High-resolution Lg attenuation structure of the Colombian crust and its implications for the volcanic mechanism and plate boundary

      A typical triple junction in Colombia is critical for understanding the plate convergence and coupling among the South American plate and the subducting Nazca and Caribbean plates (González et al., 2023). However, locating this triple junction is challenging due to the complex geodynamic evolution and uncertainty in the plate boundaries. Magmatic arc activity has been diverse and discontinuous due to varying subduction angles, resulting in blocks with distinct rheological properties and thermal structures (Lagardère and Vargas, 2021). Seismic Lg waves are a prominent phase in high-frequency regional seismograms (e.g., Gutenberg). Compared with velocity data, seismic wave attenuation is more sensitive to deep materials' temperature and rheological strength (Boyd et al., 2004; Zhao et al., 2013). Therefore, we developed a high-resolution Lg-wave attenuation model for Colombia and surrounding areas to constrain crustal magmatic activity, linking deep dynamic processes with surface volcanism and determining potential plate boundaries at the crustal scale. The ancient and stable Guinan Shield is characterized by weak Lg attenuation. In contrast, the area encompassing Central America, western Colombia, and Ecuador features strong Lg attenuation and concentrated volcanoes, indicating thermal anomalies or partial melting in the crust. Low Q_Lg is shown near the Caldas tear along 5.5°N, speculating that a hydrothermal uplift channel caused by the Nazca plate tear may exist at depth. Based on our results and other geological and geophysical data, the thermal distribution due to the subduction of the Nazca and Caribbean plates suggests that the boundary between the subducting Nazca and Caribbean slabs beneath the South American plate may be located at 7.5°N, and that the potential location of the triple junction may be located at 7.5°N, 77°W. This research was supported by the National Natural Science Foundation of China (U2139206, 41974061, 41974054).

References

Boyd, O. S., Jones, C. H., & Sheehan, A. F. (2004). Foundering Lithosphere Imaged Beneath the Southern Sierra Nevada, California, USA. Science, 305(5684), 660–662.
Hey, R., 1977. Tectonic evolution of the Cocos-Nazca spreading center. Geol. Soc. Am. Bull. 88, 1404.
González, R., Oncken, O., Faccenna, C., Le Breton, E., Bezada, M., Mora, A., 2023. Kinematics and Convergent Tectonics of the Northwestern South American Plate During the Cenozoic. Geochem. Geophys. Geosystems 24, e2022GC010827.
Lagardère, C., Vargas, C.A., 2021. Earthquake distribution and lithospheric rheology beneath the Northwestern Andes, Colombia. Geod. Geodyn. 12, 1–10.
Kellogg, J.N., Vega, V., Stailings, T.C., Aiken, C.L.V., Kellogg, J.N., 1995. Tectonic development of Panama, Costa Rica, and the Colombian Andes: Constraints from Global Positioning System geodetic studies and gravity, in: Geological Society of America Special Papers. Geological Society of America, pp. 75–90.
Vargas, C.A., Ochoa, L.H., Caneva, A., 2019. Estimation of the thermal structure beneath the volcanic arc of the northern Andes by coda wave attenuation tomography. Front. Earth Sci. 7, 208. 
Zhao, L.-F., Xie, X.-B., He, J.-K., Tian, X., & Yao, Z.-X. (2013). Crustal flow pattern beneath the Tibetan Plateau constrained by regional Lg-wave Q tomography. Earth and Planetary Science Letters, 383, 113–122.