南极半岛西侧不活动陆缘陆架区新生代构造变形特征及沉积演化

摘要

基于横穿南极半岛西侧不活动陆缘陆架区的多道地震剖面解释,对该地区的新生代构造变形及沉积演化进行了研究.研究表明,南极半岛西侧陆缘陆架区可以划分为四大平行于南极半岛走向的构造单元,从陆侧至海侧,分别是陆架内缘区、陆架盆地、陆架中部隆起和陆架外缘区.同时通过地震剖面不整合面识别以及结合区域演化历史,对陆架外缘区层位进行了划分,共划分出四大构造层序:俯冲碰撞前层序S4,俯冲碰撞后层序S3,上新世冰川沉积S2及全新世冰海沉积S1.基于构造单元及构造层序的划分,将南极半岛西侧不活动陆缘陆架区的构造-沉积演化分为三期:(1)中生代—始新世,菲尼克斯板块向着南极半岛俯冲,南极半岛西侧陆缘为主动大陆边缘,陆架内缘区发生火山活动,形成海底火山岩,而在陆架盆地区和陆架外缘区沉积火山碎屑岩;(2)从始新世开始,南极洲-菲尼克斯洋中脊逐步分段式地抵达南极半岛西侧大陆边缘,南极半岛西缘逐渐转变成不活动的大陆边缘,并在陆架中部发生隆起作用,使得陆架盆地内的沉积物发生变形形成向斜构造,同时在陆架外缘区沉积硅质碎屑岩;(3)上新世开始,南极半岛西缘发生大规模的冰川作用,大陆边缘的沉积主要受控于冰川作用.%Based on the interpretation of multi channel seismic profiles across the continental shelf of Western Antarctic Peninsula inactive continental margin,the Cenozoic structural characteristics and sedimentary evolution in this area are studied.Four structural units which parallel the strike of Antarctic Peninsula are identified in this study area,from landward to seaward they are inner shelf,shelf basin,mid-shelf uplift and outer shelf.Four structural sequences are indentified in the outer shelf through identifying the unconformities on the seismic profiles,they are pre-subduction-collision unit S4,post-subduction-collision unit S3,Pliocene glacial unit S2 and Pleistocene glacial-marine unit S1.Combined with the division of the structural units and sequences,we divide the structural-sedimentary evolution into three periods.(1) During the Mesozoic to Eocene,the Phoenix plate subducted beneath the Antarctic Peninsula,resulting in the western continental of Antarctica active,exhibited by the volcanic activity in the inner shelf.Meanwhile volcaniclastic rocks deposited in the shelf basin and outer shelf.(2) Since the Eocene,the different parts of Antarctic-Phoenix ridge began to sectionally arrive at the Antarctic Peninsula.After each part of Antarctic-Phoenix ridge arrived,both the plate subduction and ridge expansion ceased and the western continental margin of Antarctic Peninsula gradually changed into inactive margin.At this time,uplift formed in the middle of the shelf,which helped forming the syncline structure in the shelf basin.In the outer shelf area,siliciclastic rocks started to deposit.(3) Since the Pliocene,large-scale glaciation happened in the Antarctic Peninsula,which controlled the deposition of the studied area.