Abstract Although orogenesis commonly lasts 100 million years, a maximum of three foliations are usually preserved within any outcrop. They record little of the total history due to the effects of preferential partitioning of progressive shearing along S 0 . Such reactivation eventually destroys or rotates multiple successive foliations into parallelism with any layering that is present. Plate motion subjects a collisional orogen to spatially partitioned, episodic, but non-stop deformation. The bulk forces operating are horizontal and intermittently vertical (associated with gravitational load due to crustal thickening) forming sub-vertical and sub-horizontal foliations. These orientations are preserved in the strain shadows of anything competent that hinders reactivation of the compositional layering. Deformation partitioning results in portions of rock remaining unaffected for many events. Gravitational collapse of over-thickened orogen cores leads to significant extrusion in orogen rims and a dominance of sub-horizontal foliations in the latter and episodically continues throughout orogenesis. Reactivation causes decrenulation and/or rotation of foliations into parallelism with S 0 , destroying evidence that multiple sub-vertical and sub-horizontal foliations have developed except where preserved as inclusion trails in porphyroblasts and multiply truncated foliations in mylonites. However, the same processes operate in both the cores of orogens and ductile portions of their margins.

Orogenesis within the New England Appalachians has classically been regarded as occurring discontinuously even though the collision of plates driving it was essentially continuous for 200 million years from the Taconic through the Alleghanian orogenies. Structural, metamorphic, and age data obtained from the cores of porphyroblasts reveal a near continuous history of tectonism that is partitioned within and between outcrops as well as regionally. Very prolonged deformation and metamorphic histories predate the foliation parallel to bedding, and the oblique matrix foliations only reflect brief increments of the uplift path of these rocks back to the earth's surface. The matrix shows none of the structural effects of the path down into the crust. This deepening path is revealed by the sequences of foliations that developed about regionally consistent successions of foliation intersection axis trends preserved within porphyroblasts (FIAs). Indirect coupling between plates throughout the period of collision resulted in horizontal shortening accompanied by subvertical foliation development, followed by crustal instability, collapse, and the formation of subhorizontal foliation, repeated over and over until orogenesis ceased. These cycles repeat on time scales as short as 100,000 to 500,000 years, but because of partitioning of the deformation, only the weakest rocks preserve much of this history. Shifting directions of relative plate motion every 5 to 30 million years also results in easily deformed rocks being protected by more competent ones, with none of them seeing the total history. Furthermore, if the bulk composition is not suitable for porphyroblast growth, none of this history will be recorded. The recurring role of gravitational collapse and the variable scale of partitioning of this type of deformation is obscured by repeated reactivation of the bedding parallel foliation in multiply deformed rocks containing porphyroblasts in the New England Appalachians. It is also obscured by the lack of topographic relief relative to total crustal thickness.