<p> The Proterozoic' Coldwell Alkaline Complex is the
southernmost intrusion of a number of N -S trending igneous bodies
occurring in the Midcontinental Rift system exposed in the Lake
Superior area. The Coldwell complex is host to several Ni-Cu-PGEbearing
intrusions two of which; the Two-Duck Lake intrusion
(Marathon deposit) and the Geordie Lake gabbro (MacRae
occurrence) have been investigated in some detail with respect to
PGE mineralisation. Both of these have been suggested to have
experienced crustal contamination in conjunction with
mineralisation. As a test of this possibility, a detailed Sm-Nd, oxygen
isotope, and whole-rock geochemical study of these mineralised
occurrences as well as of the Dunlop occurrence and the Middleton
occurrence, together with unmineralised rocks of the complex was
undertaken. The primary objectives are to determine whether crustal
contamination is indicated in mineralised rocks and to try and
ascertain the nature of the magma which formed the complex. </p> <p> The Coldwell complex is thought to have been formed by
emplacement of magma at three intrusive centres. Sm-Nd data for
rocks from these three centres reveal similar isotopic values, with
slight variations; samples taken from the western gabbros exhibit eNd
values averaging -0.9 ranging from -2.9 to 0.9, whereas rocks from the
eastern margin and centre of the complex have eNd values of about
an average of 0.5 ranging from -0.5 to 1.2 suggesting that the magma
that formed these rocks has undergone a lesser degree of crustal
contamination. This data, supported by oxygen isotope and wholerock
geochemical information indicates that crustal contamination
seems to play a small, and varied role in the genesis of the Coldwell
magmas. The Nd isotope data all clusters at values for CHUR, which
indicates that it has been enriched relative to the depleted mantle.
It has been postulated that an enriched mantle plume resided under
the rift and promoted rift-related magmatism. The data from this
study would seem to support this supposition. </p> <p> Geochemical parameters utilised to define fields to
geochemically delineate possible end member contributors to this
primarily plume-derived magma indicate, that in addition to small,
variable amounts of assimilation of upper and lower crust, the plume
magmas also interacted with the lithospheric upper mantle to a small
degree. </p> / Thesis / Master of Science (MSc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/19209 |
| Date | 05 1900 |
| Creators | Bohay, Trevor |
| Contributors | Crocket, J. H., Geology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
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