Tectonic and sedimentary history of the Argo Abyssal Plain, eastern Indian Ocean

Bathymetric and seismic reflection profiles totalling about 2800 km, and covering about 110 000 km2 of the Argo Abyssal plain, have been analysed. The early emplacement of oceanic crust and volcanic edifices (Late Jurassic and Early Cretaceous) was followed by cooling, and marked subsidence until the Miocene. The principal structural features have been identified as the right-laterally sheared Wombat Graben in the south, the N-S trending Joey Rise in the west, the parallel sediment-filled Joey Graben to its east, a NW-trending eastward tilted and subsided volcanic massif to its east, a NW-trending linear volcanic massif on the old oceanic plate farther east, the deformed and uplifted sediments and basement in the north, and the central basin with 1.2 km thick sediments. The Joey, Wombat and Kivi Grabens are newly identified. The N- S trending Joey Graben is 400-450 km long, parallel to and east of the Joey Rise, and it is filled with up to 1 km of sediment. Beneath it, the mantle has been identified at depths of 12-15 km and deepening westward. The other two grabens form moats hundreds of metres deep, at the foot of the Australian margin in the south. The right-lateral displacements in the axis of the Wombat Graben reflect the initial shearing and rifting of the thinned crust. The widespread faulting in the basement, and the persistence of some faults upward into sediments as young as early Miocene, indicate that tectonism was marked until then. The eastern and northern parts of the abyssal plain have been uplifted as they came within the peripheral fore-bulge south of the Sunda Trench. Five sequences (A-E) overlie the oceanic crust and they have been correlated with the lithology of ODP Site 765 and DSDP Site 261. They probably represent Plio-Pleistocene, upper Miocene-lower Pliocene, middle Miocene, upper Oligocene-lower Miocene and uppermost Jurassic to Lower Cretaceous strata, respectively. The depositional trends in the Mesozoic and Miocene sediments are controlled by basement structure. Isopach maps of the Mesozoic and Cainozoic sediments reveal that their maximum thicknesses are about 0.6-0.8 km and 0.2-0.4 km, respectively, with the bulk of the sediments (calcareous turbidites and claystone) laid down in the Early Cretaceous and the middle Miocene to Pliocene. During the Oligocen e to early Miocene period (37-16 Ma), a remarkable geologic event led to non-deposition or erosion of sediments.

本次研究分析了总计约2800千米的水深测量与地震反射剖面，其覆盖阿尔戈深海平原（Argo Abyssal Plain）约11万平方千米的区域。洋壳与火山构造的早期形成（晚侏罗世至早白垩世）之后，区域经历冷却作用并伴随显著沉降，直至中新世。已识别的主要构造特征包括：南部为右旋剪切形成的沃姆巴特地堑（Wombat Graben）；西部为南北走向的乔伊海隆（Joey Rise）；其东侧为与之平行、被沉积物充填的乔伊地堑（Joey Graben）；再东侧为北西走向、向东倾斜并沉降的火山地块；更东侧的古老洋壳之上，分布有北西走向的线性火山地块；北部为变形抬升的沉积物与基底；中部为沉积厚度达1.2千米的盆地。乔伊、沃姆巴特与基维地堑（Kivi Grabens）为本次新识别的构造。其中，南北走向的乔伊地堑长400~450千米，平行于乔伊海隆且位于其东侧，内部充填最大厚度达1千米的沉积物。其下方地幔埋深为12~15千米，且埋深向西逐渐加深。其余两处地堑形成了南部澳大利亚大陆边缘坡脚处的数百米深坳沟。沃姆巴特地堑轴部的右旋位移，反映了减薄地壳的初始剪切与裂谷作用。基底中广泛发育的断裂，以及部分断裂向上延伸至早中新世的沉积物中，表明构造活动直至该时期仍较为显著。深海平原的东部与北部区域，因处于巽他海沟南侧的外围前隆区域而发生抬升。覆于洋壳之上的5个地层序列（A-E），可与大洋钻探计划（Ocean Drilling Program, ODP）765站位及深海钻探计划（Deep Sea Drilling Program, DSDP）261站位的岩性进行对比。它们分别对应上新世-更新世、晚中新世-早上新世、中中新世、晚渐新世-早中新世，以及晚侏罗世至早白垩世地层。中生代与中新世沉积物的沉积展布受基底构造控制。中生代与新生代沉积物的等厚图显示，二者最大厚度分别约为0.6~0.8千米与0.2~0.4千米；绝大多数沉积物（钙质浊积岩与黏土岩）沉积于早白垩世与中中新世至上新世时期。在渐新世至早中新世（37~16 Ma）期间，发生了一次显著的地质事件，导致沉积物出现沉积间断或侵蚀作用。