Age of initiation of collision between India and Asia: A review of stratigraphic data

Dating of the oldest continental sediments from the Himalayan foreland basin

“…Here, however, we show that the melting of basalt under both H 2 O-added and lowtemperature conditions can yield extremely alkali-rich silicic liquids, the alkali content of which increases with pressure. These liquids are deficient in titanium and in the elements niobium and tantalum and are virtually identical to glasses preserved in mantle xenoliths found in subduction zones 6 and to veins found in exhumed metamorphic terranes of fossil convergent zones 7 . We also found that the interaction between such liquids and mantle olivine produces modal mineralogies that are identical to those observed in metasomatized Alpine-type peridotites 8 .…”

“…The marine to continental facies transition in the suture and foreland basin, and variation along strike, has been used to determine the timing and degree of diachrony of collision [6][7][8] , from which estimates of the amount of accommodation of strain by extrusion have been made 6 .…”

“…Rowley 6 concluded that only in western Zanskar-Hazara was dating (on the oldest syncollisional continental red beds of the Chulung La Formation in Zanskar and the Balakot Formation in Hazara) sufficiently precise to permit the accurate determination of the marine to continental facies transition at 51 Myr. Further east, stratigraphic data can constrain collision only at Ͻ45 Myr, indicating Ͼ7 Myr diachrony.…”

“…Hence, Early Eocene is only a robust maximum age for the Chulung La red beds, and the stratigraphic argument rests heavily on the Balakot Formation. Our revised Balakot Formation age of Ͻ35 Myr therefore removes all stratigraphic evidence for diachronous collision and also reduces the accuracy of the stratigraphically determined timing of collision (previously taken as 51 Myr) 6 to between 55 Myr (ref. 21) (the youngest marine facies) and Ͻ35 Myr.…”

Imaging Poisson's Ratio of the Uppermost Mantle beneath China

“…For Pn and Sn, if we rely on the classical assumption that these phases are headwaves along the mantle lid, V pn =V sn and Poisson's ratio of the uppermost mantle can be obtained by using Sn-Pn traveltime differences. Previous Pn or Sn research has shown large variations in velocity structure of the uppermost mantle between eastern China and western China (Barazangi and Ni, 1982;McNamara et al, 1997;Wang et al, 2002;Hearn et al, 2004;Liang et al, 2004;Phillips et al, 2005;Liang and Song, 2006;Sun et al, 2006Sun et al, , 2008Pei et al, 2007), which arise primarily from tectonic differences controlled by the India-Eurasia collision in the west and by subduction in the western Pacific to the east (e.g., Molnar and Tapponnier, 1975;Molnar et al, 1993;Rowley, 1996;Yin and Harrison, 2000;Tilmann et al, 2003). Earlier studies have obtained detailed Pn and Sn velocities in China separately, but no velocity ratio and Poisson's ratio have been published.…”