RESEARCH· ·1970·

HANNA
B75
·~
pentinites were emplaced within zones of weakness
produced by stress patterns related to broad areas of
folding and faulting throughout much of the present
California, Coast H.anges. The geophysical data do not
directly bear on other questions of the proposed klippe
Ol'lglll.
In summary, generalized interpretations of shallow
stubsurfa.ce rocks ·n,re shown in figure 4 (p. B76-B77) ws
profiles ..tl-..tl' tHld 13-B' -across the nor1thern and souther11
parts of the :t-ren,, •respectively. Crust~l features shown in
tJhe ·cross sections satisfy the 'ree~.dual gra.vity anmm11ly
n;nd n.erom·ttgne•tic •anoma;]y profi·les to -a. good approximation,
n.lthough only a small part of some geologic features
occur in the sections. For example, the ultramafic
serpentinite bodies producing major 1nagnetic anomnJies
may, on the basis of modeling results, extend to
depths of more than 10 miles, although physicochmnicnJ
conditions not considered here may impose restrictions
on these depths.
Construction of the idealized geologic sections was
controlled by known surface geology, a limited number
of ·well data, and assumed values for density and
magnetizn.tion contrasts of subsurface rocks. The average
density contrast between Cenozoic rocks and l\1esozoic
miogeosynclinal rocks, Franciscan rocks, or Salinian
basement was assumed to be 0.5 g/cm 3 , whereas
that between serpentinites and l\1esozoic rocks was
taken to be about 0.1 g/cm 3 • The total 1nagnetization
of serpentinites relative to nonmagnetic rocks was
assumed to be 0.0025 emu/cm 3 , whereas that of Salinian
basement rocks was taken to be half that of the
serpentinites, or 0.00125 emu/cm 3 • Total magnetization
was everywhere assumed to be parallel to the earth's
present field dh·ection. Subsurface interpretations using
these assumed values of density and magnetization
contrast are intended to provide a basis for refinement
using more detailed geophysical and geologic information
as it becomes available.
REFERENCES
Bailey, E. H., Irwin, ,V. P., and .Jones, D. r..~., 1964, Franciscan
and related rocl~s, and their significance in the geology of
western California: California Div. Mines and Geology
Bull. 183, 177 p.
Bateman, P. C., and Eaton, .J. P., 1967, Sierra Nevada batholith:
Science, v. 158, no. 3807, p. 1407-1417.
Bishop, C. C., and Chapman, R. H., 1967, Bouguer gravity map
of California, Santa Cruz sheet: California Div. Mines and
Geology, scale 1 :250,000.
Burch, S. H., 1968, Tectonic emplacement of the Burro Mountain
ultramafic body, Santa Lucia Range, California: Geol.
Soc. America Bull., v. 79, no. 5, p. 527-544.
--- 1970, Complete Bouguer gravity and general geology of
the Cape San Martin, Bryson, Piedras Blancas, and San
Simeon quadrangles, California: U.S. Geol. Survey Prof.
Paper 64~A [In Press].
Burch, S. H., Grannell, R. B., and Hanna, W. F., 1970, Bouguer
gravity map of California, San Luis Obispo·sheet: California
Div. Mines and Geology, scale 1:250,000 [In Press].
Byerly, Perry, 1938, Comment on "The Sierra Nevada in the
light of isostasy, by Andrew C. Lawson": Geol. Soc. America
Bull., v. 48, no. 12, p. 2025-2031.
Byerly, P. E., 1966, Interpretations of gravity data from the
central Coast Ranges and San Joaquin Valley, California:
Geol. Soc. America Bull., v. 77, no. 11, p. 83-94.
Chapman, R. H., 1966, The California Division of Mines and
Geology gravity base station network: California Div. Mines
and Geology Spec. Rept. 90, 49 p.
Chesterman, C. \V., 1952, Descriptive petrography of rocks
dredged off the coast of central California : California Acad.
Sci. Proc., 4th ser., v. 27, p. 359-374.
Compton, R. R., 1966, Granitic and metamorphic rocl{S of the
Salinian block, California Coast Ranges 'in Bailey, E. H.,
ed., Geology of northern California: California Dlv. Mines
and Geology Bull. 190, p. 277-287.
Curtis, G. H., Evernden, J. 1!,., and Lipson, J., 1958, Age determination
of some grantic rocks in California by the potassium-argon
method: California Div. Mines Spec. Rept. 54,
16 p.
Eaton, .J. P., 1963, Crustal structure from San Francisco, California,
to Eureka, Nevada, from seismic-refraction measurements:
.Jour. Geophys. Research, v. 68, no. 20, p. 5789-5806.
--- 1966, Crustal structure in northern and central California
from seismic evidence, in Bailey, E. H., ed., Geology
of northern California: California Div. Mines and Geology
Bull. 190, p. 419-426.
Hall, C. A., and Corbat6, C. E., 1967, Stratigraphy and structure
of :Mesozoic and Cenozoic rocl{s, Nipomo quadrangle, southern
Coast Ranges, California: Geol. Soc. America Bull.,
v. 78, no. 5, p. 559-582. ·
Hanna, G. D., 1952, Geology of the continental slope off central
California: California Acad. Sci. Proc., 4th ser., v. 27, no. 9,
p. 325-358.
Healy, J. H., 1963, Crustal ·structure along the coast of California
from seismic-refraction measurements: Jour. Geophys.
Research, v. 68, no. 20, p. 5777-5787.
Hill, M. I.-., and Dibblee, T. \V., Jr., 1953, San Andreas, Garlock,
and Big Pine faults, California-A .Study of the character,
history, and tectonic significance of their displacements:
Geol. Soc. America Bull., v. 64, no. 4, p. 443-458.
Hsu, K. J., 1966, On the klippe origin of the Franciscan rocks
of Santa Lucia Range, California-A working hypothesis:
Geol. Soc. America Spec. Paper 87, p. 82-83.
--- 1967, Mesozoic geology of the California Coast Ranges­
A new working hypothesis, in I~tages tectoniques. Colloque
de Neuchatel, Neuchatel Univ. Inst. Geol., 1966: Neuchatel,
Switzerland, La Baconniere, p. 279-296.
--- 1968, Principles of melanges and their bearing on the
Franciscan-Knoxville paradox: Geol. Soc. America Bull.,
v. 79, no. 8, p. 1063-1074.
Hutton, C. 0., 1959, Mineralogy of beach sands between Halfmoon
and Monterey Bays, California: California Div. Mines
Spec. Rept. 59, 32 p.
.Jennings, C. "'·• 19~8, Geologic map of California, Olaf P.
Jenkins edition, San Luis Obispo sheet: California Div.
Mines, scale 1 :250,000.
.Jennings, C. "'·• and Strand, R. G., 1959, Geologic map of California,
Olaf P. Jenkins edition, Santa Cruz sheet: California
Div. Mines, scale 1 :250,000.
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