T029-08
Receiver Function Mapping of Mantle Transition Zone Discontinuities Beneath Western Alps Using Scaled 3-D Velocity Corrections

Thursday, 10 December 2020: 16:28
Virtual
Dongyang Liu1,2, Liang Zhao2, Huaiyu Yuan3,4 and Anne Paul5, (1)University of Chinese Academy of Sciences, College of Earth and Planetary Sciences, Beijing SHI, China, (2)Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China, (3)Centre for Exploration Targeting, University of Western Australia, Perth, Australia, (4)ARC Centre of Excellence for Core to Crust Fluid Systems, Macquarie University, North Ryde, Australia, (5)Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, IRD, IFSTTAR, ISTerre, Grenoble, France
Recorded Presentation
Abstract:
The Alps orogenic belt resulted from continental collision between the Eurasian and Adriatic plates. The Western Alps orogenic belt has a complex tectonic history and the deformation in and around the Alps are significantly affected by several microplates and orogenic belts. The mantle transition zone is delineated by seismic velocity discontinuities around the depths of 410 and 660 km which are generally interpreted as polymorphic phase changes in the olivine system and garnet-pyroxene system. Previous tomographic models have revealed fast velocity anomalies localized deep in the mantle transition zone and piled up at 660km depth. Earlier seismic results however have not revealed the actual range extent of the subducting slab. In this study, we use P-to-S converted waves to study the 410 km and 660 km discontinuities beneath Western Alps.

This study uses data collected from 293 permanent and temporary broadband seismic stations (e.g., CIFALPS). Teleseismic events are selected from 30o to 90o epicentral distrance with magnitudes (Mw) between 5.3 and 8.5. Data are carefully checked by automated and manual procedures to give a total of 20514 receiver functions. Both 1D velocity model of the IASP91 and 3D velocity model of the EU60 are used for time-to-depth migration. The structure of the mantle transition zone revealed by the two velocity models has very similar characteristics but there are differences in the absolute depth of the discontinuity, suggesting large effects on the receiver functions caused by 3D velocity heterogeneities in the alps.

In the northern part of the study area, along the alpine orogenic belt, we find a localized arc-shaped thinning area with a depressed 410 discontinuity, which is attributed to hot mantle upwellings. The uplift is hardly seen on the 660 discontinuity, suggesting that the thermal material originates within transition zone. The depth of 410-discontinuity is found close to the global average depth in other regions. For the 660 discontinuity, the whole Alpine region has greater depth than global model predictions: the transition zone thickness in the western Alps is up to 40 km thicker than global model. This thickened mantle transition zone is likely attributed to the remnants from the oceanic mantle lithosphere that detached from the Eurasian plate after closure of the Alpine Tethys.

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