 2005). The THO is the end result of the closure of the Manikewan Ocean (Stauffer, 1984) which resulted in the formation juvenile crust which was eventually accreted onto the Archean Superior and Hearne cratons as well as a number of smaller cratons including the Sask Craton (Lewry et al.,1994). The THO preserves a relatively complete tectonostratigraphic evolutionary history including evidence for rifting (ca. 2450-1950 Ma), the formation of oceanic crust (ca. 2000-1800 Ma), and sedimentary assemblages deposited along continental margins and younger (1880-1830 Ma) collisional and foredeep basins (Ansdell, 2005). The southwest exposed portion of the THO in the Canadian Shield is known as the Manitoba – Saskatchewan Trans-Hudson Orogen (MS-THO). The MS-THO is subdivided into three zones: Hearne Province, Superior Boundary Zone and the Reindeer Zone the latter of which encompasses the Flin Flon greenstone belt. The rock assemblages in the Flin Flon greenstone belt can be recognized to have formed in distinct, dominantly oceanic tectonic settings related to the Manikewan Ring of Fire, an island-arc – back-arc-basin subduction zone complex broadly analogous to Japan and the Sea of Japan today but with a wider range of complexities including the presence of ocean island settings and subduction occurring at the north continental margin, whereas the contact between the Sea of Japan oceanic crust and mainland China is a passive margin today. This complex collage of rock assemblages was accreted between the Hearne craton to the north and the Sask craton to the south by approximately 1815 Ma (Ansdell, 2005). In contrast to the rocks of the THO to the northeast, the Reindeer Zone preserves large areas that have undergone at most upper greenschist to lower amphibolite metamorphic conditions which increases the preservation potential for mineral deposits originally emplaced at mid to upper crustal levels (Corrigan, 2007). From a metallogenic perspective the Flin Flon belt is well known for its world class volcanogenic massive sulphide deposits.
Fig. 1 – Geologic map of section 4
Location and Field Relationships – The sample was...