六盘山地区新生代构造演化:来自锆石和磷灰石裂变径迹的证据

Cenozoic tectonic evolution of the Liupan Shan area:Evidence from zircon and apatite fission tracks

青藏高原的隆升与扩展不仅导致欧亚大陆内部发生强烈的构造变形,亦对高原周缘的地貌格局及气候变化产生了重大影响.青藏高原东北缘新生代以来的隆升时代与响应过程一直备受争议,而界定青藏高原东北缘构造带隆升时序是解决争议的关键之一.本研究围绕青藏高原东北缘,在陇中盆地、六盘山褶皱逆冲带和鄂尔多斯地块西南缘地区进行了磷灰石和锆石裂变径迹测试分析和热史模拟.测试分析结果表明研究区样品的磷灰石裂变径迹年龄范围分布于136~16 Ma,裂变径迹的长度范围介于11.9~13.3μm;锆石裂变径迹年龄结果为258~79 Ma,但多数样品的年龄介于160~99 Ma;热史模拟结果揭示了研究区新生代以来至少经历了两期隆升和冷却降温事件,即始新世期间(55~30 Ma)和中中新世(17~12 Ma)以来.始新世期间(55~30 Ma)发生的隆升事件可能是印度大陆与欧亚大陆陆陆碰撞远程效应的直接响应,表明印度与欧亚大陆碰撞之初或不久,其应力即已传导至东北缘边界;中中新世(17~12 Ma)以来的隆升剥露冷却事件奠定了青藏高原东北缘现今构造格局.

The uplift and expansion of the Tibetan Plateau not only resulted in strong deformation in the Eurasian continent, but also had a significant impact on the geomorphic pattern and climate change around the plateau. The uplift of its northeastern margin since the Cenozoic has been a subject of controversy, with the age of uplifted mountains in the northeastern plateau being a key factor in resolving this debate. To further determine the uplift age of Liupan Shan and its surrounding areas, we conducted apatite and zircon fission track analyses and thermal history inversion in the Longzhong Basin, Liupan Shan fold and thrust belt and the southwestern margin of Ordos block. The results of the apatite fission track tests reveal that the ages of apatite fission track in the bedrock samples from the study area range from 136 to 16 Ma, with track lengths ranging from 11.9 to 13.3 μm. Zircon fission track ages range from 258 to 79 Ma, with the majority falling between 160 and 99 Ma. The thermal history models based on the apatite fission track data indicate that the Liupan Shan area experienced at least two periods of cooling events during the Cenozoic era. The first period occurred during the Eocene (55~30 Ma), while the second period occurred since the Middle Miocene (17~12 Ma). The uplifting during the Eocene may be attribute to a rapid response to the collision between Indian and Eurasian continents, which had a far-reaching effect on the region. The more recent uplifting events since the Middle Miocene are likely associated with tectonic activities that shaped the current tectonic framework in the northeastern Tibetan Plateau.