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Palaeogene volcanic rocks of central and southern Tibet show arc affinities (Coulon et
al. 1986) and Ar/Ar ages ranging between 110 and 80 Ma in the north and between 60
to 50 Ma in the south. Coulon et al. (1986) relate this ages to north directed subduction
beneath Lhasa, with shallow subduction until 80 Ma, followed by steeper subduction.
The plutonic Gangdese/Transhimalaya belt of the southern margin of Lhasa is the
manifestation of this subduction zone (e.g. Schärer et al. 1984, Harris et al. 1988, Miller
et al. 2000). Miller et al. (2000) compared several own and published age data of
magmatic rocks from different parts of the whole Transhimalayan magmatic belt and
could define two major intervals of calc-alkaline magmatism: a mid-Cretaceous peak at
about 120-90 Ma and a Palaeocene and Eocene time interval at around 60 to 40 Ma. The
first interval fits very well the findings of this study, even so in the Pamirs it is
concluded that the Cretaceous magmatism may have been bimodal with peaks at ~120
Ma and ~75 Ma.
The amalgamaltion history beween the Indus –Yarlung and the Rushan Pshart sutures
is in many aspects speculative (e.g. Hildebrand et al. 2000, Fraser et al. 2001). South of
the southern Pamirs and Lhasa follow the Wakhan, eastern Hindu Kush, and Karakoram
blocks. Whereas the South Pamirs comprises mainly undifferentiated Cretaceous and
Tertiary intrusives, the Karakorum is composed of metamorphic and sedimentary rocks
intruded by subduction related granitoids with predominately Early Cretaceous and
locally Jurassic ages. The boundary between the East Hindu Kush block and the
Karakorum is supposed along the Rich Gol Metamorphic Complex (RGMC), a narrow
strip along the Tirich Mir fault (Zanchi et al. 1997). The RGMC is composed of highgrade
metabasites with serpentinites and metapelites. Zanchi et al. (1997) conclude,
that the East Hindu Kush and Karakorum share a common history at least since Mid-
Cretaceous, as both blocks are intruded by the East Hindu Kush granitoids. One of
these, the Tirich Mir pluton, records a Rb/Sr whole rock age of 115±4 Ma (Desio et al.
1964), but is probably poorly constrained (Hildebrand et al. 2000). The Kafiristan pluton
yield a Rb/Sr whole rock age of 480 Ma (Debon et al. 1987), which is a typical
Gondwanan age. Within the Tirich Mir fault, pegmatite dikes crosscut staurolith
schists; the latter yield U-Pb monazite ages of 135-126 Ma near Gharam Chasma. U-Pb
dating of uraninites from one of these pegmatites revealed an age of 114±2 Ma
(Hildebrand et al. 2001). Thrusting along the Tirich Mir fault took place during the
Cretaceous (Hildebrand 1998). The southern margin of the eastern Hindu Kush region
was discriminated by a continental margin type above a north-dipping Tethyan
oceanic subduction zone. The collision between the Karakorum and the southerly
adjacent Kohistan-Ladakh arc was about ~80 Ma along the Shyok/Northern suture (e.g.
Chandra et al. 1999). Finally, India collided with the amalgamated Eurasia at about 55-
50 Ma. A major phase of crustal continental melting in the South Pamirs, East Hindu
Kush, and Karakorum regions led to the emplacement of leucogranites, like the Gharm
Chasma pluton (~24 Ma) in the Hindu Kush and the Baltoro granite in the central and
eastern Karakorum (Hildebrand et al. 2001).
Zircon geochronology of Cretaceous and Cenozoic granitoids from the southern
Qiangtang to northern South Pamirs and from crustal xenoliths erupted from 90-100 km
depth in the south-eastern Pamirs during the Miocene (Ducea et al. 2003) chronicles
multiple Phanerozoic additions to a Proterozoic crust derived from Gondwana. The