Mineralogy of Sediments from the Chile Triple Junction

Abstract

Quaternary and Pliocene terrigenous sediments recovered during Ocean Drilling Program Leg 141 on the Chile Trench continental slope are represented by hemipelagic mud and distal and proximal turbidites with minor gravity-flow deposits. The coarse fraction is composed mainly of quartz and feldspars, with hornblende, epidote, and clinopyroxene dominating the heavy fraction. Volcanic glass, mica, orthopyroxene, tremolite-actinolite, olivine and "sialic" accessories (garnet, zircon, apatite, tourmaline, and sphene) occur in minor amounts. Clay minerals consist mainly of hydromica (illite) and chlorite, and smectite is a common minor component. The mineral assemblage found in the sediment sequences is derived from the adjacent Andean orogenic source area. Only the basal beds of the sedimentary blanket over the Taitao Ridge contains volcanic minerals possibly derived from local submarine outcrops of mafic igneous rock. Both the clay mineralogy and coarse-fraction mineralogy of the sediments are generally uniform, irrespective of the location of the holes on the accretionary wedge, of water depth, of depth below seafloor, of lithologic units, of tectonic deformation, or of lithification, and they do not change markedly with grain size or depositional style. The accretionary wedge terrigenous sediments are affected by hydrothermal alteration over the subducted Chile spreading ridge (Site 863). The hydrothermal effects are best demonstrated by extensive secondary smectite formation in the sediments. Subduction of the spreading ridge produces a "hydrothermal trace" in the accretionary wedge.

Clay minerals in late Quaternary sediments from the south Chilean margin as indicators of provenance and palaeoclimate

“…This difference can mostly be attributed to the variety of source rocks. The clay association is comparable to that of sediments from the relatively close Chile triple junction (Kurnusov et al, 1995), but is different from sediments in the Chile margin at 43ºS, which are characterized by greater smectite contents, reflecting a warmer climate and stronger chemical weathering processes (Lamy et al, 1998a,b).…”

“…The bulk sediment composition of hemipelagic sediments from the the southern Chilean margin differs from that of sediments deposited in more northern sectors of the South American continental margin in terms of the large biogenic carbonate content, as in the latter areas they are much smaller (Kurnusov et al, 1995;Hebbeln et al, 2000). As we did not acid-treat the silicate samples to remove the The sediments of the cores studied are characterized by slightly smaller contents of quartz and plagioclase, and increased alkali feldspar and mica contents, with respect to sediments collected at the northernmost latitude such as the Chile triple junction (Kurnusov et al, 1995) and Chilean continental margin at 43ºS (Lamy et al, 1998a). In general, the quartz content of the sediments along the Chilean margin decreases from northern to southern latitudes.…”

“…Works concerning the mineralogical composition of marine sediments in the Pacific Ocean off South America include surface sediments of the Peru-Chile continental margin, northern Chile (Krissek et al, 1980;Rosato & Kulm, 1982;Scheidegger & Krissek, 1982), the Chilean continental margin between 25ºS and 43ºS (Lamy et al, 1998a,b;Stuut et al, 2007), the Chile Trench (Thornburg & Kulm, 1987a,b) and the Strait of Magellan (Brambati et al, 1991;Marinoni et al, 1997Marinoni et al, , 2000Presti et al, 2000;Schiozzi et al, 2000). Other works are concerned with the mineralogical and geochemical composition of Quaternary sediments from the Chile triple junction (Kilian & Behrmann, 2003;Kurnusov et al, 1995) and Cenozoic sediments from the Peruvian continental margin (Clayton & Kemp, 1990).…”

Terrigenous sediment supply along the Chilean continental margin: modern regional patterns of texture and composition

“…For adjacent areas examinations of surface sediments exist for the continental margin off Peru and northern Chile (Krissek et al 1980;Rosato and Kulm 1981;Scheidegger and Krissek 1982) and shelf areas of the Chilean archipelago (Siegel et al 1981). Additionally, terrigenous sediments, recovered during ODP leg 112 on the Peruvian continental margin (Clayton and Kemp 1990) and ODP leg 141 near the Chile triple junction (Kurnosov et al 1995), were analyzed concerning mainly the clay mineralogy.…”

“…42°S-55°S (Siegel et al 1981) and at ca. 46°S (Kurnosov et al 1995) revealed illite-and chlorite-dominated assemblages. Therefore, the differing clay mineralogy of these offshore samples might indicate lateral input from southern areas or pelagic areas to the west as the Antarctic Circumpolar Current approaches South America in this area (see Oceanographic setting).…”