344 R. A. DALY THE OKANAGAN COMPOSITE BATHOLITH 



brownish green biotite, orthoclase, quartz, and imzoned andesine, Ab 5 An 3 . 

 The accessory minerals are apatite, magnetite, and titanite ; none of these 

 may be called abundant. Allanite in rather large amount is accessory in 

 the basified contact zone. Colorless epidote is invariably present, but is 

 regarded as of metamorphic origin. Where it becomes abundant the iron 

 ore has partially or wholly disappeared; then probably entering into the 

 composition of the epidote. Biotite is generally dominant over horn- 

 blende and plagioclase over orthoclase. 



Along the eastern contact of the batholith the average plagioclase is 

 labradorite, A^An^ and it so far replaces the orthoclase that the rock 

 here verges on quartz diorite. In the hand specimen this somewhat basi- 

 fied contact phase is indistinguishable from the true granodiorite. The 

 limits of the orthoclase-poor zone were therefore not closely fixed in the 

 field. It is probable that the zone is not more than a few hundred yards 

 in width, and that the original rock of the batholith was, in the large, 

 homogeneous. A second exceptional phasal variation is founded on the 

 disappearance of hornblende in rock that shows decided cataclastic struc- 

 ture, other constituents remaining the same as in the normal grano- 

 diorite. This phase — gneissic biotite granite rich in andesine — occurs 

 sporadically in the heart of the batholith. Very possibly it is not of orig- 

 inal composition, the hornblende having been removed through meta- 

 morphic action. 



Dynamic and hydrothermal metamorphisin of the granodiorite. — In the 

 mapped area of the batholith scarcely a single outcrop can be found that 

 does not show the powerful effects of intense orogenic strains. Even the 

 most massive phases show, under the microscope, the varied phenomena of 

 crushing stress — granulation, bending of crystals, undulatory extinctions, 

 recrystallization, etcetera. Because of the crushing, the average rock is 

 no longer the original rock. The granodiorite has been changed into sev- 

 eral metamorphic types, of which three may be noted. 



The commonest transformation is that into a biotite-epidote-hornblende 

 gneiss, with essential and accessory constituents like those in the original 

 granodiorite, but in somewhat different proportions. The color is light 

 gray, with a green cast on surfaces transverse to the schistosity ; parallel 

 to the schistosity a dominant and darker green color is given by abundant 

 fine-textured leaf aggregates of biotite. These aggregates are not simply 

 crushed and rotated original mica foils, but, like the epidote, represent 

 true recrystallization and the incipient migration of material within the 

 granulated, plutonic rock. At the same time much of the original horn- 

 blende, apatite, and magnetite have been removed. 



