柴达木盆地古近系下干柴沟组上段碎屑锆石U- Pb测年及盆山耦合探讨

柴达木盆地被祁连山、阿尔金山及昆仑山所环绕，盆地古近系下干柴沟组(E23)地层独特的岩性和沉积格局指示了复杂盆山体系和源区多样成因。本文选取了盆地内部不同构造带5口钻井下干柴沟组的中粗砂岩样品，利用碎屑锆石U- Pb定年等分析方法对柴达木盆地进行了构造、物源系统分析。研究结果表明，位于祁连山前的XX- 1井样品下干柴沟组锆石年龄介于2692~156 Ma之间，主要峰值年龄为448 Ma和249 Ma，L6- 1井样品锆石年龄介于2693~220 Ma之间，主要峰值年龄为499 Ma和415 Ma；位于盆地西部沉降中心内部的YIT- 1井样品下干柴沟组锆石年龄介于2796~266 Ma之间，主要峰值年龄为423 Ma和255 Ma；阿尔金山前的N- 105井样品下干柴沟组锆石年龄介于2481~242 Ma之间，主要峰值年龄为422 Ma和259 Ma，N- 109井样品锆石年龄介于2638~228 Ma之间，主要峰值年龄为444 Ma和246 Ma。通过与主要源区年龄对比可知，盆地不同构造带下干柴沟组的物源差异较大，靠近祁连山前的XX- 1井、L6- 1井的物源主要来自于祁连山内部；位于阿尔金山前相邻的N- 105、N- 109井物源主体来自于阿尔金山内部，但N- 109井存在祁连山物源贡献；柴西坳陷内部YIT- 1井物源受祁连山及东昆仑共同控制。物源分析结果表明祁连山在古近纪已大规模隆升，并且作为青藏高原北部边界为柴达木盆地持续提供物源；阿尔金山及昆仑山在下干柴沟组沉积时期已经形成雏形，但并未大规模隆升，造成了山前带复杂的物源体系。

Detrital zircon U- Pb dating of the Paleogene lower Ganchaigou Formation in the Qaidam basin and discussion of basin- mountain coupling

The Qaidam basin is surrounded by the Qilian Mountains, Altun Mountains and Kunlun Mountains. The unique lithology and sedimentary pattern of the Paleogene lower Ganchaigou Formation (E23) in the basin indicate the complex basin mountain system and the diverse genesis of the source area. In this paper, the structure and provenance of the Qaidam basin are systematically analyzed by using detrital zircon U- Pb dating and other analytical methods. The results show that the E23 zircon ages of the samples from well XX- 1 in the front of the Qilian Mountains range from 2692 Ma to 156 Ma, and the main peak ages were 448 Ma and 249 Ma. The E23 zircon ages of samples from the well L6- 1 ranged from 2693 Ma to 220 Ma, with the main peak ages of 499 Ma and 415 Ma. The E23 zircon ages of samples from the well YIT- 1 located in the Western subsidence center of the basin ranged from 2796 Ma to 266 Ma, with the main peak ages of 423 Ma and 255 Ma. The E23 zircon ages of samples from the well N- 105 in front of the Altun Mountains ranged from 2481 Ma to 242 Ma, and the main peak ages were 422 Ma and 259 Ma. The E23 zircon ages of samples from the well N- 109 ranged from 2638 Ma to 228 Ma, and the main peak ages were 444 Ma and 246 Ma. Compared with the ages of the main source areas, the provenance of E23 in different structural zones of the basin is different. The provenance of E23 in wells XX- 1 and L6- 1 near the front of the Qilian Mountains mainly comes from the interior of the Qilian Mountains. The main source of wells N- 105 and N- 109 located in front of the Altyn Tagh Mountains is from the interior of the Altyn Tagh Mountains, but well N- 109 has the contribution of the Qilian Mountains. The source of the well YIT- 1 in the Chaixi depression is jointly controlled by the Qilian Mountains and the East Kunlun Mountains. The results of provenance analysis show that the Qilian Mountain has been uplifted on a large scale in the Paleogene, and as the northern boundary of the Qinghai- Tibet Plateau, it continues to provide provenance for the Qaidam basin. The Altun Mountains and Kunlun Mountains had taken shape in the E23 period, but did not rise on a large scale, resulting in a complex provenance system in the piedmont zone.