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Along the volcanic front of the Southern Volcanic Zone of the Andes between 33°Sand 42°S the continental crust increases in thickness from south to north, and erupted lavas define several along-arc geochemical trends. These geochemical trends are the integrated effects of processes occurring in the subducted oceanic crust, the overlying mantle, and the continental crust. Major-and trace-element abundances and isotopic ratios are used to distinguish the effects of crustal and mantle processes. In the relatively thin crust region south of 37°S, lavas evolve dominantly by low-pressure crystallization and incorporate insignificant amounts of continental crust. Abundance ratios of most incompatible elements and isotopic ratios in these lavas reflect components derived from the mantle and subducted oceanic crust. Compared to basalts from north of 37°S, basalts from 37 to 42°S have higher CaO but lower Na2Û and incompatible element contents. These differences are consistent with a north to south increase in degree of mantle melting, perhaps controlled by variable fluxing from the subducted slab (Rb/Cs ratios decrease from north to south), or variations in the thickness of the mantle column that undergoes melting (thicker crust in the north leads to a thinner mantle column and lower degree of melting). In the thicker crust region north of 37°S crustal contamination exerts a greater control on lava compositions. In the interval from andesite to rhyolite, upper crustal contamination causes Rb, Cs, and Th enrichment and isotopic variability. The evolution from basalt to basaltic andesite in this region occurs in the lower crust and crustal contamination causes enrichment in Rb, Cs, and Th and increased La/Yb. The most probable lower crustal protolith for the contaminant is a young, arc-derived garnet granulite.

These Guidelines are intended to help improve the conservation and management of geoheritage and geodiversity in protected and conserved areas and recognition of the interrelationships and interactions with biological features and processes. They are not a textbook on geoconservation management practice, but rather set out the essential background, context and principles; summarise relevant material to make it more readily accessible to users in one volume; and provide links to the key literature and additional sources that include detailed practical guidance. The use of best practice examples from around the world will hopefully give users renewed confidence in looking after geoheritage and in connecting geoconservation with biodiversity conservation.

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Traditionally volcanism is thought to require an extensional state of stress in the crust. This review examines recent relevant data demonstrating that volcanism occurs also in compressional tectonic settings associated with reverse and strike-slip faulting. Data describing the tectonic settings, structural analysis, analogue modelling, petrology, and geochemistry, are integrated to provide a comprehensive presentation of this topic. An increasing amount of field data describes stratovolcanoes in areas of coeval reverse faulting, and shield volcanoes, stratovolcanoes, and monogenic edifices along strike-slip faults, whereas calderas are mostly associated with pull-apart structures in transcurrent regimes. Physically-scaled analogue experiments simulate the propagation of magma in these settings, and taken together with data from subvolcanic magma bodies, they provide insight into the magma paths followed from the crust to the surface. In several transcurrent tectonic plate boundary regions, volcanoes are aligned along both the strikeslip faults and along fractures normal to the local least principal stress (σ 3 ). At subduction zones, intraarc tectonics is frequently characterised by contraction or transpression. In intra-plate tectonic settings, volcanism can develop in conjunction with reverse faults or strike slip faults. In most of these cases, magma appears to reach the surface along fractures striking parallel to the local σ 1 . In some cases, there is a direct geometric control by the substrate strikeslip or reverse fault: magma is transported beneath A. Tibaldi ( ) Department of Geological Sciences and Geotechnologies, University of Milan-Bicocca, Italy e-mail: alessandro.tibaldi@unimib.it the volcano to the surface along the main faults, irrespective of the orientation of σ 3 . The petrology and geochemistry of lavas erupted in compressive stress regimes indicate longer crustal residence times, and higher degrees of lower crustal and upper crustal melts contributing to the evolving magmas when compared to lavas from extensional stress regimes. Small volumes of magma tend to rise to shallow crustal levels, and magma mixing is common in the compressional regimes. In detailed studies from the Andes and Anatolia, with geographic and temporal coverage with which to compare compressional, transcurrent and extensional episodes in the same location, there do not appear to be changes to the mantle or crustal source materials that constitute the magmas. Rather, as the stress regime becomes more compressional, the magma transport pathways become more diffuse, and the crustal residence time and crustal interaction increases.

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