/pdf/global-continental-and-ocean-basin-reconstructions-since-200-huopwd2ldv.pdf

Global continental and ocean basin reconstructions since 200 Ma

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2019GC008515

The Generic Mapping Tools Version 6

Gravity models are powerful tools for mapping tectonic structures, especially in the deep ocean basins where the topography remains unmapped by ships or is buried by thick sediment. We combined new radar altimeter measurements from satellites CryoSat-2 and Jason-1 with existing data to construct a global marine gravity model that is two times more accurate than previous models. We found an extinct spreading ridge in the Gulf of Mexico, a major propagating rift in the South Atlantic Ocean, abyssal hill fabric on slow-spreading ridges, and thousands of previously uncharted seamounts. These discoveries allow us to understand regional tectonic processes and highlight the importance of satellite-derived gravity models as one of the primary tools for the investigation of remote ocean basins.

http://science.sciencemag.org/content/sci/346/6205/65.full.pdf

New global marine gravity model from CryoSat-2 and Jason-1 reveals buried tectonic structure

Late Jurassic–Cenozoic reconstructions of the Indonesian region and the Indian Ocean

We have created a digital age grid of the ocean floor with a grid node interval of 6 arc min using a self-consistent set of global isochrons and associated plate reconstruction poles. The age at each grid node was determined by linear interpolation between adjacent isochrons in the direction of spreading. Ages for ocean floor between the oldest identified magnetic anomalies and continental crust were interpolated by estimating the ages of passive continental margin segments from geological data and published plate models. We have constructed an age grid with error estimates for each grid cell as a function of (1) the error of ocean floor ages identified from magnetic anomalies along ship tracks and the age of the corresponding grid cells in our age grid, (2) the distance of a given grid cell to the nearest magnetic anomaly identification, and (3) the gradient of the age grid: i.e., larger errors are associated with high age gradients at fracture zones or other age discontinuities. Future applications of this digital grid include studies of the thermal and elastic structure of the lithosphere, the heat loss of the Earth, ridge-push forces through time, asymmetry of spreading, and providing constraints for seismic tomography and mantle convection models.

Digital isochrons of the world's ocean floor

17 The Pacific Plate underwent a significant change in motion during the early Eocene. 18 The motion change has been linked to plate boundary reconfiguration, particularly in 19 relation to the evolution of its subduction margins. The reconfiguration also resulted in 20 a new Pacific-Australian plate boundary section transecting the rifted Gondwanan frag21 ment of Zealandia. In the period ca. 47-32 Ma, the relative rotation axis of the Pacific 22 and Australian Plates was located close to (often within) continental Zealandia. Previ23 ous studies have speculated that the Zealandia continental boundary could have acted 24 as a pivot point for Pacific-Australia relative motion. Here we investigate the extent to 25 which collision resistance along the intra-continental Zealandia boundary (∼ 1000 km) 26 might have impacted the motion of the Pacific Plate, which is characterised by trench 27 and ridge lengths more than one order of magnitude higher. We first highlight a signif28 icant change in the radial component of the absolute Pacific Plate rotation at 47 Ma (i.e. 29 the spin around the plate centroid axis) which helps to facilitate the relative pivoting 30 between the Pacific and Australia. We then consider how parameterised plate bound31 ary forces impact the tangential and radial components of the net torque vector (which 32 includes both fictitious and true torque components). We show that during the Eocene 33 transition, both the Zealandia boundary and the IBM subduction zone were well-oriented 34 in terms of partitioning boundary-normal forces into CCW radial torques. The radial 35 torque components were complimentary, while the tangential components were opposed, 36 i.e. the two boundaries operate in the sense of a force couple. The analysis predicts that 37 the IBM should have had an anomalous influence on the radial component of Pacific torque, 38 relative to the rest of the paleo-subduction margin at 47 Ma. This is supported by re39 sults from recent global scale numerical mantle convection simulations. The role of Zealan40 dia cannot be established unambiguously, based on our analysis, but effects can be quan41 tified under different assumptions. For instance, if collision resistance along the Zealan42 dia boundary was comparable to the subduction force density at the IBM, the ratio of 43 radial torque components is about 1/3. Zealandia could plausibly constitute a ‘first or44 der’ effect, albeit only on the radial component of Pacific rotation, and probably sub45 ordinate to the role of the IBM. Overall the study suggests that the onset of Pacific-Australia 46 pivoting at 47 Ma was a consequence of broader changes in the plate driving/resisting 47 forces, as was unlikely to have been dominated by collision resistance across Zealandia. 48

A push in the right direction: exploring the role of Zealandia collision in Eocene Pacific-Australia plate motion changes

We present highlights of the first multibeam and bottom sampling survey surrounding the UNESCO World
Heritage listed Heard and McDonald Islands (HIMI), conducted in the HIMI Marine Reserve InnerMarine
Zone. These insular shelf data reveal that persistent eastward flowing currents and retreating glaciers drive
patterns of sediment distribution. Sedimentary bedform directionality, corroborated by drifter data, suggest
that the prevailing energy in this region dominates from west to east, and is deflected in an anticlockwise
direction around Heard Island, causing sediment deposition to be concentrated on the eastern (downcurrent)
side of the islands. Sediment bedform morphology likely mirrors the eastward flowing Antarctic
Circumpolar Current and oscillating east!west tidal currents. Thick sediment accumulations north of
Heard Island may be related to deglaciation since the Last Glacial Maximum. 
Sample sites on the northern down-current side of Heard Islands and on the western up-current
side of the McDonald Islands contain a diverse range of taxonomic groups compared to all other
sample sites. Benthic specimens obtained in rock dredges and sediment grabs show a range of
invertebrate species that are likely endemic to the HIMI region.

Submarine sedimentary bedforms and benthos surrounding the Heard and McDonald Islands World Heritage site

Kroenke Canyon on the Ontong Java Plateau (OJP) extends for approximately 500 km between
its hypothesized origin at Ontong Java and Nukumanu atolls and its mouth at the transition
between the Plateau and the Nauru Basin. For FK141015, RV Falkor departed Pohnpei,
Federated States of Micronesia, on 15 October 2014, and arrived in Guam, USA, on 3 November
2014. During the voyage we acquired primarily EM302 multibeam data along 6,288 line-km over
the 13 days in the survey area, augmented by EM710 multibeam data in shallower water. Overall,
the EM302 ensonified 23,439 km2 of seafloor in the survey area, in water depths ranging from 87
m to 4,444 m (Figure ES1). XBT data (12 casts) were acquired routinely, and the CTD was
tested, returning useful data from one cast. 
Of similar scale and relief to the Grand Canyon (Arizona, USA), and with multiple tributaries,
Kroenke Canyon incises pelagic sediment, sedimentary rock, and igneous rock of OJP. We
mapped the thalweg of Kroenke Canyon from approximately 150 km northeast of the atolls to its
mouth at the transition between the OJP and the Nauru Basin (Figure ES1). Due to the loss of
HROV Nereus several months prior to FK141015, seafloor sampling that had been planned for
the voyage was not possible, and the Knudsen CHIRP 3260 sub-bottom profiling system did not
yield any sub-bottom data that had planned to be acquired. Due to shipyard delays, the number of
ship-days available for FK141015 was reduced from the original 30 to 20, and correspondingly
the number of ship-days available for science in the survey area was reduced from the original 23
to 13. 
Ultimate project goals for FK141015 include: 1) understanding and modeling how submarine
canyons and atolls form and evolve on oceanic plateaus, isolated from terrestrial influences and
subject to sea level fluctuations; 2) testing potential genetic relationships between a) the atolls
and Kroenke Canyon, and b) the atolls and OJP; and 3) contributing to assessing tsunami risk on
low-lying atolls. Intended impacts are to advance knowledge of canyon and submarine landslide
development globally, to better understand emplacement and post-emplacement volcanism of
LIPs, and to improve tsunami risk assessment.

Deciphering Ontong Java Atoll, Nukumanu Atoll, and Kroenke Canyon, Western Equatorial Pacific final project report for RV Falkor FK141015 15 October – 3 November 2014

Joanne M. Whittaker

Papers

A push in the right direction: exploring the role of Zealandia collision in Eocene Pacific-Australia plate motion changes

Submarine sedimentary bedforms and benthos surrounding the Heard and McDonald Islands World Heritage site

Deciphering Ontong Java Atoll, Nukumanu Atoll, and Kroenke Canyon, Western Equatorial Pacific final project report for RV Falkor FK141015 15 October – 3 November 2014