Geology of a transect of the Northern Argus Range, California

Includes bibliographical references (pages 99-105)Study of a transect of the northern Argus Range reveals\ud Mesozoic structural features, recognized regionally,\ud in complex relationship with local plutons and intrusion-related\ud deformation. These have affected a 2,000-m-thick\ud section of miogeoclinal, predominantly carbonate rock ranging\ud in age from Devonian to Permian.\ud During the Mesozoic the study area was located on the\ud inland margin of a major Andean-type arc, represented by\ud the Sierra Nevada batholith. Lithosphere adjacent to the\ud batholith was greatly weakened by heating and experienced\ud repeated episodes of compressive shortening.\ud What may be the oldest folds in the area, northeast-trending\ud (FA) folds, are located predominantly on Lookout\ud Mountain and may be either rotated younger (FB) folds \ud or related to the early Mesozoic Last Chance thrust system.\ud Northwest-trending FB folds are members of a regionally\ud recognized fold set characterized by a well developed axial\ud surface cleavage and by vergence or overturning to the\ud northeast. The Argus anticline is the main FB fold and\ud is the most prominent structural feature of the study\ud area. In the northern and southern portions of the study\ud area, plutons have intruded and disrupted the hinge area\ud of the Argus anticline.\ud Three plutons of known or probable Middle Jurassic\ud age have chemistry, normative mineralogy and modal mineralogy\ud that are similar to calc-alkaline plutons making up\ud the bulk of the Sierra Nevada batholith. One of these\ud plutons has a unique and complex history of forcible emplacement.\ud At least three fault sets, including a preintrusive,\ud northwest-trending fault, thrust faults and\ud northeast-trending faults are not regionally correlative\ud and may be at least partly resultant of local intrusion-related\ud stresses.\ud The left-normal-slip Osborne Canyon fault significantly\ud offsets the hinge area of the Argus anticline and cuts\ud the Osborne Canyon granite. This fault is probably related\ud to a widespread set of northwest-trending, left-separation\ud faults which, in part, may pre-date Independence dikes of\ud Late Jurassic age. Late Cenozoic Basin and Range normal\ud faulting and basalt volcanism characterize the most recent\ud phase of structural and igneous activity