Detrital Geochemical Fingerprints Of Rivers Along The Yalu Suture Zone In Tibet: Implications For Drainage Evolution, Timing Of Arc Development And Erosion

The Yalu suture zone between India and Asia comprises today a central depression occupied by the Yulu River, flanked to the north and to the south by high-elevation ranges. Rivers along the suture zone are derived from such ranges and drain into the Yulu River, which in turns drains eastward. Modern sands from these rivers provide an opportunity to broadly sample rocks present within the suture zone and study their regional geochemical fingerprints and tectono-erosional implications. Seven sand samples from rivers along the suture zone in Tibet between Xigatze to the east and Mt. Kailas to the west were collected for detrital zircon U-Pb geochronological analyses, white mica 40Ar/39Ar and apatite fission track thermochronology. Zircon U-Pb ages for all rivers range between 15 and 3568 Ma. Rivers draining the northern side of the suture zone mainly yield ages between 40 and 60 Ma, similar to the age of the Gangdese arc. Samples draining the southern side of the suture zone record a Tethyan signal characterized by age clusters at 500 Ma and 1050 Ma. Samples collected from the western rivers yield zircon ages that are younger compared to those from the east; with ages predominantly <100 Ma. U-Pb zircon ages indicate that ~85% of the zircon are younger than 100 Ma in the farthest west side of the river samples (near Mt. Kailas) whereas only ~5% of zircons are younger than 100 Ma in the farthest east side of the river samples (near Xigatze). A more detailed analysis of the youngest zircon U-Pb age components reveal strong signals between 30 Ma and 100 Ma with significant peaks at 47 - 50 Ma and at 37 - 40 Ma, 57 - 63 Ma and 94 - 97 Ma, recording the activity of the magmatic arc along strike. Further analysis of the young age components (below 100 Ma) suggest a trend in age along the suture zone, with younging direction towards the west - and probably younging northward. However, the variation in ages is small. Our U-Pb detrital zircon ages are overall in agreement with previous work (Zhang et al.,2012); however, the details of our age spectra show some differences, including an age component at 94 - 97 Ma which was previously not recognized. Detrital thermochronology of the same samples is undergoing and will provide information regarding the timing of erosion of the suture zone and potential along-strike variability.