Unilateral Magma Emplacement of the Telimbela Batholith in the Central Ecuadorian Arc: Implications for Kinematics of Oblique Subduction of the Farallon-Nazca Plate

Abstract

The N-S elongated granodioritic Telimbela batholith (TB, ∼220 km2) was emplaced at the restraining bend of the dextral strike-slip Calacalí-Pujilí-Pallatanga Fault (CPPF) developed at the ca. 120 km wide Tertiary Ecuadorian arc. Our and previous zircon U-Pb ages indicate that the batholith has a westward younging trend, with the oldest and youngest ages of 25.5 ± 0.5 and 17.5 ± 0.3 Ma, respectively, and a minimum duration of 8 ± 0.6 Ma was acquired. The Al-in-hornblende geobarometer results show that the TB was emplaced in the upper crust (∼4.7–5.3 km). The anisotropy of magnetic susceptibility (AMS) results of TB show three distinct groups of magnetic foliations, with a mean orientation of (64°/SE ∠ 39°) (0°/E ∠ 83°), and (16°/NW ∠ 83°) in the eastern, central and western parts of TB, respectively. As the TB was syntectonically emplaced with the evolution of CPPF, the vorticity numbers (Wn) of eastern, central, and western parts are determined by the angle between CPPF and mean orientation of AMS with Wn values of 0.79, 0, and 0.53, respectively. According to previous geodynamic studies on Northern Andes, the early and late kinematic transitions recorded in the TB may correspond to the change of plate subduction direction and the decrease in subduction angle, respectively. Comparing the estimated growth rate of TB to the tempo of Tertiary Ecuadorian arc magmatism revealed by detrital zircon ages and previous plate convergence velocity models, the good consistency among them will help to restore a detailed kinematic evolution of the Ecuadorian arc.