Geology Reference
In-Depth Information
Figs. 6.26 and 6.27
Magnitude of the angular
acceleration vector (
blue
line
) and variations of
angular velocity (
red line
)
for Eurasia and India since
thelateTriassic(230Ma).
Boxes
indicate possible
events of traction
j
d
¨/
dt
j
can be observed at 120 Ma (anomaly M0)
in the plots of N. America, S. America, Eurasia,
India, Australia, and E. Antarctica.
This peak is associated with a phase of global
reorganization of the plate boundaries during
the early Aptian, but no events of traction can
be observed at that age. However, large peaks
of scalar acceleration are always accompanied
by peaks in the magnitude of the angular
acceleration vector. The plots in Figs.
6.24, 6.25
,
6.26, 6.27
,
6.28, 6.29
,
6.30, 6.31
,and
6.32
show
that central Africa, east Antarctica and possibly
Australia never experienced a remarkable episode
of traction, although the latter was subject to three
strong increments of angular velocity during
the Tertiary that could be indicative of ongoing
accelerated motion (Figs.
6.28, 6.29
). The
oldest event of lithospheric traction during the
time interval considered here possibly occurred
between 154 Ma (M25 - Kimmeridgian) and
148 Ma (M21 - Tithonian). It consisted into
a clockwise acceleration of Laurasia about a
pole located in the present day Xinjiang region,
central Asia (44.88
ı
N, 88.45
ı
E). The event can
be observed on the plots of both N. America and
Eurasia (Figs.
6.24, 6.25
,
6.26, 6.27
), which at
that time formed a unique Laurasian plate, and
coincided with a phase of accelerated spreading
