Petrology and geochemistry of komatiites and tholeiites from Gorgona Island,Colombia |
| |
| Authors: | Aitken Bruce G Echeverría Lina M |
| |
| Institution: | (1) Abteilung Geochemie, Max Planck Institut für Chemie, Saarstr. 23, D-6500 Mainz, Federal Republic of Germany;(2) Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, 20015 Washington D.C., USA;(3) Present address: Research and Development Division, Corning Glass Works SP FR 05-1, 14831 Corning, New York, USA |
| |
| Abstract: | Komatiitic rocks from Gorgona Island, Colombia, in contrast to their Archaean counterparts, occur as rather structureless flows. In addition, textural and mineralogical features indicate that the Gorgona komatiites may have crystallized from superheated liquids. Komatiitic rocks have MgO contents which range from 24 to 11 wt.% and plot on well-defined olivine (Fo90) control lines. Calculations show that potential evolved liquids (MgO<11 wt%) will be SiO2-poor. Komatiites, in this case, cannot be regarded as parental to the associated tholeiitic basalt sequence.On the basis of REE concentrations and Sr, Nd isotopic compositions, the associated basalts are found to be of two types. One type (K-tholeiite) is characterized by noticeably fractionated REE patterns and relatively primitive isotopic compositions similar to those of the komatiites. K-tholeiites, together with komatiites, are regarded as comprising a distinctive komatiitic suite. REE patterns within this suite show progressive depletion in the LREE from K-tholeiites to komatiites, and represent increasingly higher degrees of melting of the same mantle source region. The other type (T-tholeiite), representative of the bulk of the exposed basalt sequence, has flat REE patterns and relatively evolved isotopic compositions. This tholeiitic suite is clearly genetically unrelated to the komatiitic suite. |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
