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