The When and Where of the Growth of the Himalaya and the Tibetan Plateau

Abstract

Over the past 50 million years, collision between India and Asia has produced the highest and most extensive plateau on Earth today and the greatest present-day topographic relief (Fig. 1). The Tibetan Plateau and Himalaya may be the largest such feature seen on Earth in the Phanerozoic (i.e., since approximately 542 million years ago). Although this tremendous geographic feature has been ascribed to the effects of the collision between India and Asia since the early part of this century,1 there are still many important questions regarding the tectonic and geographic history of the region that remain unanswered. As plate tectonic theory has been applied to the region, a detailed understanding has begun to emerge regarding certain small areas, mostly on the edge of the plateau. The ability to integrate information from sources such as seismology and geodesy makes study of this ongoing collision particularly valuable in understanding more ancient orogens, where such information is generally not available. The relative FIGURE 1. Geographic location of the Himalaya and the Tibetan Plateau showing major geologic features. Heavy lines are faults; thin lines are 3000 and 5000 m topographic contours. Diagonal ruled areas are the Gangdese and related batholiths formed by the subduction of the Tethys oceanic crust in the Cretaceous and Paleogene. Stippled areas are regions of east-west extension of the southern Tibetan Plateau since the late Miocene. MKT = Main Karakoram Thrust, MMT = Main Mantle Thrust, MCT = Main Central Thrust, MBT = Main Boundary Thrust, ITS =Indus-Tsangpo Suture, STDS = Southern Tibetan Detachment System, NQTL = Nyainqentanghla range. After Harrison et al.2 youth of this orogen allows a precise temporal resolution of events by a variety of methods, which allows better evaluation of the possible mechanisms responsible for the growth of the plateau.2 The Tibetan Plateau has had an unquestioned and significant effect on the climate of Asia as well as on global circulation patterns,3–5 and it is our growing understanding of the tectonics of this region that allows more detailed investigations into the variation of Cenozoic climate. We can in many cases date the time of initiation or cessation of important tectonic structures in this orogen, but the evaluation of the relationships between these features and the elevation of the surface of the Earth is a generally less straightforward process.