264 



STRUCTURAL GEOLOGY OF NORTH AMERICA 



TOBIN THRUST. 



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GOLCONDA 



THRUST 

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SECTION IN MOUNT TOBIN QUADRANGLE <> 



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SECTION IN WINNEMUCCA QUADRANGLE 



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Fig. 17.6. Representative cross sections of northwest central Nevada. Top section shows the 

 Tobin thrust of Late Jurassic age and the angular unconformity between the Permian Koipato 

 and Havallah formations. Middle section shows the Dewitt thrust of late Mississippian or Early 

 Pennsylvanian age and the associated angular unconformity between the Pennsylvanian Battle 



and, again, mild orogeny at the end of the Permian is noted. See top 

 and middle sections of Fig. 17.6. 



Large-scale thrusting occurred in the late Jurassic probably correspond- 

 ing in time to the major deformation in the Hawthorne and Tonopaw 

 quadrangles. Considering the time of intense deformation of the Mariposa 

 slate in eastern California, to be discussed immediately, the orogeny is 

 thought to have culminated in Kimmeridgian time of the Late Jurassic. 

 The distribution of the major thrusts of this age, the Tobin and Golconda, 

 is shown in Fig. 17.6. The two may actually be one and the same. At 

 least, the horizontal translation has been so great that two suites of 

 formations of different facies probably deposited an appreciable distance 

 apart, have been brought into juxtaposition. In the four quadrangles the 

 upper thrust plate covers an area extending 50 miles from north to 

 south and 40 miles from east to west. The Permian formations are 



Mountain formation and the Ordovician Comus formation. Lower section shows the succession of 

 thrusts; first the Thomas, then the Sonoma, and then the Clear Creek, all of Late Jurassic age. 

 The Tobin thrust nearby cuts the Clear Creek thrust. 



common to both plates. The direction of relative movement of the upper 

 plate is uncertain. In the Sonoma Range a succession of four thrusts, all 

 occurring in the Late (?) Jurassic orogeny, is recognized, and the three 

 lower ones moved from east to west. It seems possible that the Tobin 

 thrust plate could have moved toward the north (Ferguson et al., 1951). 

 See lower section of Fig. 17.6. 



NORTHWESTERN NEVADA 



Lower and probably Upper Cretaceous rocks have been found in north- 

 western Nevada, and these record a continuation of deformational phases 

 beyond the Late Jurassic Tobin and Golconda thrusting. According to 

 Willden (1958): 



