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Geology; June 2006; v. 34; no. 6; p. 473-476; DOI: 10.1130/G22259.1
© 2006 Geological Society of America
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Why is lawsonite eclogite so rare? Metamorphism and preservation of lawsonite eclogite, Sivrihisar, Turkey

Donna L. Whitney1 and Peter B. Davis1

1 Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA

A rare occurrence of lawsonite eclogite crops out in a belt of high-pressure rocks in the Sivrihisar Massif, Turkey. Although lawsonite eclogite is predicted to be common at depths of ~45–300 km in subduction zones, lawsonite seldom survives exhumation. In the Sivrihisar Massif, lawsonite eclogite occurs as 5-cm-long to 3.5-m-long pods in lawsonite blueschist and blueschist facies quartzite and marble. We have identified >70 eclogite pods within an ~14 km2 area; most of them are lawsonite bearing. Phase diagrams calculated for Sivrihisar eclogite bulk compositions indicate metamorphic conditions of 21– 24 kbar, ~422–580 °C. High-pressure minerals (omphacite, lawsonite) are synkinematic with respect to the main fabric, and therefore preserve chemical and structural features of high-pressure subduction metamorphism. The presence of both pristine and retrogressed lawsonite eclogite within meters of each other suggests that lawsonite eclogite preservation is related to rapid exhumation and other factors. For example, the effects of exhumation-related deformation ± fluid infiltration may locally overprint some rocks, producing clinozoisite and/or epidote, whereas rocks that escape these effects retain primary lawsonite.

Key Words: eclogite • exhumation • lawsonite • subduction metamorphism • Turkey




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A. H. F. Robertson, O. Parlak, and T. Ustaomer
Melange genesis and ophiolite emplacement related to subduction of the northern margin of the Tauride-Anatolide continent, central and western Turkey
Geological Society, London, Special Publications, January 1, 2009; 311(1): 9 - 66.
[Abstract] [Full Text] [PDF]


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