1992 and Mattern et al. 1996 considered the ophiolites of the Oytag-Kudi suture to have formed in the Proto-Tethys
between the Sinian and Early Paleozoic. Further time constraints on the formation of these rocks is provided by
the age of subduction-related magmatites see below which formed during subduction of the Proto-Tethys Ocean since
oceanic lithosphere must first be created before it can be subducted and since ocean-spreading can be coeval with
subduction.
4. Paleozoic subduction of Proto-Tethys beneath the South Kunlun
The basement of the South Kunlun is characterized by the occurrence of gneisses, amphibolites and migmatitic gneisses.
The gneisses and amphibolites were intruded by basic and acidic dikes which experienced amphibolite facies conditions
Pan et al., 1992. Protoliths of the migmatites south of Kudi seem to be of Proterozoic age Matte et al., 1996.
40
Ar
39
Ar age spectra on K-feldspars suggested to Matte et al. 1996 a
minimum age of 380–350 Ma for metamorphism. Zhang et al. 1992 distinguished two arc granitoid belts
in the South Kunlun, an older, Paleozoic one in the north, and a younger, Late Paleozoic to Mesozoic one in the south.
In this section we concentrate on the northern belt which is discontinuous at the surface, and relatively small compared
to the southern belt Fig. 8. Considering the geochemical characteristics of the granitoids and their geological setting,
which includes the presence of parallel-trending suture zones, as well as the long, linear, orogen-parallel extent of
the belts, Zhang et al. 1992 suggested that their genesis is closely related to subduction. Geochemical data Pan et al.,
1992 support this interpretation. Hsu¨ 1988 had already
F. Mattern, W. Schneider Journal of Asian Earth Sciences 18 2000 637–650 642
Fig. 7. Roadside outcrop of a brittle, steeply south-dipping, eastwest-trending fault in the 460 Ma granodiorite; ca. 15.5 km north of Kudi, directly at the first bridge north of Kudi.
attributed the presence of batholiths to a former active plate margin. The two granites from the northwest-trending part
of the western Kunlun dated by Fan and Wang 1990 as 445 Ma KAr and 480.43 5 Ma UPb belong to this belt.
These ages indicate Ordovician subduction. It cannot be ruled out that subduction occurred also during the Cambrian
and Silurian. Southward subduction is indicated by the northern position of this older arc granitoid belt within the
South Kunlun and its occurrence south of the Oytag-Kudi suture. The interpretation of an Early Paleozoic episode of
subduction is difficult to reconcile with coeval granitoid intrusions into oceanic lithosphere, unless some ophiolite
obduction occurred relatively early, or unless the upper plate also had an oceanic back-arc region north of the
South Kunlun, whose associated oceanic arc was first intruded by more or less M-type? arc granitoids “M-
type” sensu Pitcher, 1982 and then obducted?.
5. Mid-Paleozoic suturing of Proto-Tethys
