Geological manifestations of ridge collision: Evidence from the Golfo de Penas‐Taitao Basin, southern Chile

Abstract

Recent geological and geophysical studies in the southern Andes adjacent to the intersection of the Chile Rise with the Peru‐Chile Trench (ANT‐NAZ‐SAM triple junction) have revealed a number of features and a Neogene geologic history that are unique along the Pacific margin of South America. This history includes (1) development of a Tertiary‐Quaternary marine basin with up to 3 km of sediment infill (Golfo de Penas‐Taitao basin, GTB), (2) disruption of the region by a series of faults with both normal and strike slip movements, and (3) localization of silicic, near‐trench volcanism and epizonal plutonism and related hydrothermal activity. The northern portion of the GTB began to subside in the Late Miocene (possibly earlier), and has subsequently been deformed, uplifted, and exposed. Gravity and seismic reflection data suggest that the basin continues offshore where it is still actively subsiding today (Golfo de Penas). Subsidence and uplift have thus occurred diachronously in the region, although it is unclear when subsidence began in the Golfo de Penas. Tectonic disruption of the region is likely related to the Liquiñe‐Ofqui fault (LOF), a major, NS‐trending, crustal shear zone that curves westward and terminates in the Golfo de Penas. The LOF has both down‐to‐the‐west and right lateral offset and separates the main Andean Cordillera on the east from a large crustal block (the Chiloe block) on the west. We hypothesize that the GTB has developed as a pull‐apart basin in response to northward movement of the Chiloe block along the LOF. We propose a dynamic model whereby a stress gradient that decreases longitudinally away from the Chile Rise/Peru‐Chile Trench intersection is set up because the youngest, most buoyant, oceanic lithosphere is being subducted at the triple junction. The Chile Rise is viewed as a type of indenter which is acting to drive the Chiloe block northward in front of the northward‐migrating triple junction. This model explains the unique set of geologic features found in the region, and suggests that ridge‐trench interactions may be an important factor in orogenesis at active continental margins.

Seismicity distribution in the vicinity of the Chile Triple Junction, Aysén Region, southern Chile

“…Wang et al (2007) reported the first geodetic evidence on the current dextral shear of the LOFS, finding a trench-parallel slip rate of 6.5 mm yr À1 between 42 and 44 S, which accommodates about 75% of the current margin-parallel component of the Nazca-South America relative plate motion. Lange et al (2008) observed local crustal seismicity along a 130 km long segment of the fault at w42 S. At this latitude, the Chiloé block mentioned above has been decoupled from South America by the action of the LOFS (Forsythe and Nelson, 1985;Wang et al, 2007;Melnick et al, 2009).…”

“…Several consequences of the Chile Ridge subduction beneath the CTJ have been observed including: tectonic erosion, plutonism near the trench and uplift during the Upper Cretaceous in the Taitao Peninsula (Cande and Leslie, 1986), emplacement of an ophiolitic complex in the Taitao Peninsula (Forsythe et al, 1986) and the displacement of a fore-arc sliver (Forsythe and Nelson, 1985;Wang et al, 2007). Another important consequence is the occurrence of a 350 km long volcanic gap within the arc (Ramos and Kay, 1992), whilst in the back-arc zone widespread basaltic-plateau volcanism takes place (e.g.…”

The generation of small melt-fractions in truncated melt columns: constraints from magmas erupted above slab windows and implications for MORB genesis

“…N America, Thorkelson and Taylor, 1989; San Quintin (Baja California), Dickinson and Snyder, 1979;Saunders et al, 1987;S California, Johnson and O'Neil, 1984;British Columbia, Bevier, 1983; S Chile, Forsythe and Nelson, 1985;Antarctic Peninsula, Hole, 1988, 1990Hole and Larter 1993;Hole et al, 1991Hole et al, , 1995. In this paper we will concentrate on one of the simplest tectonic scenarios for slab window formation and related magmatism, that of the Antarctic Peninsula.…”

Ophiolite Emplacement and the Effects of the Subduction of the Active Chile Ridge System: Heterogeneous Paleostress Regimes Recorded in the Taitao Ophiolite (Southern Chile)

“…3 Ma and 0.3 Ma to Present (Cande and Leslie, 1986). The particular confi guration of the active Chile Ridge system, the alternated migration pattern and the change in convergent directions and velocities are expected to induce contrasting stress conditions in the forearc (e.g., Forsythe and Nelson, 1985;Cembrano, 2000, 2004) and the entire belt (Lagabrielle et al, 2004).…”