Geochemistry and protoliths of the Hatta metamorphic sole marbles, northern Oman Mountains, United Arab Emirates

Citation

Osman AF & Taman ZI (2011) Geochemistry and protoliths of the Hatta metamorphic sole marbles, northern Oman Mountains, United Arab Emirates. Egyptian Journal of Geology, 55, pp. 349-373.

Abstract
Banded marbles constitute a distinct unit of the Hatta metamorphic sole in the Northern Oman Mountains. The pure and impure marbles were studied petrographically and geochemically to determine their geochemical characteristics and decipher the metamorphic history and variations in their protoliths mineralogy. The marbles are made up mainly of calcite beside pelitic and feldspathic phases. Authigenic albite, with the peculiar "Roe Tourne twinning", is recorded in the marble samples. Crystal and twin morphologies of the calcite define a spectrum that corresponds to increasing temperature from thin twins at very low temperatures to straight thick twins and finally to recrystallization at grain boundaries at high temperatures. All the components necessary for albite authigenesis during metamorphism are supplied by the host rocks. Microstylolites with filling materials are recorded in the marbles; the latter are the product of metamorphic reactions between the detritus and the host rock component (calcite). The metamorphic rocks in the study area show polyphase deformation, mylonitic fabrics, foliation, stretching lineation and folding. The sub-ophiolite metamorphic sole and the upper sedimentary melange (Hawasina Complex) comprise a distinct thrust slice in the Hatta area. The absence or rarity exposures of amphibolites in the Hatta zone may be attributed to the higher level of detachment of the basement blocks during the initial separation from the oceanic crust. Trace elements and REE contents are lower in the pure marbles as compared to in the impure (siliceous) marbles. This is attributed mostly to the concentration of REE in the clay fractions and the authigenic Fe-Mn coats of sediment grains rather than concentration in heavy minerals such as zircon. The marbles show a relatively flat REE normalized pattern with no to fair negative Ce anomaly and positive Eu anomaly. The presence of a positive Eu anomaly is consistent with the authigenic plagioclase enrichment. The (La/Yb), values of the studied marbles are similar to the average values recorded for the Arabian Sea limestone and the Indian ocean carbonates. Evidently, the banded marbles are metamorphosed "Oman Exotic" limestone which crop out within imbricated thrust sheets of the Hatta metamorphic sole beneath the Semail ophiolite .

Keywords
Oman Mountains; Semail ophiolite; metamorphic sole; Hatta marble

Journal
Egyptian Journal of Geology: Volume 55