[1] Alternative reconstructions of the Jurassic northern extent of Greater India differ by up to several thousand kilometers. We present a new model that is constrained by revised seafloor spreading anomalies, fracture zones and crustal ages based on drillsites/dredges from all the abyssal plains along the West Australian margin and the Wharton Basin, where an unexpected sliver of Jurassic seafloor (153 Ma) has been found embedded in Cretaceous (95 My old) seafloor. Based on fracture zone trajectories, this NeoTethyan sliver must have originally formed along a western extension of the spreading center that formed the Argo Abyssal Plain, separating a western extension of West Argoland/West Burma from Greater India as a ribbon terrane. The NeoTethyan sliver, Zenith and Wallaby plateaus moved as part of Greater India until westward ridge jumps isolated them. Following another spreading reorganization, the Jurassic crust resumed migrating with Greater India until it was re-attached to the Australian plate $95 Ma. The new Wharton Basin data and kinematic model place strong constraints on the disputed northern Jurassic extent of Greater India. Late Jurassic seafloor spreading must have reached south to the Cuvier Abyssal Plain on the West Australian margin, connected to a spreading ridge wrapping around northern Greater India, but this Jurassic crust is no longer preserved there, having been entirely transferred to the conjugate plate by ridge propagations. This discovery constrains the major portion of Greater India to have been located south of the large-offset WallabyZenith Fracture Zone, excluding much larger previously proposed shapes of Greater India.

Published models for the Cretaceous seafloor‐spreading history of East Gondwana result in unlikely tectonic scenarios for at least one of the plate boundaries involved and/or violate particular constraints from at least one of the associated ocean basins. We link East Gondwana spreading corridors by integrating magnetic and gravity anomaly data from the Enderby Basin off East Antarctica within a regional plate kinematic framework to identify a conjugate series of east‐west‐trending magnetic anomalies, M4 to M0 (~126.7–120.4 Ma). The mid‐ocean ridge that separated Greater India from Australia‐Antarctica propagated from north to south, starting at ~136 Ma northwest of Australia, and reached the southern tip of India at ~126 Ma. Seafloor spreading in the Enderby Basin was abandoned at ~115 Ma, when a ridge jump transferred the Elan Bank and South Kerguelen Plateau to the Antarctic plate. Our revised plate kinematic model helps resolve the problem of successive two‐way strike‐slip motion between Madagascar and India seen in many previously published reconstructions and also suggests that seafloor spreading between them progressed from south to north from 94 to 84 Ma. This timing is essential for tectonic flow lines to match the curved fracture zones of the Wharton and Enderby basins, as Greater India gradually began to unzip from Madagascar from ~100 Ma. In our model, the 85‐East Ridge and Kerguelen Fracture Zone formed as conjugate flanks of a “leaky” transform fault following the ~100 Ma spreading reorganization. Our model also identifies the Afanasy Nikitin Seamounts as products of the Conrad Rise hotspot.

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Ar age, Sr, Nd, Hf and high-precision Pb isotope analyses of volcanic rocks from the province with plate tectonic reconstructions. We find that the seamounts are 47-136 million years old, decrease in age from east to west and are consistently 0-25 million years younger than the underlying oceanic crust, consistent with formation near a mid-ocean ridge. The seamounts also exhibit an enriched geochemical signal, indicating that recycled continental lithosphere was present in their source. Plate tectonic reconstructions show that the seamount province formed at the position where West Burma began separating from Australia and India, forming a new mid-ocean ridge. We propose that the seamounts formed through shallow recycling of delaminated continental lithosphere entrained in mantle that was passively upwelling beneath the mid-ocean ridge. We conclude that shallow recycling of continental lithosphere at mid-ocean ridges could be an important mechanism for the formation of seamount provinces in young ocean basins.Volcanic seamounts are one of the most abundant features on the ocean floor (>20,000 at least 1 km high 4 ), yet the origin of most seamounts remains elusive. The diffuse Christmas Island Seamount Province (CHRISP) extends from the Argo Basin to the Wharton Basin, west of the Investigator Rise, covering ∼1,000,000 km 2 ( Fig. 1). In addition to Christmas Island and the Cocos/Keeling Islands, it consists of ∼50 large, up to 4,500 m high seamounts, and abundant smaller volcanic structures. During the RV Sonne SO199 CHRISP Expedition, 54 seamounts were partially mapped with the SIMRAD EM 120 multi-beam echo-sounding system and 38 were sampled by dredging. The recovered rocks indicate that all structures are volcanic in origin. Compositions range from tholeiitic to basanitic to trachytic, with alkali basalts being the main parental lava type. The abundant large guyots indicate that this was a former province of ocean island volcanoes, which were eroded to sea level and subsequently subsided (1,200-3,000 m). The goal of this study was to constrain the origin of the CHRISP and to determine if its source(s) could have affected the chemistry of the Indian upper mantle.Step-heating plateau ages on plagioclase, hornblende, Kfeldspar, glass and matrix separates were generated from 32 seamount and 10 Christmas Island samples (Supplementary Information S1). The ages of the seamounts and the underlying crust decrease from east to west: from Argo Basin Province (AP, 136 Myr; to Eastern Wharton Basin Province (EWP, Myr from SE to NW) to Vening-Meinesz Province (VMP, 95-64 Myr; crust ∼100-78 Myr from SE to NW) to Cocos-Keeling Province (CKP, refs 5,6; Fig. 1). A plot of longitude versus age forms a good linear correlation (r 2 = 0.87). The age difference between a seamount sample and the underlying crust is 0-25 Myr, indicating that the seamounts formed on or near the West Burma-Australian/Indian spreading ridge. Christmas Island and its submarine flanks record two younger, intraplate phases of volcanism: (1) the Eocene shi...

Transform-margin development around the Arctic Ocean is a predictable geometric outcome of multi-stage spreading of a small, confined ocean under radically changing plate vectors. Recognition of several transform-margin stages in the development of the Arctic Ocean enables predictions to be made regarding tectonic styles and petroleum systems. The De Geer margin, connecting the Eurasia Basin (the younger Arctic Ocean) and the NE Atlantic during the Cenozoic, is the best known example. It is dextral, multi-component, features transtension and transpression, is implicated in microcontinent release, and thus bears close comparison with the Equatorial Shear Zone. In the older Arctic Ocean, the Amerasia Basin, Early Cretaceous counterclockwise rotation around a pole in the Canadian Mackenzie Delta was accommodated by a terminal transform. We argue on geometric grounds that this dislocation may have occurred at the Canada Basin margin rather than along the more distal Lomonosov Ridge, and review evidence that elements of the old transform margin were detached by the Makarov–Podvodnikov opening and accommodated within the Alpha–Mendeleev Ridge. More controversial is the proposal of transform along the Laptev–East Siberian margin. We regard an element of transform motion as the best solution to accommodating Eurasia and Makarov–Podvodnikov Basin opening, and have incorporated it into a three-stage plate kinematic model for Cretaceous–Cenozoic Arctic Ocean opening, involving the Canada Basin rotational opening at 125–80 Ma, the Makarov–Povodnikov Basin opening at 80–60 Ma normal to the previous motion and a Eurasia Basin stage from 55 Ma to present. We suggest that all three opening phases were accompanied by transform motion, with the right-lateral sense being dominant. The limited data along the Laptev–East Siberian margin are consistent with transform-margin geometry and kinematic indicators, and these ideas will be tested as more data become available over less explored parts of the Arctic, such as the Laptev–East Siberia–Chukchi margin.