Abstract

40Ar/39Ar dating of detrital white mica from Cenozoic sediments from the nonmarine Qaidam Basin in western China yields several age groups. These include (1) ca. 350–450 Ma, (2) 220–280 Ma, subordinate clusters with (3) 122–140 Ma, and (4) a minor group ca. 500 Ma. Ages between 350 and 450 Ma are the most common and dominating in the analyzed samples.

Detrital mica in the western Qaidam Basin can be of a northern (Altyn Mountains) and/or a southern (Qimantagh–Kunlun Mountains) provenance. The main age group of 350–450 Ma is well known from intrusions in the Altyn Mountains, whereas the young ages (120–126 Ma) have been found within shear zones along the Central Kunlun and Altyn Tagh faults. However, hinterland sectors beyond the Altyn Tagh and Central Kunlun faults must be considered as potential source areas, because the imbalance between the amount of basin fill to eroded basement material requires additional sources. Early Paleozoic ages (ca. 500 Ma) have been documented so far only in the Hongliugou suture zone north of the Altyn Tagh fault. This suggests late or slow continuous uplift of the southern Altyn Range, and because of sinistral slip along the Altyn Tagh fault, further units of the same age are now exposed farther westward. The age group of 220–280 Ma has been documented only from the northern basin margin. This age group may indicate recycling from Triassic–Jurassic cover sequences of the Altyn Mountains or provenance from Permian–Triassic granite bodies that possibly originated in the Qilian Mountains.

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