Basement Architecture and Formation of an Ocean-continent Transform Boundary off Western Tasmania: Insights from Aeromagnetic and Seismic Reflection Data Collected from a Frontier Petroleum Province

Basement architecture off western Tasmania is a legacy of late Neoproterozoic-Cambrian subduction-related processes, ocean basin closure and multiple accretionary events, culminating in formation of the Delamerian-Ross and western Lachlan orogens. Structures associated with these fold belts were subsequently reactivated during late Mesozoic-Cenozoic Gondwana breakup and the separation of Australia from Antarctica, strongly influencing the pattern and geometry of offshore rifting, including formation of an ocean-continent transform boundary off western Tasmania. Seismic reflection profiles combined with recently acquired high resolution aeromagnetic data permit this boundary and its associated reactivated basement structures (Avoca-Sorell fault system) to be mapped in greater detail than has hitherto been possible and point to a transform margin dominated by steeply outward-dipping structures and deep sedimentary basins similar to other transform margin ocean-continent boundaries, including the highly prospective Côte d'Ivore-Ghana region off the west African coast. Basement highs and rotated pre-rift crustal blocks adjacent to the west Tasmanian transform margin incorporate significant volumes of granite as well as a lower crust of probable Mesoproterozoic age that is locally juxtaposed against lower Paleozoic sequences intruded and/or floored by basaltic and ultramafic material. Aeromagnetic anomalies sourced from these basement rocks change orientation from NW- to NE-trending across the Avoca-Sorell fault system and can be traced laterally into regions of known onshore basement geology, highlighting both the tectonic significance of this structure and its origins during lower Paleozoic deformation accompanying the Delamerian-Ross orogeny.

塔斯马尼亚西部近海的基底构造，是新元古代晚期-寒武纪（late Neoproterozoic-Cambrian）俯冲相关过程、洋盆闭合及多期增生事件的产物，最终形成了德拉梅里-罗斯造山带（Delamerian-Ross Orogen）与西拉克伦造山带（western Lachlan Orogen）。与这些褶皱带相关的构造，在中生代晚期-新生代（late Mesozoic-Cenozoic）冈瓦纳大陆（Gondwana）裂解及澳大利亚与南极洲分离期间被再次活化，强烈影响了近海裂谷作用的模式与几何形态，包括塔斯马尼亚西部近海洋-陆转换边界的形成。地震反射剖面结合近期获取的高分辨率航磁数据，使得该边界及其相关的活化基底构造（阿沃卡-索雷尔断裂系，Avoca-Sorell Fault System）能够以比以往更精细的尺度进行制图，并揭示出一个以陡倾向外的构造和深沉积盆地为主导的转换边缘，其特征与其他转换边缘的洋-陆边界相似，包括西非海岸外极具勘探前景的科特迪瓦-加纳地区（Côte d'Ivoire-Ghana region）。塔斯马尼亚西部转换边缘附近的基底隆起和旋转的裂前地壳块体，包含大量花岗岩以及可能为中元古代（Mesoproterozoic）的下地壳，这些下地壳在局部与被玄武质及超镁铁质物质侵入和/或底部覆盖的下古生界（lower Paleozoic）地层并列。源自这些基底岩石的航磁异常，在跨越阿沃卡-索雷尔断裂系时，走向从北西向转变为北东向，且可横向追踪至已知的陆上基底地质区域，既突显了该构造的构造意义，也揭示了其形成于伴随德拉梅里-罗斯造山带的下古生代变形期间。