Cretaceous slab break-off in the Pyrenees: Iberian plate kinematics in paleomagnetic and mantle reference frames

AbstractThe Pyrenees at the Iberia–Europe collision zone contain sediments showing Albian–Cenomanian high-temperature metamorphism, and coeval alkaline magmatic rocks. Stemming from different views on Jurassic–Cretaceous Iberian microplate kinematics, two schools of thought exist on the trigger of this thermal pulse: one invoking hyperextension of the Iberian and Eurasian margins, the other suggesting slab break-off. Competing scenarios for Mesozoic Iberian motion compatible with Pyrenean geology, comprise (1) transtensional eastward motion of Iberia versus Eurasia, or (2) strike-slip motion followed by orthogonal extension, both favoring hyperextension-related heating, and (3) scissor-style opening of the Bay of Biscay coupled with subduction in the Pyrenean realm, favoring the slab break-off hypothesis. We test these kinematic scenarios for Iberia against a newly compiled paleomagnetic dataset and conclude that the scissor-type scenario is the only one consistent with a well-defined ~35° counterclockwise rotation of Iberia during the Early Aptian. We proceed to show that when taking absolute plate motions into account, Aptian oceanic subduction in the Pyrenees followed by Late Aptian–Early Albian slab break-off should leave a slab remnant in the present-day mid-mantle below NW Africa. Mantle tomography shows the Reggane anomaly that matches the predicted position and dimension of such a slab remnant between 1900 and 1500km depth below southern Algeria. Mantle tomography is therefore consistent with the scissor-type opening of the Bay of Biscay coupled with subduction in the Pyrenean realm. Slab break-off may thus explain high-temperature metamorphism and alkaline magmatism during the Albian–Cenomanian in the Pyrenees, whereas hyperextension that exhumed Pyrenean mantle bodies occurred much earlier, in the Jurassic

Sedimentary geology of the Middle Carboniferous of the Donbas region (Dniepr-Donets basin, Ukraine)

Peer reviewedPublisher PD

Subduction and Slab Detachment Under Moving Trenches During Ongoing India-Asia Convergence

The dynamics of slab detachment and associated geological fingerprints have been inferred from various numerical and analog models. These invariably use a setup with slab-pull-driven convergence in which a slab detaches below a mantle-stationary trench after the arrest of plate convergence due to arrival of continental lithosphere. In contrast, geological reconstructions show that post-detachment plate convergence is common and that trenches and sutures are rarely mantle-stationary during detachment. Here, we identify the more realistic kinematic context of slab detachment using the example of the India-Asia convergent system. We first show that only the India and Himalayas slabs (from India's northern margin) and the Carlsberg slab (from the western margin) unequivocally detached from Indian lithosphere. Several other slabs below the Indian Ocean do not require a Neotethyan origin and may be of Mesotethys and Paleotethys origin. Additionally, the still-connected slabs are being dragged together with the Indian plate forward (Hindu Kush) or sideways (Burma, Chaman) through the mantle. We show that Indian slab detachment occurred at moving trenches during ongoing plate convergence, providing more realistic geodynamic conditions for use in future numerical and analog experiments. We identify that the actively detaching Hindu Kush slab is a type-example of this setting, whilst a 25–13 Ma phase of shallow detachment of the Himalayas slab, here reconstructed from plate kinematics and tomography, agrees well with independent, published geological estimates from the Himalayas orogen of slab detachment. The Sulaiman Ranges of Pakistan may hold the geological signatures of detachment of the laterally dragged Carlsberg slab

Long-term Phanerozoic global mean sea level: Insights from strontium isotope variations and estimates of continental glaciation

Global mean sea level is a key component within the fields of climate and oceanographic modelling in the Anthropocene. Hence, an improved understanding of eustatic sea level in deep time aids in our understanding of Earth's paleoclimate and may help predict future climatological and sea level changes. However, long-term eustatic sea level reconstructions are hampered because of ambiguity in stratigraphic interpretations of the rock record and limitations in plate tectonic modelling. Hence the amplitude and timescales of Phanerozoic eustasy remains poorly constrained. A novel, independent method from stratigraphic or plate modelling methods, based on estimating the effect of plate tectonics (i.e., mid-ocean ridge spreading) from the 87Sr/86Sr record led to a long-term eustatic sea level curve, but did not include glacio-eustatic drivers. Here, we incorporate changes in sea level resulting from variations in seawater volume from continental glaciations at time steps of 1 Myr. Based on a recent compilation of global average paleotemperature derived from δ18O data, paleo-Köppen zones and paleogeographic reconstructions, we estimate ice distribution on land and continental shelf margins. Ice thickness is calibrated with a recent paleoclimate model for the late Cenozoic icehouse, yielding an average ∼1.4 km thickness for land ice, ultimately providing global ice volume estimates. Eustatic sea level variations associated with long-term glaciations (>1 Myr) reach up to ∼90 m, similar to, and is at times dominant in amplitude over plate tectonic-derived eustasy. We superimpose the long-term sea level effects of land ice on the plate tectonically driven sea level record. This results in a Tectono-Glacio-Eustatic (TGE) curvefor which we describe the main long-term (>50 Myr) and residual trends in detail

Atlas of the Underworld : Paleo-subduction, -geography, -atmosphere and -sea level reconstructed from present-day mantle structure

In this thesis, I aimed at searching for new ways of constraining paleo-geographic, -atmosphere and -sea level reconstructions, through an extensive investigation of mantle structure in seismic tomographic models. To this end, I explored evidence for paleo-subduction in these models and how this may allow for a new avenue towards reconstructing the plate tectonic history of our planet. The major findings can be summarized as follows: Initially 28 slabs were characterized in terms of ranges of depth and timing of subduction. This effort led to 1) a determination of the sinking rates of slabs as a novel implicit observation of the rate of lower mantle flow; 2) to constrain how far back in time ‘mantle memory’ of past subduction extends, being a maximum of 250-300 Myr; and 3) to test whether slab remnants of paleo-subduction can be used as a constraint on absolute plate position yielding a new approach to constrain absolute plate reconstructions by ‘slab-fitting’ reconstructions. This methodology is applied to the mantle underneath the Pacific Ocean. Geological evidence from east Asia suggested that accreted exotic terranes with Lower Mesozoic volcanic arcs should have originated from central Panthalassa Ocean locations, yet how these fitted in plate kinematic reconstructions remained poorly constrained. Remnants of paleo-subduction were identified in the mantle, revealing the location of Mesozoic intra-Panthalassa subduction zones and shedding light on the plate tectonic configuration of the Panthalassa Ocean. Subsequently we interpret paleo-subduction zone configurations at a series of depth slices of the mantle and calculate total slab, and hence subduction zone length versus depth. This provided a first-order estimate of global subduction zone length for the last 235 Myr. This was used to compute volcanic degassing of CO2 from subduction and ridge spreading and served as input into a carbon-cycle climate model. The new degassing estimate resulted in an improved fit between modelled atmospheric CO2 and proxy data. In addition, it provided a good first-order fit of 87Sr/86Sr ratios from marine carbonates, a record of paleo-seawater composition. This correlation between the 87Sr/86Sr record and plate tectonic activity was improved by correcting for weathering of continents and used to calculate global ocean floor production rates to compute a eustatic sea level curve. We compare this curve with previous sea level and flooded shelf area curves derived from sequence stratigraphy and from plate motion models. Aside from providing a novel method of estimating sea level variation as a function of global plate tectonic activity, it extended sea level curves back to ~840 Myr. The identification and geological interpretation of slabs is further expanded to 94 slabs. This compilation is named ‘Atlas of the Underworld’, which provides a complete overview of the present interpretation of slab remnants by the scientific community and ourselves. The slabs' subduction age-depth data provided new average and in situ sinking rates. Slab deceleration in the top of the lower mantle is modelled as well as the required associated slab thickening or buckling. Instead of stagnated slabs, we observe that all slabs sink further towards the core-mantle-boundary

Atlas of the Underworld : Paleo-subduction, -geography, -atmosphere and -sea level reconstructed from present-day mantle structure

In this thesis, I aimed at searching for new ways of constraining paleo-geographic, -atmosphere and -sea level reconstructions, through an extensive investigation of mantle structure in seismic tomographic models. To this end, I explored evidence for paleo-subduction in these models and how this may allow for a new avenue towards reconstructing the plate tectonic history of our planet. The major findings can be summarized as follows: Initially 28 slabs were characterized in terms of ranges of depth and timing of subduction. This effort led to 1) a determination of the sinking rates of slabs as a novel implicit observation of the rate of lower mantle flow; 2) to constrain how far back in time ‘mantle memory’ of past subduction extends, being a maximum of 250-300 Myr; and 3) to test whether slab remnants of paleo-subduction can be used as a constraint on absolute plate position yielding a new approach to constrain absolute plate reconstructions by ‘slab-fitting’ reconstructions. This methodology is applied to the mantle underneath the Pacific Ocean. Geological evidence from east Asia suggested that accreted exotic terranes with Lower Mesozoic volcanic arcs should have originated from central Panthalassa Ocean locations, yet how these fitted in plate kinematic reconstructions remained poorly constrained. Remnants of paleo-subduction were identified in the mantle, revealing the location of Mesozoic intra-Panthalassa subduction zones and shedding light on the plate tectonic configuration of the Panthalassa Ocean. Subsequently we interpret paleo-subduction zone configurations at a series of depth slices of the mantle and calculate total slab, and hence subduction zone length versus depth. This provided a first-order estimate of global subduction zone length for the last 235 Myr. This was used to compute volcanic degassing of CO2 from subduction and ridge spreading and served as input into a carbon-cycle climate model. The new degassing estimate resulted in an improved fit between modelled atmospheric CO2 and proxy data. In addition, it provided a good first-order fit of 87Sr/86Sr ratios from marine carbonates, a record of paleo-seawater composition. This correlation between the 87Sr/86Sr record and plate tectonic activity was improved by correcting for weathering of continents and used to calculate global ocean floor production rates to compute a eustatic sea level curve. We compare this curve with previous sea level and flooded shelf area curves derived from sequence stratigraphy and from plate motion models. Aside from providing a novel method of estimating sea level variation as a function of global plate tectonic activity, it extended sea level curves back to ~840 Myr. The identification and geological interpretation of slabs is further expanded to 94 slabs. This compilation is named ‘Atlas of the Underworld’, which provides a complete overview of the present interpretation of slab remnants by the scientific community and ourselves. The slabs' subduction age-depth data provided new average and in situ sinking rates. Slab deceleration in the top of the lower mantle is modelled as well as the required associated slab thickening or buckling. Instead of stagnated slabs, we observe that all slabs sink further towards the core-mantle-boundary

Atlas of the underworld : Slab remnants in the mantle, their sinking history, and a new outlook on lower mantle viscosity

Across the entire mantle we interpret 94 positive seismic wave-speed anomalies as subducted lithosphere and associate these slabs with their geological record. We document this as the Atlas of the Underworld, also accessible online at www.atlas-of-the-underworld.org, a compilation comprising subduction systems active in the past ~ 300 Myr. Deeper slabs are correlated to older geological records, assuming no relative horizontal motions between adjacent slabs following break-off, using knowledge of global plate circuits, but without assuming a mantle reference frame. The longest actively subducting slabs identified reach the depth of ~ 2500 km and some slabs have impinged on Large Low Shear Velocity Provinces in the deepest mantle. Anomously fast sinking of some slabs occurs in regions affected by long-term plume rising. We conclude that slab remnants eventually sink from the upper mantle to the core-mantle boundary. The range in subduction-age versus – depth in the lower mantle is largely inherited from the upper mantle history of subduction. We find a significant depth variation in average sinking speed of slabs. At the top of the lower mantle average slab sinking speeds are between 10 and 40 mm/yr, followed by a deceleration to 10–15 mm/yr down to depths around 1600–1700 km. In this interval, in situ time-stationary sinking rates suggest deceleration from 20 to 30 mm/yr to 4–8 mm/yr, increasing to 12–15 mm/yr below 2000 km. This corroborates the existence of a slab deceleration zone but we do not observe long-term (> 60 My) slab stagnation, excluding long-term stagnation due to compositional effects. Conversion of slab sinking profiles to viscosity profiles shows the general trend that mantle viscosity increases in the slab deceleration zone below which viscosity slowly decreases in the deep mantle. This is at variance with most published viscosity profiles that are derived from different observations, but agrees qualitatively with recent viscosity profiles suggested from material experiments

Atlas of the underworld : Slab remnants in the mantle, their sinking history, and a new outlook on lower mantle viscosity

Across the entire mantle we interpret 94 positive seismic wave-speed anomalies as subducted lithosphere and associate these slabs with their geological record. We document this as the Atlas of the Underworld, also accessible online at www.atlas-of-the-underworld.org, a compilation comprising subduction systems active in the past ~ 300 Myr. Deeper slabs are correlated to older geological records, assuming no relative horizontal motions between adjacent slabs following break-off, using knowledge of global plate circuits, but without assuming a mantle reference frame. The longest actively subducting slabs identified reach the depth of ~ 2500 km and some slabs have impinged on Large Low Shear Velocity Provinces in the deepest mantle. Anomously fast sinking of some slabs occurs in regions affected by long-term plume rising. We conclude that slab remnants eventually sink from the upper mantle to the core-mantle boundary. The range in subduction-age versus – depth in the lower mantle is largely inherited from the upper mantle history of subduction. We find a significant depth variation in average sinking speed of slabs. At the top of the lower mantle average slab sinking speeds are between 10 and 40 mm/yr, followed by a deceleration to 10–15 mm/yr down to depths around 1600–1700 km. In this interval, in situ time-stationary sinking rates suggest deceleration from 20 to 30 mm/yr to 4–8 mm/yr, increasing to 12–15 mm/yr below 2000 km. This corroborates the existence of a slab deceleration zone but we do not observe long-term (> 60 My) slab stagnation, excluding long-term stagnation due to compositional effects. Conversion of slab sinking profiles to viscosity profiles shows the general trend that mantle viscosity increases in the slab deceleration zone below which viscosity slowly decreases in the deep mantle. This is at variance with most published viscosity profiles that are derived from different observations, but agrees qualitatively with recent viscosity profiles suggested from material experiments