High-resolution reconstructions and GPS estimates of India–Eurasia and India–Somalia plate motions: 20 Ma to the present

Abstract

Summary We reconstruct the movement of the India plate relative to Eurasia at ≈1-Myr intervals from 20 Ma to the present from GPS site velocities and high-resolution sequences of rotations from the India-Somalia-Antarctic-Nubia-North America-Eurasia plate circuit. The plate circuit rotations, which are all estimated using the same data fitting functions, magnetic reversal sampling points, calibrations for magnetic reversal outward displacement, and noise mitigation methods, include new India-Somalia rotations estimated from numerous Carlsberg and northern Central Indian ridge plate kinematic data and high-resolution rotations from the Southwest Indian Ridge that account for slow motion between the Nubia and Somalia plates. Our new rotations indicate that India-Somalia plate motion slowed down by 25-30 percent from 19.7 Ma to 12.5-11.1 Ma, but remained steady since at least 9.8 Ma and possibly 12.5 Ma. Our new India-Eurasia rotations predict a relatively simple plate motion history, consisting of NNE-directed interplate convergence since 19 Ma, a ≈50 percent convergence rate decrease from 19.7 Ma to 12.5-11.1 Ma, and steady or nearly steady plate motion since 12.5-11.1 Ma. Instantaneous convergence rates estimated with our new India-Eurasia GPS angular velocity are 16 percent slower than our reconstructed plate kinematic convergence rates for times since 2.6 Ma, implying either a rapid, recent slowdown in the convergence rate or larger than expected errors in our geodetic and/or plate kinematic estimates. During an acceleration of seafloor faulting within the wide India-Capricorn oceanic boundary at 8-7.5 Ma, our new rotations indicate that the motions of the India plate relative to Somalia and Eurasia remained steady. We infer that forces acting on the Capricorn rather than the India plate were responsible for the accelerated seafloor deformation, in accord with a previous study. India-Eurasia displacements that are predicted with our new, well-constrained rotations are fit poorly by a recently proposed model that attributes the post-60-Ma slowdown in India-Eurasia convergence rates to the steady resistance of a strong lithospheric mantle below Tibet.

Crustal deformation rates in Kashmir valley and adjoining regions from continuous GPS measurements from 2008 to 2019

“…Velocities of all the cGPS sites of the present study are estimated using the methodology detailed in Data and Methods section. ITRF14 and Indian plate frame of reference 17 velocities and the associated uncertainties are given in Table 1 . India fixed velocities of cGPS sites in Kashmir valley and adjoining regions are plotted in Fig.…”

“…For the rest of northwest Himalaya, we plotted arc-normal and arc-parallel rates from the published GPS velocities of continuous and campaign sites 15 , 19 . All the published GPS velocities are transformed to ITRF14 reference frame and converted to India fixed reference frame using the angular velocity of Indian plate given by 17 . Arc normal rates indicate total convergence of about 14 mm/year partitioned as 5 mm/year in the Kashmir valley, 5 mm/year south of the valley and 4 mm/year in the Zanskar range north of valley.…”

“…Blue velocity vectors at Pakistan GPS sites PS01, PS03, PS05, PS13, PS19, PS21 from 10 denote post seismic displacements of October 2005 Muzaffarabad earthquake during March 2007 to August 2009 and Indian GPS site KERN 11 soon after the earthquake. Published post seismic displacements were transformed to ITRF14 reference frame and converted to India fixed reference frame using the angular velocity of Indian plate given by 17 . Fault lines and ruptures are same as Fig.…”

“…ITRF2014 velocities and the associated uncertainties are given in Table 1 for all the cGPS sites used in the present study. India fixed velocities (Table 1 ) and associated uncertainties of the cGPS sites are determined using the angular velocity of India-ITRF14 as given by 17 .…”

Initiation of Clockwise Rotation and Eastward Transport of Southeastern Tibet Inferred from Deflected Fault Traces and GPS Observations

“…For convergence between India and Eurasia, which is directly related to our study area, the rate and direction have changed little since ca. 10 Ma or more (e.g., DeMets et al, 2020;Molnar and Stock, 2009). Changes in bottom boundaries, such as by the removal of mantle lithosphere, seem also to be possible in the few-million-year time scale (e.g., Bird and Baumgardner, 1981;Houseman et al, 1981), but such events also seem to be rare.…”