Riku Metsaranta HBSc thesis abstract

Thesis Title: 
Preliminary results of geochemical sampling from the Mesoarchean Balmer assemblage, Birch-Uchi greenstone belt

This study examined metavolcanic and metasedimentary strata from the about 3.0 Ga Balmer assemblage of the Birch-Uchi greenstone belt, Western Superior province.  ICP-AES wholerock geochemical analyses coupled with field and petrographic observations were used to better define the tectonic setting in which these rocks developed.  The geochemistry of 21 of 34 samples was taken to be representative of geochemical variation amongst the volcanic rocks of the study area and showed them to be comprised of two distinct suites.  The first suite is characterized by mafic volcanic rocks of basaltic to andesitic composition and was found to be tholeiitic in character.  The second suite is characterized by intermediate to felsic volcanic rocks of andesitic to rhyolitic and rhyodacitic composition and is calc-alkaline in character.  The geochemistry of these samples seems consistent with an arc-like setting.  Sedimentary rocks crop out poorly in the study area but may represent a submarine volcaniclastic apron or submarine fan/ramp feeding into an arc-related basin. The geochemistry of 16 samples of sedimentary rocks were analyzed in order to study their provenance.  Results from these analyses suggest that the Balmer assemblage sedimentary rocks are derived from the Balmer assemblage volcanic rocks and primarily the intermediate to felsic calc-alkaline suite.  This is consistent with the Balmer assemblage sedimentary rocks being deposited in an arc-related basin.  Suggestions made here should be tested through geochronological study of detrital zircons in the sedimentary rocks and high precision geochemical techniques with a more complete suite of trace elements.