Paleomagnetism of a Late Cretaceous Island arc complex from South Sakhalin, East Asia: Convergent boundaries far away from the Asian continental margin?
Ml. Bazhenov et al., Paleomagnetism of a Late Cretaceous Island arc complex from South Sakhalin, East Asia: Convergent boundaries far away from the Asian continental margin?, J GEO R-SOL, 106(B9), 2001, pp. 19193-19205
The Hokkaido-Sakhalin fold system stretches for similar to 1500 km along th
e eastern coast of Asia and consists of several N-S trending tectonic belts
. Studies in South Sakhalin show that the northern part of the Tonino-Aniva
Peninsula (Ozersk unit) is a counterpart of the Tokoro belt on Hokkaido. J
apan. In the eastern part of the Ozersk unit, 195 hand samples were sampled
at 20 sites from Campanian-Maastrichtian tuffaceous siltstones and sandsto
nes of the Chayka Formation of island arc affinity, Stepwise thermal demagn
etization isolates a postfolding low- to intermediate-temperature component
(B) of normal polarity. A high-temperature component (A) is isolated from
about half the samples. Because of strong overlap of unblocking temperature
spectra of these two components in other samples, direct observations and
remagnetization circles were combined for calculation of site-mean directio
ns. Component A is mostly of reversed polarity: a fev samples of normal pol
arity are found at three sites. The presence of two polarities with approxi
mately antipodal directions and the positive fold test imply a prefolding,
and most probably primary origin of component A. A formation-mean inclinati
on of 45 0 degrees +/- 6.4 degrees calculated with the aid of inclination-o
nly statistics corresponds to a latitude of 26.6 degrees +/- 5.2 degrees N.
A similar inclination is derived from a late Cretaceous island arc complex
from the Tokoro belt on Hokkaido. Since both mean inclinations are similar
to 30 degrees lower than the coeval Eurasian reference value, a large-scal
e northward transport of the entire Tokoro island are is inferred. We exclu
de the possibility of displacement with the Kula plate and coast-parallel t
ransport. instead, intra-oceanic motion with the Pacific plate and docking
at the Eurasian margin at circa 30 Ma are inferred. Combined paleomagnetic
data from the Tokoro belt, the Nemuro belt and Kamchatka region imply that
a system of intra-oceanic island arcs existed in the northwest Pacific in L
ate Cretaceous time.