Petrogenesis of the Boundary Intrusions Flin Flon Area, Saskatchewan-Manitoba
Date
1975
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
Type
Degree Level
Masters
Abstract
The Precambrian (Aphebian) Boundary intrusions are a set
of dike-like or lensoid, ultramafic to felsic intrusions that
occur in a linear zone centred on the town of Flin Flon,
Manitoba. The intrusions are emplaced in Amisk metavolcanic
rocks and Missi metasedimentary rocks.
Cross-cutting relationships, petrography, and chemical
features of Boundary rocks indicate the intrusions are comprised
of three compositionally distinct, sequentially emplaced rock
groups. The mafic (mela-dioritic) group is the oldest; early,
melanocratic, augite- and biotite-bearing members of this group
were intruded and brecciated by successive differentiates
containing augite and, eventually, hornblende. Crystallization
at relatively high fH20 and f02 produced an unusual differentiation
trend in which successive differentiates became slightly
enriched in MgO relative to FeO. Crystal fractionation of
augite, possibly subordinate olivine, and minor magnetite from
a tholeiitic olivine basalt magma accounts for the observed
chemical variation in the mafic eroup.
Felsic group rocks (lellco-diorite to granodiorite) cut
and brecciate all mafic group rock types. Members of the
felsic group are chemically similar to post-Missi granodiorite
plutons, and do not represent Si02-rich residual liquids
produced by fractionation of augite and olivine from a mafic
Boundary magma.
The youngest Boundary rocks are members of the olivine-
bearing group (wehrlite to olivine gabbro). The major occurrence
of wehrlite is in the core of a large mafic Boundary
intrusion, with which wehrlite is in intrusive contact.
Crystal fractionation of subequal amounts of olivine and
clinopyroxene, and minor magnetite, from a tholeiitic olivine
basalt magma accounts for the observed chemical variation in
the olivine-bearing group. A regular increase in the amount
of intercumulus hornblende in wehrlite, from the centre to the
margins of the body, indicates that there was a greater water
content in the marginal zones of the intrusion.
Folding and faulting of the Amisk and Missi Groups occurred
during the Hudsonlan Orogeny, and involved three separate phases
of deformation. S2 axial-plane foliations (produced during the
second phase of deformation) are developed only in the older
members of the Boundary mafic group. All Boundary rock types
contain structures produced during the third phase of deformation.
Emplacement of the intrusions occurred during the
interval late-P2 to late-P3.
Description
Keywords
Citation
Degree
Master of Science (M.Sc.)
Department
Geological Sciences
Program
Geological Sciences