Cooling histories and deformation of plutonic rocks along the Liquiñe-Ofqui Fault Zone, Southern Chile (41°-42°15'S)

Abstract

Structural and microstructural observations combined with apatite and zircon fission track thermochronology within two sectors of the Main Andean Range in the Los Lagos Region of Chile reveal an episodic history of intrusion and deformation in the North Patagonian Batholith (NPB). A dextral displacement of ~30 km along the Liquifle-Ofqui fault zone (LOFZ) is inferred from the correlation of corresponding Cretaceous intrusions of the NPB across the fault zone at Reloncavi. Relative uplift of the western block in the late Miocene is indicated by apatite and zircon fission-track cooling histories. Microstructures in samples from Miocene and Cretaceous plutons along the fault zone generally indicate deformation at temperatures below ~300°C, with the exception of some samples from Cretaceous intrusions showing deformation at higher temperatures. In the Hornopirén area, significant relative uplift of the eastern block is indicated by 1. the different styles of deformation observed across the fault zone, 2. kinematic analysis of a shear zone in tonalite and 3. geobarometry of contact metamorphic mineral assemblages. For the plutonic rocks in the Hornopirén area, extremely rapid cooling is indicated by thermochronometry, suggesting the activity of hydrothermal systems or thermal effects of late shallow intrusions.