Formation of sapphirine during retrogression of a basic high-pressure granulite,Roan, Western Gneiss Region,Norway |
| |
Authors: | Leif Johansson Charlotte Möller |
| |
Institution: | (1) Department of Mineralogy and Petrology, Institute of Geology, University of Lund, Sölvegatan 13, S-223 62 Lund, Sweden |
| |
Abstract: | Sapphirine-bearing rocks occur in the northern part of the Western Gneiss Region, Vestranden, central Norway. The sapphirine-bearing rocks are characterized by a high MgO/(MgO + FeO) ratio, high Al2O3, MgO and CaO, and low SiO2 contents. These rocks form layers within larger complexes which originated as layered magmatic rocks. High PT-metamorphism produced a cpx+ky+gt assemblage. The P and T estimates are P = 14.5±2 kbar and T= 870±50° C. During retrogression, the high-P granulite assemblage broke down to form an intermediate-P granulite mineralogy comprising orthopyroxene, spinel, anorthite, andesine, sapphirine and corundum. Textural relationships suggest that sapphirine formed by the reaction: spinel+kyanite sapphirine+corundum, and probably also by a reaction between corundum, spinel and orthopyroxene. All reactions took place within the stability field of kyanite. Textural and micro-chemical relationships indicate equilibrium, conditions during the peak metamorphism, whereas pronounced disequilibrium characterizes the mineral associations formed during the early retrogression at low P
H2O. The investigation shows that parts of the northern segment of the Western Gneiss Region underwent a metamorphic evolution similar to the Caledonian one recorded from eclogite/granulite terrains further south. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|