Plate Reorganization Event Research Articles

The Role of Slab Remnants in Modulating Free Subduction Dynamics: A 3‐D Spherical Numerical Study

AbstractSeismic tomography of Earth's mantle images abundant slab remnants, often located in close proximity to active subduction systems. The impact of such remnants on the dynamics of subduction remains underexplored. Here, we use simulations of multi‐material free subduction in a 3‐D spherical shell geometry to examine the interaction between visco‐plastic slabs and remnants that are positioned above, within and below the mantle transition zone. Depending on their size, negatively buoyant remnants can set up mantle flow of similar strength and length scales as that due to active subduction. As such, we find that remnants located within a few hundred km from a slab tip can locally enhance sinking by up to a factor 2. Remnant location influences trench motion: the trench advances toward a remnant positioned in the mantle wedge region, whereas remnants in the sub‐slab region enhance trench retreat. These motions aid in rotating the subducting slab and remnant toward each other, reducing the distance between them, and further enhancing the positive interaction of their mantle flow fields. In this process, the trench develops along‐strike variations in shape that are dependent on the remnant's location. Slab‐remnant interactions may explain the poor correlation between subducting plate velocities and subducting plate age found in recent plate tectonic reconstructions. Our results imply that slab‐remnant interactions affect the evolution of subducting slabs and trench geometry. Remnant‐induced downwelling may also anchor and sustain subduction systems, facilitate subduction initiation, and contribute to plate reorganization events.

Rapid Formation of the Ellice and Osbourn Basins and Ontong Java Nui Breakup Kinematics

AbstractBreakup of the proposed greater Ontong Java Nui large igneous province during the Cretaceous Normal Superchron can be constrained by the opening of the Ellice Basin (EB) separating the Ontong Java and Manihiki Plateaus and the Osbourn Basin separating the Manihiki and Hikurangi Plateaus. Dating of recovered dredged samples using plagioclase 40Ar/39Ar and zircon U/Pb geochronology methods indicates that spreading was well underway in the EB by 118 Ma with full spreading rates up to 3X faster than any observed today of 30–45 cm/yr and spreading likely continued until 112‐108 Ma. Ellice Basin samples show diverse geochemical affinities ranging from mid‐ocean ridge basalt (MORB) or Ontong Java‐like to more enriched OIB‐like. Pb and Nd isotopes from six samples contain varying influences from Pacific MORB and possibly Ontong Java. The geochemistry shows a lack of a clear mantle plume influence despite EB's close temporal and spatial relationship to Ontong Java, while some data resemble the Louisville Seamounts. This compositional diversity complements morphological differences among dredge sites and shows that both in situ MORB and younger overprinted features related to the nearby Tuvalu Seamounts were sampled. 40Ar/39Ar geochronology confirms the age of International Ocean Discovery Program Site U1365 near the Osbourn Trough (OT) to be 102.60 ± 0.26 Ma (2σ, n = 18). This age constrains the timing of a spreading reorientation event observed in the OB to coincide with a global plate reorganization event around 105 Ma and estimates the cessation of spreading at the OT to 96 Ma.

The Onset of Gondwanide Orogeny in Eastern Australia: Insight From the Provenance of Syn‐Orogenic Strata in the New England Orogen (Australia)

AbstractThe last major episode of cordilleran‐style tectonism in eastern Australia was the late Paleozoic‐early Mesozoic Gondwanide Orogeny. When exactly this deformation commenced and what caused this phase of orogenesis is still debated. Using previous stratigraphic and sedimentological data from pre‐orogenic to syn‐orogenic strata, integrated with new detrital zircon U‐Pb geochronology, we investigated the onset of the Gondwanide Orogeny in the northern New England Orogen (Gogango Overfolded Zone, eastern Australia). The lowermost syn‐orogenic strata display evidence of rapid base‐level change coeval with increasingly abundant and more proximal mass‐wasting deposits, which reflect a shift to static loading‐induced subsidence and the establishment of a ∼1,600‐km long foreland basin system. The syn‐orogenic strata contain abundant detritus sourced from syn‐depositional magmatism, alongside an up‐section increase in detritus derived from uplifted older rocks of the New England Orogen. Detrital zircons show maximum depositional age of ∼276 Ma from immediately above the sequence boundary, and ∼269 Ma from an overlying formation. These results confirm previous suggestions that tectonic forcing of the orogenic hinterland affected subsidence and sedimentation patterns in the easternmost part of the basin during the middle Permian, >11 Myr prior to deformation in the western part of the foreland basin. The onset of the Gondwanide Orogeny in eastern Australia, and in other sectors of the Gondwanan margin, likely resulted from a tectonic switch from crustal extension to contraction, which was driven by increased convergence rates due to a plate reorganization event following the final assembly of Pangea.

Exhumation history of late Mesozoic intrusions in the Tongling–Xuancheng area of the Lower Yangtze region, eastern China: Evidence from zircon (U–Th)/He and apatite fission track thermochronology

The Lower Yangtze region is one of the most important metallogenic belts in eastern China, yet there are few precise low-temperature geochronological data to constrain the evolution of the orefield. We collected samples from 12 late Mesozoic intrusions in the Tongling–Xuancheng area for zircon (U–Th)/He (ZHe) and apatite fission track (AFT) dating. These intrusions are divided into early and late periods on the basis of their emplacement ages. The ZHe and AFT ages of the early intrusions are 144.6–111.0 Ma and 123.1–89.4 Ma, respectively, and those of the late intrusions are 119.9–71.3 Ma and 96.7–66.9 Ma, respectively, with rare outliers. The ZHe and AFT age distributions and the modeled low-temperature thermal histories of these intrusions reveal that the Tongling–Xuancheng area underwent three stages of rapid cooling: during the earliest, middle, and end of the Early Cretaceous. During the earliest Early Cretaceous, rapid cooling resulted from regional compression and in situ cooling of magma. The middle Early Cretaceous phase of cooling occurred in a regional extensional regime characterized by the development of large rift basins and the emplacement of intrusions. The rapid cooling at ~ 100 Ma was concurrent with a global plate reorganization event that resulted in regional basin inversion and the development of unconformities between the Lower and Upper Cretaceous strata in East Asia. Although Cenozoic uplift is not seen in the cooling paths of our samples, regional compression since the Paleogene has uplifted the orebodies to near-surface level, favoring ore exploration and mining.

Closure of the Proterozoic Mozambique Ocean was instigated by a late Tonian plate reorganization event

Plate reorganization events involve fundamental changes in lithospheric plate-motions and can influence the lithosphere-mantle system as well as both ocean and atmospheric circulation through bathymetric and topographic changes. Here, we compile published data to interpret the geological record of the Neoproterozoic Arabian-Nubian Shield and integrate this with a full-plate tectonic reconstruction. Our model reveals a plate reorganization event in the late Tonian period about 720 million years ago that changed plate-movement directions in the Mozambique Ocean. After the reorganization, Neoproterozoic India moved towards both the African cratons and Australia-Mawson and instigated the future amalgamation of central Gondwana about 200 million years later. This plate kinematic change is coeval with the breakup of the core of Rodinia between Australia-Mawson and Laurentia and Kalahari and Congo. We suggest the plate reorganization event caused the long-term shift of continents to the southern hemisphere and created a pan-northern hemisphere ocean in the Ediacaran.

Long-term evolution of a plume-induced subduction in the Neotethys realm

The head of a mantle plume can weaken the oceanic lithosphere through the combined action of its buoyancy forces and excess temperature, which eventually induces intra-oceanic subductions. However, the dynamics of plume-induced subductions, their lifetime and their ability to propagate at the scale of an entire ocean remain unknown. Here, we combine a quantitative synthesis of the ophiolitic record of the Neotethys subduction in the Late Cretaceous with 3D spherical modeling of mantle convection self-generating plate-like tectonics to propose that the pre-Deccan plume initiated the Southern Neotethys Subduction. We suggest that this subduction retreated at 5-10 cmyr−1 until it reached the continental margins of Arabia and India. The sequential segmentation of this subduction during its retreat and the diachronous deactivation of the resulting segments drove the Late Cretaceous-Eocene series of plate reorganization events recorded in the Indian Ocean's fabric.

Extent and Cessation of the Mid‐Cretaceous Hikurangi Plateau Underthrusting: Impact on Global Plate Tectonics and the Submarine Chatham Rise

AbstractSubduction of oceanic plateaux are events that have occurred infrequently in Earth's history. Although rare, these events are thought to considerably influence regional tectonics and global plate motions. In the mid‐Cretaceous the oceanic Hikurangi Plateau collided with the formerly active East Gondwana margin: An event which falls into the same of a sudden change from subduction to extensional processes, including graben formation, development rift basin development, and exhumation of metamorphic core complexes in the Zealandia continent as well as a global‐scale plate reorganization event. In this study, we use recently acquired seismic refraction and gravity data along one profile across the submarine Chatham Rise, which represent a former accretionary wedge of the East Gondwana subduction zone. We demonstrate that the southward extent of the subducted Hikurangi Plateau in the lower crust beneath the submarine Chatham Rise along our profile is only ~150. This is ~150 km less than the previously suggested extent. Furthermore, we interpret that a slice of the subducted Phoenix Plate remains attached to the southern edge of the Hikurangi Plateau. We suggest that cessation of subduction in response to the Hikurangi Plateau jamming as well as the rollback and detachment of the Phoenix Plate slab played an important role in the changing tectonic forces across Zealandia in mid‐Cretaceous. Moreover, we suggest that the subduction cessation along the Hikurangi Plateau segment led to the fragmentation of the Gondwana subduction zone and Phoenix Plate, which significantly influenced and potentially prolonged the global mid‐Cretaceous plate reorganization event.

Cenozoic increase in subduction erosion during plate convergence variability along the convergent margin off Trujillo, Peru

Subduction erosion is a long-term, large-scale geological process that dominates the structural inventory of a large number of convergent margins. Along the Peruvian convergent margin, this process has controlled the structural deformation of the forearc as a consequence of spatio-temporal variations during the Cenozoic. However, the pace at which tectonic erosion occurred has not been linked to regional, subduction-related events. The aim of this study is to show that subduction erosion along the Central Peruvian convergent margin off Trujillo (7∘S–9∘S) was influenced by plate convergence variability since the Late Cretaceous. Drilling data, multi-channel seismic (MCS) data and subsidence analyses are used to investigate the long-term effect of subduction erosion on the tectonic evolution of the Peru margin. Our study shows that subduction erosion (1) did not occur between the Cretaceous and Early Eocene (110–56 Ma), (2) increased and fluctuated between the Eocene and Pliocene (56–5 Ma) with a maximum average trench retreat of 3 km.Myr−1 between the Middle Miocene and Late Miocene (20–5 Ma), and (3) has decreased since the Pliocene (5 Ma) (1 km.Myr−1 of average trench retreat). A remarkable finding is that shorter periods of faster subduction erosion coincide with or follow major plate reorganization events that were marked by changes in the velocity and direction of relative plate convergence as well as with well-known phases of Andean orogeny. Based on our analyses, we therefore conclude that convergence variability off Peru is a primary mechanism controlling the pace at which tectonic erosion occurred along the Trujillo Basin during the Cenozoic.

Geochronology of calcite‐filled joints, southeast Canada: Insight into Late Cretaceous deformation of eastern North America

AbstractResolving the timing of brittle tectonism is a challenge. We examined intra‐cratonic Middle Ordovician limestone bedrock that overlies Mesoproterozoic crystalline basement, which are both cut by ENE‐WSW trending fault zones that have historic M4‐5 earthquakes along their trace. Calcite‐filled mode I joints are ubiquitous within the strata, and are parallel to the modern stress field. Calcite δ18O and δ13C values are analogous to the bulk composition of Middle Ordovician limestones, and suggest vein formation from a source dominated by connate fluids of the host rock. U‐Pb geochronology of six calcite veins sealing ENE‐WSW oriented joints produced similar Cretaceous dates and were regressed together yielding a date of 96.8 ± 1.1 Ma (MSWD: 2.9). A Cenomanian age is consistent with the most recent reorientation of North America's compressive stress field, which is attributed to a change in spreading direction along the northern Mid‐Atlantic Ridge and is linked to a global plate reorganization event at ca. 105–100 Ma. These results suggest that the most recent redistribution of lateral stress was not a passive event, and generated brittle deformation and fluid flow at least 500 km inland of North America's Atlantic passive margin.

Timing and causes of the mid-Cretaceous global plate reorganization event

Global plate reorganization events (GPREs) can have profound impact on plate velocities, climate and the biotic cycle but the timing and triggers for GPREs remain debated. The timing and causes of the mid-Cretaceous GPRE, one of only two GPREs since the breakup of Pangea, remains poorly constrained because it occurred during the Cretaceous Normal Superchron. Here, we provide a new plagioclase 40Ar/39Ar age of 103.82±0.54 Ma (2σ) at DSDP site 256 along the world's clearest curved fracture zones in the Wharton Basin, off NW Australia. Using Monte Carlo simulations, we compute that the mid-Cretaceous GPRE commenced at 111.2−1.2+1.3 Ma (95% confidence). The mid-Cretaceous GPRE was associated with a significant plate deceleration (minimum ∼26%), similar to the Eocene GPRE, implying that this process is fundamental to plate reconfigurations. We propose that the mid-Cretaceous GPRE was caused by slab-breakoff and cessation of the south-dipping subduction zone in the Mesotethys Ocean at ca. 111 Ma. Ultimately, we posit that subduction zone initiations and cessations are the primary triggers for both post-Pangean GPREs and that top-down processes may be the fundamental drivers for GPREs.

Episodic behavior of the eastern Gondwanan margin: Insights from detrital zircon petrochronology from the Murihiku Terrane, New Zealand

Late Paleozoic and Mesozoic tectonostratigraphic terranes are exposed in New Zealand and New Caledonia but their original positions and tectonic configuration along the eastern Gondwanan margin are not well understood. To better constrain Mesozoic reconstructions, we sampled marine and non-marine sandstones in the Murihiku Terrane (New Zealand) and obtained 935 new UPb detrital zircon ages and trace-element data. Our results show that late Permian to Early Triassic volcaniclastic successions in the Murihiku Terrane are characterized by unimodal age spectra (260–245 Ma), indicating a proximal arc source. In contrast, a mixed provenance is recognized in Middle Triassic to Late Jurassic rocks, containing Devonian–Triassic (380–240 Ma) and Triassic–Jurassic (240–145 Ma), as well as minor early Paleozoic–Proterozoic (500–1000 Ma) detrital zircon ages. The detrital zircon age spectra from the Murihiku Terrane match magmatic pulses in the adjacent Tuhua Intrusives (Median Batholith), which is thus interpreted as the main source of the detrital sediments. Our petrochronological data show that a prominent change in the sandstone provenance occurred at 235–230 Ma, simultaneously with the transition from the Longwood Suite (261–252 Ma) to the Darran Suite (232–125 Ma) magmatism in the Median Batholith. The transitional period at 235–230 Ma also overlaps with an episode of magmatism, deformation, and uplift in New Caledonia and eastern Australia (Hunter-Bowen Orogeny). We therefore conclude that this ubiquitous tectonic episode, during the Late Triassic, marks a large-scale secular change within the Gondwanide Orogen, which was possibly driven by increased convergence rates following a plate reorganization event.

Constraints on Trenchward Arc Migration and Backarc Magmatism in the North Patagonian Andes in the Context of Nazca Plate Rollback

AbstractGeochemical and geochronological data reveal that late Oligocene‐early Miocene time is a break point in the evolution of Andean magmatism. The Patagonian Andes registered the onset of arc volcanism since the late Eocene forming part of the El Maitén Belt, whose development was driven by the subduction of the Farallon/Nazca plates beneath the Andean margin. During the Oligocene, the El Maitén Belt shows a change in the geochemical signature of its magmas from tholeiitic to calc‐alkaline compositions, reflecting a more mature stage in the magmatic arc evolution. Toward the early Miocene, a striking event is registered in Andean volcanic sequences as mafic tholeiitic lava flows of the El Maitén are interbedded with marine deposits, suggesting their development in the context of a fast subsiding regime. Geochemical analyses presented in this paper show that these rocks resemble enriched mid‐ocean ridge basalt‐like and ocean island basalt compositions, isotopically depleted, which strongly contrast with previous arc products. By this time, a global plate reorganization event had caused an increase in convergence rates, accelerated rollback, and a more orthogonal geometry of subduction, triggering widespread magmatism and the development of extensional basins in the overriding plate. Arc‐related volcanism during the early Miocene can be found only in the western slope of the Andes, suggesting the retreat of the volcanic front toward the trench. The proposed model highlights a strong linkage between the geochemical signature of magmatic products and changes in the subduction zone configuration and mantle dynamics during the evolution of the Patagonian Andes (41–44°S).

118–115 Ma magmatism in the Tethyan Himalaya igneous province: Constraints on Early Cretaceous rifting of the northern margin of Greater India

Understanding the dynamics of Large Igneous Provinces (LIPs) is critical to deciphering processes associated with rupturing continental lithosphere. Microcontinental calving, the rifting of microcontinents from mature continental rifted margins, is particularly poorly understood. Here we present new insights into these processes from geochronological and geochemical analyses of igneous rocks from the Tethyan Himalaya. Early Cretaceous mafic dikes are widely exposed in the eastern and western Tethyan Himalaya, but no such rocks have been reported from the central Tethyan Himalaya. Here we present an analysis of petrological, geochronological, geochemical, and Sr–Nd–Hf–Os isotopic data for bimodal magmatic rocks from the center-east Tethyan Himalaya. Zircon U–Pb dating yields six weighted-mean concordant 206Pb/238U ages of 118±1.2 to 115±1.3 Ma. Mafic rocks display MORB-like compositions with flat to depleted LREE trends, and positive εNd(t) (+2.76 to +5.39) and εHf(t) (+8.0 to +11.9) values. The negative Nb anomalies and relatively high 187Os/188Os ratios (0.15–0.19) of these rocks are related to variable degrees (up to 10%) of crustal contamination. Geochemical characteristics indicate that mafic rocks were generated by variable degrees (2–20%) of partial melting of spinel lherzolites in shallow depleted mantle. Felsic rocks are enriched in Th and LREE, with negative Nb anomalies and decoupling of Nd (εNd(t) = −13.39 to −12.78) and Hf (εHf(t) = −4.8 to −2.0), suggesting that they were derived mainly from garnet-bearing lower continental crust. The geochemical characteristics of the bimodal magmatic associations are comparable to those of associations that form in a continental rift setting. Results indicate that Early Cretaceous magmatism occurred across the whole Tethyan Himalaya, named here as the “Tethyan Himalaya igneous province”. Separation of the Tethyan Himalaya from the Indian craton may have occurred during ongoing Early Cretaceous extension related to the Kerguelen mantle plume during the nascent stages of a global plate-reorganization event. If this is the case, our findings provide clues to the nature of the Tethyan Himalaya, challenging traditional view of the India–Asia single-stage collision model.

Examining the influence of tectonic inheritance on the evolution of the North Atlantic using a palinspastic deformable plate reconstruction

Abstract To accurately reconstruct plate configurations, there is a need for a quantitative method to calculate the amount and timing of crustal extension independent of any one model for the formation of rifted margins. This paper evaluates the suitability of the various plate modelling methods for structural inheritance studies and proposes a classification scheme for the methods that are currently in use. A palinspastic deformable margin plate kinematic model is most suitable for tectonic inheritance studies, particularly at hyperextended margins. This type of plate model provides a valuable analytical tool that can be used to show the temporal and spatial relationship between pre-existing orogenic structures, evolving rift axes and global plate reorganization events. We use a palinspastic deformable margin plate model for the southern North Atlantic and Labrador Sea to quantitatively restore up to 350 km of Mesozoic–Cenozoic extension. This provides us with a pre-rift restoration of the Proterozoic and Paleozoic terranes and structural lineaments on the conjugate margins that helps us to analyse their relationship to evolving rift axes and global plate reorganization events through time. Interpretation of these modelling results has led to a clearer understanding of the relationship between inherited structural features and their control on rifting and the break-up history.

Constraining shifts in North Atlantic plate motions during the Palaeocene by U-Pb dating of Svalbard tephra layers

Radioisotopic dating of volcanic minerals is a powerful method for establishing absolute time constraints in sedimentary basins, which improves our understanding of the chronostratigraphy and evolution of basin processes. The relative plate motions of Greenland, North America, and Eurasia changed several times during the Palaeogene. However, the timing of a key part of this sequence, namely the initiation of compression between Greenland and Svalbard, is currently poorly constrained. The formation of the Central Basin in Spitsbergen is inherently linked to changes in regional plate motions, so an improved chronostratigraphy of the sedimentary sequence is warranted. Here we present U-Pb zircon dates from tephra layers close to the basal unconformity, which yield a weighted-mean 206Pb/238U age of 61.596 ± 0.028 Ma (2σ). We calculate that sustained sedimentation began at ~61.8 Ma in the eastern Central Basin based on a sediment accumulation rate of 71.6 ± 7.6 m/Myr. The timing of basin formation is broadly coeval with depositional changes at the Danian-Selandian boundary around the other margins of Greenland, including the North Sea, implying a common tectonic driving force. Furthermore, these stratigraphic tie points place age constraints on regional plate reorganization events, such as the onset of seafloor spreading in the Labrador Sea.

Three-dimensional imaging of impact of a large igneous province with a subduction zone

How the thickened crust of a large igneous province on an incoming oceanic plate is accommodated at a subduction zone remains an open question. New Zealand is one of the few places to study this, as at ca. 105 Ma the ca. 35 km-thick Hikurangi Plateau impacted the Gondwana subduction zone in what is now the South Island. Here we report on results from a forty-station portable seismograph array in the southern South Island, designed to delineate the leading edge of the subducted plateau. Three-dimensional images of Vp and Vp/Vs reveal the southwestern part of the plateau was a relatively narrow salient, and the first part to be subducted. The plateau then rotated clockwise about this salient until the southern edge of the plateau was parallel to subduction strike and subduction ceased at ca. 100 Ma. Our results suggest that the global-scale plate reorganization event at 105–100 Ma was due to a cessation of subduction caused by the Hikurangi Plateau choking the Gondwana subduction zone, rather than the subduction of mid ocean ridges as previously proposed. The choking of Gondwana subduction by the plateau also led to a concentration of slab pull in the adjacent subducted oceanic crust, explaining the episode of basin opening and intraplate magmatism there that occurred at the same time. Our study underlines the havoc caused by impact of a large igneous province with a subduction zone.

Tracking the paleogene India-Arabia plate boundary

The location of the India-Arabia plate boundary prior to the formation of the Sheba ridge in the Gulf of Aden is a matter of debate. A seismic dataset crossing the Owen Fracture Zone, the Owen Basin, and the Oman Margin was acquired to track the past locations of the India-Arabia plate boundary. We highlight the composite age of the Owen Basin basement, made of Paleocene oceanic crust drilled on its eastern part, and composed of pre-Maastrichtian continental and oceanic crust overlaid by ophiolites emplaced in Early Paleocene on its western side. A major fossil transform fault system crossing the Owen Basin juxtaposed these two slivers of lithosphere of different ages, and controlled the uplift of marginal ridges along the Oman Margin. This transform system deactivated ∼40 Myrs ago, coeval with the onset of ultra-slow spreading at the Carlsberg Ridge. The transform boundary then jumped to the edge of the present-day Owen Ridge during the Late Eocene-Oligocene period, before seafloor spreading began at the Sheba Ridge. This migration of the plate boundary involved the transfer of a part of the Indian oceanic lithosphere formed at the Carlsberg Ridge to Arabia. This Late Eocene-Oligocene tectonic episode at the India-Arabia plate boundary is synchronous with a global plate reorganization event corresponding to geological events at the Zagros and Himalaya belts. The Owen Ridge uplifted later, in Late Miocene times, and is unrelated to any major migration of the India-Arabia boundary.

Tectonics of the Dalrymple Trough and uplift of the Murray Ridge (NW Indian Ocean)

The Dalrymple Trough is a 150-km-long, 30-km-wide basin located at the northern termination of the Owen Fracture Zone (OFZ), which is the present-day active India–Arabia plate boundary. The Dalrymple Trough is closely associated with the Murray Ridge, a complex of prominent bathymetric highs located on its eastern flank. Recent multibeam mapping of the connection between the Dalrymple Trough and the OFZ revealed a horsetail structure, which suggests a close relationship between geological histories of both structures. However, the 3–6Ma age of initiation of the OFZ contrasts with the commonly accepted Early Miocene emplacement of the Dalrymple Trough. Recent seismic lines document a new tectonic history of the Dalrymple Trough, involving two major episodes of deformation along the India–Arabia plate boundary at ~8–10Ma and ~1.9±0.9Ma. The 8–10Ma episode is marked by a system of folds linked to the main uplift of the southern Murray Ridge and the first uplift of the northern Murray Ridge. This episode is related to a global plate reorganization event in the Late Miocene, well expressed by intraplate deformation in the Central Indian Ocean. The Dalrymple Trough opened at ~1.9±0.9Ma subsequently to the formation of a stepover at the India–Arabia plate boundary, coeval with the regional M-unconformity in the Oman abyssal plain, which marks a structural reorganization of the Makran accretionary wedge, and the last uplift of the northern Murray Ridge.

Geodynamic context for the deposition of coarse‐grained deep‐water axial channel systems in the Patagonian Andes

AbstractWe present field and seismic evidence for the existence of Coniacian–Campanian syntectonic angular unconformities within basal foreland basin sequences of the Austral or Magallanes Basin, with implications for the understanding of deformation and sedimentation in the southern Patagonian Andes. The studied sequences belong to the mainly turbiditic Upper Cretaceous Cerro Toro Formation that includes a world‐class example of conglomerate‐filled deep‐water channel bodies deposited in an axial foredeep depocentre. We present multiple evidence of syntectonic deposition showing that the present internal domain of the fold‐thrust belt was an active Coniacian–Campanian wedge‐top depozone where deposition of turbidites and conglomerate channels of Cerro Toro took place. Cretaceous synsedimentary deformation was dominated by positive inversion of Jurassic extensional structures that produced elongated axial submarine trenches separated by structural highs controlling the development and distribution of axial channels. The position of Coniacian‐Campanian unconformities indicates a ca. 50–80 km advance of the orogenic front throughout the internal domain, implying that Late Cretaceous deformation was more significant in terms of widening the orogenic wedge than all subsequent Andean deformation stages. This south Patagonian orogenic event can be related to compressional stresses generated by the combination of both the collision of the western margin of Rocas Verdes Basin during its closure, and Atlantic ridge push forces due to its accelerated opening, during a global‐scale plate reorganization event.

A global-scale plate reorganization event at 105−100 Ma

A major plate reorganization is postulated to have occurred at approximately 100Ma. However, this reorganization has received limited attention, despite being associated with the most prominent suite of fracture zone bends on the planet and many other geological events. We investigate tectonic events from the period ∼110 to 90Ma and show that the reorganization occurred between 105 and 100Ma, was global in scale, and affected all major plates. Seafloor evidence for plate motion changes is abundant during this period, with either fracture zone bends or terminations preserved in all ocean basins. Long-lived eastern Gondwanaland subduction ended along a 7000km long section of the margin, while elsewhere around the proto-Pacific rim subduction continued and there is evidence that compressional stresses increased in the overriding plates. Thrusting in western North America, transpression and basin inversion in eastern Asia, and development of the present-day Andean-style margin along western South America occurred contemporaneous with the development of an extensional regime in eastern Gondwanaland. Basin instability in Africa and western Europe further demonstrates that lithospheric stress regime changes were widespread at this time. Considering the timing of the reorganization and the nature of associated plate boundary changes, we suggest that eastern Gondwanaland subduction cessation is the most likely driving mechanism for the reorganization. Subduction is the dominant driver of plate motion and therefore this event had the potential to strongly modify the balance of driving forces acting on the plates in the southwestern proto-Pacific and neighboring plates, whereby producing widespread changes in plate motion and continental lithospheric stress patterns. We propose that major changes in ridge–trench interaction triggered the cessation of subduction. The progressive subduction of two closely spaced perpendicular mid ocean ridges at the eastern Gondwanaland subduction zone, to the east of Australia and New Zealand, respectively, resulted in very young crust entering the trench and we suggest that by 105−100Ma there was insufficient negative buoyancy to drive subduction. Finally, we propose that the plume push force of the Bouvet plume, that erupted near the African–Antarctic–South American triple junction, contributed to plate motion changes in the southern Atlantic region.