Abstract
The tectono-magmatic relationships along obliquely convergent plate boundaries, where strain partitioning promotes strike-slip structures along the volcanic arc, are poorly known. Here it is unclear if and, in case, how the strike-slip structures control volcanic processes, distribution and size. To better define the possible tectono-magmatic relationships along strike-slip arcs, we merge available information on the case study of Sumatra (Indonesia) with field structural data. The Sumatra arc (entire volcanic belt) consists of 48 active volcanoes. Of these, 46% lie within 10 km from the dextral Great Sumatra Fault (GSF), which carries most horizontal displacement on the overriding plate, whereas 27% lie at >20 km from the GSF. Among the volcanoes at <10 km from GSF, 48% show a possible structural relation to the GSF, whereas only 28% show a clear structural relation, lying in pull-aparts or releasing bends; these localized areas of transtension (local extensional zone) do not develop magmatic segments. There is no relation between the GSF along-strike slip rate variations and the volcanic productivity. The preferred N30 •-N40 • E volcano alignment and elongation are subparallel to the convergence vector or to the GSF. The structural field data, collected in the central and southern GSF, show, in addition to the dextral motions along NW-SE to N-S striking faults, also normal motions (extending WNW-ESE or NE-SW), suggesting local reactivations of the GSF. Overall, the collected data suggest a limited tectonic control on arc volcanism. The tectonic control is mostly expressed by the mean depth of the slab surface below the volcanoes (130 ± 20 km) and, subordinately, local extension along the GSF. The latter, when WNW-ESE oriented (more common), may be associated with the overall tectonic convergence, as suggested by the structural data; conversely, when NE-SW oriented (less common), the extension may result from co-and post-seismic arc normal extension, as supported by the 2004 mega-earthquake measurements. Overall, the strike-slip arc of Sumatra has intermediate features between those of extensional and contractional arcs.
Highlights
The relations between magmatism and regional tectonics have been object of several studies in the last decades, especially along divergent plate boundaries, where the crucial role of magmatism on the development of the plate boundary has been repeatedly highlighted
We review and discuss the available data concerning the tectono-magmatic features of western Sumatra, in particular those regarding the tectonic setting of the plates, the structure of the Great Sumatra Fault (GSF) and the volcanic arc; these features have been mostly quantified and summarized in Table 1, which includes an essential reference list
The selection of the Quaternary volcanoes has been made merging the data from the Smithsonian Global Volcanism Program (SGVP; http://volcano.si.edu) and the information contained in the detailed study of Sieh and Natawidjaja (2000); the latter includes 13 more volcanoes with respect to the SGVP database, inferred to be
Summary
The relations between magmatism and regional tectonics have been object of several studies in the last decades, especially along divergent plate boundaries, where the crucial role of magmatism on the development of the plate boundary has been repeatedly highlighted. Many magmatic arcs are characterized by significant strike-slip motion promoted by strain partitioning induced by the oblique convergence between the two interacting plates (e.g., McCaffrey, 1992; Lallemant, 1996; Acocella and Funiciello, 2010): examples include the Southern Andes, the Central American Volcanic Arc, the Mexican Trans Volcanic Belt, the Philippines, the Kurile arc and the Sumatra arc These arcs undergoing strike-slip motions are known only in their very general features, with volcanism inferred to be often associated with local extension created by the activity of pullaparts, releasing bends or dilational jogs (i.e., DeMets, 1992; Tibaldi, 1992; Ego and Ansan, 2002; Pasquarè and Tibaldi, 2003; Corti et al, 2005; Rosenau et al, 2006; Cembrano and Lara, 2009; Tibaldi et al, 2010; Shabanian et al, 2012). Recent studies on active volcanic arcs inferred to experience significant strike-slip motion, as the central Aeolian arc (Italy; De Astis et al, 2003), suggest a tectonic reorganization with predominant magma-induced extension at the surface, without evident strikeslip faulting (Ruch et al, 2016)
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