Ct. Klootwijk et al., FURTHER PALEOMAGNETIC DATA FROM CHITRAL (EASTERN HINDUKUSH) - EVIDENCE FOR AN EARLY INDIA ASIA CONTACT, Tectonophysics, 237(1-2), 1994, pp. 1-25
The Eastern Hindukush forms part of an elongate belt (''Central Domain
'', collage of Cimmerian microcontinents) that encircles the northern
part of the Indian subcontinent. A Gondwanan origin is commonly assume
d for this belt, but a ''Laurasian'' origin for the Chitral region has
been argued on palaeontological (Talent and Mawson, 1979) and palaeom
agnetic (Klootwijk and Conaghan, 1979) grounds. The ''Laurasian'' view
was based on a pilot study we undertook of Upper Devonian pisolitic i
ronstones from a thrust sheet at Kuragh Spur in Chitral. Preliminary r
esults showed a characteristic magnetization component [D = 318-degree
s, I = 6.5-degrees, N = 7 (block samples), k = 14, alpha95 = 16.5-degr
ees] indicating an equatorial palaeoposition. This component was thoug
ht to be of primary origin and was interpreted in terms of a Late Devo
nian ''Laurasian'' affinity of the Kuragh Spur rocks. This controversi
al conclusion has been tested in the present more comprehensive study
of the thrust pile of sedimentary rocks in the Reshun-Kuragh-Buni regi
on of Chitral and the primary origin of the characteristic magnetizati
on component refuted. Thermal demagnetization of 333 block samples fro
m Middle to Upper Devonian variegated sediments, Permian quartz flysch
, Permo-Triassic carbonates, and mid-Cretaceous redbeds showed two int
erpretable components. A softer component of recent origin (A); and a
harder characteristic component (B) of both normal and reverse polarit
y whose mean direction [D = 314.1-degrees, I = 6.0-degrees, N = 4 (thr
ust sheets), k = 198.2, alpha95 = 6.5-degrees] is comparable to the ch
aracteristic component observed in our preliminary study. However, the
universal presence of this component throughout the thrust pile prove
s its overprint origin, which we attribute to initial India-Asia conta
ct. Palaeomagnetic information pertinent to the controversy of a ''Lau
rasian'' versus a Gondwanan origin of the Chitral region has not been
obtained in this further study because primary magnetizations could no
t be identified beyond doubt. Hence, we retract herewith our original
conclusion of a Late Devonian ''Laurasian'' affinity of the Chitral re
gion on the basis of the palaeomagnetic evidence. The secondary compon
ent (B) comprises a suite of secondary magnetizations, acquired at equ
atorial-to-low-northern palaeolatitudes, and is attributed to initial
contact between Greater India and southern Asia. Component B has been
observed previously in the Himalayan-Tibetan region, both north and so
uth of the Indus-Tsangpo Suture zone. Identification is herein extende
d to the Hindukush region north of the Northern Korhistan (or Shyok) S
uture zone, which is a western continuation of the Indus-Tsangpo Sutur
e. Comparison of this suite of collision-attributed equatorial palaeol
atitude data from the India-Asia convergence zone with new palaeolatit
ude constraints from the Ninetyeast Ridge on the northward movement of
the Indian plate, contrained additionally by a recent minimal estimat
e of the palaeogeographic northern extent of Greater India, indicates
that initial contact between northwestern Greater India and southern A
sia was established at, or before, the Cretaceous-Tertiary boundary. T
he overprint origin of component B at about this time is further suppo
rted by observations by Zeitler (1985) on rocks from the sampled area
in Chital of partially reset zircon fission-track ages around 68-55 Ma
. The NW-SE declination axis of component B indicates a 60-70-degrees
counterclockwise rotation of the sampled thrust pile with respect to E
urasia and a counterclockwise rotation between 10 and 30-degrees with
respect to India. Some of the recent field components (A) show a compa
rable rotation and indicate that the tectonic activity that led to the
formation of the Hindukush-Pamir-Karakorum syntaxial zone has continu
ed into recent times.