xenolith-type orbicular gabbro boulder from jussinjärvi ... - Arkisto.gsf.fi

oulder no. 85). This boulder is roundish, only about
15 cm in diameter, and consists of closely spaced
multishelled orbicules in a homogeneous gabbroic
matrix (Fig. 176). The cores of the orbicules are also
composed of dark-green rounded xenoliths of schist,
most likely fragments of calc silicate rocks.
Because the general appearance of the rocks - the
core material, the shells and matrix - closely resernble
each other in both the Jussinjämi and Onneton
orbicular rocks, the authors believe that both erratics
may be derived from a common, presently unknown
source, although the distance between the localities
is considerable (nearly a hundred kilomehres).
ne roun&sh fom of the Onneton boulder, furthemore,
indicates that it was trmsported a long dstance
by the ice.
Fig. 176. Weathered swface of a xenolith-type orbicular rock h m
Onneton, Haapaj-Wi. The cores of the orbicules are calc-silicate rocks.
A sample (about 20 cm wide) belonging to V. Autio. Photomh: J. Keskinen.
ORBICULAR GABBRO BOULDER FROM KANGASPAANJARVI, REIS JARVI
Seppo 1. Lahti, Ilkka Laitakari and Paula Raivio
Fig. 177. Weathered swface of orbicular gabbro boulder from Kangaspahjrvi, Reisjárvi. The orbicules
are medium-sized (0 5-8 cm), single-shelled and often deformed. A sample from the Mineralogical Museum
of the Geological Survey of Finland. Photograph: J. Keskinen.
Geologist Eero Pehkonen discovered this orbicu- cal Survey of Finland. The chemical analysis indilar
rock in 1958 west of lake Kangaspaanjärvi in cate that the rock is syenodiorite in composition (Ta-
Lehtoranta, near Reisjärvi. The boulder that is ble 15, Fig. 173).
rounded and about 120 x 80 x 70 cm in size was The KangaspWjämi orbicular rock consists of
found during geological fieldwork of the Geologi- very closely spaced orbicules, 4-6 cm in diarneter,