Sedimentary Processes, Environments and Basins || 40Ar/39Ar Dating of Detrital White Mica as a Complementary Tool for Provenance Analysis: A Case Study from the Cenozoic Qaidam Basin (China)
✍ Scribed by Nichols, Gary; Williams, Ed; Paola, Chris
- Publisher
- Blackwell Publishing Ltd.
- Year
- 2007
- Tongue
- English
- Weight
- 786 KB
- Edition
- 1
- Category
- Article
- ISBN
- 1405179228
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✦ Synopsis
When classic petrographic analysis of the modal composition of sandstones yields no distinction between different source regions, 40 Ar/ 39 Ar dating of detrital white mica can provide vital information on the age of a source area and thus link the sediments to a specific provenance in the hinterland. This approach is exemplified by a case study of the intramontane Qaidam Basin (western China). While the geology of the surrounding mountains of the Qaidam Basin shows considerable lithological variation and the basin's palaeoclimate changed from semi-arid to arid, modal analysis of sandstones from two sections in the northwestern basin, as well as a section on the eastern margin, yielded no significant spatial or temporal differences. All sandstones, most of them classified as lithic wackes with matrix/cement contents between 14 and 39%, plot mainly in the recycled orogenic field of Dickinson's ternary discrimination diagrams for a tectonic environment. The sandstones are quartz dominated, with quartz contents of 33-65% and relative high contents of feldspar and lithic grains. On the other hand, 40 Ar/ 39 Ar total-fusion age data obtained from detrital white mica of between 123 and 546 Ma yielded three age clusters that could be assigned to certain provenance areas within the early Palaeozoic and Permian basement in the Altyn and Qimantagh mountains. This contrasts with the Lulehe section in the east of the basin, where exclusively Permian ages between 250 and 279 Ma were found. This significant difference in age distribution, and thus provenance, could not be deduced from sandstone composition. The results of this study show how 40 Ar/ 39 Ar thermochronology can complement classic point-count analysis.
Keywords Tibetan plateau, Qaidam Basin, provenance, 40 Ar/ 39 Ar age dating, Inner Asian orogens, sandstone composition.