GEOLOGY OF THE NORTH CREEK QUADRANGLE 



37 



Table 8 

 Mineralogical composition of each contact zone 





v 



























-!-> 









i> 



















« :g 



d 



a> 



0) 



T3 



c 







« 













!2 ti 



£3 



ci 



C 



.n 







*j 











o 



is <o 



*7^ 





4) 



-t-i 

















c 

 c 



c5 



Orthoc 

 M icrop 



1 



O 

 'S) 



C 



V. 



O 





3 



Ot 



0) 



.0 



S 



c 



c 







t5 



'y: 



e5 





c 



C 











Ol-lab 















• 







I 



5 







45 

 01-lab 



14 



20 





6 



2 







I 



2 

























2 



^2 







10 



45 







6 



? 



httle 





little 



5 



^ 



Biotite-s( 



:hist 



with some 



i feldspar 















A 



Like No. 



6 



01-and 





















5 



28 







50 



Ol-and 



20 





I 





1 



2 



Httle 



Httle 













6 



IS ' . . . . 





5 



72 









7 



1 



1 

 2 



httle 





7 



Like No. 



5 





















01-and 





















8 



"^"^ 





55 

 01-and 



10 





I 







1 



1 



httle 































9 



40 



15 



4 



5 



5 





30 





1 

 2 



little 







1 









A noteworthy feature is the fact that the strike of the foliation 

 of the very gneissoid country rock is nearly at right angles to the 

 gabbro-granite contact, while the clearly defined contact zones are 

 parallel to the contact. 



Other features of special interest are the syenitic border (except 

 for the secondary biotite-schist) of the gabbro near the contact, 

 and the almost complete absence of quartz from the granite within 

 a dozen feet of the main contact. Thus the country rock (granite) 

 is distinctly more basic near the contact, while the gabbro is dis- 

 tinctly more acidic near the contact. 



Whether these interesting endomorphic and exomorphic change^; 

 are to be accounted for on the basis of assimilation of some of the 

 country rock during the intrusion of the gabbro, or on the basis of 

 the action of vapors from the intrusive, it at least appears quite 

 certain that the gabbro must have been considerably superheated in 

 order to have so notably affected the granite. As judged by the 

 mode of occurrence of the gabbro stock, the stoping hypothesis 

 recently advocated by Daly or the hypothesis of marginal assimila- 

 tion might be applied to account for the more acidic border phase 

 of the gabbro, but the sharp contact of the gabbro against the granite 

 would seem to preclude the possibility of accounting for the more 

 basic contact zones of the country rock on the basis of actual assimi- 

 lation of some of the granite by the gabbro. 



