Mid Permian rifting and crustal separation along the northern margin of Arabia led to initiation of the Neo-Tethys ocean and deposition of sediments typified by the Hawasina. Subsequently, the Neo-Tethyan oceanic crust was consumed in a late Cretaceous subduction zone, generally easterly dipping in the Oman sector, and its sedimentary cover built up an accretion wedge (Hawasina; Coloured Melange) until the late Campanian, when the buoyant crust of the Arabian continental margin seemingly choked the subduction process.Continuing convergence caused increased activity on, or the creation of, another subduction trench running between and extending south and east of the Central Iran-Lut and Sanandaj-Sirjan microcontinents (the proto-Makran trench). The resulting crustal relaxation on the earlier subduction site permitted uplift of the half-buried Oman continental margin; the overlying Hawasina and former hanging wall of Semail ophiolite then spread gravitationally further onto the Arabian shelf.The Makran accretion wedge of Mesozoic Coloured Melange-type rocks and a thick pile of Maastrichtian to Eocene flysch underlies an ophiolitic hanging wall. Post-Eocene collisions between Arabia, Eurasia and intervening microcontinents resulted in: movement of the Naiband Fault in Iran and associated change in trend of the main subduction trench from NW-SE to E-W; thrusting of the Kahnu-Daragar and Alpine-type ophiolite over the SE Sanandaj-Sirjan Zone and rotation of part of its basement; westward thrusting of Musandam, and was associated with the Oligocene uplift of the Oman Mountains. The Zagros plicate folds began their main development in the Pliocene. Continent-continent collision has not occurred between Oman and the Makran.
Off the southern coast of Australia, exploration results and deep-water reconnaissance seismic data support the concept of an aseismic Atlantic-type continental margin. Characteristic is a sedimentary wedge which extends from the shelf to the abyssal plains and includes crustal elements of continental and oceanic origin.Oceanward, a continuous level of diffractions ascribed to the top of oceanic crust can be observed on seismic records, steeply dipping beneath the continental rise towards a smooth, flat, often faulted reflector which is correlated with top Precambrian or Palaeozoic continental basement.The sedimentary wedge which overlies the block-faulted and collapsed continental basement is subdivided by unconformities into: (a) a continental Lower Cretaceous unit and a fluviodeltaic unit of Upper Cretaceous-Danian age which are taken to represent rift valley stages of deposition controlled by extensional tectonics and (b) a post-breakup sequence of Tertiary units representing regional collapse and out-building of the shelf. The Upper Cretaceous sequence is missing along much of the continental edge where Tertiary sediments appear to rest directly on the Lower Cretaceous unit.Our interpretation suggests that a prolonged period of uplift took place along the axis of the rift valley prior to continental break-up. On the basis of palaeomagnetic data and biostratigraphic analysis the breakup phase started in the Upper Paleocene.From the continent outward several structural zones can commonly be recognised: (a) a zone of shallow basement with a thin Lower Cretaceous cover normally faulted and overlain by thin gently dipping Tertiary beds, (b) a zone of faulted and landwards tilted basement blocks and Lower Cretaceous sediments overlain (sometimes with clear unconformity) by thick Upper Cretaceous sediments, (c) a zone of thick, moderately deformed Tertiary sediments whose axis of deposition is generally offset to the south of the Upper Cretaceous basinal axis, (d) a zone of rotational faults and associated toe thrusts affecting the Cretaceous sediments and apparently related to the time of margin collapse, (e) an area of little disturbed Cretaceous and Tertiary sediments overlying continental basement. This zone extends into the "magnetic quiet zone" which is therefore believed to be, at least in part, a collapsed portion of the continental margin adjacent to oceanic crust.The interpretation of the geological evolution of the southern Australian margin based on the stratigraphic and structural data presently available can be related to current theoretical models on continental margin development.
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