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Chapter 10: Earthquake, Tomographic, Seismic Reflection, and Gravity Evidence for a Shallowly Dipping Subduction Zone beneath the Caribbean Margin of Northwestern Colombia
Earthquake hypocenter relocations, earthquake focal mechanisms, P-wave velocity anomaly tomography, interpretation of deep-penetration seismic reflection lines, and gravity modeling are integrated to define an ESE, 110°-dipping zone of shallow subduction beneath northwestern Colombia. These data define a 15- to 16-km-thick (9.3–9.9 mi), late Cretaceous oceanic plateau (Caribbean plate) that is actively subducting with anomalous low Benioff zone seismicity at a dip of 3–8° over a down-dip distance of 200 km (124 mi) beneath a deformed sedimentary wedge (South Caribbean deformed belt). At a down-dip distance of 450 km (280 mi) from the frontal thrust of the accretionary wedge and at a depth of 130 km (81 mi), tomographic data show that the largely aseismic, subducting Caribbean plate bends and steepens to a dip of 28°–50°. In the depth range of 80–130 km (50–81 mi), tomographic data show that the subducted Caribbean slab exhibits a low-velocity anomaly that we interpret as evidence for slab delamination and enhanced dehydration by rising asthenosphere. Tomographic data beneath the middle Magdalena Basin of northern Colombia show a thick, cold continental lithosphere (ca 60–100 km [37–62 mi]) while gravity data beneath the lower Magdalena Basin show a thin continental crust (24–27 km [15–17 mi] thick) beneath which the Caribbean slab dips in the range of 40–50°. Minor subduction-related volcanism is present in the eastern Cordillera likely as a result of shallow subduction limiting the size of the mantle wedge that is needed for slab melting and arc-related volcanism. Understanding the subduction setting of northern Colombia is fundamental for understanding its heat flow, tectonic history, controls on subsidence, and other parameters needed for petroleum exploration both onshore and offshore.
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