WHY CONTROVERSIES SURROUNDING THE CENOZOIC EVOLUTION OF THE HIMALAYAN-TIBETAN OROGENIC SYSTEM PERSIST (Invited Presentation)

Since the rise of plate tectonics paradigm, the Himalayan-Tibetan system has been regarded widely as the quintessential example of continent-continent collisional orogenesis. It sometimes surprises those who do not actively do research in the Himalaya or Tibet that so many aspects of their Cenozoic evolution remain highly controversial. Perhaps the most frustrating example is a lack of consensus on the age of collision between India and Eurasia, with estimates ranging from greater than 60 Ma to less than 40 Ma. Some of this controversy reflects disagreements about the definition of collision, which influences which lines of evidence one chooses to use to constrain the age of the event. Conflicting lines of evidence – and conflicting interpretations of the same lines of evidence – have been used to argue when Tibet reached its current status as the largest and highest orogenic plateau on Earth. Over two decades have passed since it was first suggested that lower crustal flow may have had a profound geodynamic influence on the evolution of the orogen, yet there is little consensus today regarding how this process has evolved over time and, in particular, how it influenced Himalayan tectonics. Debates continue to rage over whether extensional tectonics has been a major factor in Himalayan tectonics or was relatively inconsequential, and whether or not modern deformation within the Himalayan arc can be attributed solely to strain accumulation and episodic major slip events on the sole fault at the base of the Himalayan orogenic wedge. The current states of such controversies will be reviewed in this presentation, and the argument will be made that effective, evidence-based testing of competing hypotheses will require much more complete datasets than are presently available for most of the orogenic system. At present, in the absence of more and better data, strongly held opinions about Himalayan-Tibetan tectonics often rely on sparse datasets and the insufficiently critical acceptance of tectonic models based on them.