OSCILLATORY- AND SECTOR-ZONED GARNETS RECORD CYCLIC (?) RAPID THRUSTING IN THE CENTRAL NEPAL HIMALAYA
Both types of zoning are interpreted to result from extraordinarily rapid, possibly cyclic thrusting. If cyclic thrusting occurred, then time-scales of thrust rate inhomogeneities are ~25 Kyr. This timescale implies that (1) satellite determination of modern fault movement rates may not accurately reflect slip rates or strain partitioning in the Himalaya for times previous to the late Pleistocene, and (2) strain in the Indo-Asian collision must be cyclically partitioned on different major structures over tens of Kyr. This latter observation is consistent with variations in thrust rates within the MCT zone from ~2 to >4 cm/yr on Myr timescales (Kohn et al., 2004). Sector zoning in Ca but not Y, Mn, or Mg implies maximum intra-crystalline diffusion rates for Ca of ~10-21 cm2/sec at 550 °C (consistent with experimental determinations), but faster rates for other elements.