The Andes of southern Peru . a few inches of the borderfall into a separate class, sincethey show in general but triflingalteration and preserve theiroriginal cleavage planes. It ap-pears that the depth of the in-trusion must have been rela-tively slight or the intrusion sudden, or both shallow and sudden,conditions which produce a narrow zone of metamorphosed ma-terial and a sharp contact. The relation between shale and granite at Colpani is sho^vnin Fig. 143. Projections of granite extend several feet into the shale and slate and generally end in blunt barbs or a few places there is
The Andes of southern Peru . a few inches of the borderfall into a separate class, sincethey show in general but triflingalteration and preserve theiroriginal cleavage planes. It ap-pears that the depth of the in-trusion must have been rela-tively slight or the intrusion sudden, or both shallow and sudden,conditions which produce a narrow zone of metamorphosed ma-terial and a sharp contact. The relation between shale and granite at Colpani is sho^vnin Fig. 143. Projections of granite extend several feet into the shale and slate and generally end in blunt barbs or a few places there is an in-timate mixture of irregularslivers and blocks of crystal-lized sediments in a graniticgroundmass, with sharp linesof demarcation between igneousand included material. Thecontact is vertical for at leastseveral miles. It is probablethat other localities on the con-tact exhibit much greater modification and invasion of the weakshales and slates, but at Colpani the phenomena are both simpleand restricted in Fig. 143—Relation of granite intru-sion to schist on the northeastern borderof the Vilcapampa batholith near thebridge of Colpani, lower end of tlie graniteCanyon of Torontoy. The sections arefrom 15 to 25 feet high and represent con-ditions at different levels along the well-defined contact. EASTERN ANDES: CORDILLERA VILCAPAMPA 217 The highly mineralized character of the bordering sedimentary-strata, and the presence of numbers of complementary dikes,nearly identical in character to those in the parent granite nowexposed by erosion over a broad belt roughly parallel to the con-tact, supplies a basis for the inference that the granite may under-lie the former at a slight depth, or may have had far greater meta-morphic effects upon its sedimentary roof than the intrudedgranite has had upon its sedimentary rim. The physiographic features of the contact belt are of specialinterest. No available physiographic interpretation of the topog-raphy of a batholith i
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Keywords: ., bookcentury1900, bookdecade1910, bookidandeso, booksubjectgeology
