Abstract

The Mejillones Peninsula is thought to have one of the highest rates of tectonic uplift along the active convergent margin of northern Chile. We use exposure age dating from a flight of well-preserved marine terraces to determine the long-term tectonic history of the northern part of the Peninsula. Terrace ages suggest the area is comprised of discrete crustal blocks with differing uplift chronologies. Periods of uplift reaching rates of 0.60 ± 0.06 m/ka over the last ∼480 ka are recorded on one block, a value that is several-fold higher than is typical for the north Chilean coastline. Subsidence of an adjacent block is suggested by the anomalously old ages of terraces currently close to sea-level, and by observations of paleo-sea cliff warping and measurements of coastal sinuosity. Opposing crustal motion between adjacent blocks is compatible with the formation of intervening normal faults and the hypothesis of ongoing extension of the forearc. Comparisons with published data suggest a contemporaneous acceleration in uplift occurred throughout the Peninsula, with higher rates of mean uplift observed after 480 ka. A second, even more rapid period of uplift occurred sometime within the last 200 ka, most likely 40 ka ago. Uplift of the footwall due to downthrowing blocks on normal faults caused by crustal extension may be one of the mechanisms causing the pulses of accelerated uplift rates of the Mejillones Peninsula. Another hypothesis is an increase of subduction earthquake activity. Both hypotheses suggesting a more general link to plate coupling and are not mutually exclusive.

Keywords

Uplift, Subsidence, Crustal extension, Cosmogenic nuclides, Mejillones peninsula, Plate coupling

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