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Small Domes, Big Picture: magmatic signatures across the slab tear in central Colombia

Lydia J. Harmon1,2 , Christy B. Till2, Agustin Cardona3, Juan S. Jaramillo-Ríos3,4

  • Affiliations: 1Department of Geology, Occidental College, Los Angeles, USA; 2School of Earth & Space Exploration, Arizona State University, Tempe, USA; 3Departamento de Procesos y Energía, Universidad Nacional de Colombia Sede Medellín, Medellín, Colombia; 4Departamento Académico de Ingeniería, Pontificia Universidad Católica del Perú, Lima, Perú  

  • Presentation type: Talk

  • Presentation time: Thursday 16:15 - 16:30, Room S160

  • Programme No: 3.7.7

  • Theme 3 > Session 7

Abstract

Modern-day Colombia provides an active natural laboratory to better understand flat slab subduction. Here, geophysical surveys suggest the subducting Nazca plate is torn at ~5.5°N, with flat slab subduction north of the tear and classic, steeply dipping subduction to the south. We investigate small domes that postdate the Caldas tear to interrogate the tectonic and magmatic processes that led to their formation. We present whole-rock data, new mineral compositions and whole-rock isotopes (Sr, Nd, Pb) from three dome fields -- with two domes to the north and six to the south of the tear. Overall, the domes have a calc-alkaline arc-like signature and are compositionally similar to modern polygenetic Colombian arc volcanism. The northern and southern domes are distinguished by mineralogy (amphibole ± biotite in the north; pyroxene in the south), mineral chemistry, and whole-rock isotopic signatures (higher 87Sr/86Sr and lower 208Pb/206Pb in the south), indicating differences in their origins north and south of the Caldas tear. Further, multiple plagioclase populations within single domes reveal complex histories of magma evolution even at individual domes. These geochemical similarities and differences between the domes allow us to contextualize them in the wider Colombian volcanic history. Together, their geochemical signatures point towards a difference in the petrologic origins of the northern and southern domes after the slab tear formed. On-going work aims to understand the P-T-H2O conditions of magma formation and storage and details of the petrologic mechanisms that gave rise to these magmas.