THE DETRITAL ZIRCON SIGNATURE OF MOUNTAIN BUILDING IN NORTHEAST TIBET

Detrital zircon has proven a powerful tool for determining provenance, with past work focusing primarily on delimiting regional source terrains. Here we explore the limits of spatial resolution and stratigraphic sensitivity of detrital zircon in ascertaining provenance, and we demonstrate its ability to detect source changes with an order of magnitude greater spatial resolution than previously realized. For such an analysis to be fruitful in a given mountain range and basin, two conditions must be met: first, discrete intra-range source terrains must have unique U/Pb zircon age signatures; and second, the basin strata must have well defined depositional ages. Here we use ~1400 single-grain U/Pb zircon dates from NE Tibet to first identify and then analyze an area which satisfies the above conditions. This analysis shows that the edges of intermontane basins are stratigraphically sensitive to discrete, punctuated changes in local source terrains. By tracking eroding rock units chronologically through the stratigraphic record, this sensitivity permits the detection of the differential rock uplift and progressive erosion that begins at ~8 Ma in the Laji Shan, a 10-to-25-km-wide range in NE Tibet with a unique U/Pb age signature.