Could the Réunion plume have thinned the Indian craton?

Thick and highly viscous roots are the key to cratonic survival. Nevertheless, cratonic roots can be destroyed under certain geological scenarios. Eruption of mantle plumes underneath cratons can reduce root viscosity and thus make them more prone to deformation by mantle convection. It has been proposed that the Indian craton could have been thinned due to eruption of the Réunion plume underneath it at ca. 65 Ma. In this study, we constructed spherical time-dependent forward mantle convection models to investigate whether the Réunion plume eruption could have reduced the Indian craton thickness. Along with testing the effect of different strengths of craton and its surrounding asthenosphere, we examined the effect of temperature-dependent viscosity on craton deformation. Our results show that the plume-induced thermomechanical erosion could have reduced the Indian craton thickness by as much as ~130 km in the presence of temperature-dependent viscosity. We also find that the plume material could have lubricated the lithosphere-asthenosphere boundary region beneath the Indian plate. This could be a potential reason for acceleration of the Indian plate since 65 Ma.

Supplemental Material: Could the Réunion plume have thinned the Indian craton?

Supplemental Figures S1–S5 and Videos S1–S4.<br>

Supplemental Material: Could the Réunion plume have thinned the Indian craton?

Supplemental Figures S1–S5 and Videos S1–S4.<br>

Discovery of Deccan Inclination Anomaly and its possible geodynamic implications over the Indian Plate

The rapid northward drift of the Indian plate during Deccan volcanism assumes a gradual shallowing of paleomagnetic inclinations in subsequent lava flow formations. A comparison of palaeomagnetic data produced during the last six decades reveals an inclination anomaly during Chron C29r (66.398–65.688 Ma) along with brief clockwise-counter-clockwise rotations during and after the main phase Deccan eruption. This interval temporally coincides with i) an accelerated Indian ocean spreading rates, ii) brief incursion of an inland ‘seaway’ and iii) a major drop in the sea level at the southern tip of the Indian Peninsula. Furthermore, the restoration of tilt later during C29n agrees with the withdrawal of the inland seaway and the development of a regional southward dip of the Deccan lava flow formations. Here, we produce an evolutionary model to postulate the interaction of the Réunion plume with the Indian lithospheric plate with coincident geological evidences demanding further exploration.

Discovery of Deccan Inclination Anomaly and its possible geodynamic implications over the Indian Plate

The rapid northward drift of the Indian plate during Deccan volcanism assumes a gradual shallowing of paleomagnetic inclinations in subsequent lava flow formations. A comparison of palaeomagnetic data produced during the last six decades reveals an inclination anomaly during Chron C29r (66.398 - 65.688 Ma) along with brief clockwise-counter-clockwise rotations during and after the main phase Deccan eruption. This interval temporally coincides with i) an accelerated Indian ocean spreading rates, ii) brief incursion of an inland ‘seaway’ and iii) a major drop in the sea level at the southern tip of the Indian Peninsula. Furthermore, the restoration of tilt later during C29n agrees with the withdrawal of the inland seaway and the development of a regional southward dip of the Deccan lava flow formations. Here, we produce an evolutionary model to postulate the interaction of the Réunion plume with the Indian lithospheric plate with coincident geological evidence demanding further exploration.

Short-lived alkaline magmatism related to Réunion plume in the Deccan large igneous province: inferences from petrology, 40Ar/39Ar geochronology and paleomagnetism of lamprophyre from the Sarnu-Dandali alkaline igneous complex

Existing geochronological information on Deccan indicates prolonged (started at 68.5 Ma) alkaline magmatism related to the Réunion mantle plume based on the 40Ar/39Ar ages from Sarnu-Dandali and Mundwara alkaline complexes. We studied in detail an alkaline lamprophyre, from the Sarnu-Dandali complex, rich in groundmass (magmatic) as well as xenocrystic phlogopites and clinopyroxenes. 40Ar/39Ar age determinations of the phlogopites from this lamprophyre, reveal two distinct ages of 65.44±1.5 Ma and 68.17±1Ma. However, paleomagnetic results show a VGP at 32.31 N and 298.52 E concordant with that of the Deccan Super Pole at 65.5 Ma and support the younger eruption age at ca. 65.44±1.5Ma. Analyzed phlogopites lack any signs of retention of excess radiogenic Ar and yield similar inverse isochron ages, which suggests that the older age of ca. 68.17±1Ma belongs to the crystallization of xenocrystic phlogopite during mantle metasomatism. Trace element compositions support derivation of lamprophyre magma from an OIB- type enriched (metasomatized) mantle source with an involvement of phlogopite.This finding suggests that the pre-Deccan ages of ca. 68-69 Ma reported previously, may reflect the timing of metasomatism of the subcratonic lithospheric mantle during the separation of Greater-Seychelles from India at ca. ∼68.5 Ma. The absence of pre-Deccan alkaline rocks therefore indicates the short-duration (occurred between 67-65 Ma) of alkaline as well as small-volume, volatile-rich magmatism directly related to the Réunion (Deccan) plume.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5490881

Interaction of the Indian craton with the Reunion plume

&lt;p&gt;One of the fundamental characteristics of cratons is the presence of thick lithosphere of more than 200 km, whereas any standard non-cratonic lithosphere thickness is about 100 km thick. The thickness of Indian craton has remained quite controversial. Under the Indian plate, most seismic studies fail to recognise a thick lithosphere; however, a few studies using other geophysical methods (e.g., magnetotellurics) argue for a thick Indian craton. In the last 30 years, more than ten research articles estimated the thickness of the Indian craton that varied from less than 100 km to 260 km. Such controversy arose primarily because of the Reunion plume and Indian craton interaction at ~65 Ma. Some studies suggested that due to the Reunion plume's eruption underneath the Indian craton, the thick lithosphere of the Indian craton was thinned down. This thin lithosphere is attributed as one of the primary reasons for the acceleration of the Indian plate since 65 Ma. On the other hand, several studies advocated that the Reunion plume did not affect the thickness of the Indian craton. Still now, no study has actually investigated the nature of plume-craton interaction under the Indian plate and how the craton was deformed in the presence of a plume. In this study, we develop time-dependent global mantle convection models using CitcomS to understand the evolution of Indian craton for the last 100 Ma. The models are initiated at 100 Ma and are driven forward&amp;#160; up to the present day using reconstructed plate velocities at every 1 Myr interval. Our results show that it is possible to thin down the thicker cratonic lithosphere due to the eruption of the Reunion plume. We also observe that the plume could get bifurcated due to the craton, and eruptions could occur on both the eastern and western parts of the Indian continental lithosphere.&lt;/p&gt;

Seismic gaps and intraplate seismicity around Rodrigues Ridge (Indian Ocean) from time domain array analysis

Rodrigues Ridge connects the Réunion hotspot track with the Central Indian Ridge (CIR) and has been suggested to represent the surface expression of a sub-lithospheric flow channel. From global earthquake catalogues, the seismicity in the region has been associated mainly with events related to the fracture zones at the CIR. However, some segments of the CIR appear void of seismic events. Here, we report on the seismicity recorded at a temporary array of 10 seismic stations operating on Rodrigues Island from September 2014 to June 2016. The array analysis was performed in the time domain by time shifting and stacking the complete waveforms. Event distances were estimated based on a 1-D velocity model and the travel time differences between S and P wave arrivals. We detected and located 63 new events that were not reported by the global networks. Most of the events (51) are located off the CIR and can be classified as intraplate earthquakes. Local magnitudes varied between 1.6 and 3.7. Four seismic clusters were observed that occurred to the west of the spreading segment of the CIR. The Rodrigues Ridge appeared to be aseismic during the period of operation. The lack of seismic activity along both Rodrigues Ridge and the sections of the CIR to the east of Rodrigues may be explained by partially molten upper-mantle material, possibly in relation to the proposed material flow between the Réunion plume and the CIR.

Seismic gaps and intraplate seismicity around Rodrigues Ridge (Indian Ocean) from time-domain array analysis

Rodrigues Ridge connects the Reunion hotspot track with the Central Indian Ridge (CIR) and has been suggested to represent the surface expression of a sub-lithospheric flow channel. From global earthquake catalogues, the seismicity in the region has been associated mainly with events related to the fracture zones at the CIR. However, some segments of the CIR appear void of seismic events. Here, we report on the seismicity recorded at a temporary array of ten seismic stations operating on Rodrigues Island from September 2014 to June 2016. The array analysis was performed in the time domain – by time shifting and stacking of the complete waveforms. Event distances were estimated based on a 1-D velocity model and the travel-time differences between S- and P-waves arrivals. We detected and located 63 new events, which were not reported by the global networks. Most of the events (51) are located off the CIR and can be classified as intraplate earthquakes. Local magnitudes varied between 1.3 and 3.5. Four seismic clusters were observed along with a distinguishable swarm of earthquakes that occurred to the west of the spreading segment of the CIR during the period from March to April 2015. The Rodrigues Ridge appeared aseismic during the period of operation. The lack of seismic activity along both Rodrigues Ridge and the sections of the CIR to the east of Rodrigues may be explained by partially-molten upper-mantle material, possibly in relation to the proposed material flow between the Reunion plume and the CIR.