Beyond ‘crumple zones’: recent advances, applications and future directions in deformable plate tectonic modelling

The recent proliferation of deformable plate tectonic modelling techniques has provided a new direction in the study of plate tectonics with substantial implications for our understanding of plate deformation and past kinematics. Such models account for intraplate deformation, yet are highly variable in their inputs, capabilities and applications. The aim of this commentary is to review recent contributions to this topic, and to consider future directions and major omissions. Through this review it is apparent that the current published deformable models can be subdivided into those that as an input either: (1) solely use plate motions to drive deformation, or (2) require stretching or beta factor. Deformable models are resolving some outstanding issues with plate reconstructions, but major simplifications and modelling assumptions remain. Primarily, obtaining model constraints on the spatio-temporal evolution of deformation is an outstanding problem. Deformable plate models likely work best when the kinematics of smaller plates are included. However, questions remain regarding how to define such blocks, and their kinematic histories, whilst some work suggests that inclusion of such entities is negated through quantitative restorations.

Age and tectonic setting of the Quinebaug- Marlboro belt and implications for the history of Ganderian crustal fragments in southeastern New England, USA

Crustal fragments underlain by high-grade rocks represent a challenge to plate reconstructions, and integrated mapping, geochronology, and geochemistry enable the unravelling of the temporal and spatial history of exotic crustal blocks. The Quinebaug-Marlboro belt (QMB) is an enigmatic fragment on the trailing edge of the peri-Gondwanan Ganderian margin of southeastern New England. SHRIMP U-Pb geochronology and geochemistry indicate the presence of Ediacaran to Cambrian metamorphosed volcanic and intrusive rocks dated for the first time between ca. 540–500 Ma. The entire belt may preserve a cryptic, internal stratigraphy that is truncated by subsequent faulting. Detrital zircons from metapelite in the overlying Nashoba and Tatnic Hill Formations indicate deposition between ca. 485–435 Ma, with provenance from the underlying QMB or Ganderian crust. The Preston Gabbro (418 ± 3 Ma) provides a minimum age for the QMB. Mafic rocks are tholeiitic with trace elements that resemble arc and E-MORB sources, and samples with negative Nb-Ta anomalies are similar to arc-like rocks, but others show no negative Nb-Ta anomaly and are similar to rocks from E-MORB to OIB or backarc settings. Geochemistry points to a mixture of sources that include both mantle and continental crust. Metamorphic zircon, monazite, and titanite ages range from 400 to 305 Ma and intrusion of granitoids and migmatization occurred between 410 and 325 Ma. Age and chemistry support correlations with the Ellsworth terrane in Maine and the Penobscot arc and backarc system in Maritime Canada. The arc-rifting zone where the Mariana arc and the Mariana backarc basin converge is a possible modern analog.

Oceanic plateau of the Hawaiian mantle plume head subducted to the uppermost lower mantle

<p>The Hawaiian-Emperor seamount chain that includes the Hawaiian volcanoes is created by the Hawaiian mantle plume. Although the mantle plume hypothesis predicts an oceanic plateau produced by massive decompression melting during the initiation stage of the Hawaiian hotspot, the fate of this plateau is unclear. We discovered a megameter-scale portion of thickened oceanic crust in the uppermost lower mantle west of the Sea of Okhotsk by stacking seismic waveforms of <em>SS </em>precursors. We propose that this thick crust represents a major part of the oceanic plateau that was created by the Hawaiian plume head about 100 Ma ago and subducted 20–30 Ma ago. Our discovery provides temporal and spatial clues of the early history of the Hawaiian plume for future plate reconstructions.</p>

Implications of the detrital zircon record for global plate tectonic reconstructions in deep time

<p>Full-plate reconstructions describe the history of both past continental motions and how plate boundaries have evolved to accommodate these motions. The fluxes of material into and out of the mantle at plate boundaries is thought to deeply influence the evolution of deep Earth structure, surface environments and biological systems through deep time. Traditionally, plate tectonic reconstructions have relied on geophysical data from the oceans, which provides details of how Pangea broke apart (since ca. 200 Myr) while paleomagnetism is the primary quantitative constraint prior to Pangea formation. However, these data do not directly constrain the extent of subduction zones or other plate boundaries, so reconstructing the past plate configurations of past supercontinents must rely on alternative methods. One source of data that can resolve this problem is to use observations from detrital zircons. Previous studies have proposed classification schemes to determine tectonic settings where samples were deposited, based on the different characteristic shapes of detrital zircon age spectra found in convergent, collisional and extensional settings.</p><p>Here, we investigate the applicability of this method to test and refine global full-plate tectonic reconstructions in deep time, using a published database of zircon ages. We first use reconstructions for relatively recent times (<100 Ma), where reconstructions are reasonable well constrained, to evaluate the effectiveness of the classification method. For older times, where uncertainties in the reconstructions are far larger, we can use the results to discriminate between competing models. We analysed the proximity between reconstructed plate boundaries and zircon sample sites assigned to different tectonic classifications, and found that the classification method does well (~64－79% success depending on distance threshold used) in distinguishing convergent settings. The ability of the classification to define extensional settings such as rift basins is less clear, though samples in this class do lie preferentially further from convergent settings. Based on these insights, we apply the method to evaluate full-plate reconstructions for the Neoproterozoic as well as other competing models for the configuration of Rodinia.</p>

The Central-East Atlantic Anomaly: its role in the genesis of the Canary and Madeira volcanic provinces

<p>The Canary and Madeira provinces, located in the central-east Atlantic Ocean, are characterized by irregularly distributed hotspot tracks displaying large age differences and variable distances between volcanoes. For this reason, the geodynamic mechanism(s) that control the spatio-temporal patterns of volcanism are still unclear. Here, we use results from seismic tomography, shear-wave splitting, and gravity to show that the Central-East Atlantic Anomaly (CEAA), rising from the African large low-shear-velocity province and stalled in the topmost lower mantle, is the source of distinct upper-mantle diapirs feeding those provinces. The diapirs detach intermittently from the CEAA and seem to be at different evolutionary stages. Geochemistry data confirm the lower-mantle origin of the diapirs, and plate reconstructions constrain their temporal evolution. Our observations suggest that the accumulation of deep plume material in the topmost lower mantle can play a significant role in governing the spatio-temporal distribution of hotspot volcanism.</p><p>This is a contribution to project SIGHT (Ref. PTDC/CTA-GEF/30264/2017). The authors would like to acknowledge the financial support FCT through project UIDB/50019/2020 – IDL.</p>

Evolution of the East Africa-Arabia plume head

<p>Hot plumes rising from Earth’s deep mantle are thought to form broad plume heads beneath lithospheric plates. In continents, mantle plumes cause uplift, rifting and volcanism, often dispersed over surprisingly broad areas. Using seismic waveform tomography, we image <span>a star-shaped, low-velocity anomaly centered at Afar and composed of three narrow branches: beneath East Africa, beneath the Gulf of Aden, and beneath the Red Sea and West Arabia, extending north to Levant. We interpret this anomaly as the seismic expression of </span>interconnected corridors of hot, partially molten rock beneath the East Africa-Arabia region. The corridors underlie areas of uplift, rifting and volcanism and accommodate an integral, active plume head. Eruption ages and plate reconstructions indicate that it developed south-to-north, and tomography shows it being fed by three deep upwellings beneath Kenya, Afar and Levant. <span>These results demonstrate the complex feedbacks between the continental-lithosphere heterogeneity and plume-head evolution. </span>Star-shaped plume heads sprawling within thin-lithosphere valleys can account for the enigmatic dispersed volcanism in large igneous provinces and are likely to be a basic mechanism of plume-continent interaction.</p>

Investigating the plate kinematics of continental blocks and their role on the deformation experienced along the Iberia-Eurasia plate boundary using deformable plate tectonic models

<p>The kinematics of the Iberian plate during Mesozoic extension and subsequent Alpine compression and their implications on the partitioning of strain experienced across the Iberia-Europe plate boundary continue to be a subject of scientific interest, and debate. To date, the majority of plate tectonic models only consider the motion of rigid tectonic plates. In addition, the lack of consideration for the kinematics of intra-continental domains and intervening continental blocks in-between has led to numerous discrepancies between rigid plate kinematic models of Iberia, based mainly on tight-fit reconstruction of M-series magnetic anomalies, and their ability to reconcile geological and geophysical observations. To address these discrepancies, deformable plate tectonic models constrained by previous plate reconstructions, geological, and geophysical studies are built using the GPlates software to study the evolution of deformation experienced along the Iberia-Eurasia plate boundary from the Triassic to present day. These deformable plate models consider the kinematics of small intra-continental blocks such as the Landes High and Ebro Block situated between large tectonic plates, their interplay with pre-existing structural trends, and the collective impact of these phenomena on the deformation experienced during Mesozoic rifting and Alpine compressional re-activation along the Iberia-European plate boundary. Preliminary results suggest that the independent kinematics of the Landes High played a key role on the distribution of oblique extension between different rift arms and resultant deformation within the Bay of Biscay. Within the Pyrenean realm, deformation experienced prior to and during the Alpine Orogeny was more largely controlled by the interplay between the Ebro Block kinematics and rift segmentation induced by the orientation of inherited trends.</p>

Some evidence for a wide fan-shaped extension of the East Antarctic plate at the Mesozoic-Cenozoic transition

<p>The Transantarctic Mountains (TAM) separate the Mesozoic to recent West Antarctic rift system (WARS) from a wide and depressed triangular sector of East Antarctica spanning from 100° E to 160° E in longitude and from the Oates, George V and Adelie coastlines to 85° S in latitude. The sub-ice bedrock of this sector shows a basin and range style topography comprising two major basins of continental proportions -the Wilkes Basin and the Aurora Basin complex- and many smaller basins such as the Adventure, Concordia, Aurora and Vostok trenches. Most of these basins and trenches exhibit a triangular shape with the acutest angle pointing approximatively to a single pole towards the South, giving a fan shaped pattern of significant dimensions. We name here this region as the East Antarctic Fan shaped Basin Province (EAFBP). To the West, this province is limited by the intraplate Gamburtsev Mountains (GM).</p><p>Origins and inter-relationships between these four fundamental Antarctic tectonic units (WARS, TAM, EAFBP, GM) are still poorly understood and strongly debated. In the EAFBP, very little is known about the mechanism generating the basins, their formation time, whether they are all coeval and if and how they relate to Australia basins before Antarctica-Australia rifting. Present genetic hypotheses for some of the basins span from continental rifting to a purely flexural origin or a combination of the two. Also, post-tectonic erosional and depositional processes may have had a significant impact on the present-day topographic configuration.</p><p>Here we investigate the possibility that the EAFBP is the result of a single genetic mechanism: a wide fan-shaped intra-continental extension around a pivot point at about 135° E, 85° S that occurred at the Mesozoic-Cenozoic transition. We discuss evidence from the sub-ice topography and potential field airborne and satellite data.</p><p>We have used international community-based Antarctic compilations in public domain, including BedMachine (Morlighem et al., 2020), AntGG (Scheinert et al., 2016) and ADMAP 2.0 (Golynsky et al., 2018). We have applied image segmentation techniques to the rebounded sub-ice topography to automatically trace the first order shape of the sub-ice basins. Then we have fitted the edges of the basins by maximum circles and we have estimated the best Euler pole identified by their intersection. Potential field anomalies have been taken into account in order to enlighten major discontinuities not revealed by the sub-ice topography.</p><p>Software simulations of the EAFBP opening in the frame of global plate tectonics reconstructions indicate that it may be inserted in the frame of the later phase of the Antarctica-Australia rifting, giving constraints on timing that allow us to date the EAFBP opening at the Mesozoic-Cenozoic transition.</p><p>The reconnaissance of the EAFBP as the result of a continental-scale fan-shaped extension may have deep implications on global and regional tectonics plate reconstructions, plate deformation assumptions and new tectonic evolutionary models of WARS, TAM and GM.</p>

A mantle plume origin for the Scandinavian Dyke Complex: a “piercing point” for 615 Ma plate reconstruction of Baltica?

<p>The origin of Large Igneous Provinces (LIPs) associated with continental breakup and the reconstruction of continents older than c. 320 million years (pre-Pangea) are contentious research problems. Here we study the petrology of a 615 - 590 Myr dolerite dyke complex that intruded rift-basins of the magma-rich margin of Baltica and now is exposed in the Scandinavian Caledonides. These dykes are part of the Central Iapetus Magmatic Province (CIMP), a LIP emplaced in Baltica and Laurentia during opening of the Iapetus Ocean within the Caledonian Wilson Cycle. The >1000 km long dyke complex displays lateral geochemical zonation from enriched to depleted basaltic compositions from south to north. Geochemical modelling of major and trace elements shows these compositions are best explained by melting hot mantle 75-250°C above ambient mantle. Although the trace element modelling solutions are non-unique, the best explanation involves melting a laterally zoned mantle plume with enriched and depleted peridotite lithologies, similar to present-day Iceland and to the North Atlantic Igneous Province. The origin of CIMP appears to have involved several mantle plumes. This is best explained if rifting and breakup magmatism coincided with plume generation zones at the margins of a Large Low Shear-wave Velocity Province (LLSVP) at the core mantle boundary. If the LLSVPs are quasi-stationary back in time as suggested in recent geodynamic models, the CIMP provides a guide for reconstructing the paleogeography of Baltica and Laurentia 615 million years ago to the LLSVP now positioned under the Pacific Ocean. Our results provide a stimulus for using LIPs as piercing points for plate reconstructions.</p>