Mantle structure and the tectonic evolution of SE Asia and the SW Pacific

Robert Hall & Wim Spakman

Aims
Some important aspects of the geological evolution of SE Asia are reflected in the structure of the lithosphere in the mantle and the mantle itself. The mantle also contains a record of some of the history of plate motions in and around the region. Understanding more about the mantle beneath SE Asia and interpreting the tectonic record it contains is part of our continuing research.

Background

Subducted lithosphere produces a strong temperature anomaly in the upper mantle which causes slabs to be detectable as regions with relatively fast seismic wave speeds. P- and S-wave tomography can identify these anomalies which can then be interpreted in terms of tectonic models. The P-wave global tomographic model of Wim Spakman at Utrecht allows variation in cell dimensions as a function of local seismic data density which can show many details of mantle structure at a fine scale and thus reveal past subduction. The smallest cells have dimensions of 0.6 degrees laterally and 35 km in depth. SE Asia and the SW Pacific is a complex and actively deforming part of the globe which includes some of the fastest moving plates on Earth. Present-day plate motions offer some insight into the recent history of the region but provide only a snapshot of tectonic history. Reconstructions based on geological evidence interpret where lithosphere has been subducted and how much has been consumed but during subduction and collision evidence is destroyed. Thus, distinguishing between the many different tectonic models can be difficult. Tomography provides an independent insight into tectonic evolution which can be used to test tectonic reconstructions.

Recent Papers –

Max Webb et al., 2020. Isotopic mapping reveals the location of crustal fragments along a long-lived convergent plate boundary. Lithos.

https://doi.org/10.1016/j.lithos.2020.105687

Max Webb et al., 2020. The history of Cenozoic magmatism and collision in NW New Guinea – New insights into the tectonic evolution of the northernmost margin of the Australian Plate. Gondwana Research.

https://doi.org/10.1016/j.gr.2019.12.010

Amy Gough et al., 2020. Mid-Cenozoic fluvio-deltaic to marine environments of the Salin Sub-basin, Central Myanmar. Journal of Asian Earth Sciences.

https://doi.org/10.1016/j.jseaes.2019.104143

Recent News –

Amy Gough and Max Webb attended the Restech 2.0 Virtual Reservoir Conference. Amy Gough presented new SEARG research on the pitfalls of light mineral studies for sedimentary provenance in tropical climates.

Amy Gough was awarded an honorary research fellowship of the British Geological Survey and continues to foster collaborative relationships between SEARG and the BGS.