Petrology of clinopyroxene-amphibole inclusions from the roque nublo volcanics,gran canaria,canary islands |
| |
| Authors: | T Frisch H U Schmincke |
| |
| Institution: | 1. Department of Geological Sciences, Virginia Polytechnic Institute, Blacksburg, Va., USA
3. Mineralogisches Institut, Ruhr Universit?t, Postfach 2148, 463 Bochum, Germany
|
| |
| Abstract: | Inclusions consisting of clinopyroxene, amphibole, Fe-Ti oxides and apatitc are abundant in the Roque Nublo volcanics, a unit of Late Tertiary age that is widespread on Gran Canaria Island. The unit includes alkalic basalts and breccias. Mafic minerals in several inclusions and in one basalt host have been analysed with the electron microprobe. Although the inclusions vary in size, texture and mineralogy, they show certain common teatures. The pyroxenes analyzed are all salites-augites and their position in the Ca-Fe Mg quadrilateral suggests that they are early formed representatives of the pyroxene crystallization trend characteristic of alkaliolivine basalt. The amphibole is invariably kaersutite. A common variety of inclusion is composed largely of kaersutite and titaniferous clinopyroxene. The kaersutite (TiO2 5.27%, K2O 1.58%) is homogeneous, except for slight iron enrichment in the margins of crystals. The clinopyroxene is an hourglass-zoned, brownish titansalite, Ca 50 Mg 35 Fe 15, TiO2 3.08%, with a green core of Ca 49 Mg 38 Fe 13, TiO2 2.15%. Compositions of coexisting titanilerous magnetite and ilmenite, Usp 44 Mt 56 and Ilm 85 Hem 15, respectively, indicate they formed at approximately 975°C and pO, 10?10.5 atm. In another type of inclusion and its host basalt, pyroxene relations are more complex. Inclusion pyroxene is markedly but diffusely zoned. Predominant is a green salite, Ca 47 Mg 38 Fe 15, TiO2 1.11%, which has small, patchy core zones of brownish. Ti-rich salite. Ca 48 Mg 35 Fe 17, TiO2 1.94%. Cores of crystals in the host basalt are Ca 47 Mg 41 Fe 12, TiO2 2.23%; rims are pale green, Cr-rich diopsidic augite, Ca 44 Mg 45 Fe 11, TiO2 1.32%, Cr2O3 0.48%. This «reverse» Fe-Mg zoning is attributed to increasing partial pressure of oxygen as crystallization proceeded. Kaersutite similar to that mentioned above occurs in both the inclusion and its host, in which it is highly resorbed. The available field and analytical evidence strongly suggests that the inclusions and the associated basalts are genetically related. Resorption of the kaersutite at depth may have given rise to the alkalic basalts of the Roque Nublo series. |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
