Plio-Quaternary uplift of the Manta Peninsula and La Plata Island and the subduction of the Carnegie Ridge, central coast of Ecuador

Abstract

This paper quantifies the uplift of the Manta Peninsula and La Plata Island (Ecuador) using marine terraces. These marine terraces are part of a more extensive segment of uplifting coast extending all along the Talara arc, from 6.5°S to 1°N. Along this arc, the highest terraces are observed on the Manta Peninsula with five marine terraces up to 360 ± 10 m. On La Plata Island, four marine terraces are raised up to 170 ± 10 m. The terraces are dated using infrared-stimulated luminescence (IRSL) and U–Th methods. The calculated uplifts range from 0.3 to 0.5 mm yr −1 for the past 300 ka. The oldest terraces show a transition to the synsedimentary uplifted Plio-Pleistocene deposits of the Canoa Formation. In comparison with the lower uplift rates documented in the Santa Elena Peninsula to the south and the Esmeraldas area to the north, the uplift of the Manta Peninsula gives an account of the effect of the subduction of the Carnegie Ridge since the late Pliocene. The coastal uplift ends to the north outside the projection point of the border of the Carnegie Ridge but extends southward along the northern margin of the Gulf of Guayaquil, outside of the effect of the Carnegie Ridge, which suggests that other elements must be considered for uplift in this area. A weak scan pattern of the Carnegie Ridge along the coast is observed, but instead of a true scan motion, the context suggests the possibility of a segmented ridge and the head-on introduction in the trench of a new segment with a beveled front trending parallel to the Grijalva fracture zone. The onset of subduction of the Carnegie Ridge seems correlated with a change in the tectonic deformation of the coast, from compression conditions before the middle–late Pliocene to extension conditions during the subduction of the ridge.