Abstract:

The Tibetan Plateau  is one of  the regions  in China where  igneous rocks are very widely developed. Various  types of
volcanic and plutonic rocks are distributed over 300,000 km2 in area and take 10% area of the entire Plateau. These igneous rocks
and carried deep-seated nodules play  important  roles  in understanding geodynamic evolution of  the Tibetan Plateau, as either
lithoprobes/windows or  tectonic  records, and are closely  related  to mineralization as well. This paper discusses some  important
scientific  topics via studying  igneous  rocks.  (1) The  timing of  Indo-Asia collision: This  is a very  important scientific problem.
There  is, however, a wide  range of discrepancy about  the  timing of  initiation of  the collision  (from earlier  than 70 Ma,  to even
later than 34 Ma). According to multiple lines of evidences from the 1500 km-extending main collision zone in southern Tibet, we
deduced a conclusion that Indo-Asia collision likely started from 65/70 Ma and completed in c. 40 Ma (syn-collisional stage), and
then transformed into post-collisional stage after 40 Ma. (2) Underplating and magma mixing, an event of mantle-crust interaction
during  syn-collisional  stage: There are abundant evidences  for underplating and magma mixing  in  southern Gangdese. An

important process of continental growth and evolution took place in the Tibetan Plateau. (3) The origin of formation of extremely
thick crust of  the Tibetan Plateau: A deduction of “Two  types of crust and  two  types of mechanism”  is suggested based on  the
studies of collisional and post-collisional  igneous  rocks. There are  two  types of crust,  juvenile crust and  recycled crust,  in  the
Plateau. Crustal  thickening of  the Plateau was caused by  two  types of mechanism,  i.e., both structural compression and  input of
mantle materials via magmatism. (4) The composition, structure and evolution of the lithosphere of the Tibetan Plateau: There are
three geochemical reservoirs in the lithospheric mantle, and three types of lithospheric structure underneath the Tibetan Plateau.
Nodules and outcrops of mantle/lower crust-seated rocks are found in several locations of the Plateau. (5) Possible lateral flow of
lower crust and upper mantle: Migration of collisional and post-collisional volcanism with time shows a highly distinctive pattern,
which can be interpreted to reflect lateral flow of the lower crust and asthenospheric mantle induced by the approach and ensuing
collision of relatively thick (India and Eurasia) continental plates.

Key words:  Tibetan Plateau, magmatism, igneous rocks, continental collision, mantle-crust interaction, crust growth, lithosphere, lateral flow