COLORADO AND NEW MEXICO ROCKIES 



395 



east front of the Rocky Mountains south of the Wet Mountains. See Fig. 

 25.2. The Sangre de Cristo Range extends southward into New Mexico 

 110 miles and has a regular arclike form, convex toward the east. Its width 

 is small, ranging from 10 to 20 miles. Together with the San Luis Valley 

 on the west and the Wet Mountain Valley and Huerfano Park on the 

 east, it represents a prong of the Laramide belt. Complex folds and 

 overthrusts dominate the belt. The folds in the northern part of the range 

 consist of a major central anticline bounded on the west by a much com- 

 pressed, overturned, and faulted syncline, and on the east by a more 

 open syncline. The major anticline is complicated by the presence of a 

 metamorphic core and by several small intrusive bodies along or near 

 its axis. The overthrusts are best preserved in the Huerfano Park region, 

 where several imbricate thrust sheets were thrown into steeply inclined 

 ^positions by the compressional forces (Burbank and Goddard, 1937). 

 jSee Fig. 25.8. 



The upper section of Fig. 25.9 represents a supposed early stage of com- 

 pression and overthrusting prior to the upthrust of the Precambrian rocks 

 and the downfaulting of the San Luis Valley; the lower section, the 

 ^structures afterward. The anticline is viewed as an injective mass due to 

 'considerable mobility of the shaly beds of the Lower Pennsylvanian 

 Which were overlain by a great thickness of less mobile conglomerates. 

 When compressed, the shales flowed into the core. The belt of plastic 

 deformation is limited to an area just east of the arc-shaped bend in the 

 thrust zone. 



The belt of thrusting along the east side of the Sangre de Cristo, op- 

 posite Huerfano Park, is illustrated in Fig. 25.8. The principal thrusting 

 /Dccurred after the deposition of the Poison Canyon formation (lowermost 

 Eocene or Paleocene) and before the deposition of the Chuchara forma- 

 ion (middle ? Eocene). See stratigraphic chart of Fig. 25.10. Both the 

 Ohuchara and overlying Huerfano formations are affected by the thrust- 

 ng; but Burbank and Goddard believe the thrusting, although con- 

 inuing into Eocene time, was of declining intensity. 



West of, and inside the arc of dirusting, are two elongate masses of 

 3 recambrian rock which were buried or were much lower in elevation 

 han now during the thrusting, but which were later elevated as blocks 



bounded by high-angle faults. Accompanying the uplifting was consider- 

 able plastic deformation of the adjacent shales. The maximum vertical 

 uplift is estimated as 2 to 3 miles (Burbank and Goddard, 1937), and 

 most of it occurred in post-Huerfano (late ? Eocene) time. 



After the Precambrian "massifs" were uplifted, they were broken by 

 tensional faults, and in part settled so much as to be covered by effusions 



LEADVILLE 



ALMA 



SOUTH PARK 



MONTEZUMA 



AND 

 ARGENTINE 



CENTRAL CITY 



AND 

 IDAHO 5PRING5 



TUNGSTEN 

 BELT 



Tungsten ore 

 Limburgite 



Tellurtde ore — Telluride ore 



,Bio ti te lati te — Intrusion breccio 



Biotite monzonite 



Pynte gold ore 

 Bostonite 



Rhvo/ite agqlom/ Alkali syenite-- Hornblende 



Lead -silver ore 



i 



1 Contact met dep 



monzonite 



I Rh i, r Felsite 



I I [Sadie monzomte i P uorn Monzomte- Quartz Monzonre 

 I J '{Lincoln porphyry 



.Monzonite 



Lead- silver-, ,'< ', r-w 



qold ores i ! i Intermediate atz 

 i j i monzonite , 



Late white .' ' j 

 porphyry 



Lincoln 

 porphyry 



[Dacite I 



'[Hornblende diorite 



i i 

 i , 



I i 



Johnson Gulch > 

 porphyry / 



Diorite J W* diorite 



__,- Diabase 



Ffhyo/ite 



Monzoniti 

 Quartz rr, 



White porphyry 



Monzonite 

 Quartz monzonite 



Fig. 25.7. Laramide folding, faulting, and emplacement of igneous rocks and ore deposits in 

 the Front Range mineral belt, Colorado. Abbreviated after Lovering and Goddard (1938b). The 

 dashed lines connect intrusions and ore deposits of similar kind. Equivalent age is portrayed by 

 similar horizontal position. From southwest to northeast the intrusions and ore deposits become 

 generally progressively younger. 



