ALBERT

Description: Abstract Global deep‐time plate motion models have traditionally followed a classical rigid plate approach, even though plate deformation is known to be significant. Here we present a global Mesozoic–Cenozoic deforming plate motion model that captures the progressive extension of all continental margins since the initiation of rifting within Pangea at ~240 Ma. The model also includes major failed continental rifts and compressional deformation along collision zones. The outlines and timing of regional deformation episodes are reconstructed from a wealth of published regional tectonic models and associated geological and geophysical data. We reconstruct absolute plate motions in a mantle reference frame with a joint global inversion using hot spot tracks for the last 80 million years and minimizing global trench migration velocities and net lithospheric rotation. In our optimized model, net rotation is consistently below 0.2°/Myr, and trench migration scatter is substantially reduced. Distributed plate deformation reaches a Mesozoic peak of 30 × 106 km2 in the Late Jurassic (~160–155 Ma), driven by a vast network of rift systems. After a mid‐Cretaceous drop in deformation, it reaches a high of 48 x 106 km2 in the Late Eocene (~35 Ma), driven by the progressive growth of plate collisions and the formation of new rift systems. About a third of the continental crustal area has been deformed since 240 Ma, partitioned roughly into 65% extension and 35% compression. This community plate model provides a framework for building detailed regional deforming plate networks and form a constraint for models of basin evolution and the plate‐mantle system.

Description: Despite decades of study the prerift configuration and early rifting history between Australia and Antarctica is not well established. The plate boundary system during the Cretaceous includes the evolving Kerguelen–Broken Ridge Large Igneous Province in the west as well as the conjugate passive and transform margin segments of the Australian and Antarctic continents. Previous rigid plate reconstruction models have highlighted the difficulty in satisfying all the available observations within a single coherent reconstruction history. We investigate a range of scenarios for the early rifting history of these plates by developing a deforming plate model for this conjugate margin pair. Potential field data are used to define the boundaries of stretched continental crust on a regional scale. Integrating crustal thickness along tectonic flow lines provides an estimate of the prerift location of the continental plate boundary. We then use the prerift plate boundary positions, along with additional constraints from geological structures and large igneous provinces within the same Australian and Antarctic plate system, to compute “full-fit” poles of rotation for Australia relative to Antarctica. Our preferred model implies that the Leeuwin and Vincennes Fracture Zones are conjugate features within Gondwana, but that the direction of initial opening between Australia and Antarctica does not follow the orientation of these features; rather, the geometry of these features is likely related to the earlier rifting of India away from Australia-Antarctica. Previous full-fit reconstructions, based on qualitative estimates of continental margin overlaps, generally yield a tighter fit than our preferred reconstruction based on palinspastic margin restoration.

Description: The Eurekan Orogeny records Paleogene convergence between Greenland and the Canadian Arctic. The complexity of the region, well represented by the disputed magnitude of Cenozoic sinistral displacement of Greenland relative to Ellesmere Island, stems from the simultaneous evolution of multiple tectonic regimes, as well as overprinting of later tectonic activity. Presented here is a plate model of regional crustal deformation constructed with the interactive GPlates software that enables an evaluation of previous reconstructions of the Eurekan Orogeny. This model is built upon a synthesis of published geological and geophysical data and their interpretations. It incorporates two phases of deformation from ~63-35 Ma. Phase one, ~63 to ~55 Ma, involves ~85 km of Paleocene extension between Ellesmere and Devon Island, extension of ~20 km between Axel Heiberg and Ellesmere Island, and ~85 km of sinistral strike-slip along the Nares Strait/Judge Daly Fault System, matching a range of 50-100 km indicated by the offset of marker beds, facies contacts, and platform margins between the conjugate Greenland and Ellesmere Island margins. Phase two, ~55 to 35 Ma, results in total east-west compression of ~30 km and ~200 km of north-south compression across Ellesmere Island. This model confirms, for the first time, that key observations from sub-regions deformed by the Eurekan Orogeny are compatible on a broad scale. We have also identified potential problem areas in southwestern Ellesmere Island that are less compatible with a best-fit model, given current constraints. This deforming plate model offers a platform and base model for future research.