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Abstract

The infrastructure of the massive consists essentially of amphibolites, gneisses and micaschists intruded by a biotite granite and the successive hololeucocratic phase. The mantling rocks of the suprastructure comprise metapelitic rocks unconformably underlying metacarbonates dated as Middle Devonian- Mesozoic. The infra-suprastructure boundary is interpreted as a surface of transgressive overlap. The rocks of infra and suprastructure are involved in isoclinal folds with ductile deformation along most of the boundary conclusively suggesting in situ position of the suprastructure during the Alpine deformation. The shear planes are discontinous, en echelon and run independently of the infra-suprastructure boundary. A uniform sequence of Palaeozoic rocks, which is not intruded by the granites of the infra-structure, together with the infra-suprastructure boundary being a sedimentary contact, are conclusive evidence for the existence of a Precambrian event. Eradication of Precambrian paragenesis occurs in the flanks of major folds where a complete Alpine zoning exists from very low grade to anatectic conditions as exemplified by the Kesandere section in contrast to the preservation of Precambrian parageneses in the unsheared competent rocks of the infrastructure of the hinge areas. There is no gap in physical conditions with regard to a single episode of deformation. The gap occurring between the infra and the suprastructure is due to different physical conditions of Precambrian and Alpine deformations. Retrograde effects are presumably due to an Alpine imprint on the Precambrian parageneses, whereas they are attributed to a continuous process of deformation with contemporaneous uplift and progressive diminution of physical conditions in the case of imprint on early Alpine parageneses. The interpretation herein presented in relation to nature of infra and suprastructure boundary and metamorphism of Bitlis massive is consistent, for all aspects, with the regional geologic data showing that it is the deformed Alpine passive margin of the Arabian plate.

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