A comparison of deformation mechanisms and thermal histories in a modern and ancient arc-continent collision

Arc-continent collisions (ACC) are important in the growth of continental crust where accretion occurs through the collision of intra-oceanic volcanic arcs with continental margins. This comparative study of an active and a fossil ACC provides a 4-dimensional (space and time) perspective into the process of ACC and an overall insight into this significant plate tectonic process. Slaty rocks of the active Lishan fault of Taiwan are accommodating upper crustal deformation in the ongoing collision of the Luzon arc with the eastern Chinese continental margin. In contrast, the Blue Ridge Province of North Carolina preserves a relict Paleozoic ACC which experienced high-temperature metamorphism and deformation in the lower crust. These two settings thus record strongly contrasting conditions of metamorphism and deformation.;This study employs optical petrography, cathodoluminescent and backscattered electron imaging, X-ray diffraction and Rietveld refinement, and 40 Ar/39Ar isotopic techniques to characterize the mineralogy, microstructures, and timescales involved in the deformation of these collision zones. This analysis shows that both upper- and lower-crustal environments experienced widespread, aqueous fluid-assisted dissolution-precipitation creep. In the Lishan fault, strain was the driving force for the preferred dissolution of metastable mica and feldspar populations in unfavorable orientations, and precipitation of stable, fabric-forming minerals. Progressive recrystallization in the fault zone is recorded in narrowing of mica peaks in XRD patterns and in the younging of whole rock 40Ar/39Ar ages. In the lower-crustal environment of the Blue Ridge Province, strain energy provided the activation energy for amphibole and plagioclase dissolution and apparently large strains were accommodated by dissolution-precipitation creep. 40Ar/39Ar isotopic ages constrain the times and rates of dynamic exhumation of the Blue Ridge Province during the early Carboniferous at ∼15°C/m.y. This integrative study shows that continental growth in these two by arc accretion is accommodated by dissolution-precipitation creep in spite of the contrasting crustal levels and mineralogies involved.