Mode of intracontinental mountain building controlled by lower crustal composition and mantle lithosphere depletion

Domain: earth_science
Published: 2025-10-24
Editorial outcome: major_revision

Abstract
Tectonic plate convergence is accommodated across the continental lithosphere via discrete lithospheric subduction or distributed shortening and thickening. These end-member deformation modes control intra-plate mountain building, but their selection mechanism remains unclear. The variable composition of the continental crust and lithospheric mantle, which impacts its density and rheology, can be inferred by the distribution of magnetic-indicated crustal iron. Here we demonstrate that vertically coherent pure-shear shortening dominated the active Tian Shan orogen, central Asia, based on high-resolution aeromagnetic imaging and geophysical-geodetic observations. Integrating these findings with thermomechanical collisional models reveals that the mode of intracontinental deformation depends on contrasts in lower crust composition and mantle lithosphere depletion between the converging continents and central orogenic region. Distributed shortening prevails when the converging continents have a more iron-enriched mafic crust and iron-depleted mantle lithosphere when compared to the intervening orogenic region. Conversely, continental subduction occurs without such lithospheric contrasts. This result explains how the Tian Shan orogen formed via distributed lithospheric thickening without continental subduction or underthrusting. Our interpretation imply that iron distribution in the crust correlates with lithospheric compositional, density, and rheological structure, which impacts the preservation and destruction of Earth’s continents, including long-lived cratons, during intracontinental orogeny.

Introduction
Despite its success in quantifying the kinematics of rigid oceanic simple-shear orogeny with focused deformation at the continental plates, classical plate tectonic theory fails to account for the wide- spread occurrence of the distributed continental deformation controlled by the non-rigid behavior of the continents1. Continental deformation, best expressed by intracontinental mountain building and exemplified by the development of the Tibetan plateau and Tian Shan in the Cenozoic Indo-Asia collision zone1,2, may be accommodated by the following three end-member modes: (1) discrete subduction or underthrusting interface3–8, (2) distributed pure-shear orogeny with shortening strain distributed across the entire orogen6,9–11, or (3) ductile flow in the middle and/or lower crust causing crustal thickening or thinning12,13. Geodynamic modeling in the past decades shows that the mode of continental deformation is dictated by the thermal state and mechanical strength of the continental lithosphere2,10,14–16. Although the iron content in the continental crust and the mantle lithosphere impacts its density distribution17,18 and viscous rheology19, the role of iron enrichment and depletion in controlling continental deformation has not been systematically assessed.

The iron concentration within the continent lithosphere depends on the degree of mafic-ultramafic melt extraction during partial melting of the mantle lithosphere protolith; more melt depletion of the protolith may result in a less dense and thicker mantle lithosphere17,20,21. Thereby, the partitioning of lithospheric iron predominantly occurs during the formation of oceanic and/or continental crust, which in time may become spatially disconnected with the respective melt-depleted continental lithosphere20,21. As the result of multi-stage formation of the continental lithosphere20,21, the composition of its crustal and mantle layers can be broadly variable, which affects its rheological and density structure and thus its tectonic response to plate convergence processes.

The distribution of iron in the continent lithosphere can therefore be used as one of the key indicators of regional variations in lithospheric composition and rheological structure. However, quantifying the iron distribution in a continental lithosphere is challenging because the occasionally available xenoliths sample only a small fraction of the continental lithosphere below18 with limited spatial resolution. Fortunately, iron enrichment and its distinct magnetic signature in the crust can be detected by aeromagnetic anomalies, and the associated iron distribution in the continental lithosphere can be quantified using inverse methods22.

To leverage this knowledge and examine the role of iron redistribution in controlling continental deformation, here we investigated the lithospheric structure of the Tian Shan mountain belt, central Asia, which lies ~1500 km to the north of the Cenozoic India-Asia plate boundary (Fig. 1a). The Tian Shan is a well-known example of intracontinental orogeny that is actively deforming due to the far-field impacts of India-Asia convergence1,5. The mountain range is bounded by the Tarim and Kazakhstan blocks5,6, to the south and north, respectively. The Tian Shan orogen initiated in the Early Paleozoic, following the long-lived accretion of a series of microcontinents and island arcs and the subduction of the Paleo-Asian Ocean23,24. After Triassic-Jurassic tectonic quiescence25,26, the Tian Shan experienced localized uplift and erosion during the Cretaceous-Paleocene27, accelerated deformation in the Miocene28, and is still being actively shortened today29. Crustal shortening is evenly distributed across the orogen as revealed by geodesy30,31, Quaternary deformation studies29, and crustal seismicity24. Shear-wave splitting analysis of core-refracted XKS waves shows the fast orientations of lithospheric anisotropic fabrics parallel the trend of the Tian Shan orogen6. Receiver function studies show a relatively shallow Moho beneath the Kazakhstan and Tarim blocks at ~40–50 km depth that becomes deeper underneath the Tian Shan at ~60–70 km depth4,5. The Moho is imbricated by a series of thrusts beneath the Tian Shan5. Therefore, Cenozoic crustal deformation has been distributed across the Tian Shan during progressive India-Asia convergence32.

Here, we show how iron enrichment in the lower crust of two orogen-bounding continents is correlated with the pure-shear mode of deformation across the 1500 km-long and 200–300 km-wide active Tian Shan belt in central Asia (Fig. 1). Our numerical modeling demonstrates that such correlation can be explained by the presence of a depleted iron-poor mantle lithosphere that is rheologically coupled to the iron-rich mafic lower crust that bounds the two sides of the Tian Shan belt, the latter of which is characterized by more felsic iron-poor lower crust and less depleted, thinner mantle lithosphere.

Results
Figure 2a shows a high-resolution total-field aeromagnetic anomaly map of the Tian Shan and its adjacent regions (Supplementary Figs. S1–S3; “Methods”). The aeromagnetic imaging reveals a series of long-wavelength, high-amplitude positive anomalies distributed across the Tarim and Kazakhstan blocks, and more diffuse short-wavelength signals are generally observed within the Tian Shan interior (Fig. 2a and Supplementary Fig. S3). The northern Tarim block is characterized by long-wavelength, high-amplitude, positive magnetic highs (such as labeled A–C and circled-H in Fig. 2a) and neutral magnetic (or reversely magnetized) lows, such as along the northern margin of the Tarim craton (N in Fig. 2a). This magnetic character changes abruptly to the north at the Southern Tian Shan thrust belt (Fig. 2a), where the interior of the Tian Shan orogen is characterized by negative magnetic anomalies except for a few local short-wavelength magnetic highs. Farther north across the Northern Tian Shan fault, the Kazakhstan block is also dominated by long-wavelength, high-amplitude, positive magnetic highs (labeled D and E in Fig. 2a). The longer wavelength signals observed in the craton-like blocks are lower crustal-scale features, whereas the shorter wavelength anomalies in the Tian Shan are shallower (upper crust) (Supplementary Figs. S4 and S5; “Methods”).

Mafic lower crust and depleted mantle lithosphere drives pure-shear orogeny
A compilation of global lower crust samples shows an inverse correlation between iron and silica contents regardless of age (Fig. 4). Therefore, the high-amplitude, long-wavelength, positive magnetic anomalies of the Tarim and Kazakhstan blocks reveal that their lower crust must be more mafic than the Tian Shan orogen. Crustal scale inversions of the aeromagnetic anomaly reveal that the interpreted mafic bodies are voluminous and thick (>25 km) in blocks’ lower crust (Supplementary Figs. S4 and S5; “Methods”), indicative of a high-volume percentage of magnetite (Fe3O4) (Fig. 2b and Supplementary Figs. S6 and S7; “Methods”). In contrast, the upper crust of the Tian Shan orogen and the bounding blocks is characterized by extensive high-frequency magnetic patches (Supplementary Figs. S6 and S7) that correspond to isolated mafic magmatic bodies. Seismic and tomographic studies have imaged high-velocity crustal layers across the Tarim block, interpreted as mafic zones embedded in the middle-lower crust38. Conversely, the Tian Shan orogen, which involved Paleozoic accretion of island arcs23, should have a more felsic iron-poor lower crust possibly formed by mafic-crust delamination and felsic lower crust relamination during the arc-related crust-mantle differentiation process39. Globally, the presence of a high-Vp and highly magnetic lower crust within rigid continental blocks and the occurrence of a low-Vp and weakly magnetic lower crust in Paleozoic-Mesozoic orogens suggests that underplating of mantle-generated mafic melts may have predominantly occurred in cratonic continental areas and not in recent orogens40,41.

Voluminous mafic rocks in the lower crust contribute to higher mechanical strength for the orogen-bounding cratonic blocks compared with the Tian Shan orogen42. Furthermore, the cratonic continents should have a relatively old, thick and depleted mantle lithosphere17,20,21, which will likely contrast with the younger, thinner and more fertile lithospheric mantle of the Tian Shan orogen. Therefore, we argue that high-amplitude, long-wavelength magnetic anomalies (Figs. 2a, 3 and 4) reveal a lithosphere with a predominantly mafic lower crust underlain by a more depleted (i.e., Mg-rich and Fe-poor) buoyant, rheologically strong, and thick cratonic lithospheric mantle17,18 (Fig. 3b, c). The observed global correlation of the rheological strength and thickness of the continental lithosphere with its age2,43,44 is consistent with ancient cratons having a more mafic lower crust and a coupled refractory mantle keel.

Accordingly, we propose that such positively buoyant, iron-depleted cratonic mantle supports the overlying rigid iron-rich mafic crust to act as a stiff indenter to partition strain localization in the Tian Shan lithosphere with a relatively weak, felsic crust and coupled iron-enriched (i.e., less depleted and rheologically weaker) lithospheric mantle (Fig. 3). Iron depletion in the Tarim and Kazakhstan lithospheric mantle inhibits their subduction, which in turn favors pure-shear construction of the Tian Shan orogen (Fig. 3).

Methods
Aeromagnetic data
A regional total-field magnetic map of the Tian Shan and surrounding regions was constructed to examine the crustal magnetic character. Aeromagnetic data within and around the Tian Shan were previously acquired to aid petroleum and mineral exploration before the 2000s by the China Aero Geophysical Survey and Remote Sensing Center for Natural Resources (AGRS) (Supplementary Fig. S1), China Geological Survey. The aeromagnetic compilation combines more than 20 aero-magnetic surveys and a total of ~0.67 million-line-km, flown between the 1960s and 2000s with variable flight-line spacings (Supplementary Fig. S1). The original data were processed following previously reported protocols at the China Geological Survey-AGRS (Beijing)64,65. To fill the aeromagnetic data gaps, the aeromagnetic dataset (5-km grid and 1-km altitude) covering the China mainland, offshore and adjacent areas (CMOA) was merged into the AGRS aeromagnetic data66,67 (Supplementary Fig. S1). To be consistent with the CMOA dataset, the AGRS dataset was first processed by upward-continuation to 1 km and then resampled at 5 km grid, which was all integrated into the Geosoft Oasis Montaj software package. The total-field magnetic anomalies within and around the Tian Shan were finally compiled with 5-km resolution at 1 km altitude. Finally, the AGRS and CMOA reprocessed aeromagnetic datasets were stitched together (Supplementary Fig. S2) and processed via the differential reduction to the pole method68 to accurately relocate magnetic source locations and boundaries of the Tian Shan and its environs (Supplementary Fig. S3).

Long-wavelength magnetic anomaly analysis and crustal iron content estimation
It is thought that lower crustal mafic granulite is sufficiently magnetized to account for amplitudes of long-wavelength magnetic anomalies, corresponding to high-grade metamorphic rocks of deep-seated origin22,69. The major magnetic carriers are magnetite, which is a source of long-wavelength magnetic anomalies22,69. The amplitude and spatial patterns of magnetic anomalies are primarily caused by variations in the amount, type, and distribution of magnetic minerals, mainly magnetite (Fe3O4) with a Curie isotherm of 580 °C and its solid solutions (FeTiO3, Fe2TiO4) in crustal rocks22,69,70 (Supplementary Fig. S4a). The minimum and maximum magnetic susceptibilities from the China mainland dataset (248,756 field rock samples)71 (Supplementary Fig. S4b) correspond to two end-member rock types for the lower crust: pyroxene-dominated (iron-rich) and plagioclase-dominated (iron-poor) rocks. We assume the long-wavelength magnetic highs represent the location of mafic iron-rich domains in the lower crust (Supplementary Fig. S4).

To verify whether the long-wavelength magnetic highs reflect iron-rich mafic zones embedded within the lower crust, we used the upward continuation method to filter deeper versus shallow signals at depths of 5, 10, 20, 30, and 40 km (Supplementary Fig. S5). The positive long-wavelength magnetic signals within the Tian Shan-bounding blocks remain stable, whereas the short-wavelength magnetic highs within the Tian Shan orogens become gradually dampened. Constrained by the 15 km thickness of sedimentary rock sequences in the upper crust72,73, the thickness of the magnetic layer in the crust could be >25 km, assuming that the lower bound of the crust-scale magnetic zone is >40 km in thickness. We further employ the three-dimensional (3D) regularization inversion74 to image the crustal structure of induced magnetization intensity (M) Supplementary Fig. S6, ignoring remnant magnetism. The model consists of 271 × 121 × 60 grid cells at a resolution of 5 km × 5 km × 1 km. The lower crust of the Tarim and Kazakhstan blocks are strikingly expressed by regional high-value magnetic zones, which are the origin of these long-wavelength magnetic highs, while that of the Tian Shan presents no magnetism (Supplementary Figs. S6, S7).

In lower crustal granulite-grade rocks, bulk iron content may indicate the degree of melting of the underlying lithospheric mantle18 because enriched iron in the lower crust may reflect depletion and extraction from the underlying mantle lithosphere during melting. To approximately quantify the crust-scale iron content, we used the magnetite content in the crust as an indicator because iron-rich rocks have a higher magnetite-producing potential than iron-poor rocks in the lower crust granulite-grade rocks22,69,70. To a very good approximation, the induced magnetization is directly proportional to magnetite content. Magnetite content was calculated using an empirical correlation between the volume percentage of magnetite (Vmag) in the source rock, and the volume magnetic susceptibility (k) is calculated from k=Mμ0/ΔT75, where M is the induced magnetization intensity, μ0 is the magnetic permeability of free space (μ0 = 4π × 10−7 H/m), and ΔT is the total geomagnetic field intensity of Tian Shan and its surrounding domains (ΔT = 55000 nT).

Thermo-mechanical modeling
We use the thermomechanical code I2VIS76. The governing equations of conservation of momentum, mass and energy are resolved by using a conservative finite difference method and a marker-in-cell technique applied on a staggered non-uniform Eulerian grid. It simulates creeping flow due to thermal and chemical buoyancy forces, and accounts for the effects of adiabatic, shear, latent and radioactive heating. The initial model is 2200 km wide and 400 km deep, and is resolved with a uniform 201 × 401 rectangular grid. Over 3.6 million Lagrangian markers are randomly put in the model domain, which are used to advect material properties defined at the Eulerian mesh. The deformation of all materials is governed by visco-plastic rheology, which take account of plastic yielding at shallow depths and low temperatures, and dislocation creep at greater depths and temperatures. The details of the method can be found in the reference76.

The initial model is composed of three continental blocks: an orogen in the middle and two cratonic continents at both sides (Supplementary Fig. S13). Both the continents and orogen initially have a 40 km-thick crust (the upper and lower crust are 20 km thick) and an 80 km-thick lithospheric mantle, giving a total lithospheric thickness of 120 km. One small seed is imposed at the bottom of the orogen crust, which is used to induce deformation localization at the center of the model. According to the peneplanation of Tian Shan during the Mesozoic tectonic quiescence26, the initial pre-Cenozoic Moho interface beneath the Tian Shan could be approximately flat.

Two crustal-scale weak zones are placed at the boundaries between the continent and orogen, which are used to facilitate the continental underthrusting beneath the orogen. For the continents, the initial temperature increases linearly from 0 °C at the model surface to 600 °C at the crust base with a geothermal gradient of 15 °C/km, and continues to increase to 1330 °C at the lithosphere base with a geothermal gradient of ~9.1 °C/km. For the orogen, the temperature at the Moho is 100 °C hotter than that of the craton, giving a geothermal gradient of 17.5 °C/km (Supplementary Fig. S13). An adiabatic gradient of 0.5 °C/km is used for the sub-lithosphere mantle. All mechanical boundary conditions are free slip, except for the lower boundary, where an external free slip boundary condition is applied77. The thermal boundary conditions are constant temperature (273 K) on the top, remote fixed temperature on the bottom77, and insulating (no horizontal heat flow) on both sides. The surface of the rocky portion is treated as an internal free surface by placing an overlying 20 km-thick ‘sticky air’78, which is characterized by low viscosity (1018 Pa·s) and low density of 1 kg·m−3. A convergence rate of 10 mm/yr is imposed at the right side to drive the orogeny (Fig. 4 and Supplementary Fig. S13).

A laboratory-based viscoplastic rheology is used for all the materials. Plastic deformation follows a pressure-dependent Drucker-Prager yield criterion79:
σyield = C + Psin φeff
where σyield is the yield stress; P is the pressure; C is the cohesion at P = 0; φeff is the effective internal frictional angle that integrates the effects of internal frictional angle and pore fluid coefficient;
ηplastic = σyield / (2 εII)
εII = 0.5 εij εij 1/2 is the second invariant of the strain rate tensor εij; ηplastic is the viscosity for plastic rheology.

The viscosity for dislocation creep depends on strain rate, pressure and temperature, and can be expressed in terms of deformation invariants as follows79:
ηcreep = fA D−1/n εII(1−n)/n exp(Ea + PV)/nRT
where R is the universal gas constant, T is the absolute temperature, and f is a scaling factor80. The rheological parameters, A, n, Ea and V, are the material constant, stress exponent, activation energy and activation volume, respectively.

The effective viscosity ηeff is given by:
ηeff = min(ηplastic, ηcreep)

The laboratory-derived flow laws of ‘wet quartzite’ and ‘felsic granulite’79 are used for the orogen upper and lower crust, respectively. A scaled ‘dry olivine’ flow law (DOL × 0.25) is used for the orogen mantle80, and a ‘wet olivine’ flow law (WOL × 2) for the sub-lithospheric mantle79. The flow law for the craton mantle is a ‘dry olivine’ for an iron-depletion case, and a scaled ‘dry olivine’ (DOL × 0.25) for an iron-rich case. We use ‘wet quartzite’ and zero friction angle to represent crustal weak zones and seeds. The rheological parameters used in the study are presented in Supplementary Table S1.

All materials have a temperature- and pressure-dependent density:
ρ = ρ0(1 − α(T − T0))(1 + β(P − P0))
where ρ0 is the referenced density at room condition (P0 = 0.1 MPa and T0 = 298 K), and α = 3 × 10−5 K−1 and β = 1 × 10−5 MPa−1 are the coefficients of thermal expansion and compressibility, respectively. We employ depletion density to capture the effect of Fe depletion on the density of the lithospheric mantle (i.e., Mg# = 100 × Mg/(Mg+Fe))18. The depletion density with respect to the orogen lithospheric mantle measures the chemical depletion of the continent lithospheric mantle due to melt extraction, such as when the cratonic continent lithosphere was generated from Early-Earth higher mantle potential temperature81 and impinged by a hot mantle plume82, like the Permian plume-lithosphere interaction occurred in the Tarim Basin63,64. Here, it is expressed as Δρ = ρOLM − ρCLM, where ρOLM and ρCLM represent the reference density of the orogen and continent lithospheric mantle, respectively. The Δρ values range from −60 to +60 kg/m3, which are consistent with variations in lithospheric mantle peridotite density spanning −2.0% and +2.0%60,83. The more positive Δρ values correspond to greater percentages of partial melting that a continent lithospheric mantle experienced, whereas a negative Δρ value geologically corresponds to metasomatism of the continent lithospheric mantle peridotite. The reference density for the orogenic lithospheric mantle is fixed at 3300 kg/m3.

To assess the sensitivity of lithospheric mantle depletion density and lower crustal rheology with mafic/felsic compositions on mountain building, we conducted 20 additional model tests (Supplementary Table S2). In these models, the initial thermal structure of the bounding blocks is kept the same as the orogen. The depletion of the mantle lithosphere exerts a strong control on the mode of collisional deformation (Supplementary Fig. S14). A more mafic lower crust leads to pure-shear deformation (Supplementary Fig. S15a), whereas a more felsic lower crust leads to more limited underthrusting as pure-shear deformation (Supplementary Fig. S15b). Moreover, the thermal state of the orogenic lithosphere is also an important factor controlling the style of orogenic crustal deformation (Supplementary Fig. S16). In contrast to the pure-shear mode in the hot orogen model (Supplementary Fig. S16a, S16b), the model without lateral temperature variations behaves as a simple-shear mode, with the continent lower crust deeply underthrusting/subducting under the orogen (Supplementary Fig. S16c, S16d).

Based on parameter sensitivity analysis, integrated with the multi-method geological-geophysical data, we use the numerical simulations to test the validity and viability of our hypothesis that the lithosphere mantle depletion and associated crustal composition reflected by spatial variations in the Fe content are the two critical factors controlling the style of orogenic deformation.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This study tries to investigate mode of intracontinental mountain building by using Tianshan orogenic belt as an example. However, my opinion seems to be not supportive. Because there are so many critical issues should be addressed.\n1. One of the biggest problems in this paper is that there are already a lot of deep reflection seismic data including the book of Xiao Y.C., Liu, X., and Gao, R. et al. (2004) about the Tianshan orogenic belt, which can clearly reveal the orogenic pattern, but the authors seem to ignore it.\n2. The other major issue with the paper is regarding the interpretation of aeromagnetic data, which happens to be a crucial piece of evidence supporting the final conclusions of this study. The authors attempt to use the relationship between aeromagnetic data and Fe-bearing minerals in the crust to explain the tectonic mechanism. However, based on my long-term experience and deep understanding, such a relationship is evidently questionable. This is because aeromagnetic anomalies that could reflect such large-scale, deep-seated (crustal-scale) mineral magnetic anomalies would necessarily be low-intensity long-wavelength components, which are not demonstrated or reflected in the data processing presented in the paper. Regional aeromagnetic anomalies typically reflect regional metamorphic basement (including metamorphic magnetite, etc.), which is a basic global pattern. From a geophysical perspective, it is recommended to use gravity data for applications that aim to reflect large-scale orogenic styles because the long-wavelength anomalies in Bouguer gravity data reflect changes at the crust-mantle boundary, which may explain orogenic events more effectively than aeromagnetic data.\n3. The authors tried to validate the orogenic model using numerical simulation methods, but a major flaw is that the results of numerical simulations are highly dependent on initial and boundary conditions. However, this study fails to analyze the parameter sensitivity of these simulation results. This lack of analysis means that the conclusions drawn may not necessarily be universally applicable or stable, but rather specific to certain conditions or scenarios.", "reviewer_2": "Review:\nManuscript titled “Mode of intracontinental mountain building controlled by lower crustal composition and mantle lithosphere depletion” by Xu et al. submitted to the Nat. Comms proposes and demonstrates that the iron content in the continental crust and lithospheric mantle, could control the style of continental collisions, pure shear type-distributed shortening, (e.g., Tien Shan) vs discrete shortening involving subduction of the continental lithosphere-simple shear, (e.,g Tibet). From the aeromagnetic data they infer that the long-wavelength positive anomalies in the Tarim and Kazakh cratons are localized in the mid-lower crust whereas the short wavelength signal/negative signal in the Tian Shan Orogen corresponds to the upper-mid orogenic crust. They argue that the iron content via its dependence on the buoyancy and strength, which they report to be higher in the foreland/hinterland side lithosphere compared to the one in the orogenic lithosphere in the Tian Shan could have allowed for more distributed deformation upon convergence from the India-Eurasia collision. The authors further extended this observation with and understanding that the cratonic lithospheric mantle is depeleted in Fe and the orogenic lithospheric mantle (Paleozoic-Mesozoic) is enriched with the Fe. Further, using representative models of the continental collision using the thermomechanical models they demonstrate the feasibility of their hypothesis. The authors conclude that the depleted lithospheric mantle of the bounding cratons resists underthrusting/subduction leading to pure shear/distributed deformation in the Tian Shan.\nI find the manuscript written well, and the message is clear. Overall, I enjoyed reading it. I have to admit that I am not an expert in magnetic field data inversion, which is primary evidence for their conclusions, hence my review is based on the implications for continental lithosphere deformation. Below are some suggestions which could improve/help the authors to further strengthen their arguments and findings.\nMajor Points:\nReported thermomechanical models (two), inherently includes a weaker (Hotter orogenic lithosphere), which will lead to distributed deformation on imposed convergence. As authors argue that the since the orogenic crust in the Tian Shan is more felsic hence would be hotter that the lithospheres of the bounding cratons making is weaker and leading to the distributed deformation. This clearly hints towards the thermal state leading to weaker orogenic lithosphere to allow for the distributed deformation. However, in the second last paragraph of the manuscript the authors argue that the thermal state of the upper plate is not a decisive factor for the mode of continental deformation. May be a model-set without the higher temperatures in the orogenic lithosphere would further strengthen the inference that the lithospheric mantle and crustal compositional variations strongly control orogenic mode (Pure shear vs simple shear).\nDecreasing the density of the lithospheric mantle and increasing it for the crust (density?) of the bounding cratons results in net positive buoyancy with respect to the orogenic lithosphere mantle which is taken to be fertile, leads to no subduction of the cratonic lithosphere. It would be interesting to demonstrate which one is more dominating here, the lithosphere mantle (which is thicker) or the continental crust. May be a set of models where crust is fixed to a same thermochemical-mechanical properties in both the orogen and foreland/hinterland crust and varied mantle lithospheric mantle composition, would help to further strengthen the conclusion that the composition of the lower crust as well as the lithospheric mantle is a decisive factor. Could the other physical properties (densities in the crust, thermal conductivity and radiogenic heat production) used in the thermomechanical model be included in the SI?\nOther comments:\nLine 73-75 “Fortunately, iron enrichment in the crust can be detected by aeromagnetic anomalies, and the associated iron distribution in the cratonic lithosphere can be quantified using inverse methods21”\nIt is understood that in the crust it is possible to invert for the iron content using aeromagnetic anomalies, but how could it be used for the lithospheric mantle which could be above the Curie temperature?\nLine 126: referencing Fig 2e after “shortening”.\nLine 151: “widespread shallow crustal seismicity23 (Fig. S9a),”\nIt is difficult to see the shallow crust seismicity from the map, all the earthquakes have same colour. Depth information could be included in this figure in order to support the widespread shallow seismicity (with depth: upper crustal level?,). Looking at the depth cross-section of the seismicity, in Figure S11 the seismicity, at least, in the southern front of the Tian Shan is not strictly restricted to the shallow depth <20 km which corroborates the Pure shear deformation rather than simple shear or crustal flow (should be hot enough to flow, not the case here because there are earthquakes). Similarly in the interior of the orogen depth distribution of the earthquakes could further support the distributed deformation as well as the temperatures indirectly to support the inferred magnetic signal.\nLine: 202-206: “The spatial correspondence between strong long-wavelength magnetic signals and lack of intra plate deformation supports our interpretation that the magnetic signals may be diagnostic for identifying iron distribution in the lithosphere, with an iron-enriched lower mafic crust coupled with a depleted mantle.”\nMaybe in the crust and lower crust would be the better wording.\nLine 396:398: “A dumped ‘dry olivine’ flow law (DOL×0.25) is used for the orogen mantle, and a ‘wet olivine’ flow law (WOL × 2) for the sublithospheric mantle69.”\nCould you please explain the “dumped dry olivine” with a proper reference for the readers as well to me.\nLine 212: “To test our hypothesis, we performed a series of numerical simulations of mountain building in an intracontinental setting (Methods).”\nOnly two models are shown/reported.\nLine 213-214 “In our reference model, a weaker continental strip that represents..”\nDo you mean stripe?\nLines: 280-281 “This process explains the longevity and survival of cratonic mantle lithosphere in Earth history despite repeated orogenic cycles”\nBy process do you mean “the pure shear deformation of the cratons” or their inherent chemical composition?\nFigure S10: The panel d. figure is also a common-conversion point image and not sure what joint inversion mean here.\nThe difference with the one in panel c. is because of the gaussian widths.\nFigure S11: “Magnitude” Scale of Earthquakes.\nFigure S12: Is there a reason to truncate the negative values in the map. What does the thick green and turquoise colour line represent? If nothing then please remove to avoid the sensitive confusion/s.\nFigure S13: pink vertical bar?"}, "author_response": "We appreciate the reviewer’s comment regarding existing literature and geophysical surveys across the Tian Shan. Here we acknowledge that there have been decades of important high-resolution geophysical investigations across the Tian Shan (Figs. R1a and R1b), including the reference Xiao, X.C., Liu, X., and Gao, R. et al. (2004) provided by this reviewer. This specific reference is a Chinese book entitled “The crustal structure and tectonic evolution of Southern Xinjiang, China/新疆南部地壳结构和构造演化” （ Xiao X.C, Liu X., and Gao R. et al., 2004/肖序常，刘训，高锐等，2004）. We attach the copy of this book in the NC submission system for the reviewers and editors to further review and evaluate (the Related Manuscript File).\nWhile working on this project, we have reviewed and compiled all available deep reflection seismic profiles across the Tian Shan, including Xiao, X.C. et al. (2004), to synthesize the competing Tian Shan construction models. The stated models, including the northward underthrusting, double underthrusting, and southward underthrusting models (corresponding to the Fig. 1 in our main text), are based on deep geophysical profiles and some geological sections (e.g., Allen et al., 1999 Tectonics; Gao et al., 2013 Lithosphere; Sun et al., 2022 Geology; Zhang et al., 2020 GRL, 2022 Geology; Lei et al., 2007 PEPI; Li et al., 2022 NC). The references we cited in the manuscript are high-quality geological and geophysical sections, such as the deep seismic section across the Tian Shan (Fig. R2) (Li Wei et al., 2022 NC). Conversely, this stated reference (Xiao, X.C., Liu, X., and Gao, R. et al., 2004) is a book that is in only available in Chinese and not as accessible for international scientists. Therefore, while originally writing this manuscript, we felt that it was not the most suitable reference for a paper like this submitted to the international, and broad-readership Nature Communications.\nOur original writing and presentation of models for the orogenic architecture included a comprehensive review of all possibilities, including the one presented in the Xiao et al. (2004) book. However, we agree with this reviewer here that this is an important reference, as well as other important papers (e.g., Gao et al., 2013 Lithosphere), and therefore we now cite them in our setup of existing work.\nWe do fully appreciate that such uncited literature and highlighted comments are important to consider. Based on the P-wave velocity structure on lithospheric scale (Fig. R3a), the authors of this book proposed a double-underthrusting model that Junggar and Tarim lithosphere underthrusted beneath the Tian Shan orogen by face to face (Fig. R3b). In the revised manuscript, we have now added two additional citations (Xiao et al., 2004 Book; Gao et al., 2013 Lithosphere), especially related to our Fig.1d in the main text (double-size underthrusting beneath the Tian Shan).\nFurthermore, during this revision process we have carefully checked the geophysical data and observational figures from Xiao et al. (2004). During this evaluation process, we note only a few deep reflection profiles (i.e., two seismic sections) in the book. All the geophysical text and figures within the book involve in the pages from Page 2 to Page 53, as well as the supplementary figures at the end. We have pasted this information below, and now better cite this study in the main manuscript. Thank you.\n[...]\nWe appreciate the reviewer’s important comments about the interpretation of aeromagnetic anomaly impacting the modes of mountain building. We agree with reviewer #1’s viewpoints that “……aeromagnetic anomalies that could reflect such large-scale, deep-seated (crustal-scale) mineral magnetic anomalies would necessarily be low-intensity long-wavelength components……”. From a geophysical perspective, there are at least two methods that can be applied to delineate magnetic sources at various depths and scales. One method involves potential field conversion, which encompasses derivation and upward continuation. Derivation can emphasize shallow magnetic source (Blackly, 1996), whereas the upward continuation can effectively delineate deeper magnetic source, such as the metamorphic basement and mid-lower crust (e.g., Blackly, 1996; Xu et al., 2023 Geology). The other method is magnetic inversion, which can directly provide the magnetization intensity (magnetic susceptibility) at any depths above the Curie surface (e.g., Hu et al., 2019 Geophysics; Xu et al., 2023 Geology). Magnetic inversion is a well-established and well-proven method that has been widely utilized to delineate the magnetic structure of the whole crust (e.g., Xu et al., 2023 Geology), even the uppermost lithospheric mantle (Ferre et al., 2021 Nature REE).\n[...]\nWe appreciate and acknowledge the comments the reviewer brought up here. For these types of numerical simulations, the initial and boundary conditions are critical constraints for how the models will respond to parameter variations. In the past decade, series of numerical and physical modeling tests suggest that the lithospheric-scale rheology and density (lower crust and mantle lithosphere) primarily control the lithosphere deformation and structure in the intracontinental tectonism (e.g., Calignano et al., 2015 Tectonics; Chen et al., 2017 Nature Communications; Huangfu et al., 2021 Nature Communications).\n[...]\nWe sincerely appreciate and acknowledge the reviewer’s constructive review comments.\n[...]\nWe greatly appreciate the reviewer’s comments so that we can better clarify the text and discussion of the impact of thermal state. The thermal state of the orogenic lithosphere is an important factor controlling the style of orogenic crustal deformation. Our original writing noted how examples in the literature are not conclusive for how thermal state predictably impacts orogeny. The cited examples explored deformation involve active or recently active arc systems (e.g., the Andes or Himalaya). For the Tian Shan, there is no geological reason for the Tian Shan crust to be especially hot or cold, given arc activity had ceased by the Triassic.\n[...]\nWe here sincerely acknowledge the reviewer’s important comment and consideration. Our manuscript is an observation-based paper. The logic of our manuscript is that we decipher the crustal compositional structure and propose the geologic hypothesis (Fig.3) via our high-resolution aeromagnetic observation, and then finally test the hypothesis via the numerical modeling. Based on our magnetic observations, we propose that the lower crust composition (rheology) and lithospheric mantle depletion (density) control the mode of lithospheric-scale mountain building. We highlight in our text that the continental crust and lithospheric mantle work together to control the mode, of which the composition is chemically coupled (Fig. 3b and 3c).\n[...]\nWe do appreciate and acknowledge the comments the reviewer brought up here. Please note the Fig. 3b and 3c in the main text. The crustal scale iron content will indicate the interaction between the crust and its underlying lithospheric mantle (Grant, 1985 Geoexploration). Thus, it is assumed that the iron in the crust is geochemically coupled with the lithospheric mantle. The iron content within the crust will be inversely proportional to that within the lithospheric mantle. Therefore, we can use the iron content to indicate the state of lithospheric mantle. We expand on this discussion in the main text.\n[...]\nThanks. It is revised.\n[...]\nThe seismicity data cited in the Fig. S9a is downloaded from the USGS website (https://www.usgs.gov/). The earthquake epicenters from the USGS dataset are not all accurately relocated. In contrast, the earthquake epicenters from the China Earthquake Networks Center (CENC) in Fig. S11 are all accurately relocated with some depth uncertainties. Thus, in the Fig. S9a, we only present the distribution of earthquake epicenters. According to the reviewer’s suggestions, we replot the Fig. S9a, presenting the depth information of earthquake epicenter.\n[...]\nWe have revised the text accordingly. Thank you for the suggestion.\n[...]\nWe greatly appreciate this reviewer’s constructive comments and directional suggestions.\n“Dumped dry olivine” means that the laboratory-derived flow law is multiplied by a scaling factor f. This is because the extrapolation of laboratory data to geological conditions is subject to considerable uncertainty. The scaling approach allows for an assessment of model sensitivity to reasonable variations in viscous strength without invoking additional flow laws, each with their own uncertainties (Beaumont et al., 2006).\nIn order to keep it simple and address the reviewer’s comment here, we renamed it to be “scaled” dry olivine. In a word, it is just an olivine flow law that is scaled by a factor (Beaumont et al., 2006). We further revise the “dumped dry olivine” to be “scaled dyr onlivine” in the main text and add a proper reference for it.\n[...]\nThanks for the reviewer’s important consideration and suggestion. Actually, we have tested and conducted a series of numerical experiments for mountain building in the intracontinental setting (Please see the updated supplementary material). Considering this is a primarily observation-based study, we only put two numeral models in the main text. During the revision, the parameter sensitivity study has been extended by running 20 additional models, which are now presented in the supplementary material and discussed in the revised paper.\n[...]\nIn this case, we meant a continental checked strip, like a ribbon of continent / block. We have modified the text here to be more clear for future readers. Thank you.\n[...]\nThanks. Here we mean the former. Pure shear deformation of cratonic lithosphere will maintain and strengthen its longevity and survival, as compared with simple-shear underthrusting and subduction of continental lithosphere that will lead to its recycling in the mantle. In light of this comment, we have further clarified the text here.\n[...]\nThanks for the reviewer’s important consideration and valuable comments.\nThe panels c and d are cited from the Zhang et al. (2020 GRL) and Li et al. (2021 NC). Zhang et al. and Li et al. used same observed data and process it via different methods. Here we just cited these processed results to reinterpret the crustal deformation. More details about the data-processing methods will be traced in Zhang et al. (2020 GRL) and Li et al. (2021 NC).\n[...]\nThanks for the reviewer’s sincere reminder. It is a typo. We revise it here.\n[...]\nThanks for the reviewer’s important consideration. Here, we want to emphasize the long-wavelength, high-amplitude, positive magnetic anomalies, which directly indicate the domain of iron-rich lower crust. The thick green colour line represents the boundary of these sedimentary basins with cratonic lithosphere, including Tarim, Junggar, Qaidam, Ordos, and Sichuan. The turquoise line represents the boundary of our high-resolution aeromagnetic data. As the reviewer highlighted, we add the label expression in the caption.\n[...]\nThanks for the reviewer’s sincere reminder. It is a typo, and should be black vertical bar. We revise it here. Thanks again."}, {"round": 2, "reviewer_comments": {"reviewer_1": "I am convinced that this paper has not been well revised. The main research conclusions of this paper remain highly questionable for the following reasons:\n1.The author has added citations of related papers such as the book of Xiao Y.C., Liu, X., and Gao, R. et al. (2004) without delving deeply into the limitations of the original model. What is the advancement of the model proposed in previous studies? Which specific errors in past research does it bridge? More importantly, on which characteristics of observational data, particularly deep reflection seismic profiles, has the new model been significantly validated? This question needs to be answered affirmatively. Otherwise, the so-called model is merely a hypothesis without much evidence, which will not garner widespread interest from readers.\n2. The author acknowledges the significant role of gravity models in explaining deep structures, particularly the undulations of the Moho surface. However, there is still a lack of effective gravity data and their processed results to directly support the research in this paper. This ambiguity greatly reduces the reliability of the research findings.\n3.Moreover, from the results of multiple numerical simulations with changed parameters provided by the author, it seems to further confirm the previous doubts, indicating the uncertainty of the model. Each mode obtained from the numerical simulations is different, and the discrepancies are quite significant.\n4.It is suggested that the author continue to conduct in-depth research, using observational data, particularly deep reflection seismic data, as the primary constraint conditions for the structure. Geological, geophysical data, including gravity and magnetic data, should be integrated into a rigorous model framework, preferably a quantifiable one. Such research results would be valuable. Speculations based on certain aspects in this paper are not recommended as they do not solve the problem but rather introduce another possibility, which brings more potentially insignificant issues to the study of the Tianshan orogenic belt.\nIn all, this version of the manuscript can not be accepted for publication.", "reviewer_2": "I thank and congratulate the authors. They have addressed all the concerns and have modified the manuscript accordingly.\nI have no more concerns and recommend publication in Nat. Comms."}, "author_response": "This above referenced book proposes a key model referred to as the two-sided subduction model (Figs. 1, 2, also referenced in our original Fig. 1d). As Reviewer #1 pointed out, the deep reflection seismic profile presented in this book is confined to the interaction domain between the Tarim Basin and West Kunlun range (Fig. 3), and does not cover any part of the Tian Shan, which is the focus of our study. In preparing this manuscript, we have reviewed and compiled all available deep reflection seismic profiles across the Tian Shan from the literature, including those from the book edited by Xiao et al. (2004) (Fig. 3), Makarov et al. (2010) and Gao et al. (2013) (Figs. 4, 5).\n[...]\nWe provided a detailed reply to a similar comment in the first round of reviews.\nIt is impossible to differentiate anomalies originating from lithospheric density heterogeneity and Moho topography if there is no seismic-based Moho constraint. There is no high-resolution gravity and seismic velocity data across the whole Tian Shan. Therefore, we have no way to improve the manuscript based on this review comment. Most importantly, the lithosphere-scale receiver function imaging (Li et al., 2022 NC; Zhang et al., 2021 Geology) clearly reveals the Moho morphology of Tian Shan (Fig. 6). The Moho morphology is the key constraint for validating the model.\n[...]\nWe politely argue that this review comment does not provide any specifics. We systematically tested the parameter sensitivity at the request of both reviewers in the initial round of reviews. The additional numerical experiments together with the original ones presented in the text demonstrate that the lithosphere mantle density and associated crustal composition (and thereby rheology) reflected by spatial variations in the Fe content are two critical factors controlling the style of orogenic deformation.\n[...]\nAs we have addressed above, we politely argue against this comment. We have provided a multi-disciplinary dataset to support our model, which we test against numerical models and published geophysical and geological observations. The reviewer does not point out specific disagreements or flaws, but rather provides subjective statements.\nWe found the rejection review did not consider our detailed response to the first review. Please see our responses to this new review below, and please note that it had no specific objections to our datasets, analyses, or interpretations. Perhaps based on the Reviewer #1’s expertise, we believe they downplayed the importance of aeromagnetic imaging and exaggerated the importance of seismic reflection approach, ignoring its limitations.\nWe also found the latest review comments subjective, especially after our strong efforts to systematically respond to and address comments from the first round of reviews. Reviewer #1 raised the same comments in the second round of review as in the first round, which led us to believe that Reviewer #1's viewpoint was not aligned with the results of our paper due to personal bias, or otherwise Reviewer #1 may have conflict of interest with our research.\nTherefore, we believe that Reviewer 1 #1 is not suitable to serve as a reviewer for this manuscript."}, {"round": 3, "reviewer_comments": {"reviewer_3": "Peer Review of\nMode of intracontinental mountain building controlled by lower crustal composition and mantle lithosphere depletion\nManuscript #NCOMMS-24-13052A\nsubmitted to Nature Communications\nThis study presents the results of an aeromagnetic study of the Tian Shan orogen and the bounding Tarim Craton and Kazakh Craton. The data reveals different lithospheric composition between the Tian Shan belt and the surrounding cratons: The former has a more felsic lower crust and a less depleted mantle lithosphere, while the latter possesses a more depleted lithospheric keel and a more mafic lower crust. The authors argue that, as a result of the compositional difference, the strong and buoyant cratons resist internal deformation and subduction. The weak Tian Shan belt, on the other hand, deforms by distributed pure shearing. To test this hypothesis, geodynamic modeling is carried out with varying depletion-induced mantle lithospheric density, lower crustal compositions and thermal conditions. The models show that pure shear deformation mode is favored if the less depleted lithospheric mantle and more felsic lower crust are present in the orogenic belt. Otherwise, the crustal deformation is dominated by simple shearing mode or subduction of the bounding craton. Furthermore, the high temperature thermal state also favors distributed pure shearing deformation mode, although the thermal state per se may only play a minor role in controlling the crustal deformation in the Tian Shan belt.\nI find the multidisciplinary approaches the authors have taken to formulate and test their tectonic hypothesis interesting and the implications of the study concerning the crustal deformation are of global significance. I notice that geophysical data have been largely used to propose the tectonic model, though there are still some imperfect results that can be done in the future study. To me, the manuscript is generally well-organized and written and is worthwhile for publication in the journal. I do suggest a few improvements on the chain of logic that leads to the final conclusions. I thereby support publication of the manuscript with minor revisions. Some major comments are as follows:\n1. I don’t recommend using the term ‘Kazakh Craton’. We know that the ‘craton’ has a clearly geological definition. I would suggest using the term ‘Kazakhstan Block’ in the text.\n2. The numerical modeling results presented in Table S3 have an alternative interpretation. In model names TSM03, TSM07, TSM10, TSM13 and TSM16, the lower crustal flow law for both the orogenic the cratonic lower crust are felsic granulite and they all exhibit pure shear deformation mode. In contrast, in model names TSM04, TSM08, TSM11, TSM14 and TSM17, the lower crustal flow laws are both mafic granulite and they all display simple shear mode. This leads to the alternative interpretation that the deformation mode is strongly controlled by the lower crust rheology rather than the density (or viscosity) contrast caused by the differential depletion between the orogenic and cratonic lithosphere. This contradicts with the statement made in Lines 235-237, in the sense that the orogeny can still undergo pure shearing even when there is “no differences in lower crustal rheology and lithospheric mantle density between the orogen and its bounding continents”. We suggest the authors to provide further clarification on this in the supplementary materials if not in the main text.\n3. The authors used the Δ(cid:1) value as a proxy for depletion-induced density variation and tested models with Δ(cid:1) in -60, -30, 0 and 30 kg/m3. We suggest the authors to provide justification as to why these values are chosen and whether they are geologically reasonable.\n4. The authors discuss the impact of thermal state on the crustal deformation behavior from a geodynamic modeling perspective (Figure. S16). Although the authors preclude the thermal state as a major contributing factor to the crustal deformation in the Tian Shan belt (Lines 286- 291), We suggest the authors to briefly touch upon the role of thermal state on Precambrian orogeny (e.g. Chardon et al., 2009) and by doing this, generalize the applicability of the current modeling work to a wider range of geological time.\nReferences\nD. Chardon, D. Gapais, and F. Cagnard. Flow of ultra-hot orogens: A view from the Precambrian, clues for the Phanerozoic. Tectonophysics, 477(3-4):105–118, Nov. 2009. ISSN 00401951. doi: 10.1016/j.tecto.2009.03.008."}, "author_response": "Thank you for the positive feedback on our manuscript. We carefully read through these comments and have modified the manuscript and figures accordingly. These latest changes have further refined our paper. In particular, the suggestions regarding hot Precambrian orogeny allow us to add some more breadth to the final discussion paragraph of our paper. Consideration of this point results in a self-consistent explanation for Precambrian orogeny and cratonic growth. Thank you for these suggestions.\n[...]\nWe greatly appreciate and acknowledge the constructional suggestion.\nWe have accordingly used the term ‘Kazakhstan Block’ in the text, and further revised the term ‘Tarim Craton’ to be ‘Tarim Block’. Thank you for the suggestion. We agree that using block is a more generalized term for these pieces of continent that have remained rigid during the Mesozoic-Cenozoic time.\n[...]\nWe greatly appreciate this concern so that we can better clarify the text of these modeling results and present our main points.\n[...]\nThanks for the above comment so that we can provide justification and better clarify the text.\n[...]\nWe greatly appreciate and acknowledge the constructional suggestions. These suggestions have led to a few brief, yet important modifications to our manuscript.\nFirst, we use the observations that the hot Precambrian accretionary orogens deform via pure shear to further validate our ancillary numerical simulations in the thermal state section. We had written that these numerical simulations suggest that pure-shear deformation results from hot orogeny, and we can now refer to interpretations of Precambrian accretionary orogens to further support this inference, by citing Chardon et al. (2009).\nSecond, we expanded the final paragraph to review how our interpretations are consistent with the established interpretations for Precambrian craton growth and continental evolution. Specifically, a hotter Precambrian mantle would result in higher degrees of melting, which would predictably result in generally more melt depletion of the continental mantle lithosphere (e.g., Lee et al., 2011; Xu et al., 2023). A more melt depleted mantle lithosphere coupled with hotter orogeny would predict pure-shear styles of orogeny, as reviewed by Chardon et al. (2009) for Precambrian orogens. Pure-shear orogeny in Archean-Proterozoic would lead to lateral accretionary growth of the continents to build cratons (Pearson et al., 2021), while simultaneously preserving these growing cratons by sparing them from simple-shear continental subduction. Our newly revised paragraph links the interpretations of our orogenic model to continental evolution in a self-consistent manner, which further strengthens and supports our arguments."}, {"round": 4, "reviewer_comments": {"reviewer_3": "Peer Review of\nManuscript # NCOMMS-24-13052C\nMode of intracontinental mountain building controlled by lower crustal composition and mantle lithosphere depletion\nComments:\nThe authors have done a thorough improvement addressing all the review comments from the previous round. The manuscript presents a tightly integrated multidisciplinary study combining aeromagnetic analysis and numerical modeling, with profound implications for crustal deformation modes in both Precambrian and Phanerozoic orogenies. In its present form, the manuscript has been significantly improved in terms of logical clarity, as well as the breadth and depth of discussion. Only a few minor, mostly syntactic, edits are needed, so I am happy to recommend acceptance for publication in Nature Communications (NC) after these corrections.\nLines 132-134 Since most of the discussion (and in fact the whole article) is centered around differentiating the pure shear and simple shear modes of deformation for the Tian Shan orogenic belt and the surrounding continental blocks, it would be helpful to introduce these key concepts in the first few paragraphs of the Introduction section.\nLine 85 repetition of the word “depleted” . . . presence of a depleted iron-poor depleted mantle lithosphere that is rheologically . . .\nLines 87-88 . . . mantle lithosphere . . . bounds the two sides of the Tian Shan belt, which is the latter characterized by more felsic iron-poor lower crust and less depleted, thinner mantle lithosphere.\nLine 98 . . . accelerated deformation in the Miocene and is still being actively shortening shortened today."}, "author_response": "Thank you for the positive feedback on our manuscript. We carefully read through these comments and have modified the manuscript and figures accordingly. These latest changes have further refined our paper. Thank you for these suggestions.\n[...]\nThanks for the above comment so that we can provide justification and better clarify the text.\n[...]\nThanks. Corrected.\n[...]\nThanks. Corrected.\n[...]\nThanks. Corrected."}]

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