40Ar/39Ar Geochronological Constraints on the Age Progression Along the Juan Fernández Ridge, SE Pacific

Abstract

Juan Fernández Ridge (JFR) is a ca. 800 km long volcanic chain composed by seamounts, guyots and oceanic islands in the SE Pacific. JFR is thought to be related to a deep mantle plume and usually scores high in the hotspots catalogs (e.g., Anderson, 2005; Jackson et al., 2017). High 3 He/ 4 He in Robinson Crusoe is probably the most undoubted feature of lower mantle involvement. However, one of the most convincing pieces of evidence for a source rooted deep in the mantle is the age progression along a volcanic chain, which is poorly constrained for JFR. In fact, some scarce K-Ar dates in Alejandro Selkirk and Robinson Crusoe islands, and a total fusion age for O'Higgins Guyot published more than 20 years ago, is the only evidence available for such a hypothesis in previous works. Here we integrate recently published 40 Ar/ 39 Ar ages and 17 new results on groundmass step heating experiments from rocks corresponding to the late shield stage (O

Liquiñe-Ofqui’s fast slipping intra-volcanic arc crustal faulting above the subducted Chile Ridge

“…The oldest potential indicator of long-term Late-Cenozoic LOFZ dextral strike slip motion is from the northward movement (~ 100 km) of the CM along the LOFZ, and subsequent extension at its southern end since the Late Miocene (11.6 Ma), which caused a major gap in the coastline, the Golfo de Penas (Figs. 1 , 2 11 , 12 , 15 ). If this opening of the Golfo de Penas was not only dextral, but also due to tectonic subsidence (i.e.…”

“…1 , 2 ; e.g. 11 , 12 ) along the dextral strike slip Liquiñe-Ofqui fault zone (LOFZ 13 ). The LOFZ is one of the Earth’s major fault zones displacing continental crust and is the principal structural feature of the Main Cordillera of Chile between 38 ° S to south of the Chile Triple Junction at ~ 47 ° S near the Golfo de Penas (Figs.…”

“…The LOFZ is one of the Earth’s major fault zones displacing continental crust and is the principal structural feature of the Main Cordillera of Chile between 38 ° S to south of the Chile Triple Junction at ~ 47 ° S near the Golfo de Penas (Figs. 1 , 2 11 , 14 ). The Golfo de Penas basin (Figs.…”

“…The Golfo de Penas basin (Figs. 1 , 2 ) developed as a pull-apart basin in response to northward movement of the CM along the LOFZ in the late Miocene 11 , 15 . Globally crustal faulting and seismic hazard are associated with fast-slipping (10–40 mm/year) intra-volcanic arc strike slip crustal faults, for example the at least 1200 km-long Philippine fault (20–25 mm/year 16 ).…”

“…Although long-term Cenozoic geologic and structural evidence suggests rapid motion along the LOFZ (e.g. 17 , 18 ), in the 35 years since Forsythe and Nelson 11 postulated that the Chiloe Block is moving northward relative to South America along the LOFZ due to oblique convergence or to forces in response to ridge subduction, there are still no direct measurements or field-derived estimates of strike slip slip rates. Additionally, recent thermochronological analysis from the area overlying the CTJ subduction found no evidence for reheating or thermal uplift-driven erosion and cooling within 10 to 20 Ma of the formation of the slab window 19 .…”