Relative motion of plates related to the Chile triple junction and geodynamic significance

At the Chile triple junction (CTJ), a representative RTT-type structure, the Chile ridge is currently subducting under the South America plate. Here we show the relative Euler vectors among the Nazca, Antarctica and South America plates by constructing the NazcaAntarctica-South America-Pacific plate system based on GPS observations, seismic sliding vectors, mid-ocean ridge spreading rates and the azimuth of transform faults. The results reveal distinct subduction characteristics of the Nazca plate (eastward, 83. () mm a 1) and the Antarctic plate (southeastward, 22. 0 mm a 1) beneath the South America plate on either side of the CTJ. The CTJ moves northward since 5. 3 Ma due to the subduction of the ocean ridge, with the nature of CTJ changing between RTT-type and FTT-type in response to the modification of the Chile ridge by the transform faults. The repeated subduction of the ocean ridge induced by the southward movement of the FTT-type CTJ causes the repeated partial melting of basalts under high T (800-900 'C) and low P (10-20 km) conditions. The intermediate rocks formed in the initial phase equilibrium are transformed into acid rocks during the following partial melting processes, which is responsible for the pre-arc acid rock outcrops at the crossover location of the CTJ movement.

Automated summary

The study reveals the subduction of the Chile ridge under the South America plate at the Chile triple junction. The Nazca plate and Antarctic plate exhibit distinct subduction characteristics in different directions, leading to the change of nature of the CTJ during various processes.