Accession Number : AD0616397

Title :   PALEOMAGNETISM OF LATE CRETACEOUS GRANITIC PLUTONS IN THE SIERRA NEVADA, CALIFORNIA: FURTHER RESULTS.

Descriptive Note : Final rept., part 2, Jul 63-Dec 64,

Corporate Author : CALIFORNIA UNIV BERKELEY DEPT OF GEOLOGY AND GEOPHYSICS

Personal Author(s) : Gromme,C. S. ; Merrill,R. T.

Report Date : JAN 1965

Pagination or Media Count : 61

Abstract : Additional sampling and re-evaluation of previously rejected data have provided paleomagnetic poles from five new sites in the 85 million-year-old Cretaceous granites of the Sierra Nevada, California. The mean of these five poles and the nine poles previously reported is located at 165 west logitude and 69 north latitude, with the semi-angle of the 95% confidence cone equal to 9.6. This mean paleomagnetic pole differs only slightly from that previously reported for nine sites only, and agrees with two Cretaceous poles from rocks in Quebec; thus it appears to represent a geographic pole as well. There is no systematic distribution of individual virtual poles with respect to their mean. The only ferromagnetic mineral in all these rocks is pure magnetite, which probably accounts for the large observed dispersion of N.R.M. directions and the magnetic instability of many of the specimens. Measurements of susceptibility anisotropy indicate that only about half the dispersion can be caused by random anisotropy and that the observed uniform anisotropy at some sites has not biased the N.R.M. directions significantly. Behavior of the N.R.M. in samples cooled below the 120 K. magnetite transition suggests that the N.R.M. is more like T.R.M. or C.R.M. than like a weak-field short-time I.R.M. (Author)

Descriptors :   (*ROCK, MAGNETIC PROPERTIES), (*GRANITE, MAGNETIC PROPERTIES), (*GEOMAGNETISM, GRANITE), (*GEOLOGY, CALIFORNIA), ANISOTROPY, MINERALS, MAGNETIC PROPERTIES

Distribution Statement : APPROVED FOR PUBLIC RELEASE