Origin and emplacement of Tertiary ultramafic complexes in northwest Colombia: Evidence from geochemistry and K-Ar, Sm-Nd and Rb-Sr isotopes

Details Origin and emplacement of Tertiary ultramafic complexes in northwest Colombia: Evidence from geochemistry and K-Ar, Sm-Nd and Rb-Sr isotopes Origin and emplacement of Tertiary ultramafic complexes in northwest Colombia: Evidence from geochemistry and K-Ar, Sm-Nd and Rb-Sr isotopes

Aug 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994e%26psl.126...41t&link_type=abstract

Earth and Planetary Science Letters (ISSN 0012-821X), vol. 126, no. 1-3, p. 41-59

Physics

Geophysics

3

Basalt, Earth Mantle, Geochemistry, Geophysics, Plates (Tectonics), River Basins, Tectonics, Magnesium Compounds, Melting, Radioactive Decay, Radioactive Isotopes, Silicon Compounds, South America

Scientific paper

Si-undersaturated high-Mg basalts with early fractionated ultramafic cumulates (Viravira complex) and a zoned ultramafic Alaskan-type intrusion (Condoto complex) are located in the upper Condoto River within the Western Cordillera of Colombia. These complexes are related in space and time and originated from a common parental magma. The isotopic characteristics of the complexes are similar and plot close together near the mantle array in the epsilon(sub Nd) vs. epsilon(sub Sr) diagram. It is argued that the compositions of the Viravira basalts and of geochemically comparable hornblende-plagioclase dykes in the zoned complex are close to the parental melt from which both complexes derived. This melt probably had a mafic tholeiitic composition and was supplied from two sources: high-grade partial melting (20%) of moderately depleted mantle above a subduction zone (major part), and modification by a metasomatic LILE- and slightly LREE-enriched fluid which could have originated by dewatering of the subducting slab. K-Ar dates of hornblende of the Condoto complex indicate an emplacement age of about 20 Ma. This represents the youngest age on the earth of a zoned ultramafic intrusion. The occurrence of these (and further) ultramafic complexes along a major N-S strike-slip fault substantiates an exceptional tectonic activity on the northwestern edge of the South American continent during the Tertiary. Horizontal plate movements along the deeply penetrating fault system favored a release of pressure, and the formation of Si-undersaturated Mg-rich melts in the mantle. High heat flow and the possibility of vertical migration allowed the intrusion of mantle-derived melts into shallow levels of the upper crust.

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