Program, Abstracts, and Guidebooks - University of Minnesota Duluth

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(3) feldspars variably foliated;
(4) mafic schlieren, the attitude ot which
is conformable with the attitude of
layering;
(5) gradation into more pegmatitic or
porphyritic varieties.
The laurvikites are primarily composed of perthitic
feldspar, with variable amounts of aegirine—augite, olivine
(up to Fa100), barkevikitic amphibole, biotite, iddingsite,
quartz, zircon, fluorite and calcite. Variations in
mineral compositions, and in the thermal histories of
alkali feldspars may be cyclic.
2.4 Marathon turn—off.
0.0 Continue west on+Highway 17.
2.3
STOP 2 DARK GREEN LAIJRVIKITE - LAURVIKITE PEGMATITE (Fig. 1)
4.7
These rocks aresimilar to the laurvikites from
Oslo. The perthites from the pegmatites are extensively
exsolved, patch perthites, which are more sodic (Or27)
than the less exsolved, braided perthites (Or62) from
the less—pegmatitic, laurvikitic host.
STOP 3
CONTACT BETWEEN LAURVIKITE AND BASIC METAVOLCANIC
XENOLITH. (Fig. 1 & 4).
This section of the highway reveals a broad exposure
of the contact phase of syenite which can be seen to grade
into more normal laurvikite.
The basic metavolcanic is basaltic in composition
and comprises a portion of the so—called Coubran Lake
metavolcanic cap. Although more commonly amygdular in
appearance, fine grained to aphanitic phases are distributed
in such a manner as to suggest the contacts are
flat lying.
The contact between the overlying basaltic cap and
the medium to coarse—grained, red coloured, hornblende—
rich syenite is generally sharp and fragmented. The
syenite, which is a hydrated equivalent of the laurvikite,
contains abundant mafic clots, stringers, wisps and
veinlets from 2 to 6 inches in size. These 'enclaves',
which are amphibolite or syenodioritic in composition,
tend to be aligned parallel to the contact.
fL.5
STOP 4 TRA}ISITIONAL PHASE OF LAURVIKITE (Fig. 1).
To the south similar rocks reportedly (Tuominen)