Plate Tectonic Reconstructions Research Articles

The palaeomagnetic field recorded in Eyjafjarðardalur basalts (2.6-8.0 Ma), Iceland: Are inclination-shallowing corrections necessary in Time-Average Field analysis?

Summary The Geocentric Axial Dipole (GAD) hypothesis is key to many palaeomagnetic applications, e.g., plate-tectonic reconstructions; however, the validity of this hypothesis at high latitudes is not fully resolved. To address this, in this paper we conducted a determine the palaeomagnetic directional data of 156 lava units in Eyjafjarðardalur, Iceland, with the aim of determining the validity of the GAD hypothesis at high-latitudes using time-averaged field (TAF) analysis. In addition to the palaeomagnetic directional data, we constructed an age model for the sequences using new 40Ar/39Ar dates, magnetostratigraphy and field data. The sequence age range is 2.6 to 8.0 Ma. We show that the mean virtual geomagnetic pole (VGP) for our data, does not agree with GAD theory at 95% confidence, when only the standard tilt and tectonic corrections are made, however, when inclination-shallowing processes are accounted for, e.g., TRM anisotropy and refraction effects, the mean VGP can align with GAD at 95% confidence. These inclination-shallowing processes are shown to reduce the inclination by up to 14° for some of the basaltic units. Applying the inclination shallowing correction also reduces VGP dispersion to levels which agree with global model predictions. We propose that much of the scatter within the palaeomagnetic directional databases are due to inclination-shallowing processes effects, which become more important as the natural remanent magnetisation (NRM) intensity is high, e.g., > 2 A/m. We propose that inclination-shallowing processes can be identified and corrected for by examining the NRM intensity and dispersion.

The Davis Strait proto-microcontinent: The role of plate tectonic reorganization in continental cleaving

A prolonged period of rifting and seafloor spreading between Greenland and North America formed the Labrador Sea and Baffin Bay oceanic basins, connected by the Davis Strait. However, disagreement exists regarding the exact plate motions between Greenland and Canada as well as the tectonic evolution of the Davis Strait, with previous models unable to explain the origin of anomalously thick continental crust within the seaway. Here, we present a new plate tectonic reconstruction of Greenland’s separation from Canada, constrained by a new comprehensive set of mid-ocean ridge (MOR) and transform fault lineaments identified using free-air, vertical gradient, and filtered directional gradient maps from the Sandwell and Smith gravity data. Furthermore, the reinterpretation of seismic reflection data offshore West Greenland, along with a new combined crustal thickness model, identifies an isolated terrane of relatively thick (19–24 km) continental crust that was separated from Greenland during a newly recognised phase of E-W extension along West Greenland’s margin. We interpret this continental block as an incompletely rifted microcontinent, which we term the Davis Strait proto-microcontinent. Our reconstruction suggests release of the protomicrocontinent coincided with a change in the spreading orientation from ∼ 58 to 49 Myr and was induced by transpression along a NE-SW trending transform margin that joined the Labrador Sea and Baffin Bay, prior to development of the Ungava Fracture Zone (UFZ). The location of this transform margin is constrained using our crustal thickness model, which demonstrates a sharp NE-SW trending continent-ocean transition across the North Saglek basin. We term this structure the Pre-Ungava Transform Margin (Pre-UTM), which accommodated early NE-SW motion between Greenland and Canada. Our identified mechanism of microcontinent formation may be widely applicable to other microcontinents around the globe, and further study is merited to understand the role of plate motion changes and transpression in microcontinent calving.

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.

Insights into Caribbean tectonics from a detrital zircon U-Pb provenance study of siliciclastic strata in western and central Cuba

The tectonic affinity and origins of the Jurassic, siliciclastic San Cayetano and Constancia formations exposed in western and central Cuba in the Caribbean region remain debated. The scarcity of modern geochronologic studies on these Cuban units hampers both sedimentary provenance and palinspastic reconstructions, resulting in Caribbean models that tend to oversimplify the formation of Cuba and correlate the Jurassic strata to various regions such as North America, South America, the Yucatán margin, or the conceptual Caribeana domain. Using laser ablation−inductively coupled plasma−mass spectrometry (LA-ICP-MS), we conducted a detailed detrital zircon (DZ) U-Pb provenance study of these Cuban siliciclastic strata that provides critical insights into understanding the formation of Cuba during the Early Jurassic rifting stages of Pangea. Results from 19 San Cayetano Formation samples show a dominant Oaxaquia (ca. 1 Ga) and Chiapas batholith (ca. 250 Ma) signature, while six Constancia samples display variable ca. 1 Ga and ca. 250 Ma grains. The Lower Cretaceous Polier Formation and the Paleocene Moncada Formation also display the same ca. 1 Ga and ca. 250 Ma signatures. After comparing these Cuban data with data from other regional DZ studies, we propose that that the San Cayetano and Constancia formations are correlative to the Todos Santos Formation located in the southwestern Yucatán region of Mexico. These Cuban units were predominantly deposited adjacent to the Chiapas batholith during the Early Jurassic in northwest−southeast-trending basins created by Pangean rifting. They were eventually sheared during eastward migration of the Caribbean plate and transported northward until they collided with the North American continent in the Paleogene. This DZ study provides new constraints on the tectonic provenance of western and central Cuba and improves plate tectonic reconstructions of the Caribbean.

Provenance of the Papuan Peninsula (Papua New Guinea): Zircon Inheritance from Miocene–Pliocene Volcanics and Volcaniclastics

Plate tectonic reconstructions of Papua New Guinea prior to the late Cenozoic are characterized by a lack of provenance data to constrain the relative origin of the allochthonous terranes. At present, plate tectonic reconstructions of this region infer that the accreted New Guinea terranes at the northern Australian continental margin are likely autochthonous or para-autochthonous in nature. This study presents the results of an investigation into zircons derived from Miocene–Pliocene volcanics and volcaniclastics of the Papuan Peninsula. Results from U-Pb zircon geochronology inform the recent geological history of the Papuan Peninsula, with magmatism active in the late Miocene and early Pliocene, between approximately 9 Ma and 4.5 Ma. More significantly, however, is the recognition of extensive inherited zircon grains within the volcanic and volcaniclastic sequences. These inherited zircon grains are most likely sourced from the Owen Stanley Metamorphics, which form the basement rocks of the Papuan Peninsula. Provenance of the inherited zircon grains imply that the Cretaceous volcaniclastic protolith of the Owen Stanley Metamorphics must have had input from continental detritus, but this cannot be derived from North Queensland, Australia as inferred by current reconstructions. Instead, zircon U-Pb age spectra correlate with probable source regions further to the south, adjacent to the Shoalwater Formation of the Central Queensland margin, and New Caledonia. These findings suggest that late Mesozoic and Cenozoic regional reconstructions of eastern Australia and the Southwest Pacific require major revision and that additional work is undertaken to inform the provenance of such allochthonous terranes.

Control of Hercynian Orogeny on basin evolution on the southern margin of the Tethyan region: A review and new insights

The Hercynian Orogeny was caused by the collision of Gondwana and Laurussia in the Mid‐/Late Carboniferous–Early Permian. This orogeny strongly influenced the pattern and evolution of basins and hydrocarbon accumulation on the southern margin of the Tethyan region (i.e., North Africa and the Middle East). Research on the Carboniferous–Early Permian Hercynian Orogeny is of great value in both plate tectonic reconstructions and hydrocarbon exploration. For its influence on basin evolution, some previous studies have considered the modification of the early Palaeozoic basins, but there has been less work on the evolution of the post‐Hercynian Mesozoic basins. We review the available data and re‐analyse the spatiotemporal impacts of this key tectonic event on the evolution of the basins in this region. The Carboniferous–Early Permian Hercynian Orogeny was an important turning point in basin evolution in North Africa and the Middle East. It interrupted the stability of the Gondwana platform and heralded a huge change in the pattern of basins from the uniform pre‐Hercynian Palaeozoic basins to the post‐Hercynian Mesozoic basins characterized by strong segmentation. The Carboniferous–Early Permian Hercynian Orogeny not only modified the pre‐Hercynian Palaeozoic basins but also controlled the distribution and evolution of the post‐Hercynian Mesozoic basins. Large‐scale uplifts were generated among the basins through modification of the inherited palaeohighs and five large NE‐trending arches were newly formed. These uplifts divided the early unified basin into multiple separate basins. Five large‐scale, almost equidistant, NE‐trending arches were generated on the northern margin of Gondwana (the Allala, Sirte, Levant, Al‐Batin and Oman arches), forming the present‐day Palaeozoic Basin pattern with an alternating distribution of uplifts and depressions. The northern part of the large, NE‐trending Hercynian arches collapsed as a result of the extensional stress caused by the opening of the Neotethys Ocean in the Late Permian–Triassic and formed Mesozoic basin depocenters (the Oued Mya–Pelagian basins, the Sirte Basin, the Eastern Mediterranean Basin and the Central Arabian Basin). These depocenters are important oil and gas enrichment zones. The NE‐trending Hercynian arches, the Mesozoic basin depocenters, the opening of the Neotethys Ocean and the segmentation of the basins by the Alpine Orogeny all show relatively consistent east–west‐directed segmentation on the northern margin of Gondwana. This shows that they may have a unified dynamic genetic background. The zone of structural weakness formed by the collision of multiple terranes during the Pan‐African Orogeny may have controlled this segmentation. The inheritance between reformation of the pre‐Hercynian Palaeozoic basins and influence on the post‐Hercynian Mesozoic basins by Carboniferous–Early Permian Hercynian Orogeny, is the result of the tectonics repetitively focused in pre‐existing weaker domains, under the lithospheric mantle modification in the polyphase assembly and break‐up of the supercontinent.

The new global tectonic map—Analyses and implications

AbstractA full new tectonic model of the Earth is presented based a complete new tectonic interpretation carried out during a 10‐year project. It covers a huge amount of available geophysical and geological datasets, where ca. 11 000 tectonic elements such as faults and thrusts, transform faults, rift zones, passive margins and oceanic extension ridges and numerous other features have been mapped, and classified following the geological literature. The complete surface of the Earth has been subdivided into 1.180 larger and smaller tectonic terranes, in the domains of continental blocks, oceanic plates and mobile zones. Numerical multiscale statistical fabric analyses on orientation, length and area are presented on the digitised tectonic elements and the classified terranes using the first Digital Twin of the Earth. Graphical representation through maps with different projections and viewpoints, and planetary views, are presented to illustrate the new subdivision. Some important implications for plate tectonic reconstructions are being discussed.

SE Asia as part of Gondwana: a 1960s regional mapping project over Southern Thailand that lay behind the hypothesis

Abstract In the 1960s, anticipating the award of concessions in the Gulf of Thailand, BP carried out reconnaissance geological mapping over all of Southern Thailand including its Gulf islands. The resulting eight geological maps at 1:250 000 scale provided a database that underpinned discussions of Thailand's place in global plate-tectonic reconstructions that were emerging at that time. In particular, new light was thrown on the Paleozoic succession, and important differences were found between the Upper Thai Peninsula and the Lower Peninsula (respectively, NW and SE of the prominent bend in the peninsula's outline). The Phuket Group of the Upper Peninsula is a very thick diamictite-bearing succession of possible Devonian to Early Permian age, apparently sourced in the west, a region now occupied by the Indian Ocean. That in turn suggested a possible Gondwana origin for SE Asia, a contentious concept at the time, but one that is now widely accepted. The emphasis of field mapping these days is on obtaining detailed data that necessarily means over areas of limited extent. But a very broad regional mapping project such as BP's in Thailand revealed stratigraphic and tectonic insights that could be revealed only from a wide-ranging regional study of this kind.

Strike slip motion and the triggering of subduction initiation

Plate tectonic reconstructions of three of the best-defined Cenozoic subduction initiation (SI) events in the western Pacific, Izu-Bonin-Mariana, Vanuatu, and Puysegur subduction zones, show substantial components of strike-slip motion before and during the subduction initiation. Using computational models, we show that strike-slip motion has a large influence on the effective strength of incipient margins and the ease of subduction initiation. The parameter space associated with visco-elasto-plastic rheologies, plate weakening, and plate forces and kinematics is explored and we show that subduction initiates more easily with a higher force, a faster weakening, or greater strike-slip motion. With the analytical solution, we demonstrate that the effect of strike-slip motion can be equivalently represented by a modified weakening rate. Along transpressive margins, we show that a block of oceanic crust can become trapped between a new thrust fault and the antecedent strike-slip fault and is consistent with structural reconstructions and gravity models of the Puysegur margin. Together, models and observations suggest that subduction initiation can be triggered when margins become progressively weakened to the point that the resisting forces become smaller than the driving forces, and as the negative buoyancy builds up, the intraplate stress eventually turns from compressional into extensional. The analytical formulation of the initiation time, t SI , marking the moment when intraplate stress flips sign, is validated with a computational models. The analytical solution shows that t SI is dominated by convergence velocity, while the plate age, strike-slip velocity, and weakening rate all have a smaller but still important effect on the time scale of subduction initiation.

Deep time spatio‐temporal data analysis using pyGPlates with PlateTectonicTools and GPlately

AbstractPyGPlates is an open‐source Python library to visualize and edit plate tectonic reconstructions created using GPlates. The Python API affords a greater level of flexibility than GPlates to interrogate plate reconstructions and integrate with other Python workflows. GPlately was created to accelerate spatio‐temporal data analysis leveraging pyGPlates and PlateTectonicTools within a simplified Python interface. This object‐oriented package enables the reconstruction of data through deep geologic time (points, lines, polygons and rasters), the interrogation of plate kinematic information (plate velocities, rates of subduction and seafloor spreading), the rapid comparison between multiple plate motion models, and the plotting of reconstructed output data on maps. All tools are designed to be parallel‐safe to accelerate spatio‐temporal analysis over multiple CPU processors.

Seismotectonics of the Blanco Transform Fault System, Northeast Pacific: Evidence for an Immature Plate Boundary

AbstractAt the Blanco transform fault system (BTFS) off Oregon, 138 local earthquakes and 84 double‐couple focal mechanisms from ocean‐bottom‐seismometer recordings jointly discussed with bathymetric features reveal a highly segmented transform system without any prominent fracture zone traces longer than 100 km. In the west, seismicity is focused at deep troughs (i.e., the West and East Blanco, and Surveyor Depressions). In the east, the BTFS lacks a characteristic transform valley and instead developed the Blanco Ridge, which is the most seismically active feature, showing strike‐slip and dip‐slip faulting. Sandwiched between the two main segments of the BTFS is the Cascadia Depression, representing a short intra‐transform spreading segment. Seismic slip vectors reveal that stresses at the eastern BTFS are roughly in line with plate motion. In contrast, stresses to the west are clockwise skewed, indicating ongoing reorganization of the OTF system. As we observed no prominent fracture zones at the BTFS, plate tectonic reconstructions suggest that the BTFS developed from non‐transform offsets rather than pre‐existing transform faults during a series of ridge propagation events. Our observations suggest that the BTFS can be divided into two oceanic transform systems. The eastern BTFS is suggested to be a mature transform plate boundary since ∼0.6 Ma. In contrast, the western BTFS is an immature transform system, which is still evolving to accommodate far‐field stress change. The BTFS acts as a natural laboratory to yield processes governing the development of oceanic transform faults.

Deconstructing plate tectonic reconstructions

The evolving mosaic of tectonic plates across the surface of the Earth sets boundary conditions for the evolution of biotic and abiotic processes and helps shape the dynamics of its interior. Reconstructing plate tectonics back through time allows scientists from a range of disciplines (such as palaeobiology, palaeoclimate, geodynamics and seismology) to investigate Earth evolution through these spatiotemporal dimensions. However, the variety and complexity of plate reconstructions can lead to some of their limitations being overlooked. In this Technical Review, we discuss the domain-specific knowledge underpinning modern quantitative plate reconstructions and convey a set of principles on how to use (but not abuse) the software or results. Open-source plate tectonic reconstruction software, like GPlates, has led to a major shift in working practices, handing non-specialists the tools to develop and integrate reconstructions based on their own datasets and expertise. However, there is no ‘one-size-fits-all’ and users need to understand what data and underlying assumptions go into making different, sometimes competing reconstruction models. It is therefore essential to consider the many ways reconstructions simplify reality when interpreting them to avoid circular reasoning. Although many aspects of deep-time reconstructions remain unresolved, future work on intercomparisons between models and uncertainty quantification is an essential pathway towards next-generation plate reconstructions. The advent of advanced plate tectonic reconstruction software has instigated an explosive growth in their generation and use by the wider Earth science community. This Technical Review provides a best-practice guide for quantitative plate reconstructions and their applications.

Deposition of sandstone (early Cambrian) above the Great Unconformity in the Sino-Korean Block, Gondwana: Control of antecedent topography

The global transition between the Precambrian and Phanerozoic eons in concert with rise in eustatic sea-level caused an important change in paleoenvironments, represented by sedimentary records above the Great Unconformity. In the Sino-Korean Block, Gondwana, the unconformity has been recognized by a boundary between various basement rocks and the overlying distinctive suite of sandstone (including conglomerate, conglomeratic sandstone, and mudstone) of the early Cambrian age. A plate tectonic reconstruction of the Cambrian-Ordovician succession in the northeast Asian continent reveals that the sandstone deposited largely in the eastern part of the platform (North China Platform), including the Taebaeksan and Pyeongnam basins. In the western part of the platform, the basal sandstone is correlated to basal carbonate rocks of middle Cambrian age, forming a time-transgressive or diachronous unconformity. The disparity in sedimentary facies of the basal deposits overlying the Great Unconformity was primarily due to antecedent topography of the bounding continent: in the eastern platform, the drainage area comprised high-relief Precambrian massifs, whereas in the western part, it comprised low-relief massifs. During the initial stage of sea-level rise, the eastern part of the platform formed progressively open shoreface and foreshore environments with localized embayments in which relatively coarse-grained gravelly sandstone deposited in fan-delta and tide-dominated environments. In the western platform, however, the supply of siliciclastic sediments was limited and the sandstone formed a relatively narrow linear belt of delta and distributary mouth bars and foreshore deposits. In the rest of the platform farther west, accommodation created by subsequent sea-level rise was filled with carbonate sediments. This study demonstrates that antecedent topography of the unsubmerged drainage area played a major role for the deposition of sandstone in the initial transgression stage, forming the Great Unconformity.

EaDz: A web-based, relational database for detrital zircons from East Asia

Detrital zircon geochronology and geochemistry have become the primary methods for reconstructing the Earth's tectonic and surficial processes over geologic time. The compilation and dissemination of detrital zircon data are essential to facilitate rapid, innovative, and reliable studies and to drive new research discoveries. To this end, we present EaDz, a new web-based, relational database for detrital zircons from East Asia, which includes geochronological, geochemical, petrological, and stratigraphic datasets. The EaDz currently contains 7083 rock samples representing 570,092 U–Pb ages, 77,394 Lu–Hf isotopes, 35,045 trace elements, and 1773 oxygen isotope data entries. Within the EaDz database, 71% of the samples are siliciclastic rocks, followed by 16% metasedimentary rocks, 6% modern sediments, and 7% other rocks. The database is intended to serve as a repository for new and existing detrital zircon data and a platform for the visualization and analysis of detrital zircon data. Through a publicly accessible interactive website, EaDz allows simultaneous data retrieval, analysis, and visualization in the cloud. Additionally, EaDz provides a means for combining the detrital zircon data with global plate reconstruction models - thus providing deep-time dynamic reconstructions of detrital palaeolocations. As such, the EaDz provides a powerful resource for applications in paleogeography reconstruction, plate tectonic reconstruction, and crustal-mantle evolution. The database will continue to be developed and improved. We encourage users to collaborate on data compilation by submitting data through the website or contacting corresponding authors directly after their data is published.

Meteorite impact crater positions based on paleo-positions and its unrestrained latitudinal distribution

The paleo-positions of terrestrial meteorite impact craters along with distance and displacement registered since formation due to plate tectonics were deciphered using GPlates, an interactive GIS-based plate tectonic reconstruction and modeling software. The results of the study are intriguing as several craters have traversed across the globe, both from the Eastern to Western hemisphere and from the Southern to Northern hemisphere, and vice versa. The oldest crater studied was Foelsche, which traversed from the Southern to Northern hemisphere and from the Western to Eastern hemisphere while covering a distance of 39080 ​km in the past 981 million years and recording a relatively shorter displacement of 10470 ​km. On the other hand, Jänisjärvi and Suvasvesi South have traveled longer distances (27781 and 29050 ​km, respectively) and are among the most displaced craters (17400 and 16988 ​km, respectively). Similarly, the paleo-position, distance, and displacement for all craters, with ages <1100 ​Ma, were computed in the study. Based on the derived paleo-position, we have accessed the possibility of any selective distribution of craters across different latitudinal segments. As Earth is a planet that recorded dynamic variations in the terrestrial surface area across different geological ages, calculating the same was an arduous task. The land area within each of the three latitudinal segments, viz. 0–30°, 30–60°, and 60–90°, in which a crater formed was calculated for the geological time corresponding to an impact cratering event. This calculated land area within the respective latitudinal zone at each instance of a crater's formation was then compared with the total land area on Earth. The results showed that 0–30° and 30–60° segments have equal crater frequencies whereas the 60–90° segment has a lesser frequency. The latitudinal crater distribution on Earth was then compared with Moon and Mars. The results revealed that there is a non-selective distribution of terrestrial impact craters across different latitudinal segments, indicating a non-perceivable latitudinal dependency for impact events. • 192 Earth impact craters, formed after 1100 ​Ma, were reconstructed to its paleo-position. • The distance and displacement recorded by the craters due to plate tectonics is computed. • Latitudinal distribution of craters was studied and showed no major dependency on latitudes. • The latitudinal distribution was correlated with Moon and Mars.

Arctic sediment routing during the Triassic: sinking the Arctic Atlantis

Opening of the Arctic Ocean has been the subject of much debate, and the placement of terranes in the Early Mesozoic remains a crucial part of this important discussion. Several continental terranes complicate the palaeogeographical reconstruction. One such terrane is Crockerland, which has been inferred to explain sediment distribution in the Arctic throughout the Mesozoic. However, Triassic successions throughout the Arctic basins bear many similarities, and a common sedimentary source could offer a simpler explanation with fewer complications for the past configuration of the Arctic. The study's goal is to test the hypothesis of long-distance sediment transport from a common source in present-day Russia to all Arctic basins in the Triassic, and to demonstrate how estimates of sediment routing distances can improve pre-break-up plate-tectonic reconstructions. Results confirm that (1) the Arctic basins were closely connected prior to break-up in the Mesozoic, (2) based on regional facies distribution, sediment budgets, sediment modelling and detrital zircon age spectra, the Crockerland terrane is unlikely to have existed as a major sediment supplying area, (3) the reconstructed Arctic sediment routing system can help to constrain plate-tectonic models, and (4) statistical estimation of sediment transport is a novel and potentially important tool for improving plate-tectonic and palaeogeographical reconstructions. Supplementary material : A database for provenance study, detrital zircon age spectra and the sedimentary length calculations method are available at https://doi.org/10.6084/m9.figshare.c.6086468

Tonian evolution of an active continental margin - a model for Neoproterozoic NW India-SE Pakistan–E Oman linkage

Here we introduce a new model for a Tonian active continental margin in the Neoproterozoic western foreland of the Delhi Fold Belt of NW India. This study gives indication for a transition from continental crust into an active arc setting prior to emplacement of the volcano-plutonic Malani Igneous Suite. Erinpura Granites (890 to 860 Ma) are exposed in a large area west of the Delhi Fold Belt in NW India. The Erinpura Granites are S-type (εNd −10 to −3) whereas granites, granodiorites and gabbros exposed in the westernmost basement outcrops (Bhinmal, Harsani) are I-type granitoids and show positive Nd ratios (εNd + 4 to + 6). These intrusions are derived from crustal melting with a lithospheric component and affinity to a subduction setting, as can also be inferred from trace element ratios. Our study places the Bhinmal granite as youngest intrusion in this setting (U-Pb analyses of zircon 794 ± 17 Ma and titanite 793 ± 19 Ma). High temperature linear solid-state fabrics in the granites indicate intrusion and deformation during crustal extension. After uplift and exhumation bimodal dykes and granites of the Malani Igneous Suite (770–750 Ma) intruded into this older crust (pre-Malani basement).An evolutionary model for a Tonian active continent margin is established by integrating data from Nagar Parkar in East Pakistan and Neoproterozoic basement inliers in East Oman. The data indicate 130 Myr of ongoing subduction (900 to 770 Ma) along the continental margin. Magmatic activity is identified as episodic with three major pulses starting at ca. 840 Ma, ca. 825 Ma and ca. 770 Ma. High temperature melting constitutes the last Tonian magmatic pulse (Malani Igneous Suite) attributed to roll-back of the subducting slab. The implications for Neoproterozoic plate tectonic reconstructions are discussed.

The timing of the Svalbardian Orogeny in Svalbard: a review

Abstract. In the Late Devonian to earliest Mississippian, Svalbard was affected by a short-lived episode of deformation named the Svalbardian Orogeny. This event resulted in intense folding and thrusting in Devonian sedimentary successions. Deformation stopped prior to the deposition of Carboniferous to Permian sedimentary strata of the Billefjorden and Gipsdalen groups, which lie unconformably over folded Devonian strata. Later on, presumed Svalbardian structures were reworked during Eurekan tectonism in the early Cenozoic and partly eroded. At present, records of Svalbardian deformation are only preserved in narrow N–S-trending belts in central, northern, western, and southern Spitsbergen. Despite extensive field studies, the timing of the Svalbardian Orogeny is poorly constrained and remains a matter of debate in places because of conflicting ages and because of the complex tectonic history of Svalbard. The present contribution aims at reviewing and discussing all available age constraints for Svalbardian tectonism, including notably palynological, paleontological, and geochronological evidence. This has great implications for the plate tectonic reconstructions of Arctic regions and for the tectonic history of Svalbard. Palynological and paleontological evidence suggest that the Mimerdalen Subgroup is upper Givetian to lower Frasnian (ca. 385–380 Ma) in age and that the Billefjorden Group is mid-Famennian to Upper Mississippian (ca. 365–325 Ma) in age, constraining the Svalbardian event in central and northern Spitsbergen to 383–365 Ma if it ever occurred. Palynological ages indicate that the Adriabukta Formation in southern Spitsbergen is Middle Mississippian and therefore cannot have been involved in the Svalbardian event, thus suggesting that all the deformation in southern Spitsbergen is early Cenozoic in age and that strain-partitioning processes had a major role in localizing deformation in weaker stratigraphic units. The few geochronological age constraints yielding Late Devonian–Mississippian ages in Svalbard may reflect either Svalbardian contraction or extensional processes and are therefore of no use to validate or invalidate the occurrence of the Svalbardian event. On the contrary, the contradicting lines of evidence used to support the occurrence of the Svalbardian event and new regional geophysical studies suggest that Svalbard was subjected to continuous extension from the late Silurian to early Permian times.

Reconstructing a dismembered Neogene basin along the active Hikurangi subduction margin, New Zealand

AbstractThe East Coast Basin (ECB), New Zealand, preserves the most complete onshore stratigraphic record of the Cretaceous–Neogene development of Zealandia from Gondwana breakup, through rift-drift, to evolution of the modern Hikurangi subduction margin and Pacific-Australia plate boundary. As such, it provides important constraints for southwest Pacific plate tectonic reconstructions. The basin is, however, deformed and variably dismembered, and in previous tectonic models it has been treated as a zone of poorly constrained deformation. Here, multiple geological and geophysical data sets are integrated with a tectonic reconstruction to provide a synthesis of regional and intrabasin-scale structural evolution of the ECB during the Neogene, producing a new geologically constrained approach toward qualitative and quantitative assessment of deformation across the New Zealand plate boundary zone. We produce the first palinspastic reconstructions for the entire basin during key times in plate boundary development, within a well-constrained plate-tectonic framework, supported by independent deformation estimates. These reconstructions account for contraction, strike-slip, and vertical-axis rotation of crustal blocks. In the context of the reconstruction model, the ECB has dominantly experienced upper-plate shortening and vertical-axis rotations; strike-slip processes are considered comparatively minor. Comparison of the reconstruction model with independent data highlight several pronounced deformation intervals (26–23 Ma, 20–15 Ma, 11 Ma, and 7–4 Ma) in the structural and sedimentary evolution of the ECB, Hikurangi subduction margin, and New Zealand plate boundary zone, demonstrating that it is possible to integrate a wide range of geological data sets to develop meaningful reconstructions in highly tectonised regions.

Formation conditions and evolution of the oil and gas strata of the prospective East Siberian oil and gas province

Introduction. East Siberian Sea shelf refers to the Novosibirsk-Chukotka prospective oil and gas province. The definition of the East Siberian shelf as a prospective oil and gas province and its division into areas is based, along with the structural and geological prerequisites, on the identification of numerous bitumen occurrences in the Paleozoic, Triassic and Jurassic sediments of the Novosibirsk Islands.Aim. To construct spatio-temporal digital models of sedimentary basins and hydrocarbon systems for the main horizons of source rocks, as well as to carry out their detailed analysis based on the available information about the oil and gas content, the gas-chemical composition of sediments, the characteristics of the component composition and evolution of source rocks within the studied prospective oil and gas province. The conducted research made it possible to study regional trends in oil and gas content, features of the sedimentary cover formation and the development of hydrocarbon systems in the area under study.Materials and methods. The materials of production reports obtained for individual large objects in the water area were the source of information. A basin analysis was based on a model developed by the Equinor specialists (Somme et al., 2018) [8, 9], which covered the time period from the Triassic to Paleogene inclusive and took into account the plate-tectonic reconstructions performed by Dor’e et al. in 2015. The resulting model included four main sedimentary complexes: pre-Aptian, Apt-Upper Cretaceous, Paleogene, and Neogene-Quaternary.Results. The calculation of numerical models was carried out in two versions with different types of kerogen of oil and gas source strata corresponding to humic and sapropel organic matter. The key factor in controlling the development of hydrocarbon systems was found to be the sinking rate of the basins and the thickness of the formed overburden complexes.Conclusion. The conducted analysis allowed the most promising research objects to be identified. The main foci of hydrocarbon generation in the Aptian-Late Cretaceous and Paleogene complexes were identified, along with the area of their most probable accumulation. Significant hydrocarbon potential is expected in the Paleogene clinoforms of the Eastern Arctic. This complex is currently underestimated, thus requiring further resource assessment study. A detailed mapping of its interior structure should be carried out.