Petrogenesis and thermal history of the Kunlun Batholith, Northern Tibet
The Kunlun Terrane is the most northerly of the several microplates that comprise the
Tibetan Plateau. Geochronological data from the Kunlun batholith defines three distinct
periods of intrusion at 390 Ma, 250 Ma and 190 Ma.
A model is presented whereby the Devonian intrusions are considered to be related to a
collision event between the Kunlun and Tarim Terranes, which were part of
Gondwanaland and situated in the southern hemisphere at this time. It is proposed that in
the region of the 1985 Tibet Geotraverse route, the Golmud Fault represents the Kunlun-
Qinling suture line along which the two plates collided. Break-up of this part of
Gondwanaland, which proabably also included the Qiangtang, Lhasa and Indian plates,
occurred during the Permian along the Zangbo and Jinsha suture lines. Continental rifting
was followed by a prolonged period of northward subduction of the Qiangtang Terrane
beneath the Kunlun Terrane. This resulted in formation of the Permian batholith, and the
massive Songban-Ganzi accretionary prism. Subduction culminated in collision at about
200 Ma. Post tectonic granites were emplaced around 190 Ma.
Initial Sr ratios for the granitoids range from .7074 to .7130, and support the
geochemical modelling which suggests that they have been derived from melting midcrustal
sources. Only the Devonian Wanbaogou pluton may have resulted from anatexis
of upper crustal sediments.
A reset biotite age of 120 Ma from a pluton cut by the Xidatan Fault, supports
sedimentalogical evidence which indicates a major reactivation of thrust faults in the area,
as a result of collision between the Lhasa and Qiangtang Terranes during the Cretaceous.
Apatite fission track ages from plutons north of the Golmud Fault also document this
uplift event. A 100 Ma period of quiescence ensued, during which the Kunlun Terrane
cooled extremely slowly until a state of thermal equilibration was reached.
The collision of India with Tibet at 45 Ma thickened the Tibetan crust and resulted in
further reactivation of faults in the Kunlun Terrane. Apatites from the granites between
the Golmud and Xidatan faults give mixed ages around 20 Ma. It is calculated that uplift
in this region, as a result of the Himalayan collision, could have been as recent as 8 Ma.