Petrography,petrology and tectonic implications of Mitre Island,northern Fiji Plateau |
| |
| Authors: | Peter A Jezek Wilfrad B Bryan Stephen E Haggerty HPaul Johnson |
| |
| Institution: | 1. Mineral Sciences, Smithsonian Institution, Washington, D.C. 20560 U.S.A.;2. Woods Hole Oceanographic Institution, Woods Hole, Mass. 02543 U.S.A.;3. Department of Geology, University of Massachusetts, Amherst, Mass. 01002 U.S.A.;4. Department of Oceanography, University of Washington, Seattle, Wash. 98195 U.S.A. |
| |
| Abstract: | Mitre Island samples, Pliocene in age, can be classified together with Anuda samples, of unknown age, as island-arc basaltic andesites with tholeiitic tendencies. The presence of morphologically unusual iron—titanium oxides and of probably xenocrystic plagioclase suggest that at least part of the observed minerals crystallized in a magma chamber underlying the island. The samples apparently represent a mixture of magma fluid, cumulate plagioclase, pyroxene, and iron—titanium oxides which were ponded in a crater lava lake where they were reheated by subsequent eruptions. Many of them show symplectic magnetite formed by high-temperature oxidation of olivine. The morphological complexity and compositional homogeneity of the iron—titanium oxides cannot be explained at present.The presence of sulfide droplets inside olivine, magnetite and ilmenite crystals suggests a formation of an immiscible sulfide liquid in the magma chamber. Droplets of this liquid were overgrown by minerals crystallizing at that time and thus protected against oxidation during and after eruption.Mitre Island is a part of a currently inactive Vitiaz island arc associated in the past with a westward subduction of Pacific plate along the Vitiaz trench. Increased difficulty in subducting the large mass of the Pacific Border Plateau under the northern Fiji Plateau apparently produced counterclockwise rotation of the Vitiaz island arc. Oblique subduction was active until a steep angle was reached between the Vitiaz trench and the motion vector of the Pacific plate. Then a strike-slip fault developed in the Vitiaz trench and the subducted plate was sheared off. Recently the strike-slip zone migrated south from the Vitiaz trench across the northern Fiji Plateau and is presently extending from Aoba Island, in the New Hebrides, northeastward toward the Pacific Border Plateau. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
