东南极威尔克斯地-阿德利地大陆边缘构造及沉积特征

TECTONIC AND SEDIMENTARY CHARACTERISTICS OF THE WILKES LAND AND TERRE ADéLIE CONTINENTAL MARGIN,EAST ANTARCTICA

东南极威尔克斯地-阿德利地陆缘是研究南极洲-澳大利亚晚白垩世裂解过程的关键部位,然而该地区的地质情况研究程度较低,特别是在构造-沉积演化方面。基于横穿威尔克斯地-阿德利地大陆边缘多道地震剖面的解释,对该地区的构造变形及沉积特征进行了研究。在地震剖面上识别出区域性的两大不整合面,分别是土伦阶不整合面(tur)和始新世不整合面(eoc)。两大不整合面将研究区层序划分为三大构造层序:裂谷层序S3,后裂谷层序S2、S1。裂谷层序主要为裂谷期的火山碎屑岩,后裂谷层序多为半深海浊流沉积物如淤泥、黏土等。地震剖面解释发现,研究区不同部位构造变形及沉积特征差异显著,威尔克斯地西部S3较少发育,只在陆坡坡脚向深海盆地过渡的局部区域发育,而发育了厚层的S2、S1;威尔克斯地东部发育了厚层的S3,且S3内部普遍发育高角度正断层。阿德利地发育了一明显的裂谷地块——"阿德利地裂谷地块",其为裂谷作用下从大陆边缘裂离至深海区的海底高原,在其陆缘一侧可能发育了大型的控制断陷的正断层。威尔克斯地-阿德利地陆缘构造变形的差异可能是由于南极洲-澳大利亚板块裂解过程中发生逆时针旋转,导致陆缘裂谷作用强度不均所形成。威尔克斯地-阿德利地陆缘在洋-陆过渡带(Continent-Ocean Transition,COT)内发育了岩浆成因的基底凸脊,这些凸脊可能是在早期裂谷作用时,在地壳减薄最强烈处地幔物质上涌并遇水蛇纹石化的结果,并且导致了COT内的磁异常。

The continental margin of Wilkes Land and Terre Adélie, East Antarctic, occupies a key position for understanding the separation process of Australia and Antarctica in the Late Cretaceous. However, the geology of this area is still poorly understood, especially in the structural-sedimentary evolution. Based on the interpretation of multi-channel seismic profiles across the Wilkes Land and Terre Adélie continental margin,the characteristics of structure and sedimentation in this area were studied. Two regional unconformities were recognized in the seismic profiles, named tur unconformity and eoc unconformity. Three structural units, rift sequence S3 and post-rift sequences S2 and S1, were divided by the two unconformities. The S3 is mostly constituted by syn-rift volcaniclastic rock and fault titled volcanics. Conversely, hemipelagic turbidity sediment, ooze mud, and clay comprise the post-rift sequences S2 and S1. The structural deformation characteristics of the different parts of the Wilkes Land and Terre Adélie continental margin varied dramatically. In western Wilkes Land, S3 was limited and rarely developed in the transition region of the slope to deep-sea basin while thick S2 and S1 were deposited. In eastern Wilkes Land, thick S3 was deposited, and many high angle normal faults developed. The deformation of Terre Adélie was characterized by the development of the Adélie Rift Block, which was a submarine plateau detached from the continental margin. A major boundary normal fault may have developed on the continental side of the block. The differences in structural deformation between the west and east Wilkes Land and Terre Adélie might attribute to the heterogeneities of rifting resulting from the anticlockwise rotation of the Australia plate during the separation with the Antarctic. On the seismic profiles, basement ridges in the COT(Continent-Ocean Transition) area were clearly recognized. These basement ridges may be serpentinized peridotite formed by mantle intrusion in the crust extension area, which resulted in the magnetic anomaly in the COT.