Forearc uplift rates deduced from sediment cores of two coastal lakes in south-central Chile

Abstract

The present paper introduces a new approach for deriving information about local forearc tectonics and related uplift rates based on the study of lake sediments. We investigated two coastal lakes at the south-central Chile margin, lakes Lanalhue and Lleu Lleu, located south of the Arauco Peninsula (38°S). Both lakes developed within the valleys of ancient rivers that once drained to the Pacific Ocean, being subsequently dammed by rising sills in the late Pleistocene/early Holocene. Seismic profiling and sedimentological analyses of cores from both lakes revealed similar successions consisting of marine to brackish sediments covered by lacustrine deposits. Radiocarbon dating indicates that the marine-lacustrine transition occurred at 8 ka and 8.15 ka, respectively. The correlation of this transition with global sea-level curves allowed the calculation of local uplift rates for the Holocene. Uplift rates for the lake basins amount to 0.42 ± 0.71 and 0.49 ± 0.44 mm/a, respectively, which are consistent with rates determined from a late Pleistocene marine terrace in the area. However, conspicuously higher, though likely transient, vertical movements at 8.83 ± 2.7 mm/a and 11.36 ±1.77 mm/a, respectively, were calculated for the sills that block both lakes nowadays. These barriers are interpreted to be the surface expression of a blind reverse fault associated to the Morguilla fault system, a seismically-active structure that controls uplift and folding along the adjacent Arauco Peninsula.

Late Pleistocene landscape evolution in south-central Chile constrained by luminescence and stable cosmogenic nuclide dating

“…This does not suggest a signifi cant acceleration of uplift during the Quaternary, but rather indicates that areas of high uplift rates are spatially very restricted to the center of the Arauco Peninsula ) and offshore islands (Kaizuka et al, 1973;Nelson and Manley, 1992;Melnick et al, 2006). In fact, many parts of the southcentral Chile forearc, including our working area, appear to be undergoing uplift on the order of the long-term background uplift rate, e.g., the tips of the Arauco Peninsula with 0.36 ± 0.07 mm a -1 or the Lake Lanalhue and Lake Lleu Lleu area with ~0.4 mm a -1 (Stefer et al, 2009). The forearc thus consists of disparate areas of variable uplift rates.…”

A 7000‐year high‐resolution lake sediment record from coastal central Chile (Lago Vichuquén, 34°S): implications for past sea level and environmental variability

“…Stefer et al . () inferred from seismic profiling and sedimentological analyses of two coastal lakes located at ∼38°S that the marine to lacustrine transition occurred at 8.0 cal ka, probably controlled by tectonic uplift that ranged between 0.42 ± 0.71 and 0.49 ± 0.44 mm a −1 . In the bay of Algarrobo on the coast of Central Chile (∼33°S) Encinas et al .…”

“…The maps in (a) and (b) show the main locations discussed in the paper. Orange diamond: lacustrine records; 1: El Junco lake (Zhang et al ., ), 3: Chungará (Moreno et al ., ), four: Miscanti lake (Valero‐Garcés et al ., 1996), 8: Chepical lake (de Jong et al ., 2013), 12: L. Aculeo (Jenny et al ., ), 13: L. Matanzas (Villa‐Martínez, ), 14: L. Tagua Tagua (Valero‐Garcés et al ., ), 17–18: Lanalhue and Lleu Lleu lake (Stefer et al ., ), 20: Pichilafquén lake (Jara and Moreno, 2014). Black traingles: coastal peat swamp records; 5: Ñague (Maldonado and Villagrán, ), 6: Quereo (Villagrán and Varela, ), 7: Palo Colorado (Maldonado and Villagrán, ), 10: Quintero (Villagrán and Varela, ).…”

3-D thermo-mechanical laboratory modeling of plate-tectonics: modeling scheme, technique and first experiments

“…Theoretically, it is also possible to monitor the vertical displacement of the model surface using 2 cameras providing a stereoscopic view of the model surface (Adam et al, 2005;Riller et al, 2010). This new advance in monitoring technology would be very advantageous because the vertical motion of the model surface can be linked to the distribution of stresses along the plate boundary (Shemenda, 1992), compared with numerical modeling results (Hassani et al, 1997;Bonnardot et al, 2008a,b) or compared with natural data such as long-term uplift/subsidence derived from sedimentary record (Matsu'ura et al, 2008(Matsu'ura et al, , 2009Stefer et al, 2009;Hartley and Evenstar, 2010), short-term uplift/subsidence derived from GPS/Coral reefs dating (Taylor et al, 2005;Matsu'ura et al, 2008Matsu'ura et al, , 2009 or gravity anomalies (Shemenda, 1992;Song and Simons, 2003). However, the produced topography is very small (∼ 1-2 mm) and the distribution of passive markers is not sufficiently large to permit reliable stereoscopic imaging and therefore vertical motions.…”