塔里木新元古代裂谷底界厘定及其穿时性研究

"The bottom boundary of the Neoproterozoic rift in Tarim and its diachronous rifting” is a scientific problem characterised by production - study - research combination. Not only can the targeted research meet the urgent needs of oil and gas exploration in the ultra-deep and ancient sequences in Tarim basin at present, but also it is useful for the evolution of rodinia supercontinent. The key issues to restrict the current research progress is that the stratigraphical division and tectonic evolution history in the early Neoproterozoic strata in Tarim are not clear. Thus, we plan to start with establishing the Neoproterozoic chronological stratigraphic framework. According to the tectonic environment, lithofacies assemblage and deposition sequence, the "rift body" would be identified. Through the zircon U-Pb dating to the key geological interface in the early stage of rift evolution, the bottom boundary of Neoproterozoic rift in different outcrop areas will be defined. Thereupon we can recognize the difference of the opening time of the Neoproterozoic rift from south to north, even between each region of Tarim block. At last, through regional and global comparisons, the geological significations of the Neoproterozoic riftting in Tarim will be discussed under the background of Rodinia supercontinent evolution.

“塔里木新元古代裂谷底界及其穿时性”是一个“产学研”结合的科学问题，对其开展针对性研究不仅能满足当前塔里木盆地超深层、古老油气勘探的迫切需求，对于Rodinia超大陆演化也具有借鉴意义。制约当前研究进展的关键在于塔里木新元古代早期地层归属以及构造演化并不清晰。因此，项目拟从新元古代年代学地层格架入手，根据构造环境和岩相组合、沉积序列对“裂谷体”进行识别，并通过对关键地质界面的锆石U-Pb定年，厘定不同露头地层分区新元古代裂谷底界，明确塔里木南、北乃至全区裂谷开启的穿时性，最后通过区域、全球对比，在Rodinia超大陆演化背景下探讨塔里木新元古代裂谷开启穿时性的地质含义。

围绕“塔里木新元古代裂谷底界及其穿时性”这一关键问题，项目从新元古代年代学地层格架入手，根据构造环境和岩相组合、沉积序列对“裂谷体”进行识别，并通过对关键地质界面的锆石U-Pb定年，厘定不同露头地层分区新元古代裂谷底界，明确塔里木南、北乃至全区裂谷开启的穿时性，最后通过区域、全球对比，在Rodinia超大陆演化背景下探讨塔里木新元古代裂谷开启穿时性的地质含义。地球物理位场异常和联合反演结果显示，塔西南、阿瓦提地区深层都有新元古界广泛分布。新元古代盆地呈隆-坳相间格局，塔北和中央隆起带是前寒武系继承性基底古隆起，北部裂陷带和塔西南裂陷带均以NWW向裂谷为主，纵向上呈现断-拗结构，平面上构成大型垒-堑结构，裂谷形成演化和同沉积断裂的分布与基底岩相组成以及基底断裂分布密切相关。南、北塔里木新元古代裂谷底界分别在～890Ma和～740Ma左右，对应于青白口纪和南华纪。塔里木新元古代原型盆地演化以南华纪裂谷、早震旦世断-拗转换和晚震旦世拗陷为特征，震旦纪末期柯坪运动导致短暂的地壳抬升，构造剥蚀南强北弱。从南、北塔里木与华南、华北以及全球其他古板块同位素年代学对比结果来看，新元古代裂谷盆地形成于Rodinia超大陆裂解背景下，裂谷开启是穿时的，裂陷过程也存在地区差异性，～820Ma、～800Ma、～750Ma和～570Ma等重要幕式裂陷事件都可能构成全球区域性裂谷沉积的底界。基于上述成果，我们认识到塔西南深层古裂陷内可能发育前寒武系烃源岩，古裂陷与古隆起之间的配置关系是寒武系盐下勘探突破的关键。