柴达木盆地北缘东段第三纪构造—沉积演化

The Qaidam basin is the largest Cenozoic sedimentary basin in the northeastern Tibetan plateau, and formed in close association with outward growth of the Tibetan plateau. The northern margin of the Qaidam basin exhibits a tectonic framework typified by alternating narrow uplifts and depressions. Investigating genetic relationships of the uplift and depression zones is crucial not only for deciphering tectonic subsidence, depositional processes and structural deformation of the northern Qaidam basin but also for understanding tectonic evolution of the whole Qaidam basin. Much work has been done to unravel the coupling of subsidence and uplift in the western segment of the northern margin of the Qaidam basin. Few studies, however, were conducted on the eastern segment, and the tectonic processes of the whole northern margin of the Qaidam basin have not been well understood. This project will conduct a detailed investigation of the depression-uplift system in the eastern segment of the Qaidam basin, and aims to reveal Tertiary activities of fault systems, uplifting of the Oulongbuluk and Aimunik mountains, and time-space variations of depositional systems of the Delingha depression. Main approaches adopted in this project include field structural analysis, stratigraphic and sedimentary facies analysis, and geological interpretations of seismic profiles. This study is obviously important for reconstructing tectonic evolution of the northern margin of the Qaidam basin and has implications for the understanding of lateral expansion of the northeastern Tibet.

柴达木盆地是青藏高原东北部一个大型沉积盆地，其构造－沉积演化与青藏高原新生代侧向扩展直接相关。柴达木盆地北缘（柴北缘）表现为一系列凹陷（盆）与隆起带（山）相间的构造格局，研究柴北缘盆－山格局的形成和发展是恢复柴达木盆地构造演化的一个重要方面，对揭示整个盆地的构造沉降、沉积充填和变形过程具有重要意义。对柴北缘西段盆-山格局已开展了许多研究，但对东段研究甚少，直接影响对整个柴北缘新生代构造演化历史的恢复。该项目拟对柴北缘东段盆-山格局开展研究，通过对隆起带的构造解析、对凹陷区地层剖面的沉积学分析以及地震剖面的地质解释，恢复柴北缘东段构造变形历史、重建不同隆起带的抬升过程和凹陷区沉积作用的时空演变，揭示柴北缘东段第三纪盆－山格局的成因机制。该研究不仅对重建整个柴北缘第三纪构造发展具有重要意义，而且对了解青藏高原东北部侧向扩展方式具有重要参考。

该项目主要对柴达木盆地东部第三纪盆-山格局开展研究，研究内容包括：恢复盆地构造和地层格架，解析盆地北缘构造带变形过程，建立第三纪沉积体系格局，恢复沉积物供给体系和恢复盆地沉积充填过程；恢复沉降/沉积过程与盆内和盆缘构造带抬升的时空关系，恢复柴北缘东段的构造-沉积演化历史。为了更全面和深入了解青藏高原东北缘第三纪构造发展和抬升机制，项目扩展了研究范围和内容，对柴达木盆地东侧西秦岭和南侧可可西里第三纪地层发育、沉积过程和岩浆活动等地质过程也开展了综合分析。项目获得的主要成果如下：（1）揭示古近纪柴达木盆地和西秦岭没有经历强烈地壳挤压变形，指示欧亚-印度大陆碰撞作用在古近纪并未影响到这些区域；（2）揭示西秦岭古近系与中新统的接触关系是一个区域性平行不整合面，指示渐新世末青藏高原东北缘地表隆升是由于地壳垂向运动，而不是地壳水平挤压的结果；（3）发现中新世早、中期地壳垂向隆升与岩浆活动具有很好的时空耦合性，提出第三纪中期青藏高原东北部隆升是深部软流圈上升的结果，建立了边界驱动地幔对流模型；（4）确定柴达木盆地东部自中新世才开始形成，经历了早期向斜盆地和晚期背驮式盆地的构造-沉积演化过程。沉积作用和盆地缘构造变形分析进一步确定，柴东盆地曾与东侧共和盆地相连，晚中新世鄂拉山构造带构造变形和隆升最终将两个盆地隔离。该项目的新发现和成果对限定和重建第三纪青藏高原东北缘构造体制转换和侧向扩展历史具有重要科学意义。