Structure of the Malpelo Ridge (Colombia) from seismic and gravity modelling
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ORIGINAL PAPER
Structure of the Malpelo Ridge (Colombia) from seismic and gravity modelling Boris Marcaillou Æ Philippe Charvis Æ Jean-Yves Collot
Received: 27 March 2006 / Accepted: 28 August 2006 / Published online: 2 November 2006 Springer Science+Business Media B.V. 2006
Abstract Wide-angle and multichannel seismic data collected on the Malpelo Ridge provide an image of the deep structure of the ridge and new insights on its emplacement and tectonic history. The crustal structure of the Malpelo Ridge shows a 14 km thick asymmetric crustal root with a smooth transition to the oceanic basin southeastward, whereas the transition is abrupt beneath its northwestern flank. Crustal thickening is mainly related to the thickening of the lower crust, which exhibits velocities from 6.5 to 7.4 km/s. The deep structure is consistent with emplacement at an active spreading axis under a hotspot like the present-day Galapagos Hotspot on the Cocos-Nazca Spreading Centre. Our results favour the hypothesis that the Malpelo Ridge was formerly a continuation of the Cocos Ridge, emplaced simultaneously with the Carnegie Ridge at the Cocos-Nazca Spreading Centre, from which it was separated and subsequently drifted southward relative to the Cocos Ridge due to differential motion along the dextral strike-slip Panama Fracture Zone. The steep faulted northern flank of the Malpelo Ridge and the counterpart steep and faulted southern flank of Regina Ridge are possibly related to a rifting phase that resulted in the Coiba Microplate’s separation from the Nazca Plate along the Sandra Rift. B. Marcaillou (&) Æ P. Charvis Æ J.-Y. Collot Ge´osciences Azur, UMR CNRS, IRD, UNSA, UPMC, OOV, BP48, 06235, Villefranche-sur-mer, France e-mail: [email protected] Present Address: B. Marcaillou School of Earth and Ocean Sciences, University of Victoria, V8W 2Y2, Victoria, BC, Canada
Keywords Malpelo ridge Æ Galapagos hot spot Æ Cocos-Nazca spreading centre Æ Wide angle seismic Æ Multichanel seismic
Geological setting: tectonic history of the Panama Basin The Malpelo Ridge is a part of the Cocos-Nazca volcanic province related to the interaction between the Galapagos Hotspot and the regional spreading centres (Hey 1977; Lonsdale and Klitgord 1978). These authors proposed that the earliest stage of regional oceanic spreading started when the old Farallon Plate split into the Cocos and Nazca Plates drifting away along the east-west trending Cocos-Nazca Spreading Centre, (Fig. 1). The Galapagos Hotspot, currently located beneath the Galapagos Archipelago, marks the apex of the V-shaped Cocos and Carnegie Ridges system. These volcanic ridges are commonly related to the influence of the Galapagos Hotspot on the Cocos-Nazca Spreading Centre activity. Magnetic anomalies show that the thickened crusts emplaced near the spreading centre have been drifting away since 22.7 m.y. (Barckhausen et al. 2001) (Fig. 1a). The Cocos and Carnegie Ridges represent the tracks of the Galapagos Hotspot on the Cocos and Nazca Plates respectively (Johnson and Lowrie 1972). The c
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