When did the proto-Himalayas become non-volcanic?

Question

In the normal course of events, when continents move toward each other, at least one coast will be associated with a subduction zone and corresponding volcanic activity. When the Indian subcontinent was moving toward Asia, we would expect such to occur, as confirmed by the answer to Volcanoes in the Alps and Himalayas and the subduction of Tethys Sea

The above also observes that there is no trace of such volcanic activity nowadays; it has been thoroughly buried and erased, which is understandable.

At what point did volcanic activity cease? Would it have been around the time the sea between the two continents disappeared? Or would it have continued for some time after that, resulting in a landlocked but still highly volcanic mountain range?

Answer 1

We don't know for sure because A. the evidence has almost all been erased by the continued crustal shortening of the area where the volcanic arc(s) would have been. B. the region is huge and volcanism will have varied in duration greatly across the range as a whole. The "core range" of the Himalaya has lost on the order of 6000km (~2500 miles) of crust to subduction and subsequent orogeny. The current tops of many of the mountains of the Himalaya were once buried deeply enough to start metamorphosing and most datable volcanic deposits would have been on a surface that has long since been eroded away. There are basalt feeder dykes in the Abor formation that yield crystalisation dates as young as 25Ma so that puts a limit on that particular part of the range.

Answer 2

To begin with, the formation of the Himalayas was never volcanic which is why you don't find volcanic rocks in the Himalayas. As for the subducting Indian oceanic plate (which contained Indian continental crust) that volcanism can be found in Tibet and the eastern Himalayas, in far northern Myanmar. This would suggest an oblique component to the subduction of the Indian Plate relative to the Eurasian Plate.