Cenozoic epeirogeny of the Indian peninsula

• Published in: Geochemistry, geophysics, geosystems : G3 Vol. 17; no. 12; pp. 4920 - 4954
• Main Authors: Richards, F. D., Hoggard, M. J., White, N. J.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 01.12.2016
• Subjects: Anomalies; Banks (topography); Basins; Buoyancy; Cenozoic; Clastics; Climate change; Correlation; Depth; Depth measurement; Drainage patterns; dynamic topography; Elevation; Epeirogeny; Escarpments; Floodplains; Fluvial deposits; Gravity; high‐elevation passive margins; History; India; Instrument depth measurement; inverse modeling; landscape evolution; Lignite; Lithosphere; Low temperature; Magma; Marine; Modelling; Monsoons; Neogene; Neogene uplift; Ocean floor; P-waves; Profiles; Rivers; Rocks; Seismic waves; Sequencing; Slope; Temperature; Temperature anomalies; Topography; Topography (geology); Upper mantle; Wave velocity; India; ISW, India
• DOI: 10.1002/2016GC006545
• ISSN: 1525-2027

Peninsular India is a cratonic region with asymmetric relief manifest by eastward tilting from the 1.5 km high Western Ghats escarpment toward the floodplains of eastward‐draining rivers. Oceanic residual depth measurements on either side of India show that this west‐east asymmetry is broader scale, occurring over distances of > 2000 km. Admittance analysis of free‐air gravity and topography shows that the elastic thickness is 10 ± 3 km, suggesting that regional uplift is not solely caused by flexural loading. To investigate how Indian physiography is generated, we have jointly inverted 530 river profiles to determine rock uplift rate as a function of space and time. Key erosional parameters are calibrated using independent geologic constraints (e.g., emergent marine deposits, elevated paleosurfaces, uplifted lignite deposits). Our results suggest that regional tilt grew at rates of up to 0.1 mm a−1 between 25 Ma and the present day. Neogene uplift initiated in the south and propagated northward along the western margin. This calculated history is corroborated by low‐temperature thermochronologic observations, by sedimentary flux of clastic deposits into the Krishna‐Godavari delta, and by sequence stratigraphic architecture along adjacent rifted margins. Onset of regional uplift predates intensification of the Indian monsoon at 8 Ma, suggesting that rock uplift rather than climatic change is responsible for modern‐day relief. A positive correlation between residual depth measurements and shear wave velocities beneath the lithosphere suggests that regional uplift is generated and maintained by temperature anomalies of ±100 °C within a 200 ± 25 km thick asthenospheric channel. Plain Language Summary India&s topography is characterized by large‐scale eastward tilting that extends over 2,000 km. The reason for this youthful tilting is the subject of considerable scientific debate. By investigating anomalies in the elevation of the sea floor on either side of India, we show that this tilting is supported by processes deep beneath the Indian tectonic plate. By modelling signals of past uplift recorded within the shape profiles of rivers, our paper suggests that plate tilting was generated after 23 million years ago, much more recently than previously proposed. Interestingly, the speeds of seismic waves travelling through the upper mantle beneath India are slower on the western side of India than they are in the east. This observation suggests that hotter, less dense material sits in the shallow mantle beneath the western portion of the Indian plate. Buoyancy of this material generates regional elevation, resulting in the pronounced tilt we observe today. Key Points Oceanic residual depth anomalies show regional tilt of Indian Plate Calibrated inverse modeling of drainage networks suggests that this tilt grew in Neogene times Vertical motions can be linked to temperature anomalies within a sub‐plate asthenospheric channel