Origin of compositional layering and mechanism of crustal thickening in the high-grade gneiss terrain of Sri Lanka

Abstract:

The Highland Complex of Sri Lanka comprises a ∼ 7 km thick succession of banded para- and orthogneisses, at granulite-grade or partly retrograded. We interpret this Complex as a tectonostratigraphic unit in which no primary stratigraphy is preserved. This succession, with a probable depositional age of ∼ 2 Ga, evolved from a rift basin into a foredeep and then into a fold-and-thrust belt prior to severe flattening and transport into the lower crust during the final stages of collision some 550-620 Ma ago. Granitoid rocks were emplaced into the supra-crustal sequence at various stages of the tectonic evolution between ∼ 1950 and ∼ 670 Ma ago, and the original intrusive contacts became obscured or severely modified during progressive non-coaxial ductile deformation. Structures that predate the presently observed layering are preserved in rootless isoclinal folds, boudins and microstructures, and in deformed pre-granulite metamorphic minerals preserved in garnet porphyroblasts. The evolution of the Highland Complex is similar to that of other Precambrian granulite terrains, notably parts of the Grenville Province of Canada, and probably resulted from collisional tectonics, during which the original supracrustal assemblage was detached from its Archaean to Palaeoproterozoic basement. The paucity of structures reflecting the early deformational history is due to severe flattening and ductile deformation during predominantly non-coaxial deformation when the Highland rocks were transported into the lower crust. © 1994.

Año de publicación:

1994

Keywords:

Fuente:

scopus