Along-strike variations in crustal seismicity and modern lithospheric structure of the central Andean forearc

Kathryn Metcalf, Paul A Kapp

Research output: Chapter in Book/Report/Conference proceedingChapter

6 Citations (Scopus)

Abstract

The dynamics of the erosive central Andean forearc vary significantly along strike. In northern Chile at 20°S-27°S, and particularly at 22°S-25°S, the forearc in the Coastal Cordillera has been undergoing extension since at least the Pliocene, reactivating steep E-dipping faults of the Mesozoic Atacama fault system. This has been explained by forearc uplift driven by underplating, shallow slab dip, subduction of bathymetric features, and elastic rebound during the earthquake cycle. These processes, however, are active over a much wider area of the central Andean forearc than Coastal Cordillera extension and therefore cannot explain why extension is localized to the northern Chilean onshore outer forearc. We compiled crustal seismicity and the depth of lithospheric boundaries from existing studies to investigate other possible explanations for onshore forearc extension. At 22°S-25°S, seismicity increases above the background subduction-related level present to the north and south. Extensional focal mechanisms, consistent with steep E-dipping faults active at depths up to ∼40 km, are also present onshore within this latitude range, but absent to the north and south; this is consistent with the distribution of mapped active fault scarps. The Salar de Atacama crust is seismically active at depths up to ∼40 km. Thick lithosphere is present beneath the forearc, and the longitudinal axis of thickest lithosphere is deflected to the east at the latitude of the Salar de Atacama. To the east, the Puna Plateau lithosphere has been thinned by lithospheric removal events. The most robust correlation with onshore forearc extension is the thick, cold, strong crust and mantle lithosphere beneath the anomalous Salar de Atacama in the inner forearc of northern Chile. The combination of underplating-driven outer forearc uplift, the presence of the preexisting structure of the Atacama fault system favorable for reactivation, and the negative buoyancy beneath the Salar de Atacama is inferred to drive Coastal Cordillera normal faulting at this latitude. Recent (<10 Ma) lithospheric removal beneath the Puna Plateau to the east may have enhanced the effect of the negatively buoyant Salar de Atacama lithosphere on the forearc. This implies that both preexisting lithospheric structure and lithospheric processes in the hinterland may influence forearc dynamics.

Original languageEnglish (US)
Title of host publicationMemoir of the Geological Society of America
PublisherGeological Society of America
Pages61-78
Number of pages18
Volume212
ISBN (Print)9780813712123
DOIs
StatePublished - 2015

Publication series

NameMemoir of the Geological Society of America
Volume212
ISSN (Print)00721069

Fingerprint

lithospheric structure
seismicity
lithosphere
cordillera
underplating
active fault
subduction
uplift
plateau
crust
focal mechanism
reactivation
buoyancy
dip
slab
Pliocene
faulting
mantle
earthquake

ASJC Scopus subject areas

  • Geology

Cite this

Metcalf, K., & Kapp, P. A. (2015). Along-strike variations in crustal seismicity and modern lithospheric structure of the central Andean forearc. In Memoir of the Geological Society of America (Vol. 212, pp. 61-78). (Memoir of the Geological Society of America; Vol. 212). Geological Society of America. https://doi.org/10.1130/2015.1212(04)

Along-strike variations in crustal seismicity and modern lithospheric structure of the central Andean forearc. / Metcalf, Kathryn; Kapp, Paul A.

Memoir of the Geological Society of America. Vol. 212 Geological Society of America, 2015. p. 61-78 (Memoir of the Geological Society of America; Vol. 212).

Research output: Chapter in Book/Report/Conference proceedingChapter

Metcalf, K & Kapp, PA 2015, Along-strike variations in crustal seismicity and modern lithospheric structure of the central Andean forearc. in Memoir of the Geological Society of America. vol. 212, Memoir of the Geological Society of America, vol. 212, Geological Society of America, pp. 61-78. https://doi.org/10.1130/2015.1212(04)
Metcalf K, Kapp PA. Along-strike variations in crustal seismicity and modern lithospheric structure of the central Andean forearc. In Memoir of the Geological Society of America. Vol. 212. Geological Society of America. 2015. p. 61-78. (Memoir of the Geological Society of America). https://doi.org/10.1130/2015.1212(04)
Metcalf, Kathryn ; Kapp, Paul A. / Along-strike variations in crustal seismicity and modern lithospheric structure of the central Andean forearc. Memoir of the Geological Society of America. Vol. 212 Geological Society of America, 2015. pp. 61-78 (Memoir of the Geological Society of America).
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