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histories. The Mid-Jurassic zircon grain age group may originate from the like aged
closure of the Rushan Pshart/Bangong-Nujiang suture and associated, arc-related
magmatites of the Rushan Pshart arc along the southern margin of the Qiangtang
block. The Early Cretaceous zircon grains may have been influenced by a reheating
event in the South Pamirs and Karakoram. During the Cretaceous, the Hindu Kush-
Karakoram-South Pamirs were the active margin arc of the northward subducting
Shyok suture. The subduction/accretion processes led to widespread metamorphism
and most likely bimodal magmatism in the Cretaceous times (~120 Ma and ~80 Ma).
Only few fission track data were published from northern Tibet. Jolivet et al. (2001)
provided zircon fission track ages from basement rocks of the Kunlun mountains,
ranging from Late Triassic (220-200 Ma) to Middle and Late Jurassic (172-143 Ma), to
Late Cretaceous (~96 Ma). Apatite fission track data from the same samples were
separated into two groups >50 Ma and 50 Ma into subgroups of Middle to Late Jurassic (167 to
147 Ma), Early Cretaceous (138 to 97 Ma) and Early to Middle Eocene (55-48 Ma). The
Late Triassic zircon fission track ages of the basement rocks post-date the
Permian/Triassic peak detected by the Tertiary sediment samples from the
northernmost Pamirs, but matches very well with the post-tectonic emplacement ages
of the Karakul and Sailiak batholiths. However, the Late Jurassic and Early Cretaceous
peak ages from the Altyndara valley correspond well to the zircon and apatite age
groups from basement rocks of Jolivets et al. (2001) study. These authors interpret all
zircon ages to represent a Jurassic cooling event, with the Middle to Late Jurassic
cooling ages exhumed from deeper crustal levels due to their hanging wall structural
positions. From apatite fission track ages Jolivet et al. (2001) suggest slow long term
erosion in Jurassic time with low cooling rates of 0.1°C/Ma to 1.3°C/Ma. The
Cretaceous in north Tibet is characterised by sedimentation and in some places by a
reheating of rocks to 60°C to 70°C, probably around 120±20 Ma (Jolivet et al. (2001).
The authors conclude that there was either a previously formed relief initiated in the
Jurassic and which experienced differential subsidence in the Cretaceous and/or weak
tectonic activity in the Cretaceous after the collision of the Qiangtang and Lhasa
blocks.
Karakul-Mazar granitoid belt, Northern Pamirs
Five different granitoid locations were probed across the Triassic/Jurassic Karakul-
Mazar batholith belt. Two zircon fission track samples yielded late Early Cretaceous
cooling around 122-108 Ma, which can be interpreted as a thermal event related to
Cretaceous arc magmatism in the south (e.g. Shyok arc), or as slow denudational
cooling following the emplacement of the Triassic/Jurassic granitoids. Apparent
apatite fission track ages range from Eocene to Miocene (56-18 Ma) and young from
south to north, whereas the cooling rates increase towards the north (Fig. 4.2 and 4.3).
Detailed structural mapping is missing in the Karakul-Mazar belt and therefore the
apatite fission track age distribution is difficult to interpret. As discussed in Schwab et
al. (in press), the massive batholith in the Karakul-Mazar belt may have acted like a
rigid backbone during the Tertiary and deformation may be confined to the margins of
the batholith belt. The right-lateral transpressional Markansu fault to the north of the