罗布泊盐湖更新世晚期沉积钙芒硝包裹体特征及古气候意义探讨

STUDIES OF FLUID INCLUSIONS IN GLAUBERITE OF MIDDLEUPPER PLEISTOCENE STRATA AND THEIR PALEOCLIMATIC SIGNIFICANCE IN LOP NUR SALTY LAKE,XINJIANG,NW CHINA

罗布泊盐湖位于塔里木盆地东部，在中更新世晚期．晚更新世出现大量钙芒硝沉积。采用冷粘法制取罗布泊钙芒硝岩包裹体薄片，观察和测试钙芒硝等盐矿物包裹体特征与均一温度等，结果显示，样品单一液相包裹体均一温度以低温、中温和高温3个或2个区段的形式出现。低温区段，平均温度41．0-62．5℃；中温区段，平均温度68．7-88．0℃；高温区段，平均温度85．4-186．0℃。低温区段平均温度代表盐湖大部分古卤水温度，中温区段温度代表盐湖底部卤水温度；高温区段温度，可能因古湖水变浅，盐类矿物暴露地表被阳光暴晒加热，或盐矿物在制片过程中受力破裂等引起。研究确定罗布泊钙芒硝析出的古卤水温度多在40～75℃之问变化，部分超过75℃。据此推算，更新世晚期罗布泊夏季古气温平均多在20～35℃之间，最高可能达58℃左右，属于干热的气候条件。

Lop Nut salty lake is located in the eastern part of the Tarim Basin, Xinjiang, NW China. During the MiddleLate Pleistocene, a great deal of glaubeite had crystallized and was deposited at the bottom of the salty lake, thus, the homogeneous temperatures of inclusions in glaubeite were controlled by brine temperatures. In the study, we made the inclusion films with the cool-adhering method, thus preventing inclusions in salt minerals from being disturbed. Most of the inclusions in samples belong to single fluid phase inclusions, which are our study target. We mainly measured 12 samples of glauberite and 2 samples of bloedite. The results show that the homogenization temperatures can be divided into three ranges： low, middle and high temperatures. The low temperatures vary between 40.95 - 62.45℃, the middle temperatures between 68.7 - 88.01 ℃, the high temperatures between 85.4 - 186 ℃ on average, respectively. The low temperature range represents the temperatures of most paleolake brines, the middle temperature range represents those of lake bottom brines. The high temperature range may have been affected by Sun＇ s direct baking for the exposure of minerals to air, or other factors resulting from the film making. It is considered that the temperatures of paleolake water vary mainly from40- 75 ℃, somewhat surpassing 75 ℃. Therefore, during the Middle-Late Pleistocene, for the temperatures of heated brines were higher than air temperatures by 20 - 30 ℃, the smmner average temperatures of atmosphere in Lop Nur varied from 20 ℃（40 ℃ minus 20 ℃）to 35 ℃（75 ℃ minus 30 ℃）. It is reckoned that the highest temperature may reach 58 ℃ or so. This shows that a hot and arid climate prevailed in Luo Nur salt lake during the Mid-Late Pleistocene.