Open AccessOscillatory‐ and sector‐zoned garnets record cyclic (?) rapid thrusting in central Nepal
Author(s) -
Kohn Matthew J.
Publication year - 2004
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2004gc000737
Subject(s) - zoning , geology , main central thrust , thrust , slip (aerodynamics) , fault (geology) , seismology , thrust fault , geochemistry , mineralogy , petrology , metamorphic rock , physics , political science , law , thermodynamics
Garnets with oscillatory zoning (repeated compositional reversals) and sector zoning (crystallographically controlled compositional differences) were discovered in rocks from near the Main Central Thrust in the Langtang region, central Nepal. This zoning results from crystal growth kinetic effects related to extraordinarily rapid, possibly cyclic thrusting. If cyclic thrusting occurred, then timescales of thrust rate inhomogeneities are ∼25 Kyr, implying that satellite determination of modern fault movement rates may not accurately reflect slip rates or strain partitioning in orogens on timescales exceeding thousands of years. Sector zoning in Ca but not Y, Mn, or Mg implies maximum intracrystalline diffusion rates for Ca of ∼10 −21 cm 2 /s at 550°C but faster rates for other elements.