Basin evolution, deformation, and magmatism during variable tectonic regimes in the region linking the central and northern Andes


Cordilleran style margins exhibit significant heterogeneities both along-strike and through time. These changes in tectonic regime influence sediment routing systems and topographic growth, and are often recorded in proximal basin systems. This dissertation addresses pre-Andean through Andean tectonic regimes in northern Peru and Ecuador. Although Peru has been the site of continuous subduction since at least the Jurassic, Andean shortening and associated flexure in the foreland basin system did not initiate until the latest Cretaceous. Chapter 2 explores the pre-Andean basin system and transition to Andean shortening in northern Peru. This chapter provides new maximum depositional age constraints and demonstrates protracted accumulation in extensional and post-extensional basins preceding the late Cretaceous shift to regional shortening and associated reversal of sedimentary polarity. In Ecuador, the onset of Andean shortening briefly predates the accretion of a sliver of the Caribbean Large Igneous Province in the latest Cretaceous that now comprises the bedrock to the Ecuadorian forearc. More recently, regional Neogene deformation appears to coincide with subduction of the buoyant Carnegie Ridge in the Ecuadorian trench. Chapter 3 discusses the impact of accretion and subduction of buoyant oceanic crust on the short- and long-term magmatic and deformational evolution of the Ecuadorian arc using regional detrital zircon U-Pb constraints on arc magmatism, a new reconstruction of arc location for the past 200 Ma, and a record of isotopic evolution of the magmatic arc from detrital zircons and arc rocks (εHf [subscript t] and εNd). A dramatic shift towards more evolved arc compositions at ca. 75 Ma is attributed to rapid crustal thickening. Neogene sediment dispersal systems in western Amazonia remain highly controversial, yet are significant for the birth of the Amazon River and establishment of a continuous drainage divide along western South America. Chapter 4 provides new insights into sediment routing systems in the Andes of Ecuador from Upper Cretaceous-Miocene hinterland deposits preserved between the Eastern and Western Cordilleras at 2.5 to 3 km above sea level. Using new measured sections, facies analysis, clast counts, paleocurrents, U-Pb geochronology, and palynology, this chapter demonstrates evaluates the basin infilling in the Andean basins, along with comparisons to forearc and foreland domains through time


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