Localized rotational tectonics in the Arctic:
In order to characterize the crustal deformation, rotational tectonic processes and their relation with topography build-up along the Gakkel Ridge-Chersky Range in the Arctic, we have investigated geodetic dataset from the adjacent plate boundaries. We estimate the absolute as well as relative plate motion and Euler rotation parameters of the North America plate and Eurasia plate, considering a large number of geodetic data sets from previously published sources (i.e., ~ 684 stations for the Eurasia plate and ~ 2223 stations for the North America plate) (See the supporting documents and Table S1, S2).
From these geodetic constraints, we observe that the present-day absolute Euler rotation pole of the North America is located at -7.92 ± 0.115°N, -87.79 ± 0.030°E, with an angular rotation rate of 0.181 ± 0.0003°/Myr. Similarly, the Euler rotation pole of Eurasia is located at 55.54 ± 0.103°N, -97.58 ± 0.138°E, with an angular rotation rate of 0.254 ± 0.0004°/Myr. The residual velocity plots of the North America and Eurasia plates indicate that internal deformation within both plates is very low (~ 2–3 mm/yr) (Fig. 3c). Also, in order to understand the motion accommodated along the Gakkel Ridge to Chersky Range, the relative Euler pole (i.e., in between North America plate and Eurasia plate) (Fig. 3a) is estimated to be situated at 75.40 ± 1.7°N, 124.2 ± 1.5°E, with a rotation rate of 0.233 ± 0.008°/Myr, which is consistent with the results from earlier investigations (Table S3). The locations of all the previously estimated relative Euler poles, along with our new estimation (Fig. 3a), indicate a rotational tectonic system with contrasting deformation on either side of the rotation pole. This is in excellent agreement with the observation that moving towards the rotation pole, the extensional deformation of the Gakkel Ridge is gradually diminished, and is exchanged for compressional tectonics along the Chersky Range on the other side of the pole. This difference in tectonic setting on both sides of the rotation pole in this rotational tectonic system is excellently illustrated by topographic swath profiles (P1-P6 shown in Fig. 3a, b) across the Gakkel Ridge and Chersky Range, which clearly show the rift basins resulting from extension along the Gakkel Ridge, and the mountainous topography of the Chersky range as a result of the compressional tectonics there.
Diffuse rotational tectonics in the Central Indian Tectonic Zone (CITZ):
Next to the localized rotational tectonics situation in the Arctic, we present an overview of our results from the CITZ that represent a zone of diffuse deformation. Our geodetic constraints include 28 continuous GPS velocities from stations within the continental Indian plate interior that are used to estimate the rotation parameters of the Indian plate (See Supplementary information, Table 4). We first estimate the location of the Euler pole of the Indian plate as a whole, which is found to be situated at 50.82 ± 0.2°N, 9.28 ± 1.47°E with an angular rotation rate of 0.538 ± 0.004°/Myr in a ITRF2014 reference frame. Moreover, from the residual velocity plot presented in Fig. 4c (1-Block Indian panel), the internal Indian Plate deformation is ~ 2–3 mm/yr, indicating that the plate possibly behaves in a rigid block manner. However, this assumption appears to contradict the occurrence of unusual strong earthquakes of M > 6.0 occurrence inside the continental parts of Indian plate, which possibly implies that the entire plate may in fact not behave as a rigid block. Moreover, a unified plate kinematic model is still lacking in the view of geodetic constraints, unusual seismo-tectonic activates, variation in lithospheric structures, and diversity in topographic architecture in the central continental part of India. Hence, this contradiction in the rigid single Indian Plate assumption motivates the testing of a ‘composite’ plate hypothesis consisting of two ‘component’ plates (i.e., N-India and S-India) separated by Narmada-Son paleo rift zone.
Therefore, we re-estimate the location of the Euler pole defining potential independent plate motions north and south of the CITZ. Our analysis shows that there is a significant difference in longitudinal position (~ 10° apart) of Euler poles between the two inferred parts of the Indian plate (the North India and the South India plates), although overall latitudinal position and rotation rate remains the same as presented for the single Indian plate (Table S4, S5, Fig. 4c). This indicates that the South India plate is moving relatively faster than the North India plate, with an overall N-S shortening. Residual velocity plot of composite Indian plate (2-Block India panel in Fig. 4c) indicates two distinct clusters of segregation for the North India plate and South India plate, and overall internal deformation of the Indian plate is significantly lower (~ 3 mm/yr). Considering our ‘composite’ Indian plate hypothesis, we have computed relative pole of rotation for motion for the North India plate and South India plate, that lies very close to the boundary between both plates (25.92 ± 6.8°N, 77.09 ± 4.0°E) with an angular rotation velocity that is ~ 90% slower than that of the Indian plate (Fig. 4a). Furthermore, this relative pole of rotation of between these two component plates predicts contrasting deformation styles on both sides of the rotation pole along Narmada-Son paleo rift, with shortening in the east (~ 0.1–1.2 mm/yr) and extension in the west (~ 1.2–1.9 mm/yr) (Fig. 4b). This contrasting nature of present-day deformation as inferred from our analysis, appears to be in good agreement with the contrasting topography along the plate boundary (i.e., mountains and rift valley on the eastern and western side respectively), illustrated by swath topographic profiles (Fig. 4b). We thus find very similar rotational textonic features in both the Arctic as in Central India, and we can infer that that the Central Indian Tectonic Zone is a diffuse plate boundary counterpart to the localized Gakkel Ridge-Chersky Range system.
Topography development and associated rotational tectonics: Insight from 4D Analogue model analysis:
We revisit a brittle-viscous experimental model of rotational tectonic completed by Zwaan et al3 (2020), to get better insights into the topographic evolution we should expect of rotational tectonic systems (Fig. 5). The set-up used by Zwaan et al3 consisted of a foam base stacked between longitudinal sidewalls on top of a fixed table that allowed the foam to move freely at the base. The longitudinal sidewalls could move by means of precise computer-controlled motors, and were linked to a rotation pole below the model. As a result, outward motion of the sidewalls on one side of the rotation pole resulted in extension of the foam base there, as well as inward sidewall motion and contraction of the foam base on the other side of the pole. The rate of this deformation increased away from the location of the rotation pole, thus reproducing a rotational tectonic system. This deformation was subsequently transferred into the brittle-viscous model layering overlying the foam base. Here a layer of quartz sand simulates the brittle upper continental crust, whereas a layer of viscous mixture represents the lower continental crust (Table S6). In order to localize deformation along the centre of the model domain a ‘seed’ was used, which acted as a linear weak zone in nature. Zwaan et al3 analyzed their models via time lapse top view photographs, which provided a qualitative visual analysis of surface deformation, but also allowed a quantitative analysis of surface displacement through digital image correlation (DIC) analysis31–32 (Fig. 5a, b). Furthermore, Zwaan et al3 applied an X-ray Computed Tomography (XRCT) scanner to monitor 3D internal model evolution (Fig. 5d). XRCT data were also used to create topography maps of the model surface (Fig. 5c). Here, we reanalyze the XRCT imagery from Zwaan et al3 in profile view, in order to monitor the topography evolution of the different domains of the model (i.e., in the extensional domain, at the rotation pole, and in the contraction domain). The results are subsequently compared to the topography profiles from the Gakkel Ridge-Chersky Range system in the Arctic, and the CITZ within the Indian Plate respectively.
The relation between rotational tectonics and topography evolution related to 4D analogue model results, complementing with our geodetic measurements has been presented in Fig. 5. The final model top view photographs depict the formation of an extensional regime (i.e., V-shaped rift basin) and compressional regime (i.e., mountain belt) on either side of the rotation axis. Furthermore, digital image correlation (DIC) data clearly indicates the horizontal displacements associated with rotational tectonics with increasing displacement away from the rotation axis (Fig. 5b). The final topography map illustrates the propagation of the localized rift basin toward the rotation axis, a general subsidence in the extensional regime and regional uplift as well as formation of a thrust on the other side of rotation axis in the compressional regime. Series of CT-scanned sections (e.g., S1, S2, and S3, locations marked in Fig. 5c) taken at the end of the model run reveal the variation in internal faulting and topography on either side of the rotation axis and overall structure varies along strike. Our new topography analysis along the three XRCT sections across the deformation zone (S1, S2, and S3) provides additional insights into the impact of rotational tectonics on topography (Fig. 5e). Widespread gentle subsidence as well as a strong localized subsidence occurs along the profile of S3, representing the extensional domain, however on the other hand, a wide uplift and the formation of a thrust faults are visible along the profile of S1, representing contractional domain. This spatial diversity in the topographic build-up and relation with rotational tectonics are in good agreement with our observations from the Arctic and Central India (Fig. 3, 4).