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Figure 4. Estimated reconstruction in southwest Pacific for Late Cretaceous time (100 Ma;
Lawver et al., 1992) showing proposed locations of spreading centers and subduction zones.
CNS is boundary of Cretaceous normal superchron at location of Pacific-Phoenix ridge after
its jump to south soon after M0 time (proposed by Joseph et al., 1993). Pacific (PAC)-Phoenix
(PHN, Aluk)-Farallon (FAR) triple junction is at old end of triple junction trace (TJ) mapped by
Cande et al. (1989), but ridge configurations are conjectural. North of Chatham Rise (CR),
spreading features are interpreted from satellite gravity (Figs. 2 and 3). Extinct spreading
center (Fig. 3) is shown in its location just prior to Zealandia-Antarctica spreading. At 100 Ma
it is proposed to be located to north (double dashed lines). Extinct system of microplate
spreading is hypothesized west of there (gray pattern marks captured crust); extinct spreading
centers are older to west. Dashed line is extinct Phoenix–east Gondwana subduction zone and
solid line is active subduction zone that is mostly dextral-transpressional in West Antarctica.
AUS—Australia; LHR—Lord Howe Rise; NZ—New Zealand; CP— Campbell Plateau; MBL—
Marie Byrd Land; EANT—East Antarctica; AP— Antarctic Peninsula; SAM—South America.
GEOLOGY, April 1995 375Rise paleosubduction zone of east Gond-
wana was near 708S at this time and moving
northward.
Paleomagnetic data indicate that in Early
Cretaceous time the Pacific plate was mov-
ing southward (Larson et al., 1992). There-
fore, the Pacific-Phoenix spreading center
was moving southward from the Pacific
plate during this period and closing with the
east Gondwana subduction zone.
Capture of subducted Phoenix micro-
plates by the Pacific plate occurred when
sections of the Pacific-Phoenix spreading
center died. In Aptian time the Pacific plate
reversed and started to move slowly north-
ward (Larson et al., 1992), pulling the cap-
tured microplates with it. This resulted in
traction on the overlying Gondwana plate
margin and caused extension within it. The
rate of Pacific plate northward motion ac-
celerated dramatically during Late Creta-
ceous time. Its northward rate ultimately
reached more than 100 km/m.y. just prior to
the time sea-floor spreading started between
Zealandia and West Antarctica (Larson et
al., 1992). This could have increased shear
on the overlying margin leading to ultimate
failure and sea-floor spreading. The time lag
between the beginning of extension and sea-
floor spreading is explained if at the time of
capture, the spreading center east of the
Udintsev fracture zone was offset left
(north) a large distance and subsequently
migrated southeast to reach the tip of the
Chatham Rise before 84 Ma (Fig. 4).
ACKNOWLEDGMENTS
Supported by the National Science Foundation
Office of Polar Programs. I thank Tanya Atwater,
Roger Larson, Joann Stock, Steve Cande, Doug
Wilson, and John Bradshaw for valuable discus-
sions and suggestions; Larry Lawver and Lisa Ga-
hagan for providing me with rotation data to
make the reconstruction in Figure 4; Craig Nich-
olson for a version of Figure 1 for California slab
capture (which I modified); Dan Scheirer for
downloading and plotting the gravity map; and
Aaron Martin for computer assistance. Contribu-
tion of the Institute for Crustal Studies number
0193-48TC.