Thermochemical structure of the lithosphere and upper mantle beneath Superior craton: Results from multi-observable probabilistic inversion

<p>We present new thermochemical models of the lithosphere and upper mantle beneath the Superior craton and surrounding regions. The study area is dominated by the Archean Superior Province, surrounded by Proterozoic orogenic belts such as the Trans-Hudson Orogen (THO) to the north and the Grenville Orogen to the southeast. Portions of the Rae and Hearne cratons north of the THO are also studied, as is the Mid-continent Rift to the south. Over a period of ∼3 Ga, the region has seen assembly and modification by accretionary and orogenic events, periods of rifting, and the influence of a number of mantle hotspots. Here, we use a probabilistic inverse method to jointly invert Rayleigh wave dispersion data, Vp data, geoid anomalies, surface heat flow, and absolute elevation. The output is a 3D model of the seismic, temperature, bulk density, and compositional structure of the whole lithosphere beneath the Superior craton.</p><p>The resulting model will provide new opportunities for joint studies of the structure of the upper mantle and will shed light on the thermal and compositional variations beneath the region. In this presentation, we will discuss the results from our model and several robust features that carry important geological and geodynamical implications for this region.</p>

Crustal and Upper Mantle Density Structure Beneath the Qinghai-Tibet Plateau and Its Surrounding Areas Derived from EGM2008 Geoid Anomalies

As the most active plateau on the Earth, the Qinghai-Tibet Plateau has a complex crust-mantle structure. Knowledge of the distribution of such a structure provides information for understanding the underlying geodynamic processes. We obtains a three-dimensional density model of crustal and upper mantle beneath Qinghai-Tibet plateau and its surrounding areas from the residual geoid anomalies using the Earth Gravitational Model (EGM) 2008. We estimate a refined density model by iterations, using an initial density contrast model. We confirm that the EGM2008 mission products can be used to constrain the crust-mantle density structures. Our major findings are: (1). At 300-400 km depth, high-D anomalies terminate around Jinsha River Suture (JRS) in the central TP, suggesting that the Indian plate has been reached over the Bangong Nujiang Suture (BNS) and almost reach to the JRS. (2). On the eastern TP, low-D anomalies at the depth of 0-300 km together with high-D anomalies at 400-670 km further verified the current eastward subduction of Indian plate. The ongoing subduction provides forces to the occurrences of frequent earthquakes and volcano. (3). At 600 km depth, low-D anomalies inside the TP illustrate the existence of hot weak material beneath there, contributing to the external material inward-thrusting.