TECTONICS, VOL. 8, NO. 4, PAGES 769-790, AUGUST 1989 CORRELATIONS BETWEEN NAZCA/FARALLON PLATE KINEMATICS AND FOREARC BASIN EVOLUTION IN ECUADOR Michael C. Daly Structural Studies Group, BP Exploration Company Limited, London Abstract. The Tertiary evolution of the forearc basins of Ecuador shows a close correlation between the changing convergence rate of the Farallon, and later Nazca, oceanic plates and continental South America. The correlation occurs during the subduction of a relatively young slab and, in the Late Miocene, onset of the subduction of the Carnegie aseismic ridge. The Ecuador forearc basins lie on a basement of oceanic crust known as the Pinon terrane. The accretion of this terrance occurred in the Paleocene as the leading edge of the Farallon plate, the Macuchi island arc, collided with South America. In the Middle Eocene this forearc terrane was the site of major pull-apart basin formation and turbiditic sedimentation, coincident with a phase of very rapid convergence between chron 21 and chron 13 (48-37 Ma). This deformation was bounded by the trench and a major dextral strike-slip fault zone and resulted in the northward translation of the forearc with respect to continental South America. During the Oligocene a phase of extension normal to the trend of the active margin occurred, coincident with a phase of relatively slow convergence (chron 13 to chron 6, 37-20 Copyright 1989 by The American Geophysical Union. Paper number 89TC00707 0278-7407/89/89TC-00707510. O0 Ma). This extension was followed in the Middle Miocene by inversion of most of the forearc basins, coincident with a return to relatively fast convergence from chron 6 (20 Ma) to the present day. Subduction of the Carnegie aseismic ridge occurred during this period (circa 8 Ma to present) and may have enhanced the compressive event. Further, northward •ranslation of the forearc silver accompanied this later deformation. The relationships outlined for the forearc may be modeled in terms of a dynamic orogenic wedge which responds directly to changes in convergence rate at the subduction zone. The convergence rate appears to be an important control on the coupling between the downgoing slab and overriding continental plate. INTRODUCTION The link between plate tectonics and the evolution of active margins has attracted a large amount of attention since the acceptance of the plate tectonic paradigm. Much of this work has been focused on the North American active margin, initially by paleogeographic reconstructions [Atwater and Molnar, 1973] and more recently by quantitative plate tectonic models, from which convergence velocities through time have been calculated [Carlson, 1982; Engebretson et al. 1985]. In spite of the complexity of the geological record and the relative simplicity of such plate models, apparently convincing correlations between