Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (5) Citing Articles via Google Scholar Google Scholar Articles by Whitney, D. L. Search for Related Content GeoRef GeoRef Citation

Coexisting andalusite, kyanite, and sillimanite: Sequential formation of three Al₂SiO₅ polymorphs during progressive metamorphism near the triple point, Sivrihisar, Turkey

Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota 55455, U.S.A.

Correspondence: ^* E-mail: dwhitney{at}umn.edu

Regionally metamorphosed, muscovite-bearing quartzites from Sivrihisar, Turkey, contain coexisting andalusite, kyanite, and sillimanite. Kyanite is the most abundant polymorph and defines a lineation along with prismatic sillimanite, andalusite, staurolite, and elongate quartz. Andalusite is the most Fe-rich of the polymorphs (0.9–1.6 wt% Fe₂O₃, compared with 0.6–0.9 wt% for kyanite and sillimanite), and was ductilely deformed. Staurolite has partially pseudomorphed kyanite, and occurs intergrown with sillimanite. Garnet occurs in some metaquartzites and interlayered mica schists. Mica schists lack Al₂SiO₅ polymorphs. Porphyroblasts in mica schists are chloritoid, chloritoid + staurolite ± garnet, or staurolite ± garnet with inclusions of chloritoid and staurolite.

Textural relations and relative deformation features among the three polymorphs suggest the crystallization sequence andalusite kyanite sillimanite, with growth of staurolite primarily in the sillimanite stability field. Results of garnet-biotite thermometry and estimates of peak P-T conditions from petrogenetic grids are ~540–560 °C. Maximum pressure is not known, but there is no evidence for the high-pressure – low-temperature conditions that affected similar rocks to the northwest in the Sivrihisar massif. The stable coexistence of staurolite + sillimanite at peak metamorphic conditions suggests a maximum pressure of 5.5 kbar. The three polymorphs grew sequentially along a clockwise P-T path that looped around the Al₂SiO₅ triple point during incipient subduction of a continental margin sequence (burial: andalusite kyanite), followed by collision (heating and/or decompression: kyanite sillimanite).

This article has been cited by other articles:

				S. Aryal, P. Rulis, and W.Y. Ching Density functional calculations of the electronic structure and optical properties of aluminosilicate polymorphs (Al2SiO5) American Mineralogist, January 1, 2008; 93(1): 114 - 123. [Abstract] [Full Text] [PDF]

				D. L. Whitney and P. B. Davis Why is lawsonite eclogite so rare? Metamorphism and preservation of lawsonite eclogite, Sivrihisar, Turkey Geology, June 1, 2006; 34(6): 473 - 476. [Abstract] [Full Text] [PDF]