The Emplacement Time Of The Hegenshan Ophiolite:Constraints On The U-Pb Ages Of Detrital Zircon Of The Unconformity Paleozoic Sedimentary Rocks

The Hegenshan ophiolite in the Solonker-Hegenshan belt is the largest ophiolite in the Central Asian Orogenic Belt(CAOB).Despite its significance in constraining regional tectonic evolution,the emplacement time of the Hegenshan ophiolite is still under debate.In this study,we provide new detrital zircon ages of the Paleozoic sedimentary rocks that unconformably overlie the Wusinihei ophiolite to constrain the lower limit emplacement time of the Hegenshan ophiolite.The zircon ages obtained from the Paleozoic sedimentary rocks range from 298±8 to 363±7 Ma,and show bimodal distribution at 300-320 Ma(peak at 308 Ma)and 320-360 Ma(peak at 330 Ma).The age group of 300-320 Ma coincides with the age range of the volcanic rocks of the Late Paleozoic Gegenaobao Formation.The age group of 320 to 360 Ma with a peak at 330 Ma may be linked to local mafic-ultramafic rocks of the Hegenshan ophiolite.Accordingly,we suggest that the emplacement time of the Hegenshan ophiolite should have occurred earlier than the deposition of the Gegenaobao Formation,most likelyduring the time between 308 and 330 Ma,instead of the Silurian,Devonian or Mesozoic as previously considered.