Fig. 146—Deformative effects on limestone strata of the granite intrusion on the southwestern border of the Vilcapampa batholith above Chuquibambilla. [Fig. 147] is on the same border of the batholith several miles farther northwest. The granite mass on the right is a small outlier of the main batholith looking south. The limestone is Cretaceous. See Appendix C for locations.
These smaller intrusions are remarkable in that they appear to have been attended by little alteration of either invading or invaded rock, though the granites were observed to become distinctly more acid in the contact zone. Space was made for them by displacing the sedimentary cover and by a marked shortening of the sedimentary rim through such structures as overthrust faults and folds. The contact is observable in a highly metamorphosed belt about twenty feet wide, and for several hundred feet more the granite has absorbed the limestone in small amounts with the production of new minerals and the development of a distinctly lighter color. The deformative effects of the batholithic invasion are shown in their gross details in Figs. [141], [142], and [146]; the finer details of structure are represented in [147] , which is drawn from a measured outcrop above Chuquibambilla.
It will be seen that we have here more than a mere crinkling, such as the mica schists of the Cordillera Vilcapampa display. The diversified sedimentary series is folded and faulted on a large scale with broad structural undulations visible for miles along the abrupt valley walls. Here and there, however, the strata become weaker generally through the thinning of the beds and the more rapid alternation of hard and soft layers, and for short distances they have absorbed notable amounts of the stresses induced by the igneous intrusions. In such places not only the structure but the composition of the rock shows the effects of the intrusion. Certain shales in the section are carbonaceous and in all observed cases the organic matter has been transformed to anthracite, a condition generally associated with a certain amount of minute mashing and a cementation of both limestone and sandstone.