The Lop Nur Salt Lake, located in the eastern part of the Tarim Basin, Xinjiang, China, has become a playa in the Quaternary. Rhombic in shape, the Lop Nur depression is mainly controlled by the NE‐striking and nearly N‐S‐striking sets of faults. Since 1995, a superlarge brine potash deposit with potash resources of 2.50times108t has been found in the Luobei subbasin in the northeastern part of the Lop Nur. We intensively studied the features and formation mechanism of faults inside the Lop Nur through satellite images, geomorphologic survey and continuous conductivity imaging and found seven subparallel graben faults formed under the action of nearly N 10° E principal compressional stress during deposition of the Lop Nur Salt Lake. These faults are up to >60 km long and 1–4 km wide and may extend downward for 1000 m or more. It is just under the action of these tensional faults that potash subbasins formed. The largest subbasin is the Luobei subbasin and the smaller ones are the Luoxi hollow, Erbei hollow and Tienan hollow. Investigation also indicates that the graben faults in the Lop Nur not only control the origin of the potash subbasins, but they themselves are also good brine reservoir structures, in which abundant potash‐rich brines are stored. Therefore, The faults had played an important role in the potash formation of the Lop Nur.
Investigations on stratigraphy, geomorphology and neotectonic movement in the Eastern Kunlun Mountains show that there existed a series of ancient lakes, including some saline lakes, in the studied region about 30,000 years ago. They were distributed south of the middle Kunlun fault, from the middle‐upper reaches of the present Narin Gol River in the west to the Alag Lake‐Tosou Lake in the east. Of these the ancient Narin Gol Lake and Kunlun Lake were mainly recharged by the hot water related to valcanos, so the B, Li and K contents are relatively high.The neotectonic movement that commenced at 30,000 a B.P. caused the river system in the Eastern Kunlun Mountains to invade southwards; as a result the ancient lake water was captured to recharge the Qarhan area. Therefore, the hot springs related to recent volcanism and faulting on the southern bank of the upper reaches of the Narin Gol River became an important source of saline materials for the Qarhan Lake.
Located in the eastern part of the Tarim basin, Xinjiang, the Lop Nur was an ultimate water catchment area of the Tarim basin during the Quaternary. Through nearly ten years of investigation and research, the authors have found a superlarge brine potash deposit in the Luobei s u b b a s i w secondary basin of the Lop Nur depression. The deposit has been mined now. On that basis, the authors propose new theories on the genesis of the potash rock deposit, In the tectonic and geomorphologic contexts, the Tarim basin lies in a "high mountain-deep basin'' environment. At the beginning of the Quaternary, influenced by the neotectonk movement, the Lop Nur evolved into a "deep basin" in the Tarim basin. At the end of the middle Pleistocene, neotectonic migration began to take place in the intenor of the Lop Nur and a new secondary deep basi-e Luobei subbasin4onned gradually. Despite its small area, it is actually the deepest subbasin in the Lop N u depression, where brines of the Lop Nur Salt Lake gather and evaporate, thus providing materials for the formation of a superlarge brine potash rock deposit. With respect to the phenomenon of brine concentration and change with deepening of the lake, the authors propose a model of "high mountain-deep basin" tectonic migration for potash concentration. In the sedimentological context, the honeycomb-shaped voids developed in glauberite rock in the subbasin are good space for potash-fich brine accumulation. Study indicates that the deposition of glauberite requires recharge of calcium-rich water.In the Tarim area the calcium-rich water might come from deep formation water or oilfield water, and the river water recharging the Lop Nur Salt Lake was rich in sulfate radicals and other components; in addition, the climate in the area was very and the brine evaporated steadily, thus resulting in deposition of substantial amount of glauberite, potash accumulation in intercrystal brine and final formation of the potash deposit. Generally, potash formation in a salt lake undergoes a three-stage process of "carbonates+sulfates (gypsum and glaubente)+chlorides (halite etc.)", but in the study area there only occurred a two-stage process of "carbonates-mlfates (gypsum and glauberite)". The authors call this new geological phenomenon the "two-stage potash formation" model. In conclusion, the superlarge Lop Nor potash deposit is the result of combined "high mountain-deep basin" tectonism and "two-stage potash formation".Superscripts alalluvial sedimcats; chchemical sediments (the numbers 1.2 and 3 followhg it means the early, middle and late stages); didiluvial sediments; eoleolian sediments; Ilacushe sediments; I + chadinary lacustrine sediments occurring alternatively with chemical sediments.Boreholes ZK95-I. ZK95-2 and ZK95-3 w~t diiUed in 1995. and Z K W and ZKlzoO were drilled in 19961997 by the Third Geological Pa@ of Xinjiang.Vol. 79 No.
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