Title:
British Antarctic "Terra Nova" 1910-1913 Expedition Reports
image: of 297
176
"TERRA NOVA" EXPEDITION.
m the photograph of gneiss included in granite at Cape Geology (PI 1 Fig 1) The pyroxene-granulite inclusions, on the other hand, have reacted strongly with the invadmg granite and, except in the case of large inclusions, remain only as cores of spheroids in an orbicular granite shortly to be described. Limestone, although the most widespread of the metamorphic rocks in the Ferrar Glacier region, is represented only by two very large inclusions, Marble Dike (PI. 1, Fig. 6) and Marble w ciop, and it is believed that all the smaller ones have been completely absorbed.
Specimens of the orbicular granite mentioned above were collected at Boulder
Beach near Cape Geology (PI. l,Fig. 2), and at point K on TheFlatiron (Fic,4)
Ihe giamte in which the orbicular structure baa developed is the grey granite
described above, and the orbicular structure itself is clearly traceable to reaction
vith inclusions of the para-pyroxene-granulites, although in many of the spheroids
henuceushaaWnentirelyreplaced. Hornblendeplaysaveryimpoitantpartin
lese oibicular structures. The spheroids themselves have a well-marked concentric
s mcture combined with a less deGnite radial arrangement of the hornblende and in some cases, of biotite.
The edges of the included pyroxene-granulite are quite sharp, pyroxene dis- • appears entirely, and the first band in the orbicular structure consists mainly of hornblende crystals with well-marked sieve-structure due to numerous inclusions o loun e grains of felspar and quartz. Proceeding outwards there is a gradual increase in the size of the hornblende crystals in successive bands, felspar and quartz ecome more abundant, and there is a gradual passage to a rather basic hornblendic granite of very variable composition. Sphene, as crystals up to 1-4 mm. in length IS often conspicuous in some of the hornblendic bands. A similar development of concentric bands neb in hornblende was described at a contact of quartz-diorite and pyroxene-granulite in the account of the metamorphic rocks'
nlare1! 77 T" ^ °f the S'lheroid has disappeared, and its
Le t " hornblende and biotite forming an ellipsoidal nodular
core to successi ve concentric shells. Some of these spheroids were 15 cm. in diameter
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This report, No. 5, p. 137.
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