Exhumation of high-pressure rocks in northeastern Oman

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The exhumation of high- P rocks in the northeast Saih Hatat window, Oman Mountains, formed regional nappes associated with greenschist-facies metamorphism. Exhumation resulted in the juxtaposition of two plates with different structural style, stratigraphy, and metamorphic history. A major crustal discontinuity separates the two plates, with lower-metamorphic-grade rocks in the hanging wall. Lower-plate units were exhumed during strong top-to-the-northeast shearing, resulting in the formation of regional closures that evolved by folding and transposition of the high-pressure fabrics while the lithostatic pressure was decreasing. Upper-plate units were later exhumed with the juxtaposition of the two plates, truncation of lower-plate closures, and the formation of upper-plate nappes that are attenuated and sheathlike toward the upper and lower plate boundary. In some high- P terranes, apparent increases in metamorphic-grade down structural section and low-grade C′-type shear bands are often attributed to extensional exhumation. In Oman, however, these exhumation features formed during crustal-scale contraction at a convergent margin. The low-geothermal-gradient regimes afforded by convergent margins are critical for the generation and preservation of high- P –low- T rocks.