Cenozoic Continental Geology of South America and Its Relations to the Evolution of the Chile Triple Junction

Abstract

The Cenozoic magmatic and tectonic histories of the southern Andes adjacent to the Chile Triple Junction (CTJ) reflect the evolution and migration of the triple junction during the last 20 m.y. in a number of fundamental ways. Pliocene near-trench magmatism, including the intrusion of calcalkaline stocks within the forearc basement and the creation of the Taitao Ophiolite within the leading edge of the forearc, relates directly to ridge subduction processes. Distribution and kinematics of faulting, observed geologically and through earthquake seismology, reflect the plate margin kinematics and are also strongly influenced by the thermal, topographic, and kinematic heterogeneities related to the Chile Triple Junction. The most important structure in this respect is the 1000-km-long, trench-parallel, Liquifie Ofqui Fault (LOF). This extends north from the CTJ and has a predominantly dextral displacement. Complex faulting and related subsidence within the Golfo de Penas basin have continued throughout the late Cenozoic and appear to define a " pull-apart" basin within the South American forearc at the southern trailing edge of the LOF. The history of the Cenozoic uplift of the Andean divide appears to be dramatically different north and south of the triple junction. The backarc fold-and-thrust belt of southernmost Patagonia appears to end at the present latitude of the triple junction. Passage of slab windows corresponding to ridge segments subducted during the late Cenozoic corresponds spatially with arc gaps and centers of backarc alkalic flood basalts.