Paleogene India-Eurasia collision constrained by observed plate rotation

The Cenozoic India-Eurasia collision has had profound impacts on shaping the Tibetan plateau, but its early history remains controversial due to uneven availability of constraints. Recent plate reconstructions reveal two prominent counterclockwise rotation (azimuthal change) rate peaks of the Indian plate at 52-44 and 33-20 Ma, respectively, which could bear key information about this collision history. Using fully dynamic three-dimensional numerical modeling, we show that the first rotation rate peak reflected the initial diachronous collision from the western-central to eastern Indian front, and the second peak reflected the full collision leading to strong coupling between India and Eurasia. Further comparison with observation suggests that the initial and complete India-Eurasia collision likely occurred at 55 ± 5 and 40 ± 5 Ma, respectively, an inference consistent with key geological observations. We suggest that this collision history is instructive for studying the tectonic history of the Tibetan plateau and its surrounding areas.

Assessing plate reconstruction models using plate driving force consistency tests

Plate reconstruction models are constructed to fit constraints such as magnetic anomalies, fracture zones, paleomagnetic poles, geological observations and seismic tomography. However, these models do not consider the physical equations of plate driving forces when reconstructing plate motion. This can potentially result in geodynamically-implausible plate motions, which has implications for a range of work based on plate reconstruction models. We present a new algorithm that calculates time-dependent slab pull, ridge push (GPE force) and mantle drag resistance for any topologically closed reconstruction, and evaluates the residuals-or missing components-required for torques to balance given our assumed plate driving force relationships. In all analyzed models, residual torques for the present-day are three orders of magnitude smaller than the typical driving torques for oceanic plates, but can be of the same order of magnitude back in time-particularly from 90 to 50 Ma. Using the Pacific plate as an example, we show how our algorithm can be used to identify areas and times with high residual torques, where either plate reconstructions have a high degree of geodynamic implausibility or our understanding of the underlying geodynamic forces is incomplete. We suggest strategies for plate model improvements and also identify times when other forces such as active mantle flow were likely important contributors. Our algorithm is intended as a tool to help assess and improve plate reconstruction models based on a transparent and expandable set of a priori dynamic constraints.

New constraints on Cenozoic subduction between India and Tibet

The type of lithosphere subducted between India and Tibet since the Paleocene remains controversial; it has been suggested to be either entirely continental, oceanic, or a mixture of the two. As the subduction history of this lost lithosphere strongly shaped Tibetan intraplate tectonism, we attempt to further constrain its nature and density structure with numerical models that aim to reproduce the observed history of magmatism and crustal thickening in addition to present-day plateau properties between 83°E and 88°E. By matching time-evolving geological patterns, here we show that Tibetan tectonism away from the Himalayan syntaxis is consistent with the initial indentation of a craton-like terrane at 55 ± 5 Ma, followed by a buoyant tectonic plate with a thin crust, e.g., a broad continental margin (Himalandia). This new geodynamic scenario can explain the seemingly contradictory observations that had led to competing hypotheses like the subduction of Greater India versus largely oceanic subduction prior to Indian indentation.

Secular change of true polar wander over the past billion years

The rate of movement of Earth's solid shell relative to its spin axis, or true polar wander, depends on variations in mantle convection and viscosity. We report paleomagnetic and geochronologic data from South China that constrain the rate of rapid true polar wander (>5° per million years) between 832 million years and 821 million years ago. Analysis of the paleomagnetic database demonstrates secular change of true polar wander related to mantle cooling and thermal structure across supercontinent cycles. True polar wander rates are relatively muted with a partially insulated mantle during supercontinent assembly and accelerate as mantle thermal mixing reestablishes with supercontinent breakup. Decreasing true polar wander rate through the Neoproterozoic was succeeded by overall smaller variations in the Phanerozoic. We propose that Neoproterozoic extensive plate tectonic activities enhanced mantle cooling, giving rise to a reduction in mantle convective forcing, an increase in mantle viscosity, and a decrease in true polar wander rates into the Phanerozoic.

Plume-MOR decoupling and the timing of India-Eurasia collision

The debatable timing of India–Eurasia collision is based on geologic, stratigraphic, kinematic, and tectonic evidence. However, the collision event disturbed persistent processes, and the timing of disturbance in such processes could determine the onset of India–Eurasia collision precisely. We use the longevity of Southeast Indian Ridge (SEIR)—Kerguelen mantle plume (KMP) interaction cycles along the Ninetyeast ridge (NER) as a proxy to determine the commencement of India–Eurasia collision. The geochemical signature of the KMP tail along the NER is predominantly that of long-term coupling cycles, that was perturbed once by a short-term decoupling cycle. The long-term coupling cycles are mainly of enriched mid-ocean ridge basalts (E-MORBs). The short-term decoupling cycle is mostly derived from two distinct sources, MOR and plume separately, whereas the KMP is still being on-axis. The onset of India–Eurasia collision led to continental materials recycling into the mantle; hence the abrupt enrichment in incompatible elements at ca. 55 Ma, the MOR–plume on-axis decoupling, and the abrupt slowdown in the northward drift of the Indian plate was induced by the onset of India–Eurasia collision, thereafter MOR–plume recoupled.

Evidence for active upper mantle flow in the Atlantic and Indo-Australian realms since the Upper Jurassic from hiatus maps and spreading rate changes

Histories of large-scale horizontal and vertical lithosphere motion hold important information on mantle convection. Here, we compare continent-scale hiatus maps as a proxy for mantle flow induced dynamic topography and plate motion variations in the Atlantic and Indo-Australian realms since the Upper Jurassic, finding they frequently correlate, except when plate boundary forces may play a significant role. This correlation agrees with descriptions of asthenosphere flow beneath tectonic plates in terms of Poiseuille/Couette flow, as it explicitly relates plate motion changes, induced by evolving basal shear forces, to non-isostatic vertical motion of the lithosphere. Our analysis reveals a timescale, on the order of a geological series, between the occurrence of continent-scale hiatus and plate motion changes. This is consistent with the presence of a weak upper mantle. It also shows a spatial scale for interregional hiatus, on the order of 2000-3000 km in diameter, which can be linked by fluid dynamic analysis to active upper mantle flow regions. Our results suggest future studies should pursue large-scale horizontal and vertical lithosphere motion in combination, to track the expressions of past mantle flow. Such studies would provide powerful constraints for adjoint-based geodynamic inverse models of past mantle convection.

Indian plate paleogeography, subduction and horizontal underthrusting below Tibet: paradoxes, controversies and opportunities

The India–Asia collision zone is the archetype to calibrate geological responses to continent–continent collision, but hosts a paradox: there is no orogen-wide geological record of oceanic subduction after initial collision around 60–55 Ma, yet thousands of kilometers of post-collisional subduction occurred before the arrival of unsubductable continental lithosphere that currently horizontally underlies Tibet. Kinematically restoring incipient horizontal underthrusting accurately predicts geologically estimated diachronous slab break-off, unlocking the Miocene of Himalaya–Tibet as a natural laboratory for unsubductable lithosphere convergence. Additionally, three endmember paleogeographic scenarios exist with different predictions for the nature of post-collisional subducted lithosphere but each is defended and challenged based on similar data types. This paper attempts at breaking through this impasse by identifying how the three paleogeographic scenarios each challenge paradigms in geodynamics, orogenesis, magmatism or paleogeographic reconstruction and identify opportunities for methodological advances in paleomagnetism, sediment provenance analysis, and seismology to conclusively constrain Greater Indian paleogeography.

India Indenting Eurasia: A Brief Review and New Data from the Yongping Basin on the SE Tibetan Plateau

Successive indentations of Eurasia by India have led to the Tibet-Himalaya E–W orthogonal collision belt and the SE Tibetan Plateau N–S oblique collision belt along the frontal and eastern edges of the indenter, respectively. The belts exhibit distinctive lithospheric structures and tectonic evolutions. A comprehensive compilation of available geological and geophysical data reveals two sudden tectonic transitions in the early Eocene and the earliest Miocene, respectively, of the tectonic evolution of the orthogonal belt. Synthesizing geological and geochronological data helps us to suggest a NEE–SWW trending, ~450 km-long, ~250 km-wide magmatic zone in SE Tibet, which separates the oblique collision belt (eastern and SE Tibet) into three segments of distinctive seismic structures including the mantle and crust anisotropies. The newly identified Yongping basin is located in the central part of the magmatic zone. Geochronological and thermochronological data demonstrate that (1) this basin and the magmatic zone started to form at ~48 Ma likely due to NNW–SSE lithosphere stretching according to the spatial coincidence of the concentrated mantle-sourced igneous rocks on the surface with the seismic anomalies at depth; and (2) its fills was shortened in the E–W direction since ~23 Ma. These two dates correspond to the onset of the first and second tectonic transitions of the orthogonal collision belt. As such, both the orthogonal and oblique belts share a single time framework of their tectonic evolution. By synthesizing geological and geophysical data of both collision belts, the indenting process can be divided into three stages separated by two tectonic transitions. Continent–continent collision as a piston took place exclusively during the second stage. During the other two stages, the India lithosphere underthrust beneath Eurasia.

Detrital Zircon Provenance of the Cenozoic Sequence, Kotli, Northwestern Himalaya, Pakistan; Implications for India–Asia Collision

This study reported the detrital zircon U-Pb geochronology of the Cenozoic sequence exposed in Kotli, northwestern Himalaya, Pakistan, which forms part of the Kashmir foreland basin. The U-Pb detrital age patterns of the Paleocene Patala Formation show a major age cluster between ~130–290 Ma, ~500–1000 Ma and ~1000–1500 Ma, which mainly resembles the lesser and higher Himalayan sequence. However, the younger age pattern (~130–290 Ma) can be matched to the ages of the ophiolites exposed along the Indus–Tsangpo suture zone. In addition, two younger grains with 57 Ma and 55 Ma ages may indicate a contribution from the Kohistan-Ladakh arc. The detrital zircons in the upper Tertiary sequence show the increased input of younger detrital ages <100 Ma, with more pronounced peaks at ~36–58 Ma, ~72–94 Ma and ~102–166 Ma, indicating the strong resemblance to the Asian sources including the Kohistan–Ladakh arc, Karakoram block and Gangdese batholith. This provenance shift, recorded in the upper portion of Patala Formation and becoming more visible in the upper Tertiary clastic sequence (Kuldana and Murree formations), is related to the collision of the Indian and Asian plates in the northwestern Himalayas. Considering the age of the Patala Formation, we suggest that the Indian and Asian plates collided during 57–55 Ma in the northwestern Himalayas, Pakistan.

Mesozoic origin and 'out-of-India' radiation of ricefishes (Adrianichthyidae)

The Indian subcontinent has an origin geologically different from Eurasia, but many terrestrial animal and plant species on it have congeneric or sister species in other parts of Asia, especially in the Southeast. This faunal and floral similarity between India and Southeast Asia is explained by either of the two biogeographic scenarios, 'into-India' or 'out-of-India'. Phylogenies based on complete mitochondrial genomes and five nuclear genes were undertaken for ricefishes (Adrianichthyidae) to examine which of these two biogeographic scenarios fits better. We found that Oryzias setnai, the only adrianichthyid distributed in and endemic to the Western Ghats, a mountain range running parallel to the western coast of the Indian subcontinent, is sister to all other adrianichthyids from eastern India and Southeast-East Asia. Divergence time estimates and ancestral area reconstructions reveal that this western Indian species diverged in the late Mesozoic during the northward drift of the Indian subcontinent. These findings indicate that adrianichthyids dispersed eastward 'out-of-India' after the collision of the Indian subcontinent with Eurasia, and subsequently diversified in Southeast-East Asia. A review of geographic distributions of 'out-of-India' taxa reveals that they may have largely fuelled or modified the biodiversity of Eurasia.

Relict subduction initiation along a passive margin in the northwest Indian Ocean

The tectonic evolution of Laxmi basin, presently located along western Indian passive margin, remains debated. Prevailing geodynamic models of Laxmi basin include two mutually competing hypotheses, culminating in either a hyper-stretched continental crust or an oceanic crust overlying an extinct spreading centre. The longstanding conundrum surrounding its precise crustal affinity precludes a complete understanding of the early opening of the Indian Ocean. Here, we present distinct geochemical and geophysical imprints from the igneous crust in Laxmi basin obtained through International Ocean Discovery Program Expedition 355. The geochemical and isotopic signatures of the Laxmi basin crust exhibit uncanny similarities with forearc tectonic settings. Our observations imply a relict subduction initiation event occurred in the Laxmi basin in the Late Cretaceous-Early Cenozoic that marks a significant Cenozoic plate reorganisation record in the northwest Indian Ocean. New findings therefore warrant re-evaluation of the Gondwana breakup to account for the nascent subduction in the northwest Indian Ocean.

Mantle Sources of Recent Anatolian Intraplate Magmatism: A Regional Plume or Local Tectonic Origin?

We present an extensive study of rehomogenized olivine-hosted melt inclusions, olivine phenocrysts, and chromian spinel inclusions to explore the link between geodynamic conditions and the origin and composition of Pliocene-Quaternary intraplate magmatism in Anatolia at Kula, Ceyhan-Osmaniye, and Karacadağ. Exceptional compositional variability of these products reveals early and incomplete mixing of distinct parental melts in each volcanic center, reflecting asthenospheric and lithospheric mantle sources. The studied primitive magmas consist of (1) two variably enriched ocean island basalt (OIB)-type melts in Kula; (2) both OIB-type and plume mid-ocean ridge basalt (P-MORB)-like melts beneath Toprakkale and Üçtepeler (Ceyhan-Osmaniye); and (3) two variably enriched OIB-type melts beneath Karacadağ. Estimated conditions of primary melt generation are 23-9 kbar, 75-30 km, and 1415-1215 °C for Kula; 28-19 kbar, 90-65 km, and 1430-1350 °C for Toprakkale; 23-18 kbar, 75-60 km, and 1400-1355 °C for Üçtepeler; and 35-27 kbar, 115-90 km, and 1530-1455 °C for Karacadağ, the deepest levels of which correspond to the depth of the lithosphere-asthenosphere boundary in all regions. Although magma ascent was likely facilitated by local deformation structures, recent Anatolian intraplate magmatism seems to be triggered by large-scale mantle flow that also affects the wider Arabian and North African regions. We infer that these volcanics form part of a much wider Arabian-North African intraplate volcanic province, which was able to invade the Anatolian upper plate through slab gaps.

On the deep-mantle origin of the Deccan Traps

The Deccan Traps in west-central India constitute one of Earth's largest continental flood basalt provinces, whose eruption played a role in the Cretaceous-Paleogene extinction event. The unknown mantle structure under the Indian Ocean at the start of the Cenozoic presents a challenge for connecting the event to a deep mantle origin. We used a back-and-forth iterative method for time-reversed convection modeling, which incorporates tomography-based, present-day mantle heterogeneity to reconstruct mantle structure at the start of the Cenozoic. We show a very low-density, deep-seated upwelling that ascends beneath the Réunion hot spot at the time of the Deccan eruptions. We found a second active upwelling below the Comores hot spot that likely contributed to the region of partial melt feeding the massive eruption.

Magmatic record of India-Asia collision

New geochronological and geochemical data on magmatic activity from the India-Asia collision zone enables recognition of a distinct magmatic flare-up event that we ascribe to slab breakoff. This tie-point in the collisional record can be used to back-date to the time of initial impingement of the Indian continent with the Asian margin. Continental arc magmatism in southern Tibet during 80–40 Ma migrated from south to north and then back to south with significant mantle input at 70–43 Ma. A pronounced flare up in magmatic intensity (including ignimbrite and mafic rock) at ca. 52–51 Ma corresponds to a sudden decrease in the India-Asia convergence rate. Geological and geochemical data are consistent with mantle input controlled by slab rollback from ca. 70 Ma and slab breakoff at ca. 53 Ma. We propose that the slowdown of the Indian plate at ca. 51 Ma is largely the consequence of slab breakoff of the subducting Neo-Tethyan oceanic lithosphere, rather than the onset of the India-Asia collision as traditionally interpreted, implying that the initial India-Asia collision commenced earlier, likely at ca. 55 Ma.

Pangea breakup and northward drift of the Indian subcontinent reproduced by a numerical model of mantle convection

Since around 200 Ma, the most notable event in the process of the breakup of Pangea has been the high speed (up to 20 cm yr(-1)) of the northward drift of the Indian subcontinent. Our numerical simulations of 3-D spherical mantle convection approximately reproduced the process of continental drift from the breakup of Pangea at 200 Ma to the present-day continental distribution. These simulations revealed that a major factor in the northward drift of the Indian subcontinent was the large-scale cold mantle downwelling that developed spontaneously in the North Tethys Ocean, attributed to the overall shape of Pangea. The strong lateral mantle flow caused by the high-temperature anomaly beneath Pangea, due to the thermal insulation effect, enhanced the acceleration of the Indian subcontinent during the early stage of the Pangea breakup. The large-scale hot upwelling plumes from the lower mantle, initially located under Africa, might have contributed to the formation of the large-scale cold mantle downwelling in the North Tethys Ocean.

Interactions between continent-like ‘drift’, rifting and mantle flow on Venus: gravity interpretations and Earth analogues

Regional shear zones are interpreted from Bouguer gravity data over northern polar to low southern latitudes of Venus. Offset and deflection of horizontal gravity gradient edges (‘worms’) and lineaments interpreted from displacement of Bouguer anomalies portray crustal structures, the geometry of which resembles both regional transcurrent shear zones bounding or cross-cutting cratons and fracture zones in oceanic crust on Earth. High Bouguer anomalies and thinned crust comparable to the Mid-Continent Rift in North America suggest underplating of denser, mantle-derived mafic material beneath extended crust in Sedna and Guinevere planitia on Venus. These rifts are partitioned by transfer faults and flank a zone of mantle upwelling (Eistla Regio) between colinear hot, upwelling mantle plumes. Data support the northward drift and indentation of Lakshmi Planum in western Ishtar Terra and >1000 km of transcurrent displacement between Ovda and Thetis regiones. Large displacements of areas of continent-like crust on Venus are interpreted to result from mantle tractions and pressure acting against their deep lithospheric mantle ‘keels’ commensurate with extension in adjacent rifts. Displacements of Lakshmi Planum and Ovda and Thetis regiones on Venus, a planet without plate tectonics, cannot be attributed to plate boundary forces (i.e. ridge push and slab pull). Results therefore suggest that a similar, subduction-free geodynamic model may explain deformation features in Archaean greenstone terrains on Earth. Continent-like ‘drift’ on Venus also resembles models for the late Cenozoic–Recent Earth, where westward translation of the Americas and northward displacement of India are interpreted as being driven by mantle flow tractions on the keels of their Precambrian cratons.

Supplementary material:

Bouguer gravity and topographic images over a segment of the Mid-Atlantic ridge and Ross Island and surrounds in Antarctica, principal horizontal stress trajectories about mantle plumes on Earth, map and interactive 3D representations of cratonic keels beneath North America from seismic tomography, and a centrifuge simulation for comparison with Venus in support of our tectonic model are available at http://www.geolsoc.org.uk/SUP18736.

Greater India Basin hypothesis and a two-stage Cenozoic collision between India and Asia

Cenozoic convergence between the Indian and Asian plates produced the archetypical continental collision zone comprising the Himalaya mountain belt and the Tibetan Plateau. How and where India-Asia convergence was accommodated after collision at or before 52 Ma remains a long-standing controversy. Since 52 Ma, the two plates have converged up to 3,600 ± 35 km, yet the upper crustal shortening documented from the geological record of Asia and the Himalaya is up to approximately 2,350-km less. Here we show that the discrepancy between the convergence and the shortening can be explained by subduction of highly extended continental and oceanic Indian lithosphere within the Himalaya between approximately 50 and 25 Ma. Paleomagnetic data show that this extended continental and oceanic "Greater India" promontory resulted from 2,675 ± 700 km of North-South extension between 120 and 70 Ma, accommodated between the Tibetan Himalaya and cratonic India. We suggest that the approximately 50 Ma "India"-Asia collision was a collision of a Tibetan-Himalayan microcontinent with Asia, followed by subduction of the largely oceanic Greater India Basin along a subduction zone at the location of the Greater Himalaya. The "hard" India-Asia collision with thicker and contiguous Indian continental lithosphere occurred around 25-20 Ma. This hard collision is coincident with far-field deformation in central Asia and rapid exhumation of Greater Himalaya crystalline rocks, and may be linked to intensification of the Asian monsoon system. This two-stage collision between India and Asia is also reflected in the deep mantle remnants of subduction imaged with seismic tomography.

Indian and African plate motions driven by the push force of the Réunion plume head

Mantle plumes are thought to play an important part in the Earth's tectonics, yet it has been difficult to isolate the effect that plumes have on plate motions. Here we analyse the plate motions involved in two apparently disparate events--the unusually rapid motion of India between 67 and 52 million years ago and a contemporaneous, transitory slowing of Africa's motion--and show that the events are coupled, with the common element being the position of the Indian and African plates relative to the location of the Réunion plume head. The synchroneity of these events suggests that they were both driven by the force of the Réunion plume head. The recognition of this plume force has substantial tectonic implications: the speed-up and slowdown of India, the possible cessation of convergence between Africa and Eurasia in the Palaeocene epoch and the enigmatic bends of the fracture zones on the Southwest Indian Ridge can all be attributed to the Réunion plume.