宁武盆地中-新生代构造演化的裂变径迹证据

为深入研究宁武盆地中-新生代的构造演化及煤层气资源的赋存条件,采集样品进行裂变径迹测试。锆石裂变径迹年龄为156~139 Ma,磷灰石裂变径迹年龄为97~47 Ma。宁武盆地中-新生代的构造演化历史可分为3个阶段。晚侏罗世(156 Ma),盆地两翼的岩体开始缓慢隆升,核部坳陷沉积,到早白垩世晚期(100 Ma),宁武盆地古地温达到最高,烃源岩达到了生气高峰期。白垩世晚期-古新世(79~59 Ma),快速抬升剥蚀。之后,虽有短暂埋藏,但总体处于隆升状态。渐新世晚期(40~30 Ma)以来快速抬升到现今位置。宁武盆地抬升剥蚀具有空间上的不均衡性。北东部抬升剥蚀早于南部,周缘岩体隆升剥蚀速率大于核部。宁武盆地是在中生代山西地块上形成一系列雁行状排列的复背斜和复向斜的构造背景下,新生代受印度洋板块挤压欧亚大陆,两翼山体强烈抬升推挤作用形成,属于华北克拉通区域构造事件的响应。

Fission Track Dating of Mesozoic-Cenozoic Tectonic Evolution in Ningwu Basin

To study the Mesozoic-Cenozoic tectonic evolution of the Ningwu Basin and occurrence conditions of coalbed methane resources, samples were collected from the basin for fission track dating. The obtained fission track ages are of 156~139 Ma (zircon) and 97~47 Ma (apatite). Mesozoic-Cenozoic tectonic evolution of the basin is divided into three stages accordingly: Late Jurassic (156 Ma): granites on both sides of Ningwu basin began to uplift slowly, and the core depression was deposited; late Early Cretaceous (100 Ma): the paleo-temperature of the basin reached its peak, and the source rocks also reached the gas-generation peak; Late Cretaceous-Paleocene (79~59 Ma): rapid uplift erosion occurred. Although there was a short burial later, the region remained uplifted. Since the Late Oligocene (40~30 Ma), the region has been rapidly uplifted to the present position. Uplift erosion of the basin was spatially uneven: uplifting in the northeast was earlier than in the south, and the intrusion uplift and denudation rate on both sides was higher than that in the core. In the Mesozoic, the regional tectonics formed a series of en-echelon complex anticlines and synclines. In the Cenozoic, Indian Ocean plate compression on Eurasia may have formed the Ningwu Basin via strong uplift and thrusting of mountain ranges on both sides, which responded to the regional tectonic events in the North China Craton.