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Ar-40/Ar-39 incremental-heating analyses of supergene jarosite and yavapaiite were conducted for three weathering profiles at the Hongshan, Liuhuangshan, and Caihuagou deposits in the Tu-Ha Basin. The analyses provide numerical constraints on the timing and duration of weathering and supergene enrichment. Well constrained plateau ages and best-fitting inverse isochrons yield Ar-40/Ar-39 ages ranging from 33.3 +/- 0.5 Ma to 331 +/- 0.4 Ma (1 sigma). Our Ar-40/Ar-39 ages, combined with the published ages, indicate that a protracted history of weathering and supergene enrichment and, by inference, arid-semiarid climate (with at least a moderate amount of precipitation (>10 cm/y)) favorable to intense chemical weathering emerged at 33.3 Ma, 27.7-23.3 Ma, and 16.4-14.7 Ma, and prevailed from 11 to 7.8 Ma. Then, a progressive change from arid-semiarid toward hyperarid conditions and predominantly hyperarid conditions may have persisted since at least ca. 3.3 Ma. The climatic implications inferred from the weathering geochronology are in agreement with the chemical parameters and isotopic compositions of the Cenozoic sedimentary sequence from the Lianmuqin section in the Tu-Ha Basin, attesting to the reliability of weathering geochronology by the Ar-40/Ar-39 method as an indicator of paleoclimate in arid areas. Our results suggest that the retreat of the Paratethys Sea, which would have reduced eastward water vapor transport by the westerlies to the Tu-Ha Basin, led to its acidification in the Oligocene and that increased rain shadow effects, resulting from uplift of the Tibetan Plateau and Tian Shan Mountains, played important roles in the acidification history of the Tu-Ha Basin since the late Miocene. (C) 2016 Elsevier B.V. All rights reserved.