Alkaline Rocks and Carbonatites of the World

Setup during HiTech AlkCarb: an online database of alkaline rock and carbonatite occurrences

Santa Elena

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Occurrence number: 
039-00-005
Country: 
Costa Rica
Region: 
Guanacaste
Location: 
Longitude: -85.88024, Latitude: 10.88287
Carbonatite: 
No

The Santa Elena peninsula is located on the Pacific coast of northern Costa Rica. Most of the peninsula is formed of the serpentinised, peridotitic Santa Elena Nappe composed of spinel harzburgites, and a variety of gabbroic rocks and mafic dykes. Underlying the basal thrust of the nappe is the Santa Rosa Accretionary Complex, exposed along the southern coast around Playa Santa Rosa and in the Protero Grande tectonic window to the east. This complex represents an autochthonous basement of the region, comprising pelagic sedimentary (radiolarites, turbidites, cherts, and shales), and alkaline mafic rocks affected by a low-grade metamorphic overprint. Alkaline rocks are present in several localities both within and cutting through the stratigraphy of this unit, including alkaline basalts and basanites to phonolites. Best exposed at Playa Santa Rosa, alkaline basaltic rocks are present within the sequence of sedimentary rocks as sills, flows, tuffs, and dykes, thought to represent a small, accreted seamount. Of note is their potassic nature uncommon for seafloor basalts, which suggests this seamount formed as a petit-spot volcano. Descriptions of regional geology can be found in Tournon (1994). A database of collated geochemical data including whole rock major and trace element and Sr, Nd, Pb data can be found in Gazel et al., (2006), with further whole rock and amphibole data being found in Buchs et al., (2013).

Age: 
177 ± 0.8 and 173.9 ± 0.5 Ma Ar-Ar basaltic sills, age of accretion ~110 Ma (Buchs et al., 2013)
References: 
BUCHS, D.M., PILET, S., BAUMGARTNER, P.O., COSCA, M., FLORES, K.E. & BANDINI, A.N., 2013. Low-volume intraplate volcanism in the Early/Middle Jurassic Pacific basin documented by accreted sequences in Costa Rica. Geochemistry, Geophysics, Geosystems 14:5 pp 1552-1568. GAZEL, E., DENYER, P. & BAUMGARTNER, P.O., 2006. Magmatic and Geotectonic Significance of Santa Elena Peninsula, Costa Rica. Geologica acta: an international earth science journal 4 pp 193-202 TOURNON, J., 1994. The Santa Elena Peninsula: An ophiolitic nappe and a sedimentary volcanic relative autochthonous. Profil, 7 pp 87-96
Fig 1. Detailed map and stratigraphy of the Santa Rosa Accretionary Complex (Buchs et al., 2013)
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith