Integrated geophysical-petrological modeling of lithosphere-asthenosphere boundary in central Tibet using electromagnetic and seismic data

Abstract

We undertake a petrologically driven approach to jointly model magnetotelluric (MT) and seismic surface wave dispersion (SW) data from central Tibet, constrained by topographic height. The approach derives realistic temperature and pressure distributions within the upper mantle and characterizes mineral assemblages of given bulk chemical compositions as well as water content. This allows us to define a bulk geophysical model of the upper mantle based on laboratory and xenolith data for the most relevant mantle mineral assemblages and to derive corresponding predicted geophysical observables. One-dimensional deep resistivity models were derived for two groups of MT stations. One group, located in the Lhasa Terrane, shows the existence of an electrically conductive upper mantle layer and shallower conductive upper mantle layer for the other group, located in the Qiangtang Terrane. The subsequent one-dimensional integrated petrological-geophysical modeling suggests a lithosphere-asthenosphere boundary (LAB) at a depth of 80-120 km with a dry lithosphere for the Qiangtang Terrane. In contrast, for the Lhasa Terrane the LAB is located at about 180 km but the presence of a small amount of water in the lithospheric mantle (<0.02 wt%) is required to fit the longest period MT responses. Our results suggest two different lithospheric configurations beneath the southern and central Tibetan Plateau. The model for the Lhasa Terrane implies underthrusting of a moderately wet Indian plate. The model for the Qiangtang Terrane shows relatively thick and conductive crust and implies thin and dry Tibetan lithosphere.

Shear‐Wave Velocity Structure of Southern Africa's Lithosphere: Variations in the Thickness and Composition of Cratons and Their Effect on Topography

“…The density of the mantle lithosphere has a profound effect on topography (e.g., Fullea et al, ; Vozar et al, ). In cratons, the negative buoyancy due to the low temperatures of the cold lithospheric lid is compensated, approximately, by the positive buoyancy generated by the depletion (Jordan, ).…”

Carbonated Inheritance in the Eastern Tibetan Lithospheric Mantle: Petrological Evidences and Geodynamic Implications

“…Teleseismic tomography reveal low P-wave velocity anomalies in the mantle lithosphere (Lei & Zhao, 2016;Li et al, 2008;Replumaz et al, 2013;Wang et al, 2019), notably beneath the Eastern Qiangtang and Songpan-Ganze terranes, but with great variations, even between the most recent models, of the lateral and depth extent of the anomalies (compare, e.g., Lei & Zhao, 2016;Wang et al, 2019). This low-velocity layer has been widely interpreted as a thermal anomaly indicative of a thinned lithospheric mantle (Liang et al, 2012;Tunini et al, 2016;Vozar et al, 2014). However, S-wave velocities, which are more sensitive to temperature than to composition, and thus more adequate to map the lithosphere thickness variations (Priestley & McKenzie, 2006), are not slowed and rather suggest a thick lithosphere (∼260 km) beneath the whole Tibet Plateau (McKenzie & Priestley, 2008).…”

“…Indeed, by modeling the addition of phlogopite and magnesian carbonate to a Tibetan lithospheric mantle of normal thickness (150 km) under a normal ("cold") continental geotherm, we are able to reproduce the present-day V P anomaly (Figure 6a; Li et al, 2008;Replumaz et al, 2013), the shear wave velocity profile (Figure 6b; Vozar et al, 2014), and the low mantle density (Figure 6c) inferred from the topography and gravity data of the Tibet Plateau (Tunini et al, 2016). The persistence up to present day of a metasomatic mineralogy in the lithospheric mantle of Eastern-Central Tibet can thus explain the geophysical observations without recourse to lithospheric thinning and associated asthenospheric upwelling.…”

Possible compositional effects on the electrical conductivity of olivine: A preliminary study

“…Alternatively MT can be used to investigate very deep (100s of km) features, such as the structure of the upper mantle, with the low frequency (i.e. long wavelength) component (Tarits et al, 2004;Ichiki et al, 2006;Meqbel et al, 2014;Vozar et al, 2014;Cherevatova et al, 2015;Kahn et al, 2015;Zhang et al, 2015). In order to see deep features, such as those expected to exist within the mantle, it is necessary to record over long time periods (> 1 month) (Selway, 2014;Selway et al, 2014).…”