East European sedimentary basins long heated by a fading mantle upwelling

Domain: earth_science
Published: 2024-05-09
Editorial outcome: major_revision

Abstract
A strong negative anomaly of seismic wave velocities at the core-mantle boundary (the Perm Anomaly) beneath the East European platform is attributed to the remnant of a deep mantle upwelling. The interaction between the upwelling and the East European lithosphere in the geological past and its resulting surface manifestations are still poorly understood. Using mantle plume modelling and global plate motion reconstructions, we show here that the East European lithosphere is likely to have been situated over the weakening Perm Anomaly upwelling for about 150–200 million years. As the East European platform moved above the Perm Anomaly in post-Jurassic times, the vertical tectonic movements recorded in sedimentary hydrocarbon-rich basins show either hiatus/uplift or insignificant subsidence. Analytical modelling of heat conduction through the lithosphere demonstrates that the basins have been slowly heated for a long time by the Perm Anomaly upwelling, creating suitable conditions for hydrocarbon maturation. This suggests a profound relationship between mantle plume dynamics, basin evolution, and hydrocarbon generation.

Introduction
Seismic tomography reveals the presence of a province of low seismic shear-wave velocity at the core-mantle boundary beneath the southeastern part of the East European (EE) platform, called the Perm Anomaly (PA)1,2 (Fig. 1). The PA extends radially to an estimated 400–600 km above the core-mantle boundary3. It is separated from the two large provinces of negative seismic wave velocity anomalies below the Pacific and the Indo-Atlantic regions4–6 by the Neo-Tethys subduction to the south, the Pacific subduction to the east and north, and the Mongol-Okhotsk subduction to the north (Fig. 1). Geologic, paleomagnetic, and seismic studies show that the Neo-Tethys and Pacific subductions are long-lived features that have been active at least for the last 300 million years (My)7,8, delivering an early continuous downwelling flow of cold material on the core-mantle boundary around PA. The longevity of these downwellings and mass conservation in the mantle imply the longevity of hot upwellings there as well.

While the PA’s origin is still debated, PA was first linked to a thermally prominent mantle plume1, which was active in the Permian-Triassic times and responsible for the Siberian trap formation9,10 (see section SD1 of the Supplementary Information (SI)). Under the oceanic lithosphere, the subsequent whereabouts of such a plume would be recorded by a chain of volcanoes. Instead, the EE platform displays sedimentary basins rich in hydrocarbons, but no obvious volcanic trail. Despite significant progress made in understanding the thermal evolution of the continental lithosphere11 as well as sedimentary basins and hydrocarbon generation12,13, the links between deep mantle heat sources and hydrocarbon maturation are still poorly understood.

So, in this paper, we address the following key question: could a mantle upwelling (or mantle plume), even though it was weakening thermally with time, have influenced the evolution of sedimentary basins and hydrocarbon maturation within the EE platform? To answer this question, we (i) show that PA can be considered as the remnant part of a fading mantle plume, (ii) study the PA upwelling track on the EE platform since the Early Jurassic times, (iii) examine the subsidence history of the sedimentary basins along the PA upwelling track, and finally, (iv) analyse the thermal regimes associated with heat conduction through the lithosphere and relate them to hydrocarbon generation and maturation in the EE basins that have been heated over the thermally fading mantle plume since the Jurassic times.

Results
The Earth’s surface and its evolution are shaped by the thermal convective motions inside its mantle. Lithospheric plates descending into the mantle constitute the upper cold part of this convective system, and mantle plumes are their hot counterparts. The plumes are likely to be responsible for hotspot volcanism14, formation of large igneous provinces (LIP)5,9,15, continental stretching and break-up15, mass extinction16, and eruption of diamond bearing kimberlites17. Depending on their temperature, composition, and rheology, a wide range of morphology and temporal behaviour are expected for mantle upwellings6,18,19.

Mantle plumes are generated from the hot thermal boundary layer (TBL), which is produced by conductive heating of the material at the core-mantle boundary. When the TBL is thick enough, it becomes gravitationally unstable, generating upwellings (i.e., plumes) that drain locally the TBL19,20. The latter is replaced by cold material (such as remnants of cold subducted slabs) that will take time to reheat. A plume is therefore a transient feature. While the discrimination of low-velocity anomalies (seen in seismic tomography models) in active and less active plumes is a challenging problem, laboratory and numerical experiments provide evidence of thermal plumes fading with time20,21. They show that: (i) the mean velocity of the fluid within a plume decreases and hence thermal diffusion becomes a major agent in the heat transfer as the plume grows older; (ii) the plume tail (or conduit) begins to disappear from its bottom-half up (Fig. 2a), leaving at the end only the cooling and shrinking sub-lithospheric overhang and the plume foot; and (iii) the plume life-span can reach 200–300 My for typical lower mantle viscosity.

Figure 2 presents several stages of the PA mantle plume thermal fading from the Early Jurassic times (b) to the present (f) obtained by numerical modelling of the mantle plume diffusive decay (see Methods for the model’s detail). We assume that the PA plume was still thermally prominent in the Early Jurassic (Fig. 2b), although the plume tail was diminishing in size due to thermal diffusion (Fig. 2c) to get cut from the lower mantle TBL in the Late Cretaceous times (Fig. 2d) and to become invisible at least since the Late Paleogene (Fig. 2e, f). The remnant foot of the modelled mantle plume may explain the PA presence at the core-mantle boundary1 (Fig. 2g).

The paleogeographic and palinspastic reconstruction of the motion of the northern Eurasia based on palaeomagnetism22 shows that the EE platform moved north-eastward at the average rate of about 6 cm yr−1 in the Middle to Late Triassic times. The buoyant plume material would have been advected by the lithosphere motion, while spreading in the lateral direction under its own buoyancy23. The relatively rapid lithosphere movement may therefore have enhanced the thinning of the plume head in the direction of movement and its subsequent cooling. Meanwhile, plume heads are likely to be thermally fading within a short time (a few My) if significant melting occurs during mantle upwelling. The melting could produce massive volcanic eruptions and the development of LIP24. As the present numerical model does not consider melting processes, the modelled mantle plume head is preserved for a longer time. Nevertheless, our model shows that thermal diffusion plays a role in the fate of advecting mantle plumes21 and may provide a powerful explanation of PA at the core-mantle boundary.

The continental lithosphere is in a state of permanent relative movements due to the basal traction generated by mantle flow, oceanic slab pull, and mid-ocean ridge push as main driving forces of plate tectonics25. To determine the position of Eurasia during the past 200 My, we analyse its movement using three models of global plate motion (GPM)26–28 (hereinafter the models are referred to as Se2012, Mü2016, and Ma2016, respectively; see Methods as well as SD3 of SI). The projection of the PA fading plume on the Earth’s surface has been traced for the past 200 My (Fig. 3), starting from the present position of the plume’s centre (51°N, 52°E). In a framework where the PA plume remains fixed on the core-mantle boundary, the EE platform has been ‘dancing’ above the PA plume at least since the Early Cretaceous times (~150 My ago, Ma). A close inspection of the three modelled tracks of the projection of the PA plume’s centre (Fig. 3) shows that the tracks are close to each other from the present to the Late Cretaceous times (~100 Ma). Starting from the Early Cretaceous, the tracks diverge to the northeast, to the northwest, and to the southeast according to Se2012, Ma2016, and Mü2016 models, respectively. However, despite the tracks’ divergence, all three track models support our major finding that the EE platform has been situated above the PA fading plume for about 150–200 My.

The track models also suggest that the sedimentary basins of the EE platform have been situated above PA for a long geological time. As the Pricaspian basin moved over PA (according to the SE2012 and Mü2016 models), the basin’s area underwent significant uplift recorded in sediments as a hiatus lasting from ~208 Ma to 170 Ma29 (Fig. 4). We attribute this uplift to the PA mantle plume impinging under the EE lithosphere in the Late Triassic–Early Jurassic, at times when the upwelling would be still connected to the deep mantle and powerful enough (Fig. 2b) to generate a prolonged uplift during the Early Jurassic and then a slow subsidence of the Pricaspian basin since the Middle Jurassic times (Fig. 4).

The tectonic subsidence analysis (see Methods and SD4 of SI) based on borehole data, such as sediment lithology, thickness, porosity, and age, which have been collected in the EE basins (see Fig. 3 for the borehole locations), shows no or insignificant subsidence during the past 150 My (Fig. 4). Particularly, the Moscow basin became an area of erosion at least since the Early Cretaceous30 (~150–140 Ma) and the Timan-Pechora basin since the Late Cretaceous/Paleogene times31. The Pre-Uralian foredeep is expressed as a series of major depressions extending from the Timan-Pechora basin via the Volga-Ural basin towards the Pricaspian basin and shows no (or little) subsidence taking place for more than a hundred million years.

Magmatic events can indicate how strong thermal perturbations have been in the mantle. The passage over the PA plume is likely to have generated tholeiitic and calc-alkali basalt eruptions in the southwestern part of West Siberia in the Late Triassic times32,33. However, no track of significant volcanism has been recorded on the surface of the EE lithosphere since the Early Jurassic times34. The absence of regional volcanism is likely to be associated with the decay of the PA plume and its inability to generate significant melting, while the thick (more than 150 km; refs. 35–37; see SD2 and Supplementary Figs. S2–S4 of SI) EE lithosphere has prevented melts to reach the surface. A study on the Australian continent has shown38 that melting is likely to occur along hotspot tracks, where the lithosphere is less than 150 km thick.

Thermal evolution of the continental lithosphere and sedimentary basins has been explained by a model of instantaneous heating39. According to this model, rapid initial stretching of the lithosphere due to a mantle plume impact and the related crustal thinning are accompanied by an isostatic subsidence of its surface. The instantaneous heating of the lithosphere results in melt generation, its segregation and penetration into the uppermost lithosphere causing magmatism. The impact of a mantle upwelling normally lasts several million years, depending on the continental plate movement above the plume. The subsequent thermal cooling of the lithosphere as it moves away from the mantle plume and erosion of uplifted sediments result in a slow subsidence and sedimentary basin evolution. However, the PA plume impact on the EE lithosphere was different.

We consider that when the EE platform moved over the PA plume, the plume became thermally weaker and unable to significantly stretch the thick EE lithosphere. However, the plume could support the lithosphere beneath the Pricaspian basin to generate the 38-My hiatus in regional sedimentation. Although not hot enough anymore to produce major volcanism, this plume could keep warm the EE lithosphere for a long geological time and prevent tectonic subsidence (Fig. 4).

Conductive heating of the lithosphere by an underlying mantle upwelling is a geologically slow process, but its thermal effects are not negligible when the plume heats the lithosphere for more than a hundred million years. Here we analyse the contribution of the mantle plume’s conductive heating on the thermal evolution of the lithosphere and sedimentary basins, which were initially in a steady thermal state. We employ the plate heating model of the lithosphere11 assuming that the interaction between the plume and the base of the lithosphere started 200 Ma (see Methods for the model detail).

As the present thickness of the EE lithosphere ranges from about 150 km to about 200 km (refs. 35–37, 40), we consider these two values for the lithosphere thickness in the modelling. After the bottom temperature of the 150-km thick lithosphere (Tl = 1283 K) was perturbed by the hot PA plume in the Late Triassic, the surface heat flow has gained in 200 My up to 9 mW m−2 and 12 mW m−2 for plume excess temperatures of 487 deg. and 687 deg., respectively (Fig. 5a, blue lines). For the thicker lithosphere (200 km) with a bottom temperature Tl = 1610 K, the surface heat flow has gained in 200 My up to 3.1 mW m−2 for a plume excess temperature of 360 deg. (Fig. 5a, dashed red line). The model results show that in the case of a thick lithosphere (150–200 km), the temperature gain within 200 My at depths of 6 km to 10 km ranges between about 3 deg. and 40 deg. depending on the plume excess temperature (Fig. 5b, c).

We note that the model results are valid assuming the lithosphere base temperature to be constant. However, as the PA plume became thermally weaker with time: its head shrunk (Fig. 2) with a lower heat flux to the surface, and temperature at the base of the lithosphere decreased. Hence, the modelled temperature and heat flow gains should be considered as the upper limits to the crustal temperature gain and its heat flow. Considering the temperature gain to decrease with time over 200 My due to the PA plume’s thermal decay, the temperature increase will be not enough to generate plume-impinged rifting41.

As heat comes from the mantle and the crust, it warms sedimentary basins above, and hence influences the maturation of hydrocarbons. The temperature required to alter organic material can be reached during a gradual burial and depends on the thermal conditions in the area of burial. At some interval of temperatures and pressures42, depending on how rapid the source rock has been buried and heated, kerogens (organic compounds) release hydrocarbons (oil or gas). Analyses of hydrocarbon maturity are based on the degree of thermal degradation of kerogens after sedimentary burial and on the reflectivity of vitrinite, a primary component of kerogens43. Sedimentary organic matter buried in a basin is heated up until it reaches the oil window (333 K–473 K). The thermal history of sedimentary basins can be retrieved from the knowledge of the present temperature measured in boreholes combined with models of geodynamic and structural evolution of the basins44. The subsidence history provides constraints on depths (and pressures) of source rock layers in sedimentary basins. Thermal modelling of the basins allows determining temperatures in the layers in the past.

As the EE basins did not experience significant subsidence since the Cretaceous times, the organic matter was heated at almost the same depth until thermal degradation of kerogens and generation of oil and gas (see Table 1 for the estimated times of hydrocarbon maturation in the EE basins). With the absence of significant subsidence, the only way to bring the source rocks to the oil window is to increase the rock’s temperature. At the geotherm used in the modelling (see Methods), the crustal temperature at depths of 6 km to 10 km will range from 339 K to 366 K. A mantle plume beneath the thick lithosphere could heat sediments at a depth of 10 km from about 17 to 40 deg. within 200 My, elevating the temperature of sediments in the EE basins and providing the conditions for hydrocarbon maturation at enhanced heating.

Projecting the estimated extent of the seismically observed PA above the core-mantle boundary3 toward the lithosphere, an area of at least about 3 × 106 km2 across the lithosphere would be influenced by the plume’s excess heat flux for about 150–200 My. This additional heat source would keep the key organic matter in the oil window during no or insignificant subsidence in the EE basins. The PA plume’s presence under Eurasia would also disturb the heat flux in the affected sedimentary basins through underplating and/or hot magma dike injection into the lithosphere promoting again organic matter maturation. Some delay could be expected between the emplacement of the hot material and the time of maturation as the heat diffuses from the hot material up toward the basin.

The rate of hydrocarbon generation is assumed to follow the Arrhenius thermal maturation model45. Using this model combined with a hydrological model predicting the temperature and pressure distribution in evolving sedimentary basins, the predicted depth intervals of oil and gas generation are shown46 to be shallower at lower sedimentation rates because sediments spend a longer time in the same depth interval and are thus more thermally mature. This may explain why at lower sedimentation rates and almost no subsidence in the EE basins since Cretaceous, organic-rich sediments reached higher levels of thermal maturity, generating hydrocarbon accumulations in the EE basins at various depths, including giant oil fields like Tengiz (at depths between 3.8 km and 5.4 km)47, Kashagan (at a depth of about 4.2 km)47, and Romashkino (at a depth of about 1.7 km)48 (see Table 1; Fig. 2). Once formed, the hydrocarbons do not survive if they are submitted to conditions well exceeding those of the oil window. This could happen, for example, if the basin subsidence is rapid and the hydrocarbons progressively attain deeper and therefore hotter levels in the crust. Therefore, the absence of basin subsidence due to the long-term presence of the PA fading plume below Eurasia is an important factor keeping the hydrocarbons basins in the oil window.

In this paper, we have shown that the present PA is likely to be the remnant of a thermally prominent mantle upwelling in the geological past, and that this deep-seated mantle plume influenced the evolution of EE hydrocarbon-bearing basins. As the EE platform moved above the PA plume, vertical tectonic movements recorded in the EE basins show uplifts or insignificant subsidence during the post-Jurassic times. The EE basins have been constantly heated from below for a long geological time (~150–200 My) with elevated temperature and heat flux in the crust. The hydrocarbon basins, including giant oil- and gas-fields, are situated along the tracks of the projection of the PA plume’s centre on the surface of the central and eastern parts of the EE platform. Based on modelling of the plume decay, global plate motion models, and a conductive heating model of the lithosphere, we show that the EE basins have been heated above the thermally fading PA plume for the past 150–200 My, creating suitable conditions for hydrocarbon generation.

The study suggests a strong link between a mantle plume heating the thick continental lithosphere for a long geological time, sedimentary basins heated by the weakening plume, and the formation of hydrocarbon provinces in the basins. By the same token, we would expect the generation of oil and gas fields on oceanic passive margins preferentially along the path of hotspots. For example, hydrocarbon resources found in the North Sea and the Norwegian margins could be associated with the Eifel hotspot activity49 in the Middle-Late Jurassic times resulting in active rifting followed by thermal doming50. It may also explain the recent findings of giant resources offshore Brazil and Africa51 along the track of the Tristan da Cunha plume which begun by the Paraná-Etendeka LIP formation 132 Ma ago and triggered the opening of the South Atlantic Ocean52. This suggests that shallow or deep hydrocarbon fields within sedimentary basins are likely to be concentrated in areas of heat flow enhancements, due in particular to the prolonged presence of a fading mantle upwelling beneath these basins.

Methods
Mantle plume modelling
The evolution of mantle plumes originating at the core-mantle boundary is modelled numerically in a bottom heated three-dimensional box Ω = [0, 3H] × [0, 3H] × [0, H], where H (=2800 km) is the depth of the box. This modelling clarifies the role of thermal diffusion in the evolution of mantle plumes. The equations of momentum conservation (the Stokes equations), mass conservation (the continuity equation), and energy conservation (the heat equation) in an infinite Prandtl number Boussinesq viscous fluid,

∇P = ∇ · η(T)(∇u + ∇uT) + RaTe, x ∈ Ω, (1)

∇ · u = 0, x ∈ Ω, (2)

∂T/∂t + u · ∇T = ∇2T, t ∈ (0, ϑ), x ∈ Ω, (3)

are solved numerically by finite-element and finite-difference methods21,53. Here x, T, t, u, P, and η are the position vector in 3-D Cartesian coordinates, the temperature, the time, the velocity vector, the pressure, and the viscosity, respectively; e = (0, 0, 1) is the unit vector; Ra = 9.5 × 105 is the Rayleigh number; symbols ∇ is the gradient operator, ∇ · is the divergence operator, and T is the transposed matrix. Symmetry and perfect slip conditions are applied to the vertical and horizontal sides of the model box, respectively. The heat flux through the vertical sides is set to zero; the upper and lower sides of the box are assumed to be isothermal surfaces. At the initial time, we assume a depth-dependent temperature stratification in the model. A temperature-dependent viscosity law is employed54:

η(T) = exp [M/(T + G) - M/(0.5 + G)], (4)

where M = [225/ln(r)] – 0.25 ln(r), G = 15/ln(r) – 0.5 and r = 20 is the ratio between the uppermost and lowermost mantle viscosity.

The model box is divided into 40 × 40 × 30 rectangular finite elements to approximate the velocity potential by tri-cubic splines, and a uniform grid 120 × 120 × 90 is employed for approximation of temperature, velocity, and viscosity. The temperature in the heat equation is approximated by finite differences and determined by the semi-Lagrangian method permitting for relatively large time steps, high accuracy, and low numerical diffusion. A numerical solution to the Stokes equations is based on the introduction of a two-component vector velocity potential and on the application of the Eulerian finite-element method with a tricubic-spline basis for computing the potential. Such a procedure results in a set of linear algebraic equations, which are solved by the conjugate gradient method53. The model limitations, uncertainties, and sources of errors are discussed in SD5 of SI. The results (isothermal surfaces at 3000 K, i.e. 0.91 of the temperature difference across the mantle) are presented in Fig. 2b–f in a part of the model domain. The hot isotherms illustrate mantle upwelling, while much colder isotherms surrounding the upwelling would indicate downwelling flows (not shown in the figure).

Global plate motion modelling
The PA position projected on central Eurasia is tracked for 200 My using three models of the GPM26–28. Seton et al. (ref. 26) use a combined reference frame: the reference frame55 for the past 100 My, and the palaeomagnetically-derived true polar wander (TPW) corrected reference frame56 from 100 Ma to 200 Ma. Müller et al. (ref. 27) follow the model57 combining a rotation due to two interpolated longitudinal shift-TPW corrections and an additional correction using the Absolute Plate Motion (APM) rotation poles56. Matthews et al. (ref. 28) use also the model57 and compute an APM between 100 Ma and 250 Ma using the sum between three Euler poles: the first one derived by the palaeomagnetic poles58, the second one from a TPW correction58, and the third one from the same rotation poles as in ref. 27 due to longitudinal shift-TPW correction (see SD3 of SI for detail of the models). The parameters used in the modelling are presented in Supplementary Table S1 of SI.

Tectonic subsidence analysis
The history of regional crustal tectonic movements in EE sedimentary basins is analysed using 70 exploration boreholes drilled in the Moscow basin, the Timan-Pechora basin, and the Pre-Uralian foredeep (see SD4 of SI). To determine the tectonic subsidence, the backstripping method is employed to separate isostatic effects of sediments and water loading from those of tectonic subsidence59. The backstripping procedure consists of stripping stratigraphic units off, starting from the uppermost unit and sequentially removing each underlying unit downwards to the basin’s basement. During the procedure, the thickness of the underlying stratigraphic units is corrected for sediment decompaction due to the removal of the load associated with the stripped uppermost unit. Based on the Airy isostasy assessment, the decompacted units are shifted upwards to a prescribed datum level (sea level). Because specific paleo-bathymetric data were available for most of the boreholes. Paleo-water depths were predicted based on lithological analysis of sediments and fossils. Hiatuses are treated in most cases as non-deposition events due to uplift. Paleo-bathymetric data used in the backstripping analysis to constrain water-depth estimates through time may influence the resulting subsidence due to uncertainties and errors in the depth determination. While carbonate reefs and erosion surfaces provide rather reliable estimates of paleo-bathymetry, the use of fossil assemblages to estimate paleo-water depths may carry errors60.

In the backstripping method used here, the isostatic response of the lithosphere is local. This method does not consider the rigidity of the lithosphere and its elastic response to regional loads, which can be calculated using a flexural backstripping method61. Namely, for a given sedimentary load, the magnitude of vertical deflection under the load and its lateral wavelength are controlled by the flexural rigidity of the lithosphere (or its effective elastic thickness). Considering the effective elastic thickness of the EE lithosphere to be about 100 km (ref. 62), the deflection of the elastic lithosphere with respect to its hydrostatic deflection is about 30% if the wavelength of the topographic elevation is about 1000 km (ref. 25; see also SD4 of SI). Although the results of the backstripping analysis can be influenced by the method used (e.g., the Airy isostasy vs. the flexural isostasy), we analyse in this paper the tendency of vertical tectonic movements and not their magnitude. For this aim, we normalise the tectonic subsidence within each individual basin k (k = 1 for the Moscow basin; 2 for the Timan-Pechora basin; and 3 for the Pre-Uralian foredeep). The normalisation procedure consists of the division of the tectonic subsidence depths Sk i(t) determined at time t for borehole i (= 1, …, Nk; Nk is the number of the wells used in the analysis; N1 = 18, N2 = 37, and N3 = 15) by the maximum tectonic subsidence depth Sk max for the past 210 My in basin k, that is, Sk i(t)/Sk max < 1. Tectonic subsidence curves presented in Fig. 4 illustrate the average normalised subsidence at time t [S^k(t) = Σ i=1 to Nk (Sk i(t)/Sk max)/Nk]. Vertical lines, crossing these subsidence curves, show the maximum deviation in the normalised subsidence at time t with respect to the average normalised subsidence [max(Sk i(t)/Sk max) - S^k(t)].

Thermal conductive modelling
We consider an analytical model of conductive heat flow in the lithosphere due to its heating from below by a mantle plume. The model temperature is a solution of the 1-D heat conduction equation

∂T/∂t = κ ∂2T/∂z2 (0 < z < h), (5)

where T is the temperature, κ (= 10−6 m2 s−1) is the thermal diffusion coefficient, t is time, z denotes the depth, and h is the thickness of the lithosphere. The lithosphere’s surface is maintained at the same temperature T0 (300 K), and the temperature at the base of the lithosphere is Tl. Initially, the lithosphere’s temperature has reached steady state and follows the continental geotherm Tgeoth(z) = T0 + 6.55z, which was modelled using a temperature- and pressure-dependent thermal conductivity and a heat production within the lower crustal rocks of 0.4 μW m−3 (ref. 11) to match the surface heat flux 45 mW m−2 suitable for the EE basins63. At t = 0 the temperature at the base of the lithosphere is increased by ΔT = Tpi − Tl (the plume excess temperature), where Tpi is the plume temperature; two values of the plume temperature are considered, Tp1 = 1770 K and Tp2 = 1970 K (ref. 64).

The solution to the heat conduction Eq. (5), satisfying the prescribed initial condition Tgeoth and boundary conditions T0 at the surface and Tl at the base of the lithosphere, can be analytically derived65. The temperature gain in the lithosphere associated with the temperature increase at its base due to mantle plume heating can be expressed as a function of time and depth:

T(t, z) = ΔT [z/h + Σ n=1 to ∞ 2/nπ cos(nπ) exp(-n2π2κt/h2) sin(nπz/h)]. (6)

From this equation we can obtain the surface heat flow gain Qs as a function of time t:

Qs(t) = (kΔT/h) [1 + Σ n=1 to ∞ 2 cos(nπ) exp(-n2π2κt/h2)], (7)

where k (= 3 W m−1 K−1) is the thermal conductivity coefficient. The results discussed below are computed for n = 30 (the solution changes insignificantly for larger n).

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Review of “East European Sedimentary Basins Stewed Over an Ancient Mantle Upwelling” by Ismail-Zadeh et al.\nThe manuscript presents an interesting idea, which I enjoyed reading. The evolution of a mega-plume, now extinct, can explain sedimentary basin features not directly available in lithospheric evolutionary models. It is well known that the large basins overlying the East European craton contains thick sedimentation and long-lived unconformities that cannot be directly explained by mechanical models of lithospheric evolution. The little amount of fault-driven basin accommodation space observed to be created over geological time in many EE basins cannot justify the higher temperatures measured in the organic maturation of sediments. An additional gain of temperature over the observed mechanical subsidence and sediment burial is required in the structure of the basins to explain thermal markers such as the organic maturation. The wavelength of these basins may be considered large enough to be regionally influenced by a mega-plume. Because I believe that sub-lithospheric forcing is the way to research the observed features, I recommend publication of the novel idea presented in the manuscript. However, the idea is speculative given available information, and the authors should be less bold in their conclusions, by acknowledging better error bars and potential pitfalls. ISuch changes can be performed in a minor revision.\nSuggestions:\na) All assumptions and modelling performed in the manuscript are based on a viscous structure. Sure that this is an appropriate approach for the sub-lithospheric mantle, but this is not appropriate for the EE lithosphere. The EE craton has presently one of the thickest elastic structures. This translates at least in two approaches of the manuscript:\n- Although not well explained in the manuscript (kind of a black box in the text and appendix), the subsidence analysis appears to be simple isostatic backstripping. This is obviously inappropriate give the high elastic thicknesses of the EE craton (often more than 80 km) and flexural isostatic backstripping must be assessed because errors are certainly higher than 50%. I do not understand very well Fig. 4a, it may be that the authors refer only to unconformities in the basins. I suggest explaining better the subsidence analysis and estimate the errors bars induced by flexure (both in subsidence analysis and in other potential far-field induced effects), while providing further explanations or redrawing Fig. 4a;\n- At the higher values or enrichment of 100 degrees in the basins and given the high elasto-plastic composition, one would expect to see much larger active rifting (in the Ziegler sense, plume-impinged rifting) than the minor one observed in the basins. Ideally one should perform more an elasto-visco-plastic above a mantle plume head type of modelling, but I suggest that the authors discuss at least the influence of the EE craton elasticity in the dynamic lithospheric evolution.\nb) I suggest acknowledging and explaining better the resolution and error bars of the assumptions, which is the wavelength of the inferred plume during its evolution. Anything higher resolution is possibly inappropriate in terms of interpretation.\nc) While the idea is certainly applicable to the EE craton basins, with the methods and tools of this manuscript the speculative inferences at the end of the manuscript to regions undergoing large scale kinematic movements, such as the North Sea, Norwegian margin or offshore Atlantic are certainly too speculative and inappropriate. Plumes are not the only mechanism able to explain over-maturation of sediments. In such regions, alternative explanations (such as the asymmetry of the extension or exhumation during the formation of hyper-extended margins) are already proven to be valid scenarios. Any plume contribution must be first demonstrated at higher resolution than what the manuscript provides. I suggest removing these speculative considerations, which in my view decrease the quality of the manuscript.\nd) Far-field stresses or lithospheric folding have been used in literature to explain regional EE craton basins geometry. One should shortly include these ideas in the discussion.\nOther smaller suggestions:\n- Would be good to be specific which Tethys you are speaking about, because not all has been active in the last 300Ma. It is true that between Japan and Africa the only true large scale noteworthy features are the Pacific and Aegean subduction system, but the latter is certainly not 300 Ma old.\n- Although fancy, Fig. 1 is not very readable in the sense of understanding the structure. I do not have a good alternative solution, but maybe a depth slice with a cross-section would be more helpful?\n- The thermal model has also little explanation, although references are partly available. If there is space, I suggest considering explaining with more detail the numerical implementation.\n- Please explain more to the point the link between the mechanism proposed and the formation of mega-petroleum provinces. I guess the assumption is that because of the large wavelength, the mechanisms affect larger basinal areas, creating mega-plays. Right?\n- For the reasons explained above, the influence of the plume appears to me overstated. It is better to say simply that the additional heat source “nudge” the temperature of key organic matter accumulation in the hydrocarbon window.\n- Second page, second paragraph, you are either specific or remove “some other geophysical processes.”\n- Fig. 3a – Is it possible to change the grey area in Fig 3a with more specific evolutionary colour zones? Such as one key moment in the plume spatial evolution?", "reviewer_2": "This paper presents the intriguing hypothesis that the large hydrocarbon fields of the East European basin may have been formed owing to the heat provided by the remnants of the head of a plume whose root at the core-mantle boundary would presently be manifested by the tomographically imaged low shear velocity “PERM” anomaly.\nIn particular, the model explains the lack of sedimentary basin subsidence that is generally invoked in models of hydrocarbon reservoir formation.\nIf this interpretation is correct, it should be good news to those working on imaging deep mantle plumes, as it would add to the relevance of their work relevant to societally important near surface geology problems.\nThe geodynamic plume modeling showing how a plume can become separated from its root, and the thermodynamic modeling are sound and interesting.\nWhat is missing in this paper is a broader picture of the relationship through time of the “PERM” plume with the Eurasian lithosphere. Indeed, before getting broken up into a separate tail and head, the plume must have been continuous and upon reaching the base of the lithosphere, it must have interacted with it for a long time. The authors cite two rather different hypotheses for links between the present day PERM anomaly and near surface observations of ancient volcanism: Siberian Traps, versus the more southerly Emeishan Volcanics. These two hypotheses rely on very different “views” on the evolution of mantle plumes. The former has a plume fixed in the deep mantle since at least Permian times, the latter has the plume moving around. This deserves further discussion and clarification: the statement “The longevity of these downwellings and mass conservation in the mantle imply the longevity of the hot upwelling” is incorrect at the level of a single plume. The upwelling part of the flow could have changed location and therefore also the place of impact at the base of the lithosphere, unless the model considered is one of a plume anchored at the core-mantle boundary by a dense root (e.g. Jellinek and Manga, 2005). It is therefore not clear what the general framework of the reasoning is in this paper. Is the plume fixed in its geographical position and fading with time in its strength, or is it moving around as well as fading? Is it more likely related to the Siberian Traps or the Emeishan Volcanics? What makes the studied area special for the manifestation of the plume head activity? A geological map showing how the EE platform might have aligned through time with the plume head, or some arguments as to why the plume head would have moved and settled beneath the EE platform could help clarify this. Figure 2 is not very helpful, nor is Figure 3, which is not showing the geology.\nMore generally, the figures are awful. There must be a better way to represent the relation of the deep mantle structure to the lithosphere than what is shown in Fig 1 which is hardly understandable. Figure 3b implies that the plume head has moved around geographically, when, unless I missed the point, what the authors want to show is the absolute plate motion of the Eurasian plate with respect to the present day location of the PERM anomaly. Figure 4, which shows a welcome sketch of the different basins in the EE platform (But no other geological details) is plotted in a different projection than Fig 3a and the location of the PERM anomaly is not even indicated.\nIn summary, the model of heating due to a plume to explain the lack of subsidence (this one is clearly presented) of the EE basins in the last 150 My is plausible, but the link to the PERM anomaly, while attractive and plausible, should be further clarified.", "reviewer_3": "This thought-provoking article proposes that a plume associated with the Perm Anomaly could explain the evolution of the East European platform from about 250 million years ago. My understanding of the proposed scenario is that a mantle plume rising from the Perm Anomaly would have been strongest when it first reached the shallow mantle about 250 million years ago (Permo-Triassic), possibly causing the Siberian Traps. Laboratory and numerical experiments show that the plume could have weakened over time. Plate motions deduced from global tectonic reconstructions show that the East European platform could have been influenced by a weakening plume above the stationary Perm Anomaly from 200 million years ago. The analysis of borehole data (backstripping) reveals a lack of tectonic subsidence of basins from the East European platform from 150 million years ago, and this is attributed to dynamic support from a weakening mantle plume in the absence of volcanism due to the thickness of the East European platform lithosphere. Thermal modelling shows that a thermally weakening plume beneath the East European platform could have led to conditions favourable for hydrocarbon maturation.\nI have several questions and comments:\n- the region of interest is roughly centred on 55ºE/55ºN. The Siberian Traps are roughly centred on 85ºE/65ºN. The distance between these two points is about 2,000 km. How could a mantle plume linked to the Perm Anomaly have caused the Siberian Traps around 250 million years ago and influenced the East European platform from about 250 million years ago (Figure 2a of the manuscript)?\n- the Kola-Dnieper large igneous province (e.g. Ernst et al., 2020) erupted at ~370-360 Ma and is centred on 57ºE/40ºN. The distance between the two points is only 925 km, and the Kola-Dnieper large igneous province is in the longitudinal vicinity of the East European platform.\n- volcanism (which is part of the Kola-Dnieper large igneous province) is documented during the period of rifting of the basins of the East European platform around 370 million years ago (see Wilson and Lyashkevich, 1996 and supplementary material for the subsidence)\n- based on the above, could an earlier mantle plume (about 120 million years earlier than the proposed mantle plume) have been associated with volcanism, rifting and subsidence in the East European platform?\n- is the lack of subsidence of the East European platform from about 160 million years ago uniquely explained by dynamic support from a weakening mantle plume?\n- it might be worth mentioning that the present-day residual topography and dynamic topography of the East European platform are negative, and explaining how this fits with the proposed scenario.\n- the motion of plates is considered (Figure 3), however, the Perm Anomaly is assumed to have been stationary from 200 million years ago. Is this a reasonable assumption?\nReferences:\nErnst, R.E., Rodygin, S.A. and Grinev, O.M., 2020. Age correlation of Large Igneous Provinces with Devonian biotic crises. Global and Planetary Change, 185, p.103097.\nWilson, M. and Lyashkevich, Z.M., 1996. Magmatism and the geodynamics of rifting of the Pripyat-Dnieper-Donets rift, East European Platform. Tectonophysics, 268(1-4), pp.65-81."}, "author_response": "Manuscript NCOMMS-22-52808\n“East European sedimentary basins stewed over an ancient mantle upwelling”\nResponse to the reviewers’ comments\nThe authors are very grateful to three reviewers and to the Editor for thorough review of the initial manuscript of the paper and very constructive comments. Below is a point-to-point response (marked by red below) to the reviewers’ comments. We refer to lines (ll.) of the revised manuscript and to the revised Supplementary Information, where the revision is marked by red.\nReviewer #1 (Remarks to the Author):\nThe manuscript presents an interesting idea, which I enjoyed reading. The evolution of a mega-plume, now extinct, can explain sedimentary basin features not directly available in lithospheric evolutionary models. It is well known that the large basins overlying the East European craton contains thick sedimentation and long-lived unconformities that cannot be directly explained by mechanical models of lithospheric evolution. The little amount of fault-driven basin accommodation space observed to be created over geological time in many EE basins cannot justify the higher temperatures measured in the organic maturation of sediments. An additional gain of temperature over the observed mechanical subsidence and sediment burial is required in the structure of the basins to explain thermal markers such as the organic maturation. The wavelength of these basins may be considered large enough to be regionally influenced by a mega-plume. Because I believe that sub-lithospheric forcing is the way to research the observed features, I recommend publication of the novel idea presented in the manuscript. However, the idea is speculative given available information, and the authors should be less bold in their conclusions, by acknowledging better error bars and potential pitfalls. ISuch changes can be performed in a minor revision.\nSuggestions:\na) All assumptions and modelling performed in the manuscript are based on a viscous structure. Sure that this is an appropriate approach for the sub-lithospheric mantle, but this is not appropriate for the EE lithosphere. The EE craton has presently one of the thickest elastic structures. This translates at least in two approaches of the manuscript:\n- Although not well explained in the manuscript (kind of a black box in the text and appendix), the subsidence analysis appears to be simple isostatic backstripping.\nA description of the backstripping procedure used in this work has been added to the section Methods (lines 366-379).\nThis is obviously inappropriate give the high elastic thicknesses of the EE craton (often more than 80 km) and flexural isostatic backstripping must be assessed because errors are certainly higher than 50%.\nThe influence of flexural rigidity has been now estimated and discussed in Methods (ll. 380-390), and in more detail in Supplementary Discussion 3 (ll. S146-S164).\nThe normalization procedure applied to the subsidence curves and the maximum variations in the vertical tectonic movements are now discussed in Methods (ll. 391-399).\n- At the higher values or enrichment of 100 degrees in the basins and given the high elasto-plastic composition, one would expect to see much larger active rifting (in the Ziegler sense, plume-impinged rifting) than the minor one observed in the basins. Ideally one should perform more an elasto-visco-plastic above a mantle plume head type of modelling, but I suggest that the authors discuss at least the influence of the EE craton elasticity in the dynamic lithospheric evolution.\nIn our analytical thermal models, the thermal enrichment ranges from ~20 to ~100 degrees. Considering the excess temperature to decrease with geological times over 200 My due to the plume’s thermal decay, the enrichment will be not enough to generate plume-impinged rifting of the EE lithosphere. A discussion is added (ll. 232-234)\nb) I suggest acknowledging and explaining better the resolution and error bars of the assumptions, which is the wavelength of the inferred plume during its evolution. Anything higher resolution is possibly inappropriate in terms of interpretation.\nUncertainties, errors, and limitations in the wavelength of the PA plume (ll. 143-147) as well as in tectonic subsidence analysis (ll. 375-379) and in the modeling of mantle plume evolution (see Supplementary Discussion 4) are now discussed in more detail.\nc) While the idea is certainly applicable to the EE craton basins, with the methods and tools of this manuscript the speculative inferences at the end of the manuscript to regions undergoing large scale kinematic movements, such as the North Sea, Norwegian margin or offshore Atlantic are certainly too speculative and inappropriate. Plumes are not the only mechanism able to explain over-maturation of sediments. In such regions, alternative explanations (such as the asymmetry of the extension or exhumation during the formation of hyper-extended margins) are already proven to be valid scenarios. Any plume contribution must be first demonstrated at higher resolution than what the manuscript provides. I suggest removing these speculative considerations, which in my view decrease the quality of the manuscript.\nAs we have no strong evidence for influence of mantle plume on the hydrocarbon maturation in the North Sea, Norwegian margin or offshore Atlantic regions, the relevant sentence is removed from the manuscript.\nd) Far-field stresses or lithospheric folding have been used in literature to explain regional EE craton basins geometry. One should shortly include these ideas in the discussion.\nWe have included a discussion on the mechanisms of EE basin evolution in Supplementary Discussion 3 (ll. S130-S139).\nOther smaller suggestions:\n- Would be good to be specific which Tethys you are speaking about, because not all has been active in the last 300Ma. It is true that between Japan and Africa the only true large scale noteworthy features are the Pacific and Aegean subduction system, but the latter is certainly not 300 Ma old.\n2\n“Tethys” was replaced by “Neo-Tethys”.\n- Although fancy, Fig. 1 is not very readable in the sense of understanding the structure. I do not have a good alternative solution, but maybe a depth slice with a cross-section would be more helpful?\nFigure 1 is revised and includes now cross sections.\n- The thermal model has also little explanation, although references are partly available. If there is space, I suggest considering explaining with more detail the numerical implementation.\nWe have added a description of the numerical implementation in Methods (ll. 338-345).\n- Please explain more to the point the link between the mechanism proposed and the formation of mega-petroleum provinces. I guess the assumption is that because of the large wavelength, the mechanisms affect larger basinal areas, creating mega-plays. Right? For the reasons explained above, the influence of the plume appears to me overstated. It is better to say simply that the additional heat source “nudge” the temperature of key organic matter accumulation in the hydrocarbon window.\nThe PA mantle plume activity has influenced a wide area (about 3x106 km2) of the EE lithosphere above the PA. And we argue that the excess of the heat flux due to the presence of the plume beneath the region for about 150-200 My provided the additional heat source to keep organic matter in the oil window. A clarification is inserted (ll. 265-269; 281-283).\n- Second page, second paragraph, you are either specific or remove “some other geophysical processes.”\nRemoved\n- Fig. 3a – Is it possible to change the grey area in Fig 3a with more specific evolutionary colour zones? Such as one key moment in the plume spatial evolution?\nFigure 3 is revised and includes now the tracks showing projections of the plume onto the surface at different times.\nReviewer #2 (Remarks to the Author):\nThis paper presents the intriguing hypothesis that the large hydrocarbon fields of the East European basin may have been formed owing to the heat provided by the remnants of the head of a plume whose root at the core-mantle boundary would presently be manifested by the tomographically imaged low shear velocity “PERM” anomaly.\nIn particular, the model explains the lack of sedimentary basin subsidence that is generally invoked in models of hydrocarbon reservoir formation.\nIf this interpretation is correct, it should be good news to those working on imaging deep mantle plumes, as it would add to the relevance of their work relevant to societally important near surface geology problems.\nThe geodynamic plume modeling showing how a plume can become separated from its root, and the thermodynamic modeling are sound and interesting.\nWhat is missing in this paper is a broader picture of the relationship through time of the “PERM” plume with the Eurasian lithosphere. Indeed, before getting broken up into a separate tail and head,\nthe plume must have been continuous and upon reaching the base of the lithosphere, it must have interacted with it for a long time.\nThe numerical modeling of thermal plume evolution presents the snapshots of the Permian-Triassic (revised Fig. 2a) to the Cenozoic (revised Fig. 2e) times. This model assumes that the plume was active some 250 My ago and was fading thermally since Early Triassic. We do not link the plume to any specific area on the surface of the lithosphere in the geological past before 200 My ago, because uncertainties in paleolatitudes may pollute the GPM reconstructions beyond this geological time frame (Bess & Courtillot, 1991). It is discussed in Supplementary Discussion 1 (ll. S24-S28)\nThe authors cite two rather different hypotheses for links between the present day PERM anomaly and near surface observations of ancient volcanism: Siberian Traps, versus the more southerly Emeishan Volcanics. These two hypotheses rely on very different “views” on the evolution of mantle plumes. The former has a plume fixed in the deep mantle since at least Permian times, the latter has the plume moving around. This deserves further discussion and clarification: the statement “The longevity of these downwellings and mass conservation in the mantle imply the longevity of the hot upwelling” is incorrect at the level of a single plume. The upwelling part of the flow could have changed location and therefore also the place of impact at the base of the lithosphere, unless the model considered is one of a plume anchored at the core-mantle boundary by a dense root (e.g. Jellinek and Manga, 2005). It is therefore not clear what the general framework of the reasoning is in this paper. Is the plume fixed in its geographical position and fading with time in its strength, or is it moving around as well as fading? Is it more likely related to the Siberian Traps or the Emeishan Volcanics? What makes the studied area special for the manifestation of the plume head activity?\nAs the topic of the paper is not related to the origin of the Perm Anomaly, we would not like to debate on the origin in this article, but some comments on this topic are inserted in Supplementary Discussion 1 (ll. S16-S69). Also, as we assume that a mantle plume associated with the PA is fixed in space, the reference to the Emeishan Volcanics is removed from the main text and added to Supplementary Discussion 1 (ll. 39-43).\nA geological map showing how the EE platform might have aligned through time with the plume head, or some arguments as to why the plume head would have moved and settled beneath the EE platform could help clarify this.\nFigure 2 is not very helpful, nor is Figure 3, which is not showing the geology.\nPaleogeographic maps are inserted into Supplementary Information (see Supplementary Fig. 1), which also presents the geological features of the EE platform since the Late Permian times.\nMore generally, the figures are awful. There must be a better way to represent the relation of the deep mantle structure to the lithosphere than what is shown in Fig 1 which is hardly understandable.\nFigure 1 is redrawn.\nFigure 3b implies that the plume head has moved around geographically, when, unless I missed the point, what the authors want to show is the absolute plate motion of the Eurasian plate with respect to the present day location of the PERM anomaly.\nFigure 3 is revised, and illustrates the traces of the piercing point on the moving Eurasian lithosphere of a fixed plume associated with the PA.\nFigure 4 is revised.\nIn summary, the model of heating due to a plume to explain the lack of subsidence (this one is clearly presented) of the EE basins in the last 150 My is plausible, but the link to the PERM anomaly, while attractive and plausible, should be further clarified.\nWe have clarified the link in Supplementary Discussion 1.\nReviewer #3 (Remarks to the Author):\nThis thought-provoking article proposes that a plume associated with the Perm Anomaly could explain the evolution of the East European platform from about 250 million years ago. My understanding of the proposed scenario is that a mantle plume rising from the Perm Anomaly would have been strongest when it first reached the shallow mantle about 250 million years ago (Permo-Triassic), possibly causing the Siberian Traps. Laboratory and numerical experiments show that the plume could have weakened over time. Plate motions deduced from global tectonic reconstructions show that the East European platform could have been influenced by a weakening plume above the stationary Perm Anomaly from 200 million years ago. The analysis of borehole data (backstripping) reveals a lack of tectonic subsidence of basins from the East European platform from 150 million years ago, and this is attributed to dynamic support from a weakening mantle plume in the absence of volcanism due to the thickness of the East European platform lithosphere. Thermal modelling shows that a thermally weakening plume beneath the East European platform could have led to conditions favourable for hydrocarbon maturation.\nI have several questions and comments:\n- the region of interest is roughly centred on 55°E/55°N. The Siberian Traps are roughly centred on 85°E/65°N. The distance between these two points is about 2,000 km. How could a mantle plume linked to the Perm Anomaly have caused the Siberian Traps around 250 million years ago and influenced the East European platform from about 250 million years ago (Figure 2a of the manuscript)?\nThis paper presents the evolution of the mantle plume associated with the Perm Anomaly (PA) from 200 My ago until present. We assume that the plume was active and prominent before it, and while we do not deal with the PA origin, we consider that this plume could cause the Siberian traps at the Permian-Triassic boundary (e.g., Torsvik et al., 2016; also see Supplementary Discussion 1).\nAs discussed in the manuscript, the East European (EE) lithosphere moved northeastward at the rate of about (5N, 10E) in My in the Middle to Late Triassic according to paleogeographic/ palinspastic (Kazmin & Natapov, 1998) reconstructions (see Supplementary Fig. 1). Hence, the EE lithosphere reached the head of this mantle plume by the Early Jurassic. We should mention that the evolution of the plume since the Early Jurassic is of our research interest.\n- the Kola-Dnieper large igneous province (e.g. Ernst et al., 2020) erupted at ~370-360 Ma and is centred on 57°E/40°N. The distance between the two points is only 925 km, and the Kola-Dnieper large igneous province is in the longitudinal vicinity of the East European platform.\n- volcanism (which is part of the Kola-Dnieper large igneous province) is documented during the period of rifting of the basins of the East European platform around 370 million years ago (see Wilson and Lyashkevich, 1996 and supplementary material for the subsidence).\nThe reference to the earlier magmatic events in the region is added to Supplementary Discussion 3 (ll. S193-S199).\n- based on the above, could an earlier mantle plume (about 120 million years earlier than the proposed mantle plume) have been associated with volcanism, rifting and subsidence in the East European platform?\nAn earlier mantle plume may influence the evolution of the EE platform, and the Kola-Dnieper mantle plume associated with the KDLIP is a bright example of the impact on the EE platform in the Late Devonian times (see Supplementary Discussion 3, ll. S193-S199 and S235-S239). Meanwhile, we study the evolution of the region since the Jurassic and the Kola-Dnieper plume have no influence on the EE platform during this time.\n- is the lack of subsidence of the East European platform from about 160 million years ago uniquely explained by dynamic support from a weakening mantle plume?\nOur scientific hypothesis is supported by observations and model results, and that is what we present in this paper. Meanwhile, an alternative hypothesis may appear in the future with more data and more new knowledge on the region, which could also explain widespread unconformities in the EE basins for about two hundred My.\n- it might be worth mentioning that the present-day residual topography and dynamic topography of the East European platform are negative, and explaining how this fits with the proposed scenario.\nAn acceleration in subsidence during the Quaternary times is observed in some borehole data. There is no direct link between this subsidence and the proposed evolution of the region. The subsidence occurred during a short geological time to understand the mechanisms of this subsidence. Also, some discussion on tectonic subsidence of the EE basins since Devonian is added in Supplementary Discussion 3 (ll. S165-S175).\n- the motion of plates is considered (Figure 3), however, the Perm Anomaly is assumed to have been stationary from 200 million years ago. Is this a reasonable assumption?\nYes. Torsvik et al. (2016) provided the evidence for this on the basis of the stability of large low-shear-velocity provinces. This is discussed in Supplementary Discussion 1 (ll. S39-S43)."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have responded adequately and have considered correctly all my comments. Therefore I suggest manuscript acceptance at this time.", "reviewer_2": "This is a much improved version of the original manuscript. I only have two comments of significance:\n1) While figure 1 is much clearer, it is still a bit confusing because each panel is showing a map at 2800 km projected with a different center and two different models depending on the panel. I suggest showing the same cross section in the two models.\n2) Because this paper is still to a large extent speculative, I would tone down the assertions in the abstract:\na. “we show here that the EE lithosphere HAS BEEN situated…” replace “has been” by “MAY HAVE BEEN”\nb. “This establishes a profound relationship” : replace “establishes” by “suggests”.\nFinally, the paper would benefit from being read by a native English speaker. It is not critical, but would help with smooth reading (in particular making sure the tense of the verbs on lines 10-167 are consistent: gains-> gained, line 159: starts->started\nLine 173: “shrinks”-> shrunk etc.. and in quite a few places the ordering of words in the sentence, as well as missing or superfluous articles.", "reviewer_3": "I am not convinced by the geological and geophysical evidence presented in this manuscript. The proposed scenario is that a mantle plume existed above the fixed Perm Anomaly, triggered the Siberian Traps 250 million years ago, and then affected the subsidence and thermal evolution of the East European platform from 200 million years ago.\nProblems with this scenario include (i) that no plume is imaged above the Perm Anomaly at present-day, (ii) that there is no volcanism in the East European platform, (iii) that the link between the Perm Anomaly and the Siberian Traps is not demonstrated in the manuscript, and (iv) that deep basal mantle structures may have been mobile over time.\nThe scenario presented in Figure 2 suggests a solution to problem (i) in which the lifetime of the plume tail would be limited to 50 million years or less (specifically, Figure 2a,b,c). If this is the case, why are so many plume tails long-lived as demonstrated by oceanic hotspot tracks that span about 100 million years (see for example O'Neill et al., 2005)? As opposed to plume tails, plume heads are thought to be short-lived and to result in the eruption of large igneous provinces over 1 to 5 million years (Bryan and Ernst, 2008). In contrast, in Figure 2, the plume head persists for at least 200 million years. Is the model presented in Figure 2 applicable to Earth?\nRegarding problem (ii), it is argued that the plume was waning and that the East European lithosphere is thick, preventing melts from reaching the surface (l. 131-134). Davies et al. (2015) documented a long hotspot track beneath the eastern part of the Australian continent, and they showed that melting occurred where the lithosphere was less than 150 km thick. It is unclear that the thickness of the Eastern European lithosphere is more than 150 km in the eastern part of the region of interest (see for example Steinberger and Becker, 2018 or the global lithospheric thickness models available from Hoggard et al., 2020 at https://osf.io/twksd/).\nThe link between the Perm Anomaly and the Siberian Traps is proposed based on a reconstruction from 1998 (Supplementary Figure 1) based on which it is argued that 'the EE platform moved north-eastward at the rate of about (5°N, 10°E) in My in the Middle to Late Triassic times.' (l. 83-84). It would be helpful to quote a rate in degrees per million years. It would also be helpful to link the Perm Anomaly to the Siberian Traps as in Figure 3 of the main text (which links the Perm Anomaly to the Eastern European platform) by using a tectonic reconstruction that extends at least back to 250 million years ago (examples include the reconstructions of Matthews et al., 2016 or Young et al., 2019). In the rebuttal, it is argued that the focus of the study is the past 200 million years, however, in the absence of geophysical evidence for a plume and of any volcanism linked to the Perm Anomaly in the last 250 million years, it seems reasonable to request some geological evidence linking the Perm Anomaly to a mantle plume. If the Perm Anomaly is linked to the Siberian Traps, should there be some volcanism between the Siberian Traps and the East European platform in places where the lithosphere is less than 150 km thick?\nWhile it would be easier to link deep seismically slow anomalies to past volcanic eruptions if the structure of the deep Earth was rigid and fixed over time, Flament et al. (2022) showed that volcanic eruptions could be linked to either fixed or mobile deep mantle structures.\nReferences\nBryan, Scott E., and Richard E. Ernst. \"Revised definition of large igneous provinces (LIPs).\" Earth-Science Reviews 86.1-4 (2008): 175-202.\nDavies, D. R., et al. \"Lithospheric controls on magma composition along Earth’s longest continental hotspot track.\" Nature 525.7570 (2015): 511-514.\nFlament, Nicolas, et al. \"Assembly of the basal mantle structure beneath Africa.\" Nature 603.7903 (2022): 846-851.\nHoggard, Mark J., et al. \"Global distribution of sediment-hosted metals controlled by craton edge stability.\" Nature Geoscience 13.7 (2020): 504-510.\nO'Neill, Craig, Dietmar Müller, and Bernhard Steinberger. \"On the uncertainties in hot spot reconstructions and the significance of moving hot spot reference frames.\" Geochemistry, Geophysics, Geosystems 6.4 (2005).\nSteinberger, Bernhard, and Thorsten W. Becker. \"A comparison of lithospheric thickness models.\" Tectonophysics 746 (2018): 325-338.\nYoung, Alexander, et al. \"Global kinematics of tectonic plates and subduction zones since the late Paleozoic Era.\" Geoscience Frontiers 10.3 (2019): 989-1013."}, "author_response": "Response to the Reviewers comments\nThe authors are grateful to the Reviewers for their comments. We provide a point-by-point response to their comments below. Their comments are marked by red.\nReviewer #1:\nThe authors have responded adequately and have considered correctly all my comments. Therefore I suggest manuscript acceptance at this me.\nThe authors are grateful to Reviewer #1 for the recommendaon on acceptance.\nReviewer #2:\nThis is a much improved version of the original manuscript. I only have two comments of significance:\n1) While figure 1 is much clearer, it is sll a bit confusing because each panel is showing a map at 2800 km projected with a different center and two different models depending on the panel. I suggest showing the same cross secon in the two models.\nDone. Figure 1 has been revised as suggested by the reviewer.\n2) Because this paper is sll to a large extent speculave, I would tone down the asserons in the abstract:\na. “we show here that the EE lithosphere HAS BEEN situated…” replace “has been” by “MAY HAVE BEEN”\nb. “This establishes a profound relaonship” : replace “establishes” by “suggests”.\nWe have revised the wording in a and b, respecvely.\nA certain level of speculaon exists in many published works, and our work is based on a hypothesis as well.\nNamely, we propose that a present seismic observaon (the Perm Anomaly, PA) at the base of the mantle is linked to geological observaons at the surface. Geological interpretaons of seismic tomography images are challenging because of the limitaon of our knowledge regarding the geodynamic evoluon of the region and its surroundings, and some uncertaines associated with the inversion/assimilaon of data both in seismology and geodynamics (e.g., Ismail-Zadeh et al., 2023). Nevertheless, the present seismic evidence indicates that the PA is separated from the other two large provinces of low seismic velocies (below the Pacific and the Indo-Atlanc regions) by the Neo-Tethys subducon to the south and the Pacific subducon to the north and the east. Geology and paleomagnesm show that the Neo-Tethys and Pacific subducons are long-lived features that have been acve at least for the last 300 My, delivering a nearly connuous downwelling flow of cold material on the core-mantle boundary around the PA slow seismic velocity area, and therefore deliming a third “box” in the mantle. The longevity of these downwellings and mass conservaon in the mantle imply a nearly connuous generaon of hot upwellings within the PA box, as seen in our numerical simulaons and laboratory experiments.\nBased on the hypothesis that the PA is an ancient mantle structure linked to an old mantle plume, we have studied the thermal decay of this old plume using numerical modelling and laboratory experiments, as the first step, in supporng our findings, which are: (1) the East European (EE) lithosphere has been situated over the weakening PA upwelling for about 150-200 million years (this was obtained by careful paleomagnec, paleogeographic and global plate moon reconstrucons). (2) As the EE plaorm moved above PA in post-Jurassic mes, the vercal tectonic movements recorded in sedimentary hydrocarbon-rich basins show either hiatus/upli or insignificant subsidence (based on the tectonic analysis of EE sedimentary basins). (3) The basins have been thermally stewing above the PA upwelling, creang suitable condions for hydrocarbon maturaon (based on analycal modelling of heat conducon through the lithosphere and condions for hydrocarbon maturaon). We have presented in the manuscript convincing scienfic evidence for each of the three findings, which supports our conclusions. Namely, based on the plume decay model, global plate moon models, and conducve heang model inside the lithosphere, we have shown that the East European basins have been stewing thermally above the weakening PA plume for the last 150-200 My, creang suitable condions for hydrocarbon generaon.\nOne can sll speculate about the possible limitaons and uncertaines associated with our finding, for example, (i) whether the PA is a relavely recent negave seismic wave anomaly or it is a remnant feature of a mantle plume; (ii) if the PA is a fading mantle plume feature, whether it was linked to the Siberian trap area or to other plumes in the past; and (iii) whether a thermally fading mantle plume can generate magmac events, especially in the case of the think lithosphere. Karl Popper in his work “Alles Leben ist Problemlösen” (1994) said: ‘‘Although we do our best in science to find out the truth, we are conscious of the fact that we can never be sure to have found the truth. We know that our scienfic theories always remain hypotheses, but that in many cases, we can find out whether or not a new hypothesis is superior to an old one.” Therefore, only further invesgaons can confirm our findings or reject them based on new evidence.\nFinally, the paper would benefit from being read by a nave English speaker. It is not crical, but would help with smooth reading (in parcular making sure the tense of the verbs on lines 10-167 are consistent: gains-> gained, line 159: starts->started\nLine 173: “shrinks”-> shrunk etc.. and in quite a few places the ordering of words in the sentence, as well as missing or superfluous arcles.\nWe have been careful to revise the sentences accordingly. Also, we made further stylisc, orthographic, and syntacc revision of the text. And if the manuscript is accepted and the Editor recommends further English improvement, the authors would take care of it.\nReviewer #3:\nI am not convinced by the geological and geophysical evidence presented in this manuscript. The proposed scenario is that a mantle plume existed above the fixed Perm Anomaly, triggered the Siberian Traps 250 million years ago, and then affected the subsidence and thermal evoluon of the East European plaorm from 200 million years ago.\nWe are very sorry that we could not convince you. Let us start with the scenario you have menoned above.\nFirst at all, we did not propose this scenario. The hypothesis that the Perm Anomaly (PA) is linked to the Siberian Traps is NOT the subject of our paper, even if we discuss this possibility in the manuscript and in the Supplementary Information since it had been proposed in the literature in the past. Furthermore, in our research and findings, it is not relevant whether the plume is associated with the Siberian, Emeishan, or Icelandic LIPs. What maters is the existence of an upwelling in the geological past, which led to the heang of the lithosphere as it moved over the upwelling. Therefore, we have proposed that, in the case of an existing mantle plume (whatever its origin may be), the influence of this plume on the development of the sedimentary basins during the period of its thermal decay was profound in terms of tectonic and thermal evoluon.\nThe link between the Siberian traps and the PA was proposed by Lekic et al. (2012) based the restored locaon of the erupon of the Siberian traps (Torsvik et al., 2008), which is close to the projecon of the PA. In addion, there is another hypothesis proposed by Flament et al. (2017, Nat. Commun.) that the PA could be linked to the Emeishan LIP. However, Torsvik & Domeier (2017, Nat. Commun.) dismissed this hypothesis considering (i) the stability of large low-shear-velocity provinces (LLSVP), (ii) the locaon of the Emeishan LIP erupon site near the equator 260 My ago, and (iii) its associaon with the JASON and not the TUZO LLSVP.\nFinally, we do not discuss the origin of the PA anomaly per se, as it is not a subject of our paper; that is why, we placed the discussion of this topic in the Supplementary Information (see SD1), as supporng the main text but not a key issue for our paper.\nProblems with this scenario include (i) that no plume is imaged above the Perm Anomaly at present-day, (ii) that there is no volcanism in the East European plaorm, (iii) that the link between the Perm Anomaly and the Siberian Traps is not demonstrated in the manuscript, and (iv) that deep basal mantle structures may have been mobile over me.\n(i) According to analysis of seismic tomographic images (e.g., Fig. 1), the PA is likely to be a remnant part of potenally exisng mantle plume as it was suggested by the authors menoned above. If a plume is seismically imaged above the PA, the current manuscript would have no sense at all, as the interacon of a mantle plume with the lithosphere and impacts of prominent plumes on sedimentary basin evoluon are well-studied scienfic topics (e.g., let us just menon a classical paper on these topics by McKenzie, 1978). The new idea presented in our manuscript is that a weakened (but long survived) heat source associated with a thermally decaying plume (and hence seismically undetected) can influence the thermal condion of the lithosphere and basins, below which it was located during a long geological me (some 150-200 My).\n(ii) If the PA is a remnant of a mantle plume linked to the Siberian LIP, major magmac events were associated with the P-T boundary (Siberian traps). In the beginning of the Early Triassic, magmasm was sll acve in West Siberia (Nikishin et al., 2002). In the Late Triassic (225-207 My ago) magmasm was manifested as tholeiic and calc-alkali basalt erupons in the Turgay region to the southeast of the Urals (Bochkarev et al., 2000; Bochkarev, 2001). There have been no substanal indicaons of volcanism recorded in the EE lithosphere since the Early Jurassic mes. One of the reasons for that is that the EE lithosphere was thick enough to allow for magmac erupons. The thickness of the lithosphere exceeds 150 km in the studied area: this is visible in the S-wave velocity images of the EE lithosphere (see Fig. S3 of the Supplementary Information) ploted using the data from Shapiro & Ritzwoller (2002), and in the lithosphere-asthenosphere boundary maps based on the data from Hoggard et al. (2020) (Fig. S4 of the Supplementary Information) and from Artemieva (2006) (Fig. S5 of the Supplementary Information). According to Davis et al. (2015), the absence of magmac events in the studied region of the EE plaorm can be explained by the thick (>150 km) lithosphere. A relevant discussion is included in SD2 of the Supplementary Information. Also we revised the main text discussion briefly the points (see lines 186-194 of the revised manuscript with revision marked)\n(iii) The aim of our paper is not to explain and prove the link between the Perm Anomaly and the Siberian Traps, as it has already been done in a series of papers, one of which has been published in Nat. Commun. (Torsvik & Domeier, 2017). Please see more on this topic above.\n(iv) We agree with Reviewer 3 that there are no structures immobile over a long me in the convecng in the Earth’s mantle. Sll, there are two basic hypotheses related to the stability and mobility of mantle structures (e.g. plumes) based on two end-members views, which may each be supported by chosen geological, geophysical or geochemical observaons. One of the hypotheses is that the mantle plumes remain fixed in space, and another hypothesis is that the plumes are mobile deep structures. Of course, the reality is more complicated than any of the end-member hypotheses. Here, we assume that the PA structure remained reasonably fixed in space for at least 300 My based on the subducted lithosphere surrounding the PA (see Fig. 1).\nThe scenario presented in Figure 2 suggests a soluon to problem (i) in which the lifeme of the plume tail would be limited to 50 million years or less (specifically, Figure 2a,b,c). If this is the case, why are so many plume tails long-lived as demonstrated by oceanic hotspot tracks that span about 100 million years (see for example O'Neill et al., 2005)?\nThe exact me at which we see the tail disappearing depends on the isotherm that is being considered; a colder isotherm would disappear later. However, whatever the isotherms, the plume conduit will eventually be cut, and laboratory experiments are showing this effect on both the temperature and the velocity fields (Davaille & Vateville, 2005). Moreover, they show that within 60% of its lifeme, the velocity in most of the plume conduit would have already decayed to 30% of its overall maximum (reached during the «head» event). For a typical lower mantle viscosity, the total duraon of a plume would be about 200-300 My (e.g. Davaille & Vateville, 2005; Ismail-Zadeh et al, 2006), with about 100-150 My from a plume iniaon to its mature phase, which is characterized by a prominent plume tail throughout the mantle. Aer that, it takes addional 50-100 My for the plume tail to thermally decay and to disappear. Hence, plumes may remain acve for > 150 My generang oceanic hotspots tracks. Anyway, we have modified panels of Fig. 2 (b-f), considering the numerical results obtained at a higher Rayleigh number closer to the lab experiment of Fig. 2a to make clearer the effects of the thermal diffusion of the advected mantle plume.\nAs opposed to plume tails, plume heads are thought to be short-lived and to result in the erupon of large igneous provinces over 1 to 5 million years (Bryan and Ernst, 2008). In contrast, in Figure 2, the plume head persists for at least 200 million years. Is the model presented in Figure 2 applicable to Earth?\nBryan, Scot E., and Richard E. Ernst. \"Revised definion of large igneous provinces (LIPs).\" Earth-Science Reviews 86.1-4 (2008): 175-202.\nThe numerical model of the mantle plume evoluon presented in the manuscript does not consider melng, melt accumulaon beneath the lithosphere, melt penetraon through the lithosphere, volcanic erupons, lava flows, and a development of lava provinces. If the complicaons have been introduced in the model, we may expect the plume head to be short-lived. As melng and erupons are not topics of our research, we do not introduce these complicaons into the numerical model because this complicated model will not significantly enhance our numerical results related to diffusion of mantle plumes. The proposed simple numerical model explains the disappearing tail and the diminishing head with respect to the plume foot without melng and erupon accounted. We have added a relevant discussion into the manuscript (see lines 119-125 of the revised main text with the revision marked).\nAbout the applicability of the model to the Earth, we note that this model is based on the essenal equaons used in fluid mechanics, thermodynamics, and mantle convecon (Ismail-Zadeh and Tackley, 2010). No model can describe the dynamics of the Earth’s mantle in all detail but the dynamic processes in the planet can be idenfied in the framework of a considered model. The simpler model is (i.e., the fewer fing parameters are used), the easier is an interpretaon and the beter is understanding of numerical results. If a simple model can explain the reality, we do not need to complicate the model to explain the features which are not of research interest. “With four exponents I can fit an elephant” told Enrico Fermi on this case. A model introducing many complicaons is useful when it fits research goals. In our case, the most important was to show the evoluon of a fading mantle plume, and our simple model can do it.\nRegarding problem (ii), it is argued that the plume was waning and that the East European lithosphere is thick, prevenng melts from reaching the surface (l. 131-134). Davies et al. (2015) documented a long hotspot track beneath the eastern part of the Australian connent, and they showed that melng occurred where the lithosphere was less than 150 km thick. It is unclear that the thickness of the Eastern European lithosphere is more than 150 km in the eastern part of the region of interest (see for example Steinberger and Becker, 2018 or the global lithospheric thickness models available from Hoggard et al., 2020 at htps://osf.io/twksd/).\nDavies, D., Rawlinson, N., Iaffaldano, G. et al. Lithospheric controls on magma composion along Earth’s longest connental hotspot track. Nature 525, 511–514 (2015).\nHoggard, Mark J., et al. \"Global distribuon of sediment-hosted metals controlled by craton edge stability.\" Nature Geoscience 13.7 (2020): 504-510.\nSteinberger, Bernhard, and Thorsten W. Becker. \"A comparison of lithospheric thickness models.\" Tectonophysics 746 (2018): 325-338.\nWe thank you for the comment resulted in an analysis of the thickness of the EE lithosphere based on seismic (Shapiro & Ritzwoller, 2002; Steinberger & Becker, 2018; Hoggard et al., 2020) and heat flow data (Artemieva, 2006). The analysis has shown that the thickness of the lithosphere exceeds 150 km in the studied area. Please see Fig. S3 (based on data from Shapiro & Ritzwoller, 2002), Fig. S4 (based on the data from Hoggard et al., 2020; thanks for the link to the data), and Fig. S5 (based on data from Artemieva, 2006) in the SI. Hence, according to Davis et al. (2015), the long magmac gap observed in the studied region of the EE plaorm since the Early Jurassic mes can be explained by the thick (>150 km) lithosphere. The relevant discussion has been introduced (see lines 187-188, 192-194 of the revised manuscript with the revision marked) and in the Supplementary Information (see SD2).\nThe link between the Perm Anomaly and the Siberian Traps is proposed based on a reconstrucon from 1998 (Supplementary Figure 1) based on which it is argued that 'the EE plaorm moved north-eastward at the rate of about (5°N, 10°E) in My in the Middle to Late Triassic mes.' (l. 83-84). It would be helpful to quote a rate in degrees per million years.\nThis is replaced by 6 cm yr-1.\nIt would also be helpful to link the Perm Anomaly to the Siberian Traps as in Figure 3 of the main text (which links the Perm Anomaly to the Eastern European plaorm) by using a tectonic reconstrucon that extends at least back to 250 million years ago (examples include the reconstrucons of Mathews et al., 2016 or Young et al., 2019).\nYoung, Alexander, et al. \"Global kinemacs of tectonic plates and subducon zones since the late Paleozoic Era.\" Geoscience Froners 10.3 (2019): 989-1013.\nThe reconstrucon of the PA's posion relave to Siberia using APM by Mathews et al. (2016) is now presented in Fig. 3 of the manuscript and in Fig. S6 of the Supplementary Information. Their reconstrucon is similar to that by Kazmin and Natapov (1998) menoned in the Supplementary Information (SD1). According to this model, the PA was located to the south of the West Siberian Basin between 240 My and 260 My and likely to be responsible for the Permo-Triassic volcanism found in drilling and atributed to a plume by Saunders et al. (2004).\nIn the rebutal, it is argued that the focus of the study is the past 200 million years, however, in the absence of geophysical evidence for a plume and of any volcanism linked to the Perm Anomaly in the last 250 million years, it seems reasonable to request some geological evidence linking the Perm Anomaly to a mantle plume.\nGeophysical (seismological) evidence can illustrate only the present state of the mantle (everything beyond it is interpretaons). We are studying a fading mantle plume which is likely imaged by seismic tomography at the core-mantle boundary (the PA). As for the link between a mantle plume and the PA, this was discussed earlier and the link was proposed earlier by Lekic et al. (2012), Flament et al. (2017), and Torsvik & Domeier (2017) based on seismic and geodynamics studies. Paleogeographic and palinspasc reconstrucons based on paleomagnesm (Kazmin & Natapov, 1998) and true polar wander-corrected paleomagnec reconstrucons (Torsvik et al., 2006; Mathews et al., 2016) provide another evidence of a possible connecon between the PA and the Siberian trap province.\nIf the Perm Anomaly is linked to the Siberian Traps, should there be some volcanism between the Siberian Traps and the East European plaorm in places where the lithosphere is less than 150 km thick?\nIf the PA is linked to the Siberian traps, there is indeed evidence of volcanism in the West Siberian basin, where the seismic thickness of the lithosphere is likely to be less than 150 km (see, e.g. Fig. S1 of the Supplementary Information). See also our response about the magmasm between 250 My and 200 My ago in the West Siberia. A relevant discussion has been added in the Supplementary Information (SD2).\nWhile it would be easier to link deep seismically slow anomalies to past volcanic erupons if the structure of the deep Earth was rigid and fixed over me, Flament et al. (2022) showed that volcanic erupons could be linked to either fixed or mobile deep mantle structures.\nFlament, Nicolas, et al. \"Assembly of the basal mantle structure beneath Africa.\" Nature 603.7903 (2022): 846-851.\nThank you for the comment and reference to this interesng work. A discussion on this topic is added to SD1 of the Supplementary Information.\nSincerely,\nAlik Ismail-Zadeh, Anne Davaille, Jean Besse, and Yuri Volozh"}, {"round": 3, "reviewer_comments": {"reviewer_2": "The authors have satisfactorily addressed my comments/concerns. I am attaching an annotated manuscript with a few minor editorial suggestions (wording/grammar).", "reviewer_3": "I thank the authors for carefully considering my comments. I accept that if the Perm Anomaly was ever associated with any mantle plume, that mantle plume has not (yet) been imaged. There is therefore room for the proposed scenario, especially because the East European lithosphere is thick, which would have limited surface volcanic eruptions.\nIt would be helpful to clarify how applicable the experiment is to Earth in general and to the region of interest in particular. Figure two juxtaposes paleogeographic reconstructions with a plume model. One problem is that there are (as far as I can tell) no subduction zones or slabs in the model, but the history of subduction to the north of the Neo Tethys and to the East of Asia is long and complex (this is clear from Fig. S1). Also, how comparable is a regional cartesian 3D plume model to this region of Earth (slabs and plumes, spherical) over tens of millions of years?\nSome discussion was provided in the reply to reviewer comments, however, the discussion in the manuscript is limited to the implications of the model in terms of hydrocarbon generation. It would be helpful to discuss the merits and limitations of the model in the main text so that all readers (specialists and non-specialists) can appreciate them. It seems to me that much of the discussion is currently in the supplement (SD1. On the Perm Anomaly origin, SD2. Magmatism of the East European planform since the Triassic times, and SD5. Mantle plume diffusion modelling: Limitations, uncertainties, and sources of errors). A discussion of the applicability of the (slab-free?) model to the region of interest would also be helpful.\nThe presented experiment has been changed (it is based on a different Rayleigh number). Should more than one model be presented, and a sensitivity study be carried out?\nIn the rebuttal, it is stated that 'it is not relevant whether the plume is associated with the Siberian, Emeishan, or Icelandic LIPs.' I am not convinced as this has implications for the past motion of the plate carrying the LIP and/or the source of the plume (the Perm Anomaly).", "reviewer_4": "The paper addresses possible connections between a decaying mantle plume bellow a thick continental lithosphere, the respective paleo plate configuration and related thermal and subsidence inprints on the intracontinental basins located on this lithosphere. I consider the connection made between the thermal history recorded in the fill of intracontinental sedimentary basins as providing constraints for the plate-scale geodynamics at work during their deposition to be innovative. The mantle modelling part and the conductive cooling considerations are not new per se, but the integrated discussion with the basin record is new and links two traditionally separate scientific communities: the geodynamicists with the basin history analysts in search for hydrocarbons.\nThe authors connect the time frame of a slowly “disappearing” plume or in other words, a decaying thermal anomaly in the mantle beneath a thick and partly cratonic lithosphere to reduced subsidence rates or even uplift phases in the sedimentary basins on this continental lithosphere that nevertheless experience a thermal pulse. Such reduced subsidence and uplift and coeval thermal events are indeed recorded over much of North central Europe’s basins, even in the regions bordering the EEP to the West. Hiatuses in Mid-Late Jurassic deposits are widespread in northern Poland, Germany, Denmark and even the North Sea. There, the distinctly thinner Phanerozoic lithosphere also records magmatic activity coeval with the hiatus for which no real explanation had been found and hypotheses didn’t go any further than “thermal updoming” (Underhill et al.). To find hydrocarbons it was sufficient to know that it was hot and shallow and not why this was the case, but many studies prove that this was the case. In summary it was hot and shallow inspite of a very thick lithosphere and what the authors do in this paper is to quantitatively check if a slowly decaying former mantle plume can do the job. They further check consistency with plate reconstructions which adds an additional integration level.\nThe analytical thermal conductive modelling part doesn’t add much to the conclusion and definitely represents a very conservative estimate of any plume-related thermal effects. The internal heating is neglected, but can compose almost half of the heat in thick intracontinental (or even cratonic) crust and heat transport is very different in 3D than in 1D, especially in basins of the type considered here where radiogenic thermal blanketing severely influences the thermal field and its evolution (Stephenson, Scheck-Wenderoth and Maystrenko, Cacace and Scheck-Wenderoth). In addition, the boundary conditions chosen (lines 428-430) strongly control the result, so the result of this exercise is more a fitting exercise than a real forward simulation considering the physics at work. On the other hand, one has to start from somewhere and the authors justify their choices and provide transparency on the latter. In the end they are able to give an estimate of how the influence of the plume must have been to reach the measured and preserved maturity of the organic matter in the basins in the right time frame and this represents a value in itself. That they are able to connect the two time frames and dynamics (mantle heat and heat transport in the vertically moving lithosphere) with each other and with plate motion reconstructions makes the paper worth to be published.\nA few minor comments: I am sure the authors are aware of these works, but I would like to see a reference that can be short or partly given in the Supplementary on how far the findings of the authors are consistent with them as they addressed\n• the plume issue in 3D and gave first ideas on how the thermal imprints of plumes on cratonic lithosphere would evolve: Burov, E. & Gerya, T. 2014: https://doi.org/10.1038/nature13703 and Koptev et al., 2016 : https://doi.org/10.1016/j.gsf.2015.11.002\n• The Jurassic plume effects on Northern Europe without much of a larger plate tectonic frame: Underhill, J.R., Partington, M.A., 1993. Jurassic thermal doming and deflation in the North Sea: implications of the sequence stratigraphic evidence. In: Parker, J.R. (Ed.), Petroleum Geology of Northwest Europe: Proceedings of the 4th Conference. The Geological Society, London, pp. 337– 345.\n• thermal cooling and radiogenic heat contribution in intracontinental basins: Stephenson, 2009. Nat. Geosci; https://doi.org/10.1038/NGEO479 or Cacace, M. & Scheck-Wenderoth, 2016 JGR: https://doi.org/10.1002/2015JB012682\n• hydrocarbons at plume affected passive continental margins: Anka et al: 2010 Marine and Petroleum Geology. https://doi.org/10.1016/j.marpetgeo.2009.08.015\nFigure 2 normalized subsidence has no vertical scale and normalization info in Methods doesn’t help to understand what is shown…\nData availability statement (line 432) doesn’t say anything. Where will the data be made available?\nThere are still a few spelling errors in the manuscript and the SI"}, "author_response": "RESPONSE TO THE REVIEWERS' COMMENTS (the reviewers’ comments are marked by red)\nReviewer #2 (Remarks to the Author):\nThe authors have satisfactorily addressed my comments/concerns. I am attaching an annotated manuscript with a few minor editorial suggestions (wording/grammar).\nMany thanks for the suggestions. We have implemented them in the final manuscript.\nReviewer #3 (Remarks to the Author):\nI thank the authors for carefully considering my comments. I accept that if the Perm Anomaly was ever associated with any mantle plume, that mantle plume has not (yet) been imaged. There is therefore room for the proposed scenario, especially because the East European lithosphere is thick, which would have limited surface volcanic eruptions.\nWe thank the Reviewer as well for careful dedication to the manuscript’s review and for many constructive comments and suggestions. We would like to reiterate our comments related to the activity of the PA plume in the geological past and its present seismic imaging. We note that “if the Perm Anomaly was ever associated with any mantle plume” in the past, a prominent shape of the mantle plume could never be seismically imaged today, as the plume would have already thermally faded given large geological time lapse. This is what has become the foundation of our work.\nIt would be helpful to clarify how applicable the experiment is to Earth in general and to the region of interest in particular. Figure 2 juxtaposes paleogeographic reconstructions with a plume model. One problem is that there are (as far as I can tell) no subduction zones or slabs in the model, but the history of subduction to the north of the Neo Tethys and to the East of Asia is long and complex (this is clear from Fig. S1).\nBoth laboratory and numerical experiments presented in this manuscript are applicable to the Earth dynamics and particularly to thermal plume evolution in the mantle, as both experiments describe the fluid (mantle) thermodynamics and allow generating thermal convective patterns (plumes and slabs). Moreover, the aim of Fig. 2 was to present schematically a mantle plume evolution beneath the studied region, and hence, only the hot isothermal surface (T=3000K) obtained in the numerical model was presented in the figure. If an isothermal surface at T=600-800K, for example, were presented, it would show a descending slab. However, lithospheric slabs are not the subject of this study, and by imaging them, we would introduce unnecessarily complications into the figure. A clarification is added to the main text of the MS (lines 302303).\nFurthermore, the suggestion to model the evolution of the mantle upwelling and the lithosphere subduction in the region is fine, although we note that this suggestion is not related to the topic of this manuscript and to the essential conclusion of this work and will be considered by the authors in a future study.\nAlso, how comparable is a regional cartesian 3D plume model to this region of Earth (slabs and plumes, spherical) over tens of millions of years?\nWe would like to refer the Reviewer to the work by O'Farrell et al. (2013; https://doi.org/10.1093/gji/ggs053) on the comparison of a spherical shell model and 3D Cartesian (plane-layer) model of mantle convection, and to their conclusion that for Rayleigh numbers of greater than 105 (as in our case), the mean temperatures between the spherical shell and 3D Cartesian models “roughly converge for solution domain size(s) of 3 × 3 × 1” (the same solution domain size as used in the numerical modelling of thermal plume decay presented in this work). A related discussion is added to the SI (SD5).\nThe volume of the main body of the paper is limited, and, therefore, all the information, which the authors considered to be not essentially important for the conclusion of the paper, has been moved to the SI. Also, we note that the numerical model of mantle plume diffusion is not a ‘slab-free’ model as explained above.\nThe presented experiment has been changed (it is based on a different Rayleigh number). Should more than one model be presented, and a sensitivity study be carried out?\nThank you for the comment. A relevant discussion is added to the SI (SD5).\nIn the rebutal, it is stated that 'it is not relevant whether the plume is associated with the Siberian, Emeishan, or Icelandic LIPs.' I am not convinced as this has implications for the past motion of the plate carrying the LIP and/or the source of the plume (the Perm Anomaly).\nOur study is not related to the origin of the mantle plume, which remnant is seismically imaged as the PA. We discussed several studies related to this topic in the SI (SD1). One of the goals of our study was to understand the thermal evolution of the mantle beneath the EE platform for the last 200 My assuming that the seismically modelled PA at the core-mantle boundary is a relic of the mantle plume, which was active for a longer period of the geological time. Therefore, we analysed the evolution of the PA plume and the plate movement over the PA for the last 200 My. That is the reason of why we do not insist on the primary geographic origin of the PA plume, although this plume could very well be located beneath Siberia in the Late Permian times, as proposed by several studies mentioned in SI (SD1).\nReviewer #4 (Remarks to the Author):\nThe paper addresses possible connections between a decaying mantle plume bellow a thick continental lithosphere, the respective paleo plate configuration and related thermal and subsidence inprints on the intracontinental basins located on this lithosphere. I consider the connection made between the thermal history recorded in the fill of intracontinental sedimentary basins as providing constraints for the plate-scale geodynamics at work during their deposition to be innovative. The mantle modelling part and the conductive cooling considerations are not new per se, but the integrated discussion with the basin record is new and links two traditionally separate scientific communities: the geodynamicists with the basin history analysts in search for hydrocarbons.\nThank you very much for the comments.\nThe authors connect the time frame of a slowly “disappearing” plume or in other words, a decaying thermal anomaly in the mantle beneath a thick and partly cratonic lithosphere to reduced subsidence rates or even uplift phases in the sedimentary basins on this continental lithosphere that nevertheless experience a thermal pulse. Such reduced subsidence and uplift and coeval thermal events are indeed recorded over much of North central Europe’s basins, even in the regions bordering the EEP to the West. Hiatuses in Mid-Late Jurassic deposits are widespread in northern Poland, Germany, Denmark and even the North Sea. There, the distinctly thinner Phanerozoic lithosphere also records magmatic activity coeval with the hiatus for which no real explanation had been found and hypotheses didn’t go any further than “thermal updoming” (Underhill et al.). To find hydrocarbons it was sufficient to know that it was hot and shallow and not why this was the case, but many studies prove that this was the case. In summary it was hot and shallow inspite of a very thick lithosphere and what the authors do in this paper is to quantitatively check if a slowly decaying former mantle plume can do the job. They further check consistency with plate reconstructions which adds an additional integration level.\nWe appreciate the comment and have added some discussion related to the doming in the main body of the manuscript (lines 256-258).\nThe analytical thermal conductive modelling part doesn’t add much to the conclusion and definitely represents a very conservative estimate of any plume-related thermal effects. The internal heating is neglected, but can compose almost half of the heat in thick intracontinental (or even cratonic) crust and heat transport is very different in 3D than in 1D, especially in basins of the type considered here where radiogenic thermal blanketing severely influences the thermal field and its evolution (Stephenson, Scheck-Wenderoth and Maystrenko, Cacace and Scheck-Wenderoth). In addition, the boundary conditions chosen (lines 428430) strongly control the result, so the result of this exercise is more a fitting exercise than a real forward simulation considering the physics at work. On the other hand, one has to start from somewhere and the authors justify their choices and provide transparency on the latter. In the end they are able to give an estimate of how the influence of the plume must have been to reach the measured and preserved maturity of the organic matter in the basins in the right time frame and this represents a value in itself. That they are able to connect the two time frames and dynamics (mantle heat and heat transport in the vertically moving lithosphere) with each other and with plate motion reconstructions makes the paper worth to be published.\nThank you very much for the constructive comment. Although our aim was to analyse the specific contribution of a mantle plume to the heat transfer in the lithosphere, we have revised the model of the conductive heat transfer to include the effect of internal heating in the lithosphere. Namely, we introduce another geotherm as the initial thermal state of the lithosphere before it came to the contact with a mantle plume. The geotherm (as explained now in the Methods) was modelled for the surface heat flux 45 mW m-2 accounting for the temperature- and pressure-dependent thermal conductivity and for a heat production within the lower crustal rocks of 0.4 μW m-3. The results of the modelling have changed, but they have not changed the conclusion of the work. The manuscript has been revised accordingly (lines 171-180, 359-383).\nA few minor comments: I am sure the authors are aware of these works, but I would like to see a reference that can be short or partly given in the Supplementary on how far the findings of the authors are consistent with them as they addressed:\n• the plume issue in 3D and gave first ideas on how the thermal imprints of plumes on cratonic lithosphere would evolve: Burov, E. & Gerya, T. 2014: https://doi.org/10.1038/nature13703 and Koptev et al., 2016 : https://doi.org/10.1016/j.gsf.2015.11.002\n• The Jurassic plume effects on Northern Europe without much of a larger plate tectonic frame: Underhill, J.R., Partington, M.A., 1993. Jurassic thermal doming and deflation in the North Sea: implications of the sequence stratigraphic evidence. In: Parker, J.R. (Ed.), Petroleum Geology of Northwest Europe: Proceedings of the 4th Conference. The Geological Society, London, pp. 337– 345.\n• thermal cooling and radiogenic heat contribution in intracontinental basins: Stephenson, 2009. Nat. Geosci; https://doi.org/10.1038/NGEO479 or Cacace, M. & Scheck-Wenderoth, 2016 JGR: https://doi.org/10.1002/2015JB012682\n• hydrocarbons at plume affected passive continental margins: Anka et al: 2010 Marine and Petroleum Geology. https://doi.org/10.1016/j.marpetgeo.2009.08.015\nDiscussion and some references have been added to the SI (SD5).\nThe vertical scale is not needed, as the curves are normalized, and their vertical size ranges from 0 to 1. The normalisation procedure is rewriten in the manuscript to clarify the procedure (lines 348-356).\nData availability statement (line 432) doesn’t say anything. Where will the data be made available?\nData will be available in a ‘github’ site before the paper is published. It is now mentioned in the manuscript.\nThere are still a few spelling errors in the manuscript and the SI.\nWe have fixed them.\nWe thank the reviewer for the constructive comments."}]

Decision letter