鄂尔多斯盆地中生代晚期以来大地热流的变化及其对生态环境格局和演变的影响

Change of Terrestrial Heat Flow in Ordos Basin since Late Mesozoic and its Effects on the Pattern and Evolution of the Ecologic Environment

鄂尔多斯盆地的西北部、东北部和南部三个区域现今大地热流平均值分别为56.3、67.3和65.3mW m2,对应的生态环境格局也有明显的差异。研究表明,大地热流每增加4～5mW m2可使年均地表温度升高约1℃,使最低月均地表温度升高2℃以上。鄂尔多斯盆地东北部的平均大地热流比西北部高出11mW m2,东北部年均地表温度可能比西北部高出2～3℃,其最低月均地表温度可能比西北部高出4～6℃。西北部的大地热流平均值已经低于维持地表生态系统延续所需大地热流的临界值(57mW m2),其自然生态系统整体上已经处于脆弱境地;东北部和南部的大地热流均大于57mW m2,自然生态系统均尚较稳健。东北部的沙漠化可能是风沙侵入的结果,其生态应该是可以恢复的。整个西北部作为一个整体看,72万年以前大地热流就已衰减到临界值以下,区域生态系统渐趋脆弱,开始整体上向荒漠化演变。

The Ordos Basin can be divided into three parts as Northwestern part, Northeastern part and Southern part,and their average terrestrial heat flow are estimated to be 56.3 ,67.3 and 65.3 mW/m^(2), respectively,which respond to distinctive ecologic environment patterns. The annual mean ground temperature will raise about 1℃ and the minimum mean month ground temperature will raise more than 2℃ as the terrestrial heat flow in the region increase 4-5 mW/m^(2). The average terrestrial heat flow in the Northeastern part of Ordos Basin is 11 mW/m^(2) higher than that in the Northwestern part. Accordingly, the ground temperature in Northeastern part should be 2—3℃ higher than that in the Northwestern part, and the minimum mean month ground temperature should be 4—6℃ higher than that in the Northwestern part. The average terrestrial heat flow in the Northwestern part has become lower than the critical value for maintaining sustainable development of the ecologic system (57 mW/m^(2)), and its natural ecologic system is in a weak condition as a whole;while the average terrestrial heat flow in the Northeastern part and Southern part are greater than 57 mW/m^(2), their natural ecologic system are still robust. The desertification now in the Northeastern part may result from aggression of wind and sand, where the ecologic system could be restored to some extent. The ecologic system in the Northwestern part as a whole had become weak and begun to develop toward desertification as the terrestrial heat flow was declining to lower than the critical value 720 thousand years ago.