Correlations between Nazca/Farallon Plate kinematics and forearc basin evolution in Ecuador

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 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 translation 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.

The tectonic regime along the Andes: Present‐day and Mesozoic regimes

“…There are several factors that affect the geological processes and the final products along a continental margin. Nevertheless, there is some consensus that the main parameters that control the geometry, coupling and tectonic setting of Andean-type subduction zone are: length of the Benioff zone, relative convergence rate, age of the downgoing slab, slab dip, direction of mantle flow, absolute motion of the over-riding plate and slab retreat, among others (Jarrard 1986;Daly 1989;Doglioni et al 1999Doglioni et al , 2007Doglioni et al , 2009; Oncken et al 2006). All these first-order oceanic parameters should be combined with second order features.…”

“…The kinematics between the upper and lower plate in the Andean subduction system following Daly (1989) can be expressed by the relationship between the roll-back of the subduction trench line and the motion of the overriding plate toward or away from the trench line within an asthenospheric reference frame (Dewey 1980). This is correct only in a passive mantle model (Scholz and Campos 1995), because if a global westward motion of the lithosphere is considered these premises are not valid (see discussion in Doglioni et al 2009).…”

“…Yañez and Cembrano (2004) interpreted that the arcforeland deformation is controlled by the absolute plate velocity of the continental plate and the resistance at the slip zone. The absolute motion can be expressed by the trench roll-back velocity, which will be retreating when the overridden velocity goes away from the trench as proposed by Daly (1989) and Ramos (1999) in a passive mantle flow model (Scholz and Campos 1995) producing extension.…”

Stratigraphy of the late Cretaceous–Paleogene deposits of the cordillera occidental of central ecuador: geodynamic implications

“…However, the nature, age and accretion date of these oceanic terranes are poorly known and still debated. According to various authors, accretions took place in the Campanian (Lebrat et al, 1987;Aspden et al, 1992;Hughes and Pilatasig, 2002), the Late Paleocene (Daly, 1989;Jaillard et al, 1995;Reynaud et al, 1999), and/or the Eocene (Feininger and Bristow, 1980;Egüez, 1986;Bourgois et al, 1990;Spikings et al, 2001;Kerr et al, 2002). Most authors agree that the Cordillera Occidental of central Ecuador comprises a western island arc terrane (Macuchi terrane, Kehrer and Van der Kaaden, 1979;Baldock, 1982;Egüez, 1986;Hughes and Pilatasig, 2002), and an eastern oceanic terrane of oceanic floor to oceanic plateau nature (Lebrat et al, 1987; Pallatanga terrane of McCourt et al, 1998;Hughes and Pilatasig, 2002;Kerr et al, 2002).…”

Investigation of the Lead Isotope Signatures of Marine Sediments in Relation to the Lead Isotope Signatures of Northern Andean Ores

“…The Nazca Plate (also referred to as a slab) is oceanic crust, which is denser than continental crust and so is being subducted beneath the more buoyant South American continental plate (Capitanio et al, 2011 andDaly, 1989). The relatively young age of the plate causes it to have a comparatively low density while still being slightly buoyant.…”