5. Conclusions
Our preferred interpretation is of 3–7% partial melt in situ at the present day beneath and north of the South Tibetan Detachment in the mid-crust of the Himalaya and Tibetan plateau of NW India. The region of low velocities appears to deepen slightly to the north and continues north of the Karakoram fault, beyond the region yet sampled by MT data in western Tibet. The LVL also persists south of the ITSZ in a region where existing MT data shows lower conductivities
than further north. Our observations of an LVL confirm earlier speculations based only on MT data about a low-viscosity layer beneath the NW Himalaya, and are consistent with a southwardshallowing,mid-crustal ductile channel that may be active at the present day (cf. Beaumont et al., 2004). Our data show that the LVL is diminished or absent further south beneath the Lesser Himalaya,hence melts must be absent (or solidified) there, but the southern limit of the LVL is currently poorly defined. Additional geometrical constraints on possible structural boundaries to the LVL, or on the
composition of and anisotropy within the LVL, would greatly increase the reliability of our estimates.