Transient slab flattening beneath Colombia

Subduction of the Nazca and Caribbean Plates beneath northwestern Colombia is seen in two distinct Wadati Benioff Zones, one associated with a flat slab to the north and one associated with normal subduction south of 5.5 degrees N. The normal subduction region is characterized by an active arc, whereas the flat slab region has no known Holocene volcanism. We analyze volcanic patterns over the past 14 Ma to show that in the mid-Miocene a continuous arc extended up to 7 degrees N, indicating normal subduction of the Nazca Plate all along Colombia's Pacific margin. However, by similar to 6 Ma, we find a complete cessation of this arc north of 3 degrees N, indicating the presence of a far more laterally extensive flat slab than at present. Volcanism did not resume between 3 degrees N and 6 degrees N until after 4 Ma, consistent with lateral tearing and resteepening of the southern portion of the Colombian flat slab at that time.