Abnormal Seismological and Magmatic Features in South America Controlled by the

Tearing Flat Slabs

Jiashun Hu* and Lijun Liu

Department of Geology, University of Illinois at Urbana-Champaign, 605 E.

Springfield Ave, Champaign, IL, 61820, USA

*email: jhu16@illinois.edu

Supplementary Online Materials

Figure S1. The evolution of volcanic distribution in Peru from 14 Ma to the present day. Black lines represent the slab upper surface (300 °C cooler than the ambient mantle) at different depths. Dark gray patterns show the reconstructed locations of the Inca Plateau and the Nazca Ridge. Light gray area represents subducted seafloors at the present. Red triangles indicate the location of extrusive volcanism, while orange triangles represent that of intrusive volcanism (online catalog of Peruvian Mining and Metallurgical Geological Institute – INGEMMET, http://www.ingemmet.gob.pe). Red stars represent the adakitic eruption.

Figure S2. Same as Figure S1, except that the volcanic data is from Isotopic Dates: Andean Igneous Rocks LE 150 Ma (http://bbs.keyhole.com/ubb/showflat.php/Cat/0/Number/994404/an/0/page/0# 994404)

Figure S3. Plate velocity and seafloor age at (a) 20 Ma, (b) 10 Ma and (c) the present day. White arrows show the plate velocity. Background color represents the seafloor age. Black regions represent the reconstructed position of oceanic plateau and aseismic ridges with dashed contours delineating the already subducted part. Dark gray region shows the South American continent and light gray regions show the cratons in South America.

Figure S4. Comparison of predicted slab geometry (background color representing temperature) with Slab1.0 (Hayes et al., 2012) depth contour (thick green lines) at five different depths. Brown and transparent blue outline the reconstructed geometry of continental cratons and oceanic plateaus (including aseismic ridges). Notice the overall fit of our model with slab 1.0.

Figure S5. Further comparison of predicted slab geometry (c) where background color represents temperature variation with a recent tomography model where both P-wave velocity (a) and S-wave velocity (b) are shown (sub-figures a and b are from Scire et al., 2016).

Figure S6. Cross sections showing the subduction of Inca Plateau at (a) 9 Ma, (b) 7 Ma, (c) 4 Ma and (d) present day. All the cross sections are E-W along 6°S latitude. We see strong upwellings at 9 Ma and 7 Ma when the Inca Plateau began to subduct.

Figure S7. Intermediate-depth seismicity distribution (Mb > 4, from ISC seismic catalog) at the trench where Carnegie Ridge subducts. Yellow dots represent earthquakes at depth between 70 km and 115 km; red dots at depth between 115 km and 160 km; green dots at depth between 160 km and 205 km; blue dots at depth between 205 km and 250 km.

Reference:

Hayes, G.P., D.J. Wald & R.L. Johnson, Slab1.0: A three dimensional model of global ‐subduction zone geometries, J. Geophys. Res., 117, B01302 (2012).

Scire, Alissa, George Zandt, Susan Beck, Maureen Long, Lara Wagner, Estela Minaya, Hernando Tavera, Imaging the transition from flat to normal subduction: variations in the structure of the Nazca slab and upper mantle under southern Peru and northwestern Bolivia. Geophysical Journal International, 204(1), 457-479 (2016).