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Suomen Geologinen Seura. N: 0 35. GeologiBka Sällskapet i Finland. 3 N - Q " Q ~ , .;;> ::: , B B \ , I I \ I I , ~ o A A , "°0' I 0 , D - " " , Q [) o· , -. 0 l \.0 , , , I ~ 2 cm Fig. 2. Detail of a eontaet between porphyroblastie granite (A) and granodiorite (B). On the granitie side, potash feldspar porphyroblasts oeeur abundantly near the eontaet zone; on the other side, there is an enriehment in mafies. I------i 6cm Fig. 3. Contaet between porphyroblastie granite and quartz diorite (point A in Fig. 1). 3 000 X 500 m in size lies E of the outcrop. Granitic gneisses, quartz diorites (more or less gneissose) and gneissose granites are also present in the area (Fig. 1) . The rocks of the outcrop with which we are dealing may be classified as quartz diorite, granodiorite and porphyroblastic granite, the latter occurring in strip es and bodies of various size. Transitions from such granite to granodiorite are often gradual and in such cases megascopie variations display mainly a decrease in the amount of the potash feldspar porphyroblasts, which in the surrounding granodioritic rock become sparser and sparser until they disappear. In other instances, the contact zone is crowded with potash feldspar porphyroblasts on the granitic side and marked by an enrichment in mafic minerals along the contact in the granodiorite (Fig. 2). Such a feature has also been found I1t a granite - quartz diorite contact (Fig. 3) about 2 km SW of the outcrop (point A, Fig. 1). In the outcrop the granodiorite contains portions of quartz diorite rich in mafics and devoid of potash feldspar, other mineralogical features being similar to those of the enveloping granodioritic rock (plagioclase An 45 , green amphibole c 1\ y = 24°, pyroxene = augite, c 1\ y = 42°). Around these quartz dioritic portions, longish crystals in the enveloping rock are subparallel to
4 Bulletin de la Commission geologique de Finlande N: 0 212. \ \ , ,, , , , , " " , " , " , \ 0 0 0 () D (J t----l 10 cm Fig. 4. Quartz dioritic inclusions in granodiorite and crystal arrangement around them. • • . . -. ... , .. , N B ~ . - ~ ~Ocm Fig. 5. Pegmatite-like net at the contact granodiorite (B) porphyroblastic granite (A).
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REFERENCES ARNOULD, M. (1961) Etude
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