Origin of Late Cretaceous potash deposits in the Khorat Plateau: New evidence from δ11 B, 87Sr/86Sr and δ34 S of gypsum, anhydrite and halite
Abstract
The giant Late Cretaceous potash-bearing evaporite, located in northeastern Thailand and south-central Laos, occurs in the Maha Sarakham Formation, Khorat Plateau. The origin of this evaporite, marine, continental or hydrothermal, is still controversial.
Here, δ11B values of gypsum and anhydrite from the evaporites in two basins (the northern Sakhon Nakhon Basin and the southern Khorat Basin) of the Khorat Plateau were firstly reported. Combined with87Sr/86Sr ratios and δ34S values of these sulfates, δ11B values and 87Sr/86Sr ratios of halite, this study aims to constrain the origin of this evaporite. The δ11B values (average +16.08‰) of sulfates, halite (average +26.11‰) fall into the range of marine evaporites (+8.0‰ ~ +39.0‰). Similarly, the calculated δ11B values (average +46.08‰) of parent brines in sulfate precipitation stage are consistent with those (+39‰ ~ +70‰) of marine brines. The 87Sr/86Sr ratios of sulfates and halite, δ34S values (average +15.40‰) of sulfates together lie in the isotopic ranges of Cretaceous seawater, and deviate from those of continental or hydrothermal fluids. These comparisons simultaneously demonstrate that the evaporites in the Khorat Plateau are marine origin. This conclusion is important for the future potash exploration of Lanping-Simao and Qiangtang basins, in China, which belong to the eastern Tethys Domain in the Mesozoic, like the Khorat Plateau. Meanwhile, determination of δ11B values of gypsum and anhydrite may be a potential tool to reconstruct the boron isotopic compositions of seawater in geological time, which is useful for defining oceanic geochemical cycles.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMPP21D1647Q
- Keywords:
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- 0419 Biomineralization;
- BIOGEOSCIENCES;
- 0454 Isotopic composition and chemistry;
- BIOGEOSCIENCES;
- 0473 Paleoclimatology and paleoceanography;
- BIOGEOSCIENCES;
- 4994 Instruments and techniques;
- PALEOCEANOGRAPHY