Key in understanding the geodynamics governing subduction and orogeny is reconstructing the paleogeography of ‘Greater India’, the Indian plate lithosphere that subducted since Tethyan Himalayan ...continental collision with Asia. Here, we discuss this reconstruction from paleogeographic, kinematic, and geodynamic perspectives and isolate the evolution scenario that is consistent with all three. We follow recent constraints advocating a ~58 Ma initial collision and update a previous kinematic restoration of intra-Asian shortening with a recently proposed model that reconciles long-debated large and small estimates of Indochina extrusion. Our new reconstruction is tested against paleomagnetic data, and against seismic tomographic constraints on paleo-subduction zone locations. The resulting restoration shows ~1000–1200 km of post-collisional intra-Asian shortening, leaving a 2600–3400 km wide Greater India. From a paleogeographic, sediment provenance perspective, Eocene sediments in the Lesser Himalaya and on undeformed India may be derived from Tibet, suggesting that all Greater Indian lithosphere was continental, but may alternatively be sourced from the contemporaneous western Indian orogen unrelated to India-Asia collision. A quantitative kinematic, paleomagnetic perspective prefers major Cretaceous extension and a ‘Greater India Basin’ opening within Greater India, but data uncertainty may speculatively allow for minimal extension. Finally, from a geodynamic perspective, assuming a fully continental Greater India would require that subduction rates close to 20 cm/yr was driven by a down-going lithosphere-crust assemblage more buoyant than the mantle, which seems physically improbable. We conclude that the Greater India Basin scenario is the only sustainable one from all three perspectives. We infer that old pre-collisional lithosphere rapidly entered the lower mantle sustaining high subduction rates, whilst post-collisional continental and young Greater India basin lithosphere did not, inciting the rapid India-Asia convergence deceleration ~8 Myr after collision. Subsequent absolute northward slab migration and overturning caused flat slab subduction, Tibetan shortening, arc migration and arc volume decrease.
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•Following 58 Ma India-Asia collision, Asia shortening 1000-1200 km and 2600-3400 km of (Greater) India subducted•Combined paleogeographic, kinematic, and geodynamic constraints strongly suggest a Greater India Basin scenario•Post-58 Ma upper mantle slab buckling induced flat slab subduction causing India-Asia slowdown and Tibetan shortening
Paleomagnetic data have long been used to hypothesize that the Cenozoic extrusion of the Indochina Block along the left-lateral Ailao Shan-Red River fault, as a result of the India-Asia collision, ...may have been associated with a major southward paleolatitude shift of as much as 10–15°, and a vertical-axis rotation of as much as 25–40°. However, although numerous paleomagnetic studies have been conducted in the southeast margin of the Tibetan Plateau and in the Indochina region during the last few decades, the detailed rotation as well as the latitudinal displacement of the Indochina Block remain controversial because of apparently contradicting paleomagnetic results. Geological constraints also yield contrasting estimates on the amount of displacement along different segment of the Ailao Shan-Red River fault: 700±200km in the northwest, but only ~250km in the southeast. In this paper, the available paleomagnetic data from the southeast margin of the Tibetan Plateau and Indochina, as well as the South China Block, from Jurassic and younger rocks are compiled and critically reviewed using the new paleomagnetic toolkit on Paleomagnetism.org. Our results show that (1) the South China Block has declinations that reveal no significant rotations relative to Eurasia since latest Jurassic. Inclinations are consistently shallower than expected, which is likely the result of inclination shallowing in sedimentary rocks; (2) there is no paleomagnetically resolvable southward motion of the Indochina Block with respect to Eurasia based on the paleomagnetic data. Paleomagnetic inclinations are in fact lower than expected, probably due to inclination shallowing in sediments; (3) paleomagnetic declinations reveal large, more or less coherently rotating blocks in the northern Indochina domain and the SE Tibetan margin that rotated up to 70° clockwise, much more than the ~10–15° rotation of the stable, SE part of the Indochina Block. These blocks are bounded by fold-thrust belts and strike-slip faults, which we interpret to have accommodated these block rotations during the Cenozoic. We designed a new tool on the online open-access portal Paleomagnetism.org that allows testing whether Euler rotations in a kinematic reconstruction fulfill paleomagnetic data. Using this tool, we built a first-order kinematic reconstruction of rotational deformation of northwest Indochina in Cenozoic. We show that the northwestern part of Indochina extruded 350km more along the Ailao Shan-Red River fault than the southeastern part accommodated by internal northwest Indochina rotation and deformation. Estimates of 250km of extrusion of the southeastern part of the Indochina then predicts ~600km of left-lateral motion along the northwestern part of the Ailao Shan-Red River fault, which reconciles the small and large estimates that prevail in the literature of extrusion of Indochina from the Tibetan realm during the Cenozoic India-Asia collision.
•A critical review and compilation on the available paleomagnetic data from the South China and Indochina Blocks;•A updated kinematic reconstruction of Cenozoic deformation of Indochina;•The first reconciles regarding the small and large estimates of Indochina extrusion along the Ailao Shan-Red River fault.
Apparent polar wander paths (APWPs) calculated from paleomagnetic data describe the motion of tectonic plates relative to the Earth's rotation axis through geological time, providing a quantitative ...paleogeographic framework for studying the evolution of Earth's interior, surface, and atmosphere. Previous APWPs were typically calculated from collections of paleomagnetic poles, with each pole computed from collections of paleomagnetic sites, and each site representing a spot reading of the paleomagnetic field. It was recently shown that the choice of how sites are distributed over poles strongly determines the confidence region around APWPs and possibly the APWP itself, and that the number of paleomagnetic data used to compute a single paleomagnetic pole varies widely and is essentially arbitrary. Here, we use a recently proposed method to overcome this problem and provide a new global APWP for the last 320 million years that is calculated from simulated site-level paleomagnetic data instead of from paleopoles, in which spatial and temporal uncertainties of the original datasets are incorporated. We provide an updated global paleomagnetic database scrutinized against quantitative, stringent quality criteria, and use an updated global plate motion model. The new global APWP follows the same trend as the most recent pole-based APWP but has smaller uncertainties. This demonstrates that the first-order geometry of the global APWP is robust and reproducible. Moreover, we find that previously identified peaks in APW rate disappear when calculating the APWP from site-level data and correcting for a temporal bias in the underlying data. Finally, we show that a higher-resolution global APWP frame may be determined for time intervals with high data density, but that this is not yet feasible for the entire 320–0 Ma time span. Calculating polar wander from site-level data provides opportunities to significantly improve the quality and resolution of the global APWP by collecting large and well-dated paleomagnetic datasets from stable plate interiors, which may contribute to solving detailed Earth scientific problems that rely on a paleomagnetic reference frame.
•New paleomagnetic reference frame for the last 320 million years.•Global apparent polar wander path computed from site-level data rather than poles.•First-order geometry similar to previous models but with smaller uncertainties.•Peaks in apparent polar wander may result from a temporal bias in the data.•Future improvement of the reference frame requires new, high-quality data.
Subduction polarity reversal during arc‐continent collision has been proposed as a key mechanism to initiate new subduction zones. Despite often interpreted, well‐exposed geological record that ...document the reversal is sparse. The ophiolitic lithounits of the Andaman and Nicobar Islands have been proposed to have formed during the initiation of a new subduction zone following the collision of the Woyla Arc of Sumatra with Sundaland (Eurasia). We here present new field, petrological and geochronological data to evaluate the timing of the initiation of Andaman subduction. We targeted the previously inferred but unstudied metamorphic sole of the Andaman ophiolites that witnessed juvenile subduction. Thermodynamic modeling reveals that the exposed amphibolites of the sole formed at around 0.9 GPa and 675 °C. We dated two samples of the metamorphic sole using the Ar/Ar method on amphibole, giving cooling ages of 106.4 ± 2.1 and 105.3 ± 1.6 Ma. This is similar to published ages from plagioclase xenocrysts in recent Barren Island volcanics and in zircons from a gabbro sample from the Andaman ophiolite, which we interpret as the age of the original ophiolite formation. The Ar/Ar ages are considerably older than arc magmatic gabbros and plagiogranites of the overlying ophiolite previously dated at 99–93 Ma and thought to reflect the ophiolite age but recently reinterpreted as a volcanic arc built on the ophiolite. Combined with the ages of Woyla‐Sundaland collision, we argue that subduction polarity reversal occurred in a transient period of perhaps some 10 Myr, similar to recent settings.
Key Points
We document the condition of formation of the metamorphic sole of the Andaman Island ophiolite
We provide Ar/Ar ages for the subduction initiation leading to the formation of the Andaman Island ophiolite
We estimate the duration of subduction polarity reversal following an arc‐continent collision to 10 Myr at least
Key to understanding the plate kinematic evolution of the Neotethys oceanic domain that existed between the Gondwana-derived Indian and Australian continents in the south, and Eurasia in the north, ...is the reconstruction of oceanic plates that are now entirely lost to subduction. Relics of these oceanic plates exist in the form of ophiolites and island arcs accreted to the orogen that stretches from Tibet and the Himalayas to SE Asia that formed the southern margin of Sundaland. The intra-oceanic Woyla Arc thrusted over western Sundaland – the Eurasian core of SE Asia – in the mid-Cretaceous. The Woyla Arc was previously interpreted to have formed above a west-dipping subduction zone in the Early Cretaceous, synchronous with east-dipping subduction below Sundaland. The oceanic ‘Ngalau Plate’ between the Woyla Arc and Sundaland was lost to subduction. We present paleomagnetic results from Lower Cretaceous limestones and volcaniclastic rocks of the Woyla Arc, Middle Jurassic radiolarian cherts of the intervening Ngalau Plate, and Upper Jurassic–Lower Cretaceous detrital sediments of the Sundaland margin. Our results suggest that the Woyla Arc was formed around equatorial latitudes and only underwent an eastward longitudinal motion relative to Sundaland. This is consistent with a scenario where the Woyla Arc was formed on the edge of the Australian plate. We propose a reconstruction where the Ngalau Plate formed a triangular oceanic basin between the N–S trending Woyla Arc and the NW-SE trending Sundaland margin to account for the absence of accreted arc rocks in the Himalayas. As consequence of this triangular geometry, accretion of the Woyla Arc to the western Sundaland margin was diachronous, accommodated by a southward migrating triple junction. Continuing convergence of the Australia relative to Eurasia was accommodated by subduction polarity reversal behind the Woyla Arc, possibly recorded by Cretaceous ophiolites in the Indo-Burman Ranges and the Andaman-Nicobar Islands.
•We present paleomagnetic data from the Woyla Arc that demonstrates it was formed at equatorial latitudes.•This is consistent with a plate kinematic scenario where the Woyla Arc was formed on the Australian Plate.•We reconstruct the N–S striking Woyla Arc separated by a triangular oceanic Ngalau Plate from the West Sundaland margin.•Accretion of the Woyla Arc to the Sundaland margin was diachronous, accommodated by a southward migrating triple junction.•Continuing convergence between Australia and Eurasia was accommodated by subduction polarity reversal behind the Woyla Arc.
Key to understanding the complex Mediterranean subduction history is the kinematic reconstruction of its paleogeography after Jurassic extension between Iberia, Eurasia, and Africa. While post-Eocene ...Liguro-Provençal back-arc extension, and associated Miocene ∼50° counterclockwise (ccw) rotation of Sardinia–Corsica have been well documented, pre-Oligocene reconstructions suffer uncertainties related to the position of Sardinia–Corsica with respect to Iberia. If a previously constrained major post-middle Jurassic, pre-Oligocene rotation of Sardinia–Corsica can be quantified in time, we can test the hypothesis that Sardinia–Corsica was (or was not) part of Iberia, which underwent a ∼35° ccw during the Aptian (121–112 Ma). Here, we present new paleomagnetic results from Triassic, Jurassic, Upper Cretaceous and Lower Eocene carbonate rocks from Sardinia. Our results show a consistent well constrained post-early Eocene to pre-Oligocene ∼45° ccw rotation of Sardinia–Corsica relative to Eurasia. This rotation postdated the Iberian rotation, and unambiguously shows that the two domains must have been separated by a (transform) plate boundary. The Eocene rotation of Sardinia–Corsica was synchronous with and likely responsible for documented N-S shortening in the Provence and the incorporation of the Briançonnais continental domain, likely connected to Corsica, into the western Alps. We argue that this rotation resulted from the interplay between a southward ‘Alpine’ subduction zone at Corsica, retreating northward, and a northward subduction zone below Sardinia, remaining relatively stationary versus Eurasia.
•First paleomagnetic data from Cretaceous and Paleogene rocks from Sardinia.•Sardinia–Corsica experienced a ∼40° counterclockwise rotation in the Eocene.•The first phase of rotation of Sardinia–Corsica postdated the rotation of Iberia.•Sardinia–Corsica is an independent microcontinent, separated from Iberia by a fault.•Rotation of Sardinia–Corsica coincided with the Alpine Briançonnais collision.
SE Asia comprises a heterogeneous assemblage of fragments derived from Cathaysia (Eurasia) in the north and Gondwana in the south, separated by suture zones representing closed former ocean basins. ...The western part of the region comprises Sundaland, which was formed by Late Permian‐Triassic amalgamation of continental and arc fragments now found in Indochina, the Thai Penisula, Peninsular Malaysia, and Sumatra. On Borneo, the Kuching Zone formed the eastern margin of Sundaland since the Triassic. To the SE of the Kuching Zone, the Gondwana‐derived continental fragments of SW Borneo and East Kalimantan accreted in the Cretaceous. South China‐derived fragments accreted to north of the Kuching Zone in the Miocene. Deciphering this complex geodynamic history of SE Asia requires restoration of its deformation history, but quantitative constraints are often sparse. Paleomagnetism may provide such constraints. Previous paleomagnetic studies demonstrated that Sundaland and fragments in Borneo underwent vertical axis rotations since the Cretaceous. We provide new paleomagnetic data from Eocene‐Miocene sedimentary rocks in the Kutai Basin, east Borneo, and critically reevaluate the published database, omitting sites that do not pass widely used, up‐to‐date reliability criteria. We use the resulting database to develop an updated kinematic restoration. We test the regional or local nature of paleomagnetic rotations against fits between the restored orientation of the Sunda Trench and seismic tomography images of the associated slabs. Paleomagnetic data and mantle tomography of the Sunda slab indicate that Sundaland did not experience significant vertical axis rotations since the Late Jurassic. Paleomagnetic data show that Borneo underwent a ~35° counterclockwise rotation constrained to the Late Eocene and an additional ~10° counterclockwise rotation since the Early Miocene. How this rotation was accommodated relative to Sundaland is enigmatic but likely involved distributed extension in the West Java Sea between Borneo and Sumatra. This Late Eocene‐Early Oligocene rotation is contemporaneous with and may have been driven by a marked change in motion of Australia relative to Eurasia, from eastward to northward, which also has led to the initiation of subduction along the eastern Sunda trench and the proto‐South China Sea to the south and north of Borneo, respectively.
Key Points
We present new paleomagnetic data from Eocene‐Miocene sedimentary rocks in Kutai Basin, Borneo, and compile all available paleomagnetic data from Mesozoic and Cenozoic rocks in Sundaland and Borneo
We compare reconstructed trenches with seismic tomography to evaluate the regional or local nature of paleomagnetic results
We provide a kinematic restoration of Borneo and Sundaland since the Eocene that is consistent with paleomagnetism and tomography
In Central and Western Anatolia two continent‐derived massifs simultaneously underthrusted an oceanic lithosphere in the Cretaceous and ended up with very contrasting metamorphic grades: high ...pressure, low temperature in the Tavşanlı zone and the low pressure, high temperature in the Kırşehir Block. To assess why, we reconstruct the Cretaceous paleogeography and plate configuration of Central Anatolia using structural, metamorphic, and geochronological constraints and Africa‐Europe plate reconstructions. We review and provide new 40Ar/39Ar and U/Pb ages from Central Anatolian metamorphic and magmatic rocks and ophiolites and show new paleomagnetic data on the paleo‐ridge orientation in a Central Anatolian Ophiolite. Intraoceanic subduction that formed within the Neotethys around 100–90 Ma along connected N‐S and E‐W striking segments was followed by overriding oceanic plate extension. Already during suprasubduction zone ocean spreading, continental subduction started. We show that the complex geology of central and southern Turkey can at first order be explained by a foreland‐propagating thrusting of upper crustal nappes derived from a downgoing, dominantly continental lithosphere: the Kırşehir Block and Tavşanlı zone accreted around 85 Ma, the Afyon zone around 65 Ma, and Taurides accretion continued until after the middle Eocene. We find no argument for Late Cretaceous subduction initiation within a conceptual “Inner Tauride Ocean” between the Kırşehir Block and the Afyon zone as widely inferred. We propose that the major contrast in metamorphic grade between the Kırşehir Block and the Tavşanlı zone primarily results from a major contrast in subduction obliquity and the associated burial rates, higher temperature being reached upon higher subduction obliquity.
Key Points
Central Anatolia formed due to interplay of two simultaneous subduction zones
The Anatolian thrust belt formed by foreland‐propagating nappe stacking
Strong variations in subduction obliquity may explain contrasting metamorphic histories
During the middle Pliocene (∼3.8–3.2 Ma), both Australopithecus afarensis and Kenyanthropus platyops are known from the Turkana Basin, but between 3.60 and 3.44 Ma, most hominin fossils are found on ...the west side of Lake Turkana. Here, we describe a new hominin locality (ET03-166/168, Area 129) from the east side of the lake, in the Lokochot Member of the Koobi Fora Formation (3.60–3.44 Ma). To reconstruct the paleoecology of the locality and its surroundings, we combine information from sedimentology, the relative abundance of associated mammalian fauna, phytoliths, and stable isotopes from plant wax biomarkers, pedogenic carbonates, and fossil tooth enamel. The combined evidence provides a detailed view of the local paleoenvironment occupied by these Pliocene hominins, where a biodiverse community of primates, including hominins, and other mammals inhabited humid, grassy woodlands in a fluvial floodplain setting. Between <3.596 and 3.44 Ma, increases in woody vegetation were, at times, associated with increases in arid-adapted grasses. This suggests that Pliocene vegetation included woody species that were resilient to periods of prolonged aridity, resembling vegetation structure in the Turkana Basin today, where arid-adapted woody plants are a significant component of the ecosystem. Pedogenic carbonates indicate more woody vegetation than other vegetation proxies, possibly due to differences in temporospatial scale and ecological biases in preservation that should be accounted for in future studies. These new hominin fossils and associated multiproxy paleoenvironmental indicators from a single locale through time suggest that early hominin species occupied a wide range of habitats, possibly including wetlands within semiarid landscapes. Local-scale paleoecological evidence from East Turkana supports regional evidence that middle Pliocene eastern Africa may have experienced large-scale, climate-driven periods of aridity. This information extends our understanding of hominin environments beyond the limits of simple wooded, grassy, or mosaic environmental descriptions.
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