Detrital zircon LA-ICP-MS U-Pb dating for K-feldspar leptite of Quanji massif in the north margin of Qaidam Block: constraint on the age of Dakendaban Group

To determine the maximum deposition age of the Dakendaban Group, the authors measured detrital zircons from a K-feldspar leptite for U-Pb age using LA-ICP-MS technique. The CL images and the Th/U values show that the detrital zircons are of inherited magmatic origin. The 207Pb/206Pb age range of 36 measuring points is 2094-2280 Ma,the 207Pb/206Pb age relative probability density plot for 30 measuring points with concordant degree over 90% exhibits monomodal curve with peak age of ~2190 Ma. Combined with the age of the earliest metamorphic event,the deposition age span of the protolith sediments of the K-feldspar leptite and the Dakendaban Group is constrained to be 1.95-2.19 Ga. The previously reported ~2.42 Ga zircons from the pegmatite are of inherited magmatic origin and are considered to have been derived from the Dakendaban Group wall rock, so their age cannot be used to constrain the minimum deposition age of the protolith of the Dakendaban Group.