334 A. Tibaldi et al. dynamics and associated ignimbrite volcanism are genetically linked to the activity of NW–SE-striking zones of left-lateral transtension. In fact, most calderas in the southern central Andes are associated with NW–SE-striking transcurrent fault systems such as the Lipez, Calama-Olacapato-El Toro, Archibarca and Culampaja (Salfity, 1985) which define four major transverse volcanic zones. The recognition of a genetic relationship between caldera dynamics and regional, left-lateral transtension is strengthened by the detailed analysis of the tectono-magmatic history of the Negra Muerta Caldera, which has recently been the subject of other studies (Petrinovic et al., 2005; Ramelow et al., 2006). Riller et al. (2001) explain the formation of this partially eroded and asymmetric caldera in terms of an evolution in two successive increments, driven by left- lateral strike shear and fault-normal extension on the prominent Calama Olacapato-El Toro fault zone. Analogue Modelling In the last decade, analogue modelling in scaled exper- iments has been used to test the control exerted by strike-slip faulting on volcanic activity. van Wyk de Vries and Merle (1998) used analogue modelling to evaluate the effect of volcanic loading in strike-slip zones, as well as the effect of regional strike-slip faults on the structure of volcanic edifices. Their analogue models indicate that volcanoes in strike-slip zones develop extensional pull-apart structures. A feedback mechanism can arise, in which loading-related exten- sion enables increased magma ascent, eruptions, and hence increased loading. The authors suggest that the Tondano caldera (North Sulawesi) may be the result of feedback between volcano loading and fault- ing. Other major volcano-tectonic depressions such as Toba, Ranau (Sumatra), and Atitlan (Guatemala) might have a similar origin. Holohan et al. (2007) made scaled analogue mod- els to study the interactions between structures asso- ciated with regional-tectonic strike-slip deformation and volcano-tectonic caldera subsidence. Their results show that while the magma chamber shape mostly influences the development and geometry of volcano- tectonic collapse structures, regional-tectonic strike- slip faults may have a strong influence on the structural evolution of calderas. Considering the case of elongate magma chamber deflation in s trike-slip to transten- sional regimes, they show that regional-tectonic struc- tures can control the development of calderas. In fact, regional strike-slip faults above the magma cham- ber may form a pre-collapse structural grain that can be reactivated during subsidence. The experiments of Holohan et al. (2007) show that such faults prefer- entially reactivate when they are coincident with the chamber margins. Based on previous experiments reproducing the formation of transfer zones and transform faults (Courtillot et al., 1974; Elmohandes, 1981; Serra and Nelson, 1988), Acocella et al. (1999) use analogue models to demonstrate that the occurrence of volcanic activity at Campi Flegrei may be related to the subver- tical dip of NE–SW transfer fractures. The analogue experiments confirm that the NE–SW transverse frac- tures at Campi Flegrei and on the Tyrrhenian margin are transfer fault zones between adjacent NW–SE nor- mal faults. The experiments also show that the transfer faults are steeper than the adjacent normal faults. Girard and van Wyk de Vries (2005) have tested the effect of intrusions on strike-slip fault geometries. Their analogue models, reproducing the Las Sierras- Masaya intrusive complex in the strike-slip tectonic context of the Nicaraguan Depression, show that pull- apart basin formation around large volcanic complexes within strike-slip tectonics can be caused by the pres- ence of an underlying ductile intrusion. To generate a pull-apart basin in this context, both transtensional strike-slip motion and a ductile intrusion are required. Their experiments reveal how strike-slip motion, even transtension, does not produce pull-aparts with no intrusion. A shield-like volcanic overload has no effect either. They conclude that the pull-apart that is forming at Las Sierras-Masaya volcanic complex is produced by the transtensive regional deformation regime and by the presence of the dense, ductile intrusive complex underlying the volcanic area. A series of centrifuge analogue experiments were performed by Corti et al. (2001) with the purpose of modelling the mechanics of continental oblique exten- sion (in the range of 0 ◦ to 60 ◦ ) in the presence of under- plated magma at the base of the continental crust. The main conclusions of their modelling are the following: (i) the structural pattern is characterised by the pres- ence of en echelon faults, with mean trends not per- pendicular to the stretching vector and a component of movement varying from pure normal to strike-slip; Volcanism in Reverse and Strike-Slip Fault Settings 335 (ii) the angle of obliquity controlling the ratio between the shearing and stretching component of movement strongly affects the deformation pattern of the models. In nature, this pattern results in magmatic and volcanic belts which are oblique to the rift axis and arranged en echelon, in agreement with field examples in continen- tal rifts (i.e. Main Ethiopian Rift) and oceanic ridges. Recently, emphasis has been placed on the effects of faulting on the lateral instability of volcanic edi- fices. Two key studies address transcurrent settings using analogue models. Lagmay et al. (2000) con- ducted analogue sand cone experiments to study insta- bility generated on volcanic cones by basal strike-slip movement. Their results demonstrate that edifice insta- bility may be generated when strike-slip faults beneath a volcano move as a result of tectonic adjustments. The instability is localised on the flanks of the volcano above the strike-slip shear, manifested (Fig. 13A) as a pair of sigmoids composed of one reverse and one normal fault. Two destabilised regions are created on the cone flanks between the traces of the sigmoidal faults. Lagmay et al. (2000) compare their results to two examples of volcanoes on strike-slip faults: Iriga volcano (Philippines) which was subjected to non- magmatic collapse, and Mount St. Helens (USA). Norini and Lagmay (2005) built analogue models of volcanic cones traversed by strike-slip faulting and analysed the cones to assess the resulting deforma- tion. Their study shows that symmetrical volcanoes that have undergone basal strike-slip offset may be deformed internally without showing any change what- soever in their shape. Moreover, slight changes in the Fig. 13 (A) Surface deformation of analogue cones subjected to basal strike-slip faulting. To the left the photograph shows the superficial structures formed after 20 mm basal displace- ment. To the right, the sketch depicts the superficial features formed. Modified after Norini and Lagmay (2005). (B)Sketch of the main structures and Quaternary state of stress of the north-western Bicol Volcanic Arc. Main faults strike NW and secondary faults strike NE. The block diagram shows that the near-surface magma paths (dyking) followed the NE-striking fractures that are nearly parallel to σ 1 and perpendicular to σ 3 . PFS = Philippine Fault System. Modified after Pasquarè and Tibaldi (2003) 336 A. Tibaldi et al. basal shape of the cone induced by strike-slip move- ment can be restored by faster reshaping processes due to the deposition of younger eruptive products. The authors report the case of the perfectly symmetrical Mayon volcano (Philippines), suggesting that it may already be internally deformed and its faultless appear- ance might be misleading in terms of risk assessment. Magma Paths A few authors dealing with volcanism in a strike- slip tectonics setting have addressed, by field data or analogue modelling, the problem of identifying the paths through which magma reaches the surface to feed eruptions. In their study on analogue modelling dealing with strike-slip faulting and flank instability, Lagmay et al. (2000) consider also the case of Mount St. Helens, set on a right-lateral strike-slip fault; their experiments show that the fault strongly controlled the path of the intruding magma which resulted in t he emplacement of a cryptodome prior to the catastrophic 1980 collapse. Pasquarè and Tibaldi (2003) on two volcanoes of the Bicol Peninsula, observe by field data and ana- logue models, that the elongation of single edifices, apical depressions of domes and alignment of multi- ple centres, as well as all secondary faults in the stud- ied area, trend NE–SW, i.e. perpendicularly to the main fault trend in the region, which is roughly perpendicu- lar to the Philippine Fault System (PFS). Pasquarè and Tibaldi (2003) hypothesize that, at depth, magma prob- ably used the main NW-striking regional faults because they are the deepest and widest crustal vertical struc- tures, whereas the near-surface magma paths (dyking) followed the NE-striking fractures which are nearly parallel to σ 1 and perpendicular to σ 3 (Fig. 13B). The authors also point out that an upward change of ori- entation of magma-feeding fractures has been noticed in other transcurrent zones such as at Galeras volcano (Colombia, Tibaldi and Romero-Leon, 2000). Holohan et al. (2007), who analysed by analogue modelling the interactions between structures associ- ated with regional-tectonic strike-slip deformation and volcano-tectonic caldera subsidence, suggest a simi- larity between the roof-dissecting Riedel shears and Y-shears appearing in their models and the regional strike-slip faults that dissect the central floors of the Negra Muerta (Riller et al., 2001; Ramelow et al., 2006) and Hopong calderas. According to the authors, these fault systems might be regarded as preferential pathways in nature for the ascent of magma and other fluids before, during, or after caldera formation. Busby and Bassett (2007) document that the intra- basinal lithofacies of the Santa Rita Glance Con- glomerate record repeated intrusion and emission of small volumes of magma along intrabasinal faults. The interfingering of the eruptive products indicates that more than one vent was active at a time; hence the name “multivent complex” is applied. They pro- pose that multi-vent complexes reflect the proximity to a continuously active fault zone, whose strands fre- quently tapped small batches of magma, emitted to the surface at releasing bends. Dacitic domes grow- ing just outside the basin, were probably fed by the master, strike-slip fault, just as modern dome chains are commonly located on faults (Bailey, 1989; Bellier and Sebrier, 1994; Bellier et al., 1999). Marra (2001) on the Mid-Pleistocene volcanic activity in the Alban Hills (Central Italy) documents two nearly contemporaneous eruptions of lava flows and ignimbrites in the Alban Hills as produced by two distinct tectonic triggers, tapping different depths of a magma reservoir. The geometries of the main struc- tural dislocations in Quaternary strata indicate a struc- tural pattern which is consistent with local strain par- titioning in transpressive zones along strike-slip fault bends, superimposed on regional extension. Based on this analysis, Marra (2001) suggests that a local, clock- wise block rotation between parallel N–S strike-slip faults might have generated local crustal decompres- sion, enabling volatile-free magma to rise from deep reservoirs beneath the Alban Hills and feeding fissure lava flows. In contrast, the main ignimbrite eruptions appear to have tapped shallow, volatile-rich magma reservoirs and to have been controlled by extensional processes. Chiarabba et al. (2004), on the basis of a shallow seismic tomography of Vulcano Island (Aeolian Arc, Italy) observe that at shallow depth (i.e. <0.5 km), the plumbing system of the volcano is mainly controlled by N–S striking faults, whereas at a depth >0.5 km, the rise of magma is controlled by NW–SE fractures asso- ciated with the activity of the NW–SE striking, right- lateral strike-slip to oblique-slip, Tindari-Letojanni fault system (Mazzuoli et al., 1995). This implies that magma intrudes along the NW–SE strike-slip faults Volcanism in Reverse and Strike-Slip Fault Settings 337 but its ascent to the surface is controlled by N–S to NNW–SSE tensional structures (normal faults and tension fractures), which are orthogonal to the regional extension. Chiarabba et al. (2004) conclude that also Aydin et al. (1990) observed that in strike-slip zones, magma preferentially rises at the surface along the extensional structures rather than the main strike-slip fault segments. Also Corti et al. (2001) showed that magma emplaces at depth along faults parallel to the main shear zone but upraises to the surface along cracks that are orthogonal to the orientation of the extension. Finally, Rossetti et al. (2000) illustrate how the effu- sive and intrusive rocks belonging to the McMurdo Volcanic Group (Antarctica) were emplaced along the western shoulder of the Ross Sea during the Cenozoic. The Mc Murdo dykes are widespread in the coastal sector of Victoria Land, along the western shoulder of the Ross Sea. Based on field evidence, Rossetti et al. (2000) propose that the intrusion of the Mc Murdo dykes was triggered along a crustal-scale, non-coaxial transtensional shear zone where the strike-slip compo- nent increased over time. Petrologic and Geochemical Effects The classic view of a convergent margin is that arc- like lavas erupt along the volcanic front, and alkalic basalts with no arc signature erupt in the back arc (Gill, 1974). However, structural analysis has shown that within an overall convergent margin setting, arc-like magmas erupt in areas of local compression, transpres- sion, transtension, and extension. This summary paper does not compare the petrology and geochemistry of arc lavas to rift lavas, or even lavas of the volcanic front to those in the backarc. The focus is on smaller scale variations in stress state within the arc front of the con- vergent margin. The approach minimizes changes to petrology and geochemistry due to differences in the mantle source region, and instead allows us to compare petrology and geochemistry among magmas where the principal variable is the state of stress in the continental crust. This focus also emphasizes that interdisciplinary studies that link detailed structural information with petrology and geochemistry are relatively rare. The SVZ of the Andes between latitude 30 S and 47 S has been used as a natural laboratory for studying the relationship between tectonics and continental mag- matism for many years (Lopez Escobar et al., 1977; Hickey et al., 1986; Futa and Stern, 1988; Hildreth and Moorbath, 1988; Tormey et al., 1991; Dungan et al., 2001). This portion of the arc provides sys- tematic variation in the age of the subducting slab, angle of subduction, volume of sediments in the trench, crustal thickness, and tectonic style. The arc also has a well-defined volcanic front, zone of back-arc exten- sion, and transition zones between the two. These fea- tures also vary with time, as described in a recent compilation volume (Kay and Ramos, 2006). Consid- ering present-day volcanic activity, the Liquine-Ofqui Fault Zone (LOFZ) is the controlling fault for activity along the volcanic front between 37 and 47 S ( Hervé, 1994; Lopez-Escobar et al., 1995; Lavenu and Cem- brano, 1999; Rosenau, 2004). The LOFZ is a greater than 1,100 km intra-arc strike slip zone that merges into the foreland fold and thrust belt at about 37 S (Ramos et al., 1996). Compared to volcanic rocks in the more compressional and transpressional area north of the LOFZ, the compositions of eruptive products in the LOFZ are primarily basalt-dacite or andesitic, with little evidence for upper crustal contamination or extensive residence time (Lopez-Escobar et al., 1977; Hickey et al., 1986; Futa and Stern, 1988; Hildreth and Moorbath, 1988; Tormey et al., 1991; Dungan et al., 2001). Lava composition is primarily controlled by mantle and lower crustal processes; the strike-slip LOFZ appears to allow more rapid passage through the crust and lesser occurrence of assimilation or magma mixing compared to the more contractional setting fur- ther north in the SVZ. North of the LOFZ, the Agrio Fold and Thrust Belt and the Malargue Fold and Thrust Belt (Ramos et al., 1996; Folguera et al., 2006b) mark a transition to a transpressional and compressional zone. Within the zone of compression, basalts and basaltic andesites are rare, and the mineral assemblage becomes more hydrous. Hornblende andesite is the predominant rock type in northern centers of the SVZ, with subordinate biotite. In the compositional interval from andesite to rhyolite, crustal inputs cause Rb, Cs, and Th enrich- ment and isotopic variability indicating both lower crustal and upper crustal melts commingling with the ascending magma (Hildreth and Moorbath, 1988, Tormey et al., 1991, Dungan et al., 2001). These features are absent in the eruptive products controlled by the strike-slip LOFZ further south. The evolution 338 A. Tibaldi et al. from basalt to andesite occurs in the lower crust; there is enrichment of La/Yb as well as Rb, Cs, and Th. The most probable lower crustal protolith is a young, arc-derived garnet granulite (Tormey et al., 1991). In the northern part of the SVZ, with a greater prevalence of compression and transtension, petrologic and geo- chemical variations indicate predominantly andesitic systems with compositional variations indicating rel- atively low degrees of mantle melting, high degrees of mixing and assimilation of lower to mid crustal materials, and an overlay of upper crustal contami- nation evident in upper crustal rocks (Hildreth and Moorbath, 1988, Tormey et al., 1991, Dungan et al., 2001). The contrast between the petrology and geo- chemistry of volcanic rocks in the northern part of the SVZ (compression and transtension) compared to the strike-slip LOFZ-controlled portion of the SVZ have been attributed to a shallowing of the subducted slab and increasing crustal thickness in the north. In addi- tion, the lithology and age of the continental crust in the north also exert a control on magma compo- sitions. The thickening of the continental crust in the more compressional setting may be related to the tran- sition from the dominantly strike-slip environment of the LOFZ. Kay et al. (2005) evaluate the temporal trends in petrologic and geochemical effects in the Andean Arc between 33 and 36 S over a 27-million year period of record. The detailed study is used to compare the temporal trends at a single region to the present day north to south geographic trends among Holocene cen- ters of the volcanic front just described. In the arc seg- ment studied by Kay et al. (2005), the crustal stress regime is transtensional from 27 to 20 Ma; abun- dant mafic rocks with relatively flat REE patterns erupted, suggesting higher degrees of mantle melting. More evolved compositions have petrologic and geo- chemical variation indicating relatively low degrees of upper crustal contamination. From 19 to 7 Ma, the stress regime becomes compressional, with a signifi- cant increase in the amount of plutonic rocks. The lavas that did erupt in this compressional regime have steep REE patterns suggesting lower to mid-crustal fraction- ation of an amphibole-rich mineral assemblage. Geo- chemical data also indicate increasing degrees of upper crustal contamination. In general, as the compressional stress regime develops, there appears to be a longer crustal residence time, leading to a greater amount of plutonism, higher degrees of crustal contributions to developing magmas, and a hydrous fractionating min- eral assemblage. The petrologic and geochemical fea- tures of these lavas are very s imilar to the character- istics of Holocene activity in the northern part of the SVZ. From 6 to 2 Ma, the dip of the subducting slab decreases, leading to a waning of magmatic activity as the volume of mantle melts decreases. The SVZ of the Andes includes a belt of silicic vol- canism, both ignimbrites and flows, between 35 and 37 S (Hildreth et al., 1999). The systems appear to have initially developed in a compressional state of stress i n the crust. Voluminous eruptions of silicic magma, how- ever, appear to coincide with a transition from com- pression to transpressional or even extensional condi- tions. During the compressional phase, there appears to have been extensive interaction with the lower and upper crust. Small batches of magma appear to have incorporated crustal melts and been subject to peri- odic magma mixing. As the compressional state of stress relaxed, shallow crustal melts coalesced, ulti- mately erupting to form the surface deposits (Hildreth et al., 1999). In their study of the geology of a portion of the Peruvian Andes in the CVZ, Sebrier and Soler (1991) noted that during a transition from extensional to com- pressional states of crustal stress, there was not a cor- responding change in the petrology or geochemistry of the erupted magmas. They found that calc-alkaline magmas of similar composition were the dominant eruptive product, independent of the state of stress in the crust. Anatolia is characterised by widespread post- Oligocene volcanism associated with compression, strike-slip, and extensional crustal stress regimes. In western Anatolia, volcanic activity began during the Late Oligocene – Early Miocene in a compressional regime. Andesitic and dacitic calc-alkaline rocks are preserved, with some shallow granitic intrusions. An abrupt change from N–S compression to N–S s tretch- ing in the middle Miocene was accompanied by a gradual transition to alkali basaltic volcanism (Yilmaz, 1990). In eastern Anatolia, the collision-related com- pressional tectonics and associated volcanic activity began in the Late Miocene to Pliocene and continued almost without interruption into historical times (Yil- maz, 1990; Pearce et al., 1990; Yilmaz et al., 1998). Volcanism on the thickened crust north of the Bitlis Thrust Zone varies from the mildly alkaline volcano, Nemrut, and older Mus volcanics in the south, through Volcanism in Reverse and Strike-Slip Fault Settings 339 the transitional calc-alkaline/alkaline volcanoes Bingöl and Süphan and the alkaline volcano Tendürek to the calc-alkaline volcano Ararat and older Kars plateau volcanics in the north (Pearce et al., 1990; Yilmaz et al., 1998; Coban, 2007). After initial phases of alka- line lavas, there were widespread eruptions of andesitic and dacitic calc-alkaline rocks during the Pliocene. A second, larger-volume phase of volcanism, partly over- lapped with the initial phase, involving alkaline and transitional lavas; this phase began during the Quater- nary and is ongoing (Pearce et al., 1990). The calc-alkaline lavas of both Anatolian regions were erupted at a time when the compressional regime led to crustal thickening, as observed in the Andes. Petrology and geochemistry of the lavas from the com- pressional regime display many geochemical and iso- topic signatures indicating extensive crustal contam- ination, and polybaric crystallization ( Yilmaz, 1990; Coban, 2007). As found in the northern part of the Andean SVZ, rare earth elements are depleted in the heavier elements, indicating the importance of horn- blende crystallization at depth in the calc-alkaline series lavas, in contrast to the consistently anhydrous crystallization sequences of the alkaline lavas (Yilmaz, 1990; Coban, 2007). In the multi-vent complexes of the Santa Rita Mountains (Arizona, USA), the volcanic and subvol- canic rocks appear to record small-volume eruptions controlled by the complex faulting in the developing strike-slip basin (Busby and Bassett, 2007). Similarly, in a study of lavas from Mt. Rainier (Washington, USA) erupted during a compressional phase, Lanphere and Sisson (2003) suggest that the primary effect of compression is to lower the magma supply rate. Erup- tive products at Mt. Rainier do not bear a recognizable signature of the compressive stress regime, other than smaller volume flows. In their study of alkali basalts formed in an intraplate compressive state of stress, Glazner and Bartley (1994) note that other alkali basal fields in the southwestern USA also formed in an extensional and strike-slip state of s tress. There do not appear to be petrologic or geochemical variations that correlate with the different states of stress. A relatively uniform alkali basaltic magma appears to have reached the sur- face in variable states of crustal stress without signifi- cant alteration in composition or other chemical char- acteristics. Although focused studies on the relationship between crustal state of stress and petrology and geo- chemistry of eruptive products are uncommon, there are several traits of the petrologic and geochemical characteristics of magmas in compressional or weakly transpressional systems (Fig. 14). In general, pluton- ism tends to be favored over volcanic activity. The composition of volcanic rocks suggests longer crustal residence times, and higher degrees of lower crustal and upper crustal contributions to the magmas. Small volumes of magma tend to rise to shallow crustal lev- els (Marcotte et al., 2005, Busby and Bassett, 2007). In detailed studies with geographic to temporal cov- erage with which to compare compressive, transpres- sional and extensional episodes, there do not appear to be changes to the source materials that consti- tute the magmas. Rather, the change in crustal stress regime governs the magma transport pathway, and the crustal r esidence time. As the stress regime becomes more compressional, the magma transport pathways become more diffuse, and the crustal residence time increases. As a result, there are greater amounts of crustal melting and assimilation, greater degrees of magma mixing, and lower eruptive volumes as com- pression increases. Taken to its limits, these conditions lead to the often cited feature that compressional stress regimes tend to favour plutonism over volcanism. In the case of the silicic volcanic belt between 35 ◦ and 37 S in the Andes, the development of a plutonic belt in a compressive setting appears to have been inter- rupted by a transition in the state of stress of the crust from extension to transpressional or extensional, lead- ing to large-volume eruption of dominantly rhyolitic magmas. Conclusions Volcanism occurs in compressional tectonic settings comprising both contractional and transcurrent defor- mation. The data include field examples worldwide encompassing subduction-related volcanic arcs and intra-plate volcanic zones. Moreover, several exper- iments conducted using scaled models demonstrate magma ascent under horizontal crustal shortening. In contractional settings, reverse faults can serve as magma pathways, leading to emplacement of volcanoes at the intersection between the fault plane 340 A. Tibaldi et al. Fig. 14 Schematic petrogenetic summary diagram depicting in cross-sectional view the controls exerted by crustal stress state on contractional-derived volcanics (left) and strike-slip- derived volcanics (right), drawn based upon conditions in the Southern Volcanic Zone of the Andes and Eastern Anatolia. The cross section is not continuous between the two crustal stress states. Rough stippled pattern represents zone of lower and mid crustal partial melting and dark grey represents coa- lesced magma bodies. The source areas (mantle, lower crust, upper crust) and processes (fractional crystallization, assimila- tion, magma hybridization, mixing) occur within both crustal states, but the relative proportions vary significantly between the two states and the topographic surface (Fig. 15A). Alternatively, magma can ascend along reverse faults and then ver- tically migrate, giving rise to the emplacement of vol- canoes above the hanging wall fault block (Fig. 15B). The geometry of dykes feeding magma to the sur- face in these cases is still not clear, although it seems that within volcanic cones in contractional settings most dykes are parallel to the σ 1 . The edifice type is most frequently stratovolcanoes and satellite mono- genetic cones. In strike-slip fault zones, volcanic activ- ity is primarily related to local extensional processes occurring at pull-apart basins, which form at a releas- ing stepover (Fig. 15C) between en echelon segments of a strike-slip fault, or at releasing bend basins, which form along a gently curved (Fig. 15D) strike- slip fault. Volcanoes can also develop directly above the trace (Fig. 15E) of strike-slip faults and hence be related to purely lateral shear processes without associated extension. Less frequently, volcanic activity can develop along extensional structures at the tips of main strike-slip faults (horsetail structures, Fig. 15F). Stratovolcanoes, shield volcanoes, pyroclastic cones and domes may occur at all these types of strike- slip fault structures, whereas calderas are preferentially located within pull-apart basins. The petrology and geochemistry of lavas erupted in compressive stress regimes suggest longer crustal residence times, and higher degrees of lower crustal and upper crustal con- tributions to the magmas. Small volumes of magma tend to rise to shallow crustal levels. There do not appear to be significant changes in the mantle or crustal source materials for magmas; rather, the type of crustal stress regime governs the magma transport path- way and crustal residence time. As the stress regime becomes more compressional, the magma transport pathways become more diffuse and the crustal res- idence time and crustal contribution to the magmas increases. Volcanism in Reverse and Strike-Slip Fault Settings 341 Fig. 15 Sketch of the most frequent location of surface volcanic features in compressional tectonic settings. In a contractional environment with reverse faults, most volcanoes are placed at the intersection between the fault plane and the topographic surface (A) or above the hanging wall fault block (B). They are most commonly stratovolcanoes and satellite monogenetic cones. In strike-slip fault zones, volcanism can occur at pull- apart basins (C); at releasing bend structures (D); directly along rectilinear strike-slip faults (E); and at the tips of main strike- slip faults (horsetail structures, F). Stratovolcanoes, shield vol- canoes, pyroclastic cones and domes may occur at all the above types of strike-slip fault structures, whereas calderas are prefer- entially located within pull-apart basins Acknowledgements C.J. Busby is greatly acknowledged for her useful suggestions on a previous version of the manuscript. 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[...]... asthenosphere, and it is of fundamental importance in geodesy, since Earth rotation, polar motion and crustal S Cloetingh, J Negendank (eds.), New Frontiers in Integrated Solid Earth Sciences, International Year of Planet Earth, DOI 10.1007 /97 8 -90 -481-2737-5_10, â Springer Science+Business Media B.V 2010 3 49 350 deformation, and therefore the global reference frames are inuenced by it Despite the existence of... extension, intraplate strike-slip faulting, and tectonic inheritance J Geophys Res 102:24, 6 692 4, 696 Schafer KH, Dannapfel M ( 199 4) State of in situ Stress in Northern Chile and in Northwestern Argentina In: Reuter KJ, Scheuber E, Wigger PJ (Eds.), Tectonics of the Southern Central Andes Structure and Evolution of an Active Continental Margin Springer, New York, pp 103110 Scheuber E, Reutter K ( 199 2) Magmatic... deposits such as landslides and seismicity, trenching through the faults, dating using offset till sequences and radiocarbon dating of organic material, and geophysical investigations (e.g Lagerbọck, 197 9, 199 0; Olesen, 198 8, 199 2; Bọckblom and Stanfors, 198 9) have shown that the faults ruptured violently as large earthquakes The magnitudes of these earthquakes is estimated to have reached MW 78, based... observations in a convincing way, probably because they do not incorporate reliable rheologies and do not involve the inuence of other factors like topography (Pascal and Cloetingh, 20 09) or glacial deep erosion and sediment loading (Stein et al., 198 9) In brief, better illumination of this specic problem requires both more accurate rebound models and a more complete understanding of the pre-faulting stress... 198 8) Presumably, the ice cap inhibited seismicity and strainrelease during the Pleistocene glaciations This caused earthquakes with magnitudes up to 8 when sudden global warming and ice-retreat occurred at the Pleistocene-Holocene transition (Johnston, 198 9; Wu et al., 199 9) A second mechanism, based on glacially induced stresses, was suggested by Wu and Hasegawa ( 199 6) The present-day seismicity in. .. dyke intrusion along preexisting fractures J Geophys Res 105: 594 7 596 1 A Tibaldi et al Zapata TR, Brisson I, Dzelalija F ( 199 9) La estructura de la faja plegada y corrida andina en relacion con el control del basamento de la Cuenca Neuquina, Boletn de Informaciones Petroleras, December 199 9, pp 112121 Zollner W, Amos AJ ( 197 3) Descripcion geologica de la Hoja 32b, Chos Malal (Prov Neuquen), Bull 143, 91 ... Shield Phys Chem Earth, 28, 3 493 60 Lagerbọck, R., 197 9 Neotectonic structures in northern Sweden, Geologiska Fửreningens i Stockholm Fửrhandlingar, 100( 197 8), 271278 Lagerbọck, R., 199 0 Late Quarternary faulting and paleoseismology in northern Fennoscandia, with particular reference to the Lansjọrv area, northern Sweden Geologiska Fửreningens i Stockholm Fửrhandlingar, 112, 333354 3 69 Lagerbọck, R and... joining lines are the land uplift gravity lines, measured since the mid- 196 0s Contour lines show the apparent land uplift relative to the Baltic mean sea level 1 892 199 1, based on Nordic uplift model NKG2005LU (Vestứl, 2006; gren and Svensson, 2007) Right: Diagram of the observed relative gravity change between Vaasa and Joensuu in Finland during 40 years of measurement on the land uplift gravity lines... Mazzuoli R, Omarini R, Uttini, A, Hauser, N (2005b) Geology and petrology of the Las Burras-Almagro magmatic complex, Salta Argentina Proceedings of the XVI Congreso Geologico Argentino I, pp 4 794 84 Mazzuoli R, Tortorici L, Ventura G ( 199 5) Oblique rifting in Salina, Lipari and Vulcano islands (Aeolian islands, southern Italy) Terra Nova 7:444452 McCaffrey KJW ( 199 2) Igneous emplacement in the transpressive... Westaway R ( 199 0) Seismicity and tectonic deformation rate in Soviet Armenia: Implications for local earthquake hazard and evolution of adjacent regions Tectonics 9: 477503 Williams H, McBirney A ( 197 9) Volcanology Freeman, Cooper & Co., 397 pp Winkler W, Villagomez D, Spikingsc R, Abegglend P, Toblere St, Eguezb A (2005) The Chota basin and its signicance for the inception and tectonic setting of the inter-Andean . importance in geodesy, since Earth rotation, polar motion and crustal 3 49 S. Cloetingh, J. Negendank (eds.), New Frontiers in Integrated Solid Earth Sciences, International Year of Planet Earth, . JM ( 199 4). Eruption of alkali basalts during crustal shortening in southern California. Tectonics 13: 493 – 498 . Godoy E, Yáñez G, Vera E ( 199 9). Inversion of an Oligocene volcano-tectonic basin and. trenching through the faults, dating using offset till sequences and radiocarbon dating of organic material, and geophysical investigations (e.g. Lagerbäck, 197 9, 199 0; Olesen, 198 8, 199 2; Bäckblom