Estudio de fallas describiendo la alternancia entre deformación tectónica y supererupciones en la caldera de Ilopango, El Salvodor, América Central. Para artículo completo, favor contactarme.

1. Neotectonic deformation within an extensional stepover in El Salvador
magmatic arc, Central America: Implication for the interaction of arc
magmatism and deformation
Nicolás Garibaldi a,
⁎, Basil Tikoff a
, Walter Hernández b
a
University of Wisconsin – Madison, 1215 W. Dayton Street, Madison, WI 53706, United States
b
Servicio Nacional de Estudios Territoriales, Km. 5 1/2 Carretera a Nueva San Salvador, San Salvador, El Salvador
a b s t r a c ta r t i c l e i n f o
Article history:
Received 23 September 2015
Received in revised form 2 May 2016
Accepted 10 May 2016
Available online 16 May 2016
Dominantly westward movement of the El Salvador forearc at rates of 11 mm/yr is accommodated by a series of
E-W to WNW oriented, dextral, strike-slip fault zones herein referred to as the El Salvador Fault System (ESFS).
The geometry of the ESFS defines a series of extensional step-overs. Along the arc, basaltic volcanism in the
stepovers is associated with NNW-oriented normal faults, whereas rhyolitic volcanism is associated with
strike-slip fault zones of the ESFS.
On the ESFS, the San Salvador Extensional Stepover (SSES) is bound to the south by the San Vicente fault zone,
where the rhyolitic Ilopango caldera is located. In the SSES, tephras from Ilopango –the Tierra Blanca (TB)
sequence– track long-term elongation. Older TB units (TB5–8) contain abundant normal faults; lying unconform-
ably above these older TB units, younger TB members (TBJ, TB2–4) are generally unfaulted. Analyses of faults in
TB5–8 indicate NE- to ENE-oriented elongation in the SSES. Deformation occurred between deposition of the TB4
and TB5 units, during quiescence of the Ilopango eruptive center. Using this temporal constraint, minimum
elongation rates of 3.50 × 10−15
s−1
, 2.06 × 10−14
s−1
and 4.42 × 10−14
s−1
were calculated for three traverses.
From regional geodetic data and fault kinematics throughout El Salvador, we interpret the SSES as part of a series
of pull-apart structures along the arc axis. The calculated paleostress orientations are consistent with a pull-apart
geometry resulting from forearc movement.
The extensional deformation occurs during a ~50 k.y. lull in rhyolitic activity, suggesting an interplay between
magmatism and deformation within the arc. During significant rhyolitic volcanic activity, only minor elongation
is observed in the SSES, despite ongoing translation of the Salvadoran forearc. We speculate that rhyolitic
magmatism along upper crustal faults may facilitate strike-slip movement on the ESFS, rather than distributing
deformation throughout the extensional stepover.
© 2016 Elsevier B.V. All rights reserved.
Keywords:
Strike-slip tectonics
Pull-apart deformation
Strain rates
Volcanism cyclicity
Magmatism–deformation interaction
1. Introduction
Since the pioneering work of Fitch (1972), earth scientists
have made large efforts to understand the kinematics of strike-slip
partitioning on transpressional volcanic arcs (e.g., Beck, 1983; Ekstrom
and Engdahl, 1989; Jarrard, 1986; Liu et al., 1995; McCaffrey, 1992,
1994, 1996; Nakamura and Yamamoto, 2009; ten Brink and Lin, 2004;
Tikoff and Teyssier, 1994). It is a common observation that oblique
plate subduction causes lateral forearc migration. The strike-slip motion
of the forearc region is accommodated by a series of arc-parallel, en ech-
elon, strike-slip fault zones that occur along the arc (Funk et al., 2009;
Sieh and Natawidjaja, 2000). This fault geometry favors the develop-
ment of arc-parallel extensional stepovers between two strike-slip
fault zones where elongation is accommodated by normal faulting, lo-
cally causing crustal subsidence (e.g., Aydin and Nur, 1985; Corti and
Dooley, 2015; Petrunin and Sobolev, 2006). In strike-slip magmatic
arcs, strike-slip faults facilitate magmatic ascent through the crust and
emplacement of granitoids along the arc axis (Tikoff and Teyssier,
1992; Tikoff and de Saint Blanquat, 1997; Cloos and Sapiie, 2013). In
turn, the presence of ascending magma in strike-slip faults can have a
weakening effect and effectively localize deformation associated to
partitioning (Tommasi and Vauchez, 1994; Rosenberg and Handy,
2005). Thus, the presence of magma on strike-slip faults can be an
important factor determining how the crust deforms as a response to
an active strike-slip environment.
Numerous studies that document the kinematics of strain partitioning
have concentrated on large-scale, short-term phenomena, such as
comparisons of subduction earthquake slip directions and directions
predicted by plate motion models (e.g., Ekstrom and Engdahl, 1989;
Fitch, 1972; Jarrard, 1986; McCaffrey, 1992, 1996), slip localization and
Tectonophysics 693 (2016) 327–339
⁎ Corresponding author.
E-mail addresses: garibaldi@wisc.edu (N. Garibaldi), basil@geology.wisc.edu
(B. Tikoff).
http://dx.doi.org/10.1016/j.tecto.2016.05.015
0040-1951/© 2016 Elsevier B.V. All rights reserved.
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