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in the 18 lava flows b thermoremanent magnetization
acquired during initial cooling. A11 the lavas exhibited
reversed polarity, as is appropriate for their age be-
cause Peleocene time was dominated by periods of
reversed geomagnetic pohrity (Ness and others, 1980).
The paleornagnetic inglinations in these rocks
range from -65.8' to -87.6 , and the paleomapetic
pole calculated from the 18 sites (pole I ,gig. 51) is
close to northwestern Alaska at lat 70.0 N., long
165.4' W., with e 95-percent-confidence radius of
10.0'. Figure 51 compares this pole with Cretrceous
and Paleocene poles from aratonic North America.
Somewhat surprisingly, the Cantwell pole is much
closer to the Cretaceous reference pole (135-78 m.y.
B.P.) than to the Paleocene reference pole (67-61 m.y.
B.P.). This difference could be accounted for if the
CantweU volcanic rocks were, in fact, slightly older
than the age range of the Paleocene reference because
the interval from latest Cretaceous to early Paleocene
was a time of rapid apparent polar wander for the
North American craton. The paleomagnetic latitude
of the CantweU, calculated according to the improved
rnethcd of Kono (198O), is 63.0°, with a 95percent-
confidence deviation of t9.7 . The locus of this paleo-
latitude is shown as a dashed circle in figme 51 around
the location of the basin in which the Cantwell Porrna-
tion was deposited. The result is the same as when
poles are compared: The paleolatitude is what would
be expected for Cretaceous time and somewhat, but
not significantly, high for Paleocene time.
Pigum 51.-Locations of paleomegnetic pales Ln North
America, with 95percent+xnM&nce circles: I,
volcanic rocks of the Paleocene CnntweU Formation;
2, Paleocene intrusive rocks in Montana (Jacobson end
others, 1980); 3, Creteceous pole for North American
craton (Mankinen, 1978). Star denotes study area.
Dashed circle Is locus of poles corresponding to mean
geomagnetic latitude of the Cantwell Formation
according to Kono's (1 980) statistical method.
The timing of accretion of tectonos tro tigraphic
terranes in Alaska Is constrained by this new paleolati-
tude determination. From paleornagnetic and geologic
evidence, the general pat tern of accretion of terranes
south of the DenalI fault has been one of northward
movement: for example, WrangeUia (Hillhause, 1877;
Csejtey and others, 1982), the Peninsular terrane
(Stone and Packer, L879), and the Chugach terrane
(Grommband Hillhouse, 1981). The volcanic rocks of
the Cantwell are just north of the McKinley strand of
the DenaLi fault (flg. 50) and overlie the Plngston and
McKinley terranes, which ere also bounded on the
south by the McKinley strand of the Den& fault
(Jones and others, 1882). These terranes and, by
implication, other terranes to the north, such as the
Nixon Pork and Yukon-Tanana terranes, have under-
gone no northward displacements greater than about
500 km since Paleocene time. Moreover, recently dis-
covered evidence that strike-slip movement on the
McKinley strand has been minimal (Csejtey and others,
1982, 1983) likewise Implies that the northward rnove-
rnent and accretlon of Wrmgellia and the Peninsular
terrane were complete by Paleocene time.
REFERENCES CITED
Csejtey, ma, dr., Cox, D. P., Evarts, R. C., Stricker,
G. D., and Foster, H. L., 1982, The Cenozoic
Denali fault system and the Cretaceous accretionary
development of southern Alaska: Journal
of Geophysical Research, v. 87, no. 5, p. 3741-
3754.
Csejtey, ma, Jr., Yeend, W. E., and Goerz, D. J., IU,
1983, Occurrenae of probable CantweU Formation
rocks south of the Denali fault system in the
Healy quadrangle, south-central Alaska, in
Coomad, W. L., and Elliott, R. L., eds., Thi
United States Geological Survey in Alaska:
Accomplishments during 1981: U.S. Qeological
Survey Circular 868, p. 77-79.
Gilbert, W. G., Ferrell, V. M., and Turner, D. L., 1976,
The Teklanika Formation--a new Paleocene volcanic
formation in the central Alaska Range:
Alaska Divislon of Geological and Geophysical
Surveys, Geologic Report 47, 16 p.
~rornmd,~. S, and Hillhouse, J. W., 1981, PBleomagnetic
evidence for northward movement of the
Chugach terrane, southern and southeastern
Alaska, Albert, N. R. D., and Hudson, Travis,
eds., The United States Geologlcal Survey in
Alaska: Accomplishments during 1079: U.S.
Geologjcd Survey Circular 823-B, p. B70-B72.
HLckman, R. G., 1974, Structural geology and stratigraphy
along a segment of the DenaU Pault
system, central Alaska Range: Madison, Unlverstty
of Wisconsin, Ph. D. thesis, 276 p.
Hillhouse, J. W., 1077, Paleornagnetism of the Triassic
Nikolai Greenstone, McCarthy quadrangle,
Alaska: Canadian Journal of Earth Sctences, v.
14, no. 11, p. 2578-2592.
Jacobson, D., Beck, M. E., Jr., Diekl, J. F., and H m ,
0. C., Jr., 1980, A Paleocene paleomagnetlc pole
for North America from alkalic intrusions, central
Montana: Geophysical Research Let ters, v.
7, no. 7, p. 549-552.