Neotethys and the India-Asia collision: Insights from a palaeomagnetic study of the Dazhuqu ophiolite, southern Tibet

Since 1999, independently derived geophysical and geological models have been published arguing for an intra-oceanic subduction system along essentially the entire width of the India-Eurasia collision belt. This idea conflicts with earlier proposals, where in the eastern part of the convergence zone Neotethyan mid-ocean ridge-generated lithosphere directly north of the Indian craton was consumed beneath Eurasia in Tibet in an Andean-type plate configuration. New palaeomagnetic data are reported from three Barremian-Aptian (∼ 120 Ma) sequences of chert, siliceous mudstones and volcaniclastic rocks. These rocks form the uppermost part of the Dazhuqu supra-subduction zone ophiolite terrane, which crop out along substantial portions of the India-Eurasia (= Yarlung Tsangpo) suture zone in southern Tibet. The declination data provide little regionally-useful tectonic information; they are dominated by local rotations, presumably related to the Dazhuqu terrane's initial obduction onto the India plate in the Palaeocene and subsequent movement(s) as India later collided and indented into Eurasia. The inclination data are, however, useful because they yield consistent sub-equatorial formation sites (2.7 °S ± 3.0°, 7.9 °N ± 2.7°, 1.4 °N ± 5.7°), which correspond with the location of the Neotethyan intra-oceanic subduction system inferred from the seismic tomographic data. At the time these Dazhuqu terrane rocks formed, the intra-Tethyan subduction zone would have been about 2500 km south of Eurasia.