Holocene sediments from the Southern Chile Trench: a record of active margin magmatism, tectonics and palaeoseismicity

Abstract

Sedimentology, petrography and the provenance of Holocene sediments from the Southern Chile Trench (36-478S) were investigated in an integrated approach combining description of a collection of gravity cores, measurements of physical properties, quantitative X-ray petrography and modal analysis. The sediments studied were trench hemipelagic sediments, fan deposits, and more distal hemipelagic sediments from the Nazca Plate. The trench is mostly fed by multiple point sources via submarine canyons. Sandy turbidites show a southward increase in sediment maturity. Whereas volcanic lithic fragments and plagioclase represent the dominant fraction in the north, quartz content strongly increases in the southern part of the study area, in line with source lithologies. Further north, active volcanoes in the Main Cordillera represent almost the entire provenance signal as a result of a strong contribution of highly erodible volcanic rocks. Recurrence rates of sandy and silty turbidites in the trench fan sediments indicate a link to the palaeoseismic record on land. Our study documents the potential usefulness of proximal turbidites to reconstruct palaeoseismicity, even at a scale of single segments of the plate boundary.

Controls on submarine canyon activity during sea-level highstands: The Biobío canyon system offshore Chile

“…and the sedimentation rate is 17 cm/k.y., integrated over the second half of the Holocene. Heberer et al (2010) reported that sediment samples in this core contained black basaltic sands composed of fresh, glassy, angular, volcanic fragments that are commonly highly vesicular. The sediment composition within the BbC suggests that it has not undergone extensive transport and sorting, or prolonged periods of subaerial weathering (Heberer et al, 2010).…”

“…Heberer et al (2010) reported that sediment samples in this core contained black basaltic sands composed of fresh, glassy, angular, volcanic fragments that are commonly highly vesicular. The sediment composition within the BbC suggests that it has not undergone extensive transport and sorting, or prolonged periods of subaerial weathering (Heberer et al, 2010). The Biobío Fan sediments are very low in quartz compared to other submarine fan sediments found along the Peru-Chile Trench between 36°S and 47°S, and have the strongest volcanic provenance signal (Heberer et al, 2010).…”

Turbidite paleoseismology along the active continental margin of Chile – Feasible or not?

“…In another study located on the same seismotectonic segment, Heberer et al (2010) estimated Holocene turbidite recurrence within a similar range (192e477 years), having high associated errors (±105e346 years), because these intervals are based on the assumption of a mean sedimentation rate obtained from other cores and the thickness of the interbedded hemipelagites. Finally, V€ olker et al (2008) related the frequency of outsized turbidite events deposited on seamounts or large slide blocks (Geersen et al, 2011b) up to 300 m high to the recurrence of great Pleistocene earthquakes along the Valdivia segment, with a recurrence interval of some centuries.…”

“…Finally, V€ olker et al (2008) related the frequency of outsized turbidite events deposited on seamounts or large slide blocks (Geersen et al, 2011b) up to 300 m high to the recurrence of great Pleistocene earthquakes along the Valdivia segment, with a recurrence interval of some centuries. Taken together, these studies are promising and suggest that turbidites offshore Chile may be used as paleoseismological indicators along the Valdivia segment during the Holocene (Heberer et al, 2010) while deposits in more distal and/or elevated settings may record Pleistocene events (V€ olker et al, 2006;Blumberg et al, 2008). However, to link such turbidite sequences unambiguously to seismic triggers a large spatial coverage of individual events embedded in a sufficient geochronologic framework has to be established.…”

“…Trench locations were excluded because of great water depth below the carbonate compensation depth (CCD) (~4500 m; Hebbeln et al, 2000;Heberer et al, 2010) preventing radiocarbon dating (e.g., Patton et al, 2013). Additionally, south-north lateral transport along the trench axis complicates the stratigraphic record of the trench (V€ olker et al, 2006).…”