Pg nat ee ay ee, ee 
PE ee ea Se OES er ee ie 
of: „ - 
CRYSTALLINE BASEMENT 51 
ment into a number of great fault blocks. The downpressed sandstone- 
remnants lie between the blocks in the throws. The crushing of 
the basement rocks apparently went on through the whole complex. 
The intensity varies, however, considerably. The most complete 
granulation occurred along the overthrust planes, in whose im- 
mediate vicinity a mylonitic breccia was developed. The crushing 
and tearing was intense also where schistose rocks dominate, while 
in the granite stocks conspicuous signs of pressure have been 
observed more locally. Generally, the degree of deformation may be 
said to decrease towards the east. In the batholith of the Nevado 
the granulation of the granite structures seems to have been of a 
more local nature, while the bulk of the eruptives shows quite a 
well preserved consolidation habit. 
a) THE CRUSHED, GRANULATED GRANITES. 
In the foregoing pages the granites of the Sierra de Umango 
area are petrographically characterized only to a small extent, because 
primary granitic structures seldom occur. The greater part of the 
granite outcrops shows more or less conspicuous signs of dynami- 
cal deformation. 
In the following pages may be examined the secondary structures 
of the granites in the order as they outcrop, going from east to west. 
Above have been treated of the Famatina batholith types. They 
show generally quite a primary habit. Passing the valley to the Sierra 
de Umango side, in the next zone (schists with crossing apophyses) 
conspicuous crushing features are lacking (graphic pegmatites!) 
‚But some miles farther west, in the eastern slope of the Cerro 
Villa Union, there are already strong pressure phenomena. The 
concordant granite veins in the schists have been torn off into 
lenses and the structure is completely granulated. It is here seen a 
typically developed banded zone. As a good example of a crushed 
concordant pegmatite vein an occurrence from the western foot of 
the mentioned mountain (Carrizal) may be described. Already in 
