A Mid Cretaceous origin for the Galápagos hotspot: volcanological, petrological and geochemical evidence from Costa Rican oceanic crustal segments

Abstract

The Quepos, Nicoya and Herradura oceanic igneous terranes in Costa Rica are conspicuous features of a Mid to Late Cretaceous regional magmatic event that encompasses similar terranes in Central America, Colombia, Ecuador and the Caribbean. The Quepos terrane (66 Ma), which consists of ol-cpx phyric, tholeiitic pillow lavas overlain by highly vesicular hyaloclastites, breccias and conglomerates, is interpreted as an uplifted seamount/ocean island complex. The Nicoya ( &90 Ma) and Herradura terranes consist of fault-bounded sequences of sediments, tholeiitic volcanics (pillow lavas and massive sheet flows) and plutonic rocks. The volcanic rocks were emplaced at relatively high eruption rates in moderate to deep water, possibly forming part of an oceanic plateau. Major and trace element data from Nicoya/Herradura tholeiites indicate higher melting temperatures than inferred for normal mid-ocean-ridge basalts (MORB) and/or a different source composition. Sr-Nd-Pb isotopic ratios from all three terranes are distinct from MORB but resemble those from the Gala´pagos hotspot. The volcanological, petrological and geochemical data from Costa Rican volcanic terranes, combined with published age data, paleomagnetic results and plate tectonic reconstructions of this region, provide strong evidence for a Mid Cretaceous ( &90Ma) age for the Gala´pagos hotspot, making it one of the oldest known, active hotspots on Earth. Our results also support an origin of the Caribbean Plate through melting of the head of the Gala´pagos starting plume.

From seamount accretion to tectonic erosion: Formation of Osa Mélange and the effects of Cocos Ridge subduction in southern Costa Rica

“…[58] Accretion of the Osa Igneous Complex and Osa Mélange from the Farallon to the Caribbean plate is implied by the geochemical and isotopic composition of the their igneous component [Hauff et al, 1997;Hoernle et al, 2002].…”

“…Volcanology, petrology, and sedimentology of igneous rocks and associated sediments suggest that the Osa Igneous Unit once formed part of an aseismic ridge similar to the Cocos Ridge presently being subducted beneath the Osa Peninsula. The Osa and Quepos igneous complexes are interpreted to be part of the subsequent Galapagos hot spot track after the oceanic plateau migrated to the east [Hauff et al, 1997[Hauff et al, , 2000. Younger, 20-38 Ma, accreted Galapagos terranes have been found in the western Panama Azuero Peninsula, where Hoernle et al [2002] hypothesized the hot spot track to have been subducted between $25 and 8-5 Ma.…”

“…Here it is worth mentioning that the igneous complexes exposed in Costa Rica represent either the Caribbean Large Igneous Province (CLIP), emplaced between 74 and 94 Ma [Sinton et al, 1998], or accreted ocean islands and aseismic ridge terranes [Hauff et al, 1997;Sinton et al, 1997;Hauff et al, 2000] (Figure 2). The 60 -25 Ma Quepos and Osa terrains, in fact, are interpreted to reflect rocks accreted from subducted edifices generated by the Galapagos hot spot [Hauff et al, 1997[Hauff et al, , 2000 (Figures 1a and 2). Crucially there is no evidence that the Costa Rican forearc is composed of an accretionary complex of tectonized sediments offscraped from the currently subducting plate Vannucchi et al, 2001;Fisher et al, 2004].…”

“…Wildberg [1984] proposed an island arc affinity for the ophiolites present in the inner part of the Osa Peninsula and around Golfito. Petrographic work since then, however, has documented that the oceanic igneous rocks of Golfito and Osa do not belong to the same oceanic environment [Hauff et al, 1997[Hauff et al, , 2000Hoernle et al, 2002].…”

“…[10] Combined biostratigraphic, geochemical, petrological, and 40 Ar/ 39 Ar age dating studies indicate that the vast majority of the igneous rocks of the Golfito ophiolites formed between 92 and 75 Ma from a source compatible with the Galapagos hot spot [Hauff et al, 1997;Sinton et al, 1997;Hauff et al, 2000]. Moreover the volcanic facies of the extrusive rocks of the Golfito ophiolites and their high sulfur content in the fresh tholeiitic glasses indicate eruption in a deep marine environment [Sinton et al, 1997;Hauff et al, 2000].…”