At what stress level is the central Indian Ocean lithosphere buckling?

Abstract

Interna] contrasts in strength are responsible for lithospheric buclding. These are quantified by comparing the Indian Ooean data to two dimensional visco elasto plastic numerical models where the material properties depend on temperature and pressure. The central Indian Basin is known for its intraplate seismicity and long wavelength undulations of the sea floor and associated gravity signatures. To simula te the amplitudes of undulations that reach 1 km within about 11 Ma of compression and 60 km of shortening, the required mean yield strength of the lithosphere is 400 MPa. If either a hydrostatic fluid pressure is considered in the crust or a mechanical decoupling at the depth of the Moho, small crustal wavelengths are superimposed on the long wavelength deformation, in agreement with observations. It is then possible to match the alternative indication that buckling co=enced only 4 Ma ago, with a total amount of shortening of 30 km, and with a required yield strength of 200 MPa. About 10% of homogeneous thickening accompanies buckling. Taking into account variable thermal conductivity demonstrates that a change in the geotherm is suffi cient to increase buckling amplitudes by 10% within 5 Ma.

Folding and necking across the scales: a review of theoretical and experimental results and their applications

“…(35) indicates that plastic behaviour (n 10) can significantly increase the growth rate of a folding instability. Indeed, numerical simulations of lithospheric shortening considering representative viscoplastic yield strength profiles for the continental and oceanic lithosphere indicate that lithospheric folding most likely takes place during lithospheric compression (Zuber and Parmentier, 1996;Burg and Podladchikov, 1999;Cloetingh et al, 1999;Gerbault, 2000). The intensity of folding depends mainly on the applied bulk shortening rate and the temperature at the Mohorovičić discontinuity (Moho), which controls the integrated strength of the lithosphere (Schmalholz et al, 2009).…”

“…This value is important because the lateral variation of the gravitational potential energy, caused by the lateral crustal thickness variation between the Indian foreland and the Tibetan plateau, generates a force per unit length of ∼ 7 × 10 12 Nm −1 (Molnar and Lyon-Caen, 1988), which means that the growth of the Tibetan plateau alone could in principle have caused the folding of the Indian oceanic lithosphere (Molnar et al, 1993). The analysis of Molnar et al (1993) caused some controversy because other authors using thin viscous sheet models argued that the values for the force per unit length related to the Tibetan plateau from Molnar et al (1993) were overestimated by a factor of 2 and, hence, that the growth of the Tibetan plateau alone could not be responsible for folding of the Indian Ocean lithosphere (Ghosh et al, 2006(Ghosh et al, , 2009. However, the analysis of Molnar et al (1993) is based on total stress and differential stress (difference between maximal and minimal principal stress), whereas the results of thin viscous sheet models are based on deviatoric stress, which is half the differential stress in the thin viscous sheet model .…”

Late Neogene and Quaternary Vertical Motions in the Otway Coast, Southeast Australia (II): Epeirogenic Uplift Driven by Lithospheric Flexural Deformation

“…This lithospheric flexural mode explains vertical movements of the crust, and was recognized first in the Indian Ocean (Beekman et al, 1996;Gerbault, 2000) (Fig. 9).…”

“…Substantial compression stresses in the central Indian Ocean reactivate pre-existing crustal faults, and, in a later phase, initiate folding and buckling of the entire ocean lithosphere. Numerical model (Gerbault, 2000) also demonstrated that lithospheric folding does not develop in the absence of fault reactivation, and not start until horizontal loading has significantly reduced the mechanical strength of the lithosphere. The vertical motions associated with the Otway Ranges and a surrounding basin such as the western Otway Basin are characterised by the horizontal length of over 100 km and the amplitude of >200 m since the Pliocene that can be compared to the lithosphericscaled deformation.…”

“…Flinders Range) fits well with a wavelength deformation of order 10 2 kms, which is comparable to the thickness of the lithosphere deviations from local isostasy. Such wavelength undulations of the Earth's surface can usually be related to flexural strength of the lithosphere (Burov et al, 1993;Beekman et al, 1996;Gerbault, 2000;Cloetingh et al, 2002;). Celerier et al (2005 have suggested that the long wavelength pattern of deformation associated with the Flinders Range and surrounding basins could be understood in terms of lithospheric flexural mode.…”