Tectonophysics 706–707 (2017) 91–102 Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto An extending island arc: The case of Kamchatka Andrey Kozhurin a,b,EgorZeleninb,⁎ a Institute of Volcanology and Seismology, Piip Blvd 9, Petropavlovsk-Kamchatsky, Russia, b Geological Institute, Pyzhevsky per. 7, Moscow, Russia article info abstract Article history: We report a first estimate of the extension rate of the onshore Kamchatka island arc, it central wider part. This Received 22 November 2016 average rate is 17 ± 3 mm/yr over mid-late Quaternary time. The extension is absorbed by slip on major normal Received in revised form 10 March 2017 active faults of Central Kamchatka, and graben-producing faulting in its volcanic belt. Probable extension of the Accepted 1 April 2017 underwater portion of the arc, its rate remaining unknown, may add up to the total value. The onshore extension Available online 5 April 2017 rate, established by remote fault scarp measurements on DEMs resembles the numerical modelling estimate of Keywords: Schellart et al. (2007), suggesting that the primary driving force responsible for the extension at Kamchatka is Island arc slab and trench retreat. Trench retreat © 2017 Elsevier B.V. All rights reserved. Normal faulting Low angle faults Extension rate Kamchatka 1. Introduction docking of the Paleocene-Eocene Kronotsky arc, with the most recent thrusting deformation at approximately 2 Ma (Lander and Shapiro, The deformation of an island arc is governed by two main factors. 2007). Extension was at first slow, and the topography of Central Kam- The first factor is the relative angle of convergence between the oceanic chatka was likely gentle. Only finely laminated lacustrine sediments plate and the island arc. For example, oblique convergence can produce (Brunhes Chron) accumulated in its axial region, which subsequently a component of lateral along-arc movement in the arc, as first described evolved into the Central Kamchatka Depression. Vertical movement be- by Fitch (1972). The second factor is the proximity of the arc to the lat- tween the depression and the high-elevation Eastern Ranges, coupled eral edge of the subducting slab: the closer the arc is to the edge, the with arc-normal extension, accelerated in Kamchatka in the middle higher the possibility that the arc will extend in the direction of the Pleistocene, and it is marked by the first appearance of coarse gravel- retreating slab (Schellart et al., 2007). In any case, the rate of tectonic bearing material in the depression (Braitseva et al., 1968; Braitseva et motion within an arc (either arc-normal shortening or extension, with al., 2005). or without an along-arc component) can be used to estimate the pro- Based on numerical modelling, Schellart et al. (2007) found that portion of relative convergence accommodated by arc deformation, Kamchatka may be extending oceanward at a rate of 28 mm/yr. In con- and the relative degree of coupling between the downgoing and over- trast, Acocella and Funiciello (2010), with reference to Kozhurin per- riding plates. sonal communication, reported that 10 ± 5 mm/yr is the likely rate of Published estimates suggest that approximately half of the island extension in Kamchatka. These estimates represent tempting targets arcs around the world, including Kamchatka (Acocella and Funiciello, to verify using ground-based data. 2010), are extending by approximately 70% of their total length Two faults zones accommodating arc-normal extension are recog- (Schellart et al., 2008). The Peninsula of Kamchatka lies above the nized in Central Kamchatka (Fig. 1). The first is the East Kamchatka northern edge of the subducted portion of the PacificPlate,andcurrent- Fault Zone (EKFZ), which includes the normal faults (naming conven- ly undergoes extension, as evidenced by its basin-and-range topogra- tions after Kozhurin et al., 2006) that divide the asymmetric Central phy and pervasive normal faulting in the northern two-thirds of the Kamchatka Depression (CKD) from the Eastern Ranges to the east. peninsula (Fig.1). Shantser (1979) described this extension as “a col- Most of the faults dip north-west and produce an approximately lapse of a pre-existing orogen”. This description is quite appropriate be- 1-km-high faceted slope (Fig. 2). To the east, another zone comprises cause the ongoing extension, after some period of relative quiescence, segmented en-échelon systems of grabens and nested grabens along followed collision-related shortening in Kamchatka caused by the the axis of the Eastern Volcanic Front and may therefore be termed vol- cano-tectonic deformation. This area was first mapped by Legler (Legler fi “ ” ⁎ Corresponding author. and Parfenov, 1979), who de ned it as the Volcanic Opening, meaning E-mail addresses: [email protected] (A. Kozhurin), [email protected] (E. Zelenin). that grabens may have formed due to the splitting forces generated by http://dx.doi.org/10.1016/j.tecto.2017.04.001 0040-1951/© 2017 Elsevier B.V. All rights reserved. 92 A. Kozhurin, E. Zelenin / Tectonophysics 706–707 (2017) 91–102 Fig. 1. Active faulting and late Quaternary volcanism of Kamchatka. Faults are black lines with hatches for normal faults, triangles for reverse and thrust faults, and one-sided arrows for strike-slip faults. The larger, open arrow points at the East Kamchatka Fault Zone (EKFZ) and the smaller arrow points at the system of normal faults in the Eastern Volcanic Front (EFV). The yellow-filled, cross-hatched areas along the east margin of the Central Kamchatka Depression (CKD) are blocks of intermediate topographic height (i.e., half-elevated or half- downthrown). Blue areas are those covered by upper Pleistocene-Holocene volcanic deposits, shown as in Ponomareva et al. (2007) and in GIS “Holocene volcanism of Kamchatka”. The purple-colored area is Pleistocene ignimbrite sheets of the Eastern Volcanic Front. Thin white lines in the Kumroch Range are lines of hypsometric profiles used for measuring block tilt (see text for details). Dotted white lines east of Kamchatka are axes of oceanic trenches. Bathymetry after Seliverstov, 2009. magma intruding into the crust. Later, Florensky and Trifonov (1985) The rate at which onshore Central Kamchatka has been extending determined that the entire system of grabens is a “channel” that facili- since the middle Quaternary may be roughly determined based on the tates the transport of magma through the crust. Several relatively sum of the arc-normal components of movement on the EKFZ and on short normal faults have also been discovered west of the CKD in the the set of grabens in the East Volcanic Front. Quantifying extension in Sredinny Range. These faults are poorly expressed in topography and a rift-perpendicular direction by aggregating fault displacements pro- are obviously extremely slow moving. In addition to the faults zones al- duced at, or near, the ground surface is a standard technique used on ready described, reverse and strike-slip faults predominate north of rift-systems globally (e.g., Villamor and Berryman, 2001; Nicol et al., Central Kamchatka in the Kamchatsky Peninsula (see Fig. 1). This differ- 2006; Begg and Mouslopoulou, 2010; Giba et al., 2010; Mouslopoulou ence in faulting marks a distinctly different tectonic setting caused by et al., 2012). To date, no one has reported, based on filed measurements, the collision of the western Aleutians with Kamchatka (Kozhurin et the rates with which the Kamchatka island arc is extending. Legler and al., 2014). Transition of the kinematics, from extension in Central Kam- Parfenov (1979) attempted to estimate the rate of volcano-tectonic nor- chatka to collisional shortening in the north, remains poorly studied. mal faulting by assuming an average normal fault dip of 60° and an A. Kozhurin, E. Zelenin / Tectonophysics 706–707 (2017) 91–102 93 Fig. 2. Faceted spurs, Ganalsky Range. View to SE (see Fig. 1 for location). average thickness of dykes observed in outcrops of 2 to 3 m. The calcu- aerial photos and satellite imagery, stereoscopic models were created lated value for the average rate of extension was 3 mm/yr and was sur- and interpreted using Photomod 6.0 Lite software (Racurs Co., Russia). prisingly uniform over periods since 10, 30 and 100 ka. Nevertheless, no To estimate vertical offsets on individual faults, we used the digital details of their estimates (e.g., number of faults or individual vertical net elevation models (DEMs) ASTER GDEM (a product of NASA and METI) offsets) were reported. and SRTM X-SAR (©DLR/ASI), both with approximately 30-m spatial This paper represents the first attempt to derive an extension rate resolutions. We also built a 2-m-resolution DEM covering the Shirokoye based on geomorphological data and, partly, trench data. We focused Plateau using detailed aerial photos and Agisoft Photoscan software. on two segments of the East Volcanic Front (EVF), where faults are nu- Due to the absence of geodetic markers on the Shirokoye Plateau, the merous and well expressed topographically, and on two segments of accuracy of the detailed DEM was verified using ASTER GDEM data the EKFZ (Fig. 1). The studied features in the EVF are the faults in the and Russian topographic maps at 1:100,000 scale. All of the above Shirokoye Plateau, located immediately south of the late Pleistocene DEM measurements were ground-truthed during extensive fieldwork Uzon-Geyzernaya caldera depression, and the Semiachik Plateau, locat- on the Kamchatka Peninsula. In addition, we also excavated two trench- ed just south of the Pleistocene Bolshoi Semiachik volcano, both of es, one on each of the two plateaus, to measure fault dip angles in the which are mantled by late Pleistocene ignimbrites (Figs. 1 and 3). To de- upper 2–3moftheground. rive the necessary parameters for estimating extension rates in the EKFZ, we focused on two localities, one close to the northern termina- 3.