Douwe J. J. van Hinsbergen

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.

Nappe stacking resulting from subduction of oceanic and continental lithosphere below Greece

We quantitatively investigate the relation between nappe stacking and subduction in the Aegean region. If nappe stacking is the result of the decoupling of upper-crustal parts (5-10 km thick) from subducting lithosphere, then the amount of convergence estimated from balancing the nappe stack provides a lower limit to the amount of convergence accommodated by subduction. The balanced nappe stack combined with the estimated amount of completely subducted lithosphere indicates 700 km of Jurassic and 2400 km of post-Jurassic convergence. From seismic tomographic images of the underlying mantle, we estimate 2100-2500 km of post-Jurassic convergence. We conclude that (1) the imaged slab represents the subducted lithosphere that originally underlay the nappes, (2) since the Early Cretaceous, subduction in the Aegean has occurred in one single subduction zone, and (3) the composition of the original basement of the nappes indicates that at least 900 km of sub-upper-crust continental lithosphere subducted in the Aegean.

Restoration of Cenozoic deformation in Asia and the size of Greater India

A long‐standing problem in the geological evolution of the India‐Asia collision zone is how and where convergence between India and Asia was accommodated since collision. Proposed collision ages vary from 65 to 35 Ma, although most data sets are consistent with collision being underway by 50 Ma. Plate reconstructions show that since 50 Ma ∼2400-3200 km (west to east) of India‐Asia convergence occurred, much more than the 450-900 km of documented Himalayan shortening. Current models therefore suggest that most post‐50 Ma convergence was accommodated north of the Indus‐Yarlung suture zone. We review kinematic data and construct an updated restoration of Cenozoic Asian deformation to test this assumption. We show that geologic studies have documented 600-750 km of N‐S Cenozoic shortening across, and north of, the Tibetan Plateau. The Pamir‐Hindu Kush region accommodated ∼1050 km of N‐S convergence. Geological evidence from Tibet is inconsistent with models that propose 750-1250 km of eastward extrusion of Indochina. Approximately 250 km of Indochinese extrusion from 30 to 20 Ma of Indochina suggested by SE Asia reconstructions can be reconciled by dextral transpression in eastern Tibet. We use our reconstruction to calculate the required size of Greater India as a function of collision age. Even with a 35 Ma collision age, the size of Greater India is 2-3 times larger than Himalayan shortening. For a 50 Ma collision, the size of Greater India from west to east is ∼1350-2600 km, consistent with robust paleomagnetic data from upper Cretaceous‐Paleocene Tethyan Himalayan strata. These estimates for the size of Greater India far exceed documented shortening in the Himalaya. We conclude that most of Greater India was consumed by subduction or underthrusting, without leaving a geological record that has been recognized at the surface.

Retrodeforming the Arabia-Eurasia collision zone: Age of collision versus magnitude of continental subduction

The Arabia-Eurasia collision has been linked to global cooling, the slowing of Africa, Mediterranean extension, the rifting of the Red Sea, an increase in exhumation and sedimentation on the Eurasian plate, and the slowing and deformation of the Arabian plate. Collision age estimates range from the Late Cretaceous to Pliocene, with most estimates between 35 and 20 Ma. We assess the consequences of these collision ages on the magnitude and location of continental consumption by compiling all documented shortening within the region, and integrating this with plate kinematic reconstructions. Shortening estimates across the orogen allow for ~350 km of Neogene upper crustal contraction, necessitating collision by 20 Ma. A 35 Ma collision requires additional subduction of ~400‐600 km of Arabian continental crust. Using the Oman ophiolite as an analogue, ophiolitic fragments preserved along the Zagros suture zone permit ~180 km of subduction of the Arabian continental margin plus overlying ophiolites. Wholesale subduction of this more dense continental margin plus ophiolites would reconstruct ~400‐500 km of postcollisional Arabia-Eurasia convergence, consistent with a ca. 27 Ma initial collision age. This younger Arabia-Eurasia collision suggests a noncollisional mechanism for the slowing of Africa, and associated extension.

Origin and consequences of western Mediterranean subduction, rollback, and slab segmentation

The western Mediterranean recorded subduction rollback, slab segmentation and separation. Here we address the questions of what caused Oligocene rollback initiation, and how its subsequent evolution split up an originally coherent fore arc into circum-southwest Mediterranean segments. We kinematically reconstruct western Mediterranean geology from subduction initiation to present, using Atlantic plate reconstructions as boundary condition. We test possible reconstructions against remnants of subducted lithosphere imaged by seismic tomography. Transform motion between Africa and Iberia (including the Baleares) between ~120 and 85 Ma was followed by up to 150 km convergence until 30 Ma. Subduction likely initiated along the transform fault that accommodated pre-85 Ma translation. By the ~30 Ma inception of rollback, up to 150 km of convergence had formed a small slab below the Baleares. Iberia was disconnected from Sardinia/Calabria through the North Balearic Transform Zone (NBTZ). Subduction below Sardinia/Calabria was slightly faster than below the Baleares, the difference being accommodated in the Pyrenees. A moving triple junction at the trench-NBTZ intersection formed a subduction transform edge propagator fault between the Baleares and Calabria slab segments. Calabria rolled back eastward, whereas the Baleares slab underwent radial (SW-S-SE) rollback. After Kabylides-Africa collision, the western slab segment retreated toward Gibraltar, here reconstructed as the maximum rollback end-member model, and a Kabylides slab detached from Africa. Opening of a slab window below the NBTZ allowed asthenospheric rise to the base of the fore arc creating high-temperature metamorphism. Western Mediterranean rollback commenced only after sufficient slab-pull was created from 100 to 150 km of slow, forced subduction before ~30 Ma.

A Paleolatitude Calculator for Paleoclimate Studies

Realistic appraisal of paleoclimatic information obtained from a particular location requires accurate knowledge of its paleolatitude defined relative to the Earth’s spin-axis. This is crucial to, among others, correctly assess the amount of solar energy received at a location at the moment of sediment deposition. The paleolatitude of an arbitrary location can in principle be reconstructed from tectonic plate reconstructions that (1) restore the relative motions between plates based on (marine) magnetic anomalies, and (2) reconstruct all plates relative to the spin axis using a paleomagnetic reference frame based on a global apparent polar wander path. Whereas many studies do employ high-quality relative plate reconstructions, the necessity of using a paleomagnetic reference frame for climate studies rather than a mantle reference frame appears under-appreciated. In this paper, we briefly summarize the theory of plate tectonic reconstructions and their reference frames tailored towards applications of paleoclimate reconstruction, and show that using a mantle reference frame, which defines plate positions relative to the mantle, instead of a paleomagnetic reference frame may introduce errors in paleolatitude of more than 15° (>1500 km). This is because mantle reference frames cannot constrain, or are specifically corrected for the effects of true polar wander. We used the latest, state-of-the-art plate reconstructions to build a global plate circuit, and developed an online, user-friendly paleolatitude calculator for the last 200 million years by placing this plate circuit in three widely used global apparent polar wander paths. As a novelty, this calculator adds error bars to paleolatitude estimates that can be incorporated in climate modeling. The calculator is available at www.paleolatitude.org. We illustrate the use of the paleolatitude calculator by showing how an apparent wide spread in Eocene sea surface temperatures of southern high latitudes may be in part explained by a much wider paleolatitudinal distribution of sites than previously assumed.

Oligocene-Miocene basin evolution in SE Anatolia, Turkey: constraints on the closure of the eastern Tethys gateway

Abstract The Oligocene–Miocene was a time characterized by major climate changes as well as changing plate configurations. The Middle Miocene Climate Transition (17 to 11 Ma) may even have been triggered by a plate tectonic event: the closure of the eastern Tethys gateway, the marine connection between the Mediterranean and Indian Ocean. To address this idea, we focus on the evolution of Oligocene and Miocene foreland basins in the southernmost part of Turkey, the most likely candidates to have formed this gateway. In addition, we take the geodynamic evolution of the Arabian–Eurasian collision into account. The Muş and Elazığ basins, located to the north of the Bitlis–Zagros suture zone, were most likely connected during the Oligocene. The deepening of both basins is biostratigraphically dated by us to occur during the Rupelian (Early Oligocene). Deep marine conditions (between 350 and 750 m) prevailed until the Chattian (Late Oligocene), when the basins shoaled rapidly to subtidal/intertidal environment in tropical to subtropical conditions, as indicated by the macrofossil assemblages. We conclude that the emergence of this basin during the Chattian severely restricted the marine connection between an eastern (Indian Ocean) and western (Mediterranean) marine domain. If a connection persisted it was likely located south of the Bitlis–Zagros suture zone. The Kahramanmaraş basin, located on the northern Arabian promontory south of the Bitlis–Zagros suture zone, was a foreland basin during the Middle and Late Miocene, possibly linked to the Hatay basin to the west and the Lice basin to the east. Our data indicates that this foreland basin experienced shallow marine conditions during the Langhian, followed by a rapid deepening during Langhian/Serravallian and prevailing deep marine conditions (between 350 and 750 m) until the early Tortonian. We have dated the youngest sediments underneath a subduction-related thrust at c. 11 Ma and suggest that this corresponds to the end of underthrusting in the Kahramanmaraş region, i.e. the end of subduction of Arabia. This age coincides in time with the onset of eastern Anatolian volcanism, uplift of the East Anatolian Accretionary Complex, and the onset of the North and East Anatolian Fault Zones accommodating westward escape tectonics of Anatolia. After c. 11 Ma, the foreland basin south of the Bitlis formed not (or no longer) a deep marine connection along the northern margin of Arabia between the Mediterranean Sea and the Indian Ocean. We finally conclude that a causal link between gateway closure and global climate change to a cooler mode, recorded in the Mi3b event (δ18O increase) dated at 13.82 Ma, cannot be supported.

Paleomagnetism.org

This contribution provides an overview of Paleomagnetism.org, an open-source, multi-platform online environment for paleomagnetic data analysis. Paleomagnetism.org provides an interactive environment where paleomagnetic data can be interpreted, evaluated, visualized, and exported. The Paleomagnetism.org application is split in to an interpretation portal, a statistics portal, and a portal for miscellaneous paleomagnetic tools.In the interpretation portal, principle component analysis can be performed on visualized demagnetization diagrams. Interpreted directions and great circles can be combined to find great circle solutions. These directions can be used in the statistics portal, or exported as data and figures.The tools in the statistics portal cover standard Fisher statistics for directions and VGPs, including other statistical parameters used as reliability criteria. Other available tools include an eigenvector approach foldtest, two reversal test including a Monte Carlo simulation on mean directions, and a coordinate bootstrap on the original data. An implementation is included for the detection and correction of inclination shallowing in sediments following TK03.GAD. Finally we provide a module to visualize VGPs and expected paleolatitudes, declinations, and inclinations relative to widely used global apparent polar wander path models in coordinates of major continent-bearing plates.The tools in the miscellaneous portal include a net tectonic rotation (NTR) analysis to restore a body to its paleo-vertical and a bootstrapped oroclinal test using linear regressive techniques, including a modified foldtest around a vertical axis.Paleomagnetism.org provides an integrated approach for researchers to work with visualized (e.g. hemisphere projections, Zijderveld diagrams) paleomagnetic data. The application constructs a custom exportable file that can be shared freely and included in public databases. This exported file contains all data and can later be imported to the application by other researchers. The accessibility and simplicity through which paleomagnetic data can be interpreted, analyzed, visualized, and shared makes Paleomagnetism.org of interest to the community. Online multi-platform environment analysis of Paleomagnetic data.High quality figures of visualized paleomagnetic can be downloaded.Shareable files containing all original data and interpretations can be saved.Accessible environment in which paleomagnetic data can be evaluated and visualized.

Forearc hyperextension dismembered the south Tibetan ophiolites

Suprasubduction zone ophiolites are relics of oceanic upper plate forearcs and are typically preserved as discontinuous belts with discrete massifs along suture zones. Ophiolites usually contain an incomplete condensed section compared to average modern oceanic lithosphere. The incompleteness and discontinuity of ophiolites are frequently attributed to dismemberment, but tectonic causes remain poorly constrained. Here we show new paleomagnetic and field geological evidence for the preservation of extensional detachment faults that thinned and dismembered the south Tibetan ophiolite belt during the Early Cretaceous. Similar to those documented in modern slow- and ultraslow-spreading ridges, these detachments exhumed lithospheric mantle, and subophiolitic melange, to the seafloor, which became unconformably covered by Asia-derived forearc strata. We call this mechanism forearc hyperextension, whereby widespread detachment faults accommodate upper plate extension above a subduction zone. We propose that hyperextension is the key mechanism responsible for dismemberment of the south Tibetan ophiolitic belt shortly after its magmatic accretion.

Plate tectonic controls on atmospheric CO2 levels since the Triassic

Significance Although plate tectonics is generally considered to be the main contributor of CO2 production, despite decades of paleoproxy and solid-earth research, this very first-order assumption remains unproven. Based on estimates of total subduction-zone lengths, from a combined analysis of seismic tomography models and plate tectonic reconstructions, we have bridged a major gap between solid-earth sciences and the atmosphere and biosphere sciences by providing understanding of one of the most fundamental controls of climate: variation of plate tectonic activity of our planet. By using the subduction zone length input into the GEOCARBSULF climate model, we obtain a better fit with atmospheric CO2 proxies compared with previously used plate tectonic assumptions. Climate trends on timescales of 10s to 100s of millions of years are controlled by changes in solar luminosity, continent distribution, and atmosphere composition. Plate tectonics affect geography, but also atmosphere composition through volcanic degassing of CO2 at subduction zones and midocean ridges. So far, such degassing estimates were based on reconstructions of ocean floor production for the last 150 My and indirectly, through sea level inversion before 150 My. Here we quantitatively estimate CO2 degassing by reconstructing lithosphere subduction evolution, using recent advances in combining global plate reconstructions and present-day structure of the mantle. First, we estimate that since the Triassic (250–200 My) until the present, the total paleosubduction-zone length reached up to ∼200% of the present-day value. Comparing our subduction-zone lengths with previously reconstructed ocean-crust production rates over the past 140 My suggests average global subduction rates have been constant, ∼6 cm/y: Higher ocean-crust production is associated with longer total subduction length. We compute a strontium isotope record based on subduction-zone length, which agrees well with geological records supporting the validity of our approach: The total subduction-zone length is proportional to the summed arc and ridge volcanic CO2 production and thereby to global volcanic degassing at plate boundaries. We therefore use our degassing curve as input for the GEOCARBSULF model to estimate atmospheric CO2 levels since the Triassic. Our calculated CO2 levels for the mid Mesozoic differ from previous modeling results and are more consistent with available proxy data.